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© 2011 Pearson Education, Inc. PowerPoint ® Lecture Presentations prepared by Alexander G. Cheroske Mesa Community College at Red Mountain 3 Cellular Level of Organization
© 2011 Pearson Education, Inc. Section 1: An Introduction to Cells Learning Outcomes 3.1 Describe the cell and its organelles, including the composition and function of each. 3.2 Describe the chief structural features of the plasma membrane. 3.3 Differentiate among the structures and functions of the cytoskeleton. 3.4 Describe the ribosome and indicate its specific functions.
© 2011 Pearson Education, Inc. Section 1: An Introduction to Cells Learning Outcomes 3.5 Describe the Golgi apparatus and indicate its specific functions. 3.6 Describe mitochondria, indicate their functions, and explain their significance to cellular function.
© 2011 Pearson Education, Inc. Section 1: An Introduction to Cells Typical cell Smallest living unit in the body ~0.1 mm in diameter Could not be examined until invention of microscope in 17th century Animation: Your Cells
© 2011 Pearson Education, Inc. Section 1: An Introduction to Cells Cell theory 1. Cells are building blocks of all plants and animals 2. All new cells come from division of preexisting cells 3. Cells are smallest unit that perform all vital physiological functions
© 2011 Pearson Education, Inc. Figure 3 Section 1 Cells are the building blocks of all plants and animals. All new cells come from the division of pre-existing cells. Cells are the smallest units that perform all vital physiological functions. Cell Division Growth New cells Nutrients Wastes O2O2 CO 2 The cell theory The differentiation of the four tissue types from a single cell: the fertilized ovum Epithelial tissue Connective tissue Muscle tissue Neural tissue
© 2011 Pearson Education, Inc. Section 1: An Introduction to Cells Each cell maintains homeostasis Coordinated activities of cells allow homeostasis at higher organizational levels
© 2011 Pearson Education, Inc. Section 1: An Introduction to Cells Cells vary in structure and function but all descend from a single fertilized ovum Fertilized ovum contains genetic potential to become any cell Cell divisions occur creating smaller, different parcels of cytoplasm Cytoplasmic differences turn off/on specific genes in DNA and daughter cells become specialized = Differentiation Differentiated cells are responsible for all body functions
© 2011 Pearson Education, Inc. Section 1: An Introduction to Cells Extracellular fluid Watery medium surrounding cells Called interstitial fluid (interstitium, something standing between) in most tissues
© 2011 Pearson Education, Inc. Module 3.1: Smallest living units of life Cell components Plasma membrane (cell membrane) Separates cell contents from extracellular fluid Cytoplasm Material between cell membrane and nuclear membrane Colloid containing many proteins Two subdivisions 1. Cytosol Intracellular fluid 2. Organelles (“little organs”) Intracellular structures with specific functions
© 2011 Pearson Education, Inc. Module 3.1: Smallest living units of life Organelles Nonmembranous Not completely enclosed by membranes In direct contact with cytosol Examples: Cytoskeleton Microvilli Centrioles Cilia Ribosomes
© 2011 Pearson Education, Inc. Module 3.1: Smallest living units of life Organelles Membranous Enclosed in a phospholipid membrane Isolated from cytosol Examples: Mitochondria Nucleus Endoplasmic reticulum Golgi apparatus Lysosomes Peroxisomes
© 2011 Pearson Education, Inc. Module 3.1: Smallest living units of life Organelles Microvilli STRUCTURE: membrane extensions containing microfilaments FUNCTION: increase surface area for absorption Cytoskeleton STRUCTURE: fine protein filaments or tubes Centrosome Organizing center containing pair of centrioles FUNCTION: Strength and support Intracellular movement of structures and materials
© 2011 Pearson Education, Inc. Module 3.1: Smallest living units of life Organelles Ribosomes STRUCTURE: RNA and proteins Fixed: attached to endoplasmic reticulum Free: scattered in cytoplasm
© 2011 Pearson Education, Inc. Module 3.1: Smallest living units of life Organelles Peroxisome STRUCTURE: vesicles containing degradative enzymes FUNCTION: Catabolism of fats/other organic compounds Neutralization of toxic compounds Lysosome STRUCTURE: vesicles containing digestive enzymes FUNCTION: Removal of damaged organelles or pathogens
© 2011 Pearson Education, Inc. Module 3.1: Smallest living units of life Organelles Golgi apparatus STRUCTURE: stacks of flattened membranes (cisternae) containing chambers FUNCTION: storage, alteration, and packaging of synthesized products Mitochondria STRUCTURE: Double membrane Inner membrane contains metabolic enzymes FUNCTION: production of 95% of cellular ATP
© 2011 Pearson Education, Inc. Module 3.1: Smallest living units of life Organelles Nucleus STRUCTURE: Fluid nucleoplasm containing enzymes, proteins, DNA, and nucleotides Surrounded by double membrane FUNCTION: Control of metabolism Storage/processing of genetic information Control of protein synthesis Animation: Nucleus
© 2011 Pearson Education, Inc. Module 3.1: Smallest living units of life Organelles Endoplasmic reticulum (ER) STRUCTURE: membranous sheets and channels FUNCTION: synthesis of secretory products, storage, and transport Smooth ER No attached ribosomes Synthesizes lipids and carbohydrates Rough ER Attached ribosomes Modifies/packages newly synthesized proteins
© 2011 Pearson Education, Inc. Module 3.1 Review a. Distinguish between the cytoplasm and cytosol. b. Describe the functions of the cytoskeleton. c. Identify the membranous organelles and describe their functions.
© 2011 Pearson Education, Inc. Module 3.2: Plasma membrane Plasma membrane Selectively permeable membrane that controls: Entry of ions and nutrients Elimination of wastes Release of secretions
© 2011 Pearson Education, Inc. Module 3.2: Plasma membrane Plasma membrane components Glycocalyx Superficial membrane carbohydrates Components of complex molecules Proteoglycans (carbohydrates with protein attached) Glycoproteins (protein with carbohydrates attached) Glycolipids (lipids with carbohydrates attached) Functions Cell recognition Binding to extracellular structures Lubrication of cell surface
© 2011 Pearson Education, Inc. Module 3.2: Plasma membrane Plasma membrane components (continued) Integral proteins Part of cell membrane Cannot be removed without damaging cell Often span entire cell membrane = Transmembrane proteins Can transport water or solutes Peripheral proteins Attached to cell membrane surface Removable Fewer than integral proteins
© 2011 Pearson Education, Inc. Figure Structure of the plasma membrane EXTRACELLULAR FLUID Glycolipid Glycocalyx (extracellular carbohydrates) Integral protein with channel CYTOPLASM Integral glycoproteins Peripheral proteins Cytoskeleton (microfilaments) = 2 nm Integral (transmembrane) proteins
© 2011 Pearson Education, Inc. Module 3.2: Plasma membrane Plasma membrane structure Thin (6–10 nm) and delicate Phospholipid bilayer Mostly comprised of phospholipid molecules in two layers Hydrophilic heads at membrane surface Hydrophobic tails on the inside Isolates cytoplasm from extracellular fluid Animation: Cell Membrane Barrier
© 2011 Pearson Education, Inc. Figure Cholesterol Hydrophilic heads Hydrophobic tails The phospholipid bilayer that forms the plasma membrane
© 2011 Pearson Education, Inc. Module 3.2: Plasma membrane Plasma membrane functions Physical isolation Regulation of exchange with external environment Sensitivity to environment Structural support Lipid bilayer provides isolation Proteins perform most other functions
© 2011 Pearson Education, Inc. Figure 3.2 3
© 2011 Pearson Education, Inc. Figure 3.2 3
© 2011 Pearson Education, Inc. Module 3.2 Review a. List the general functions of the plasma membrane. b. Which structural component of the plasma membrane is mostly responsible for its ability to isolate a cell from its external environment? c. Which type of integral protein allows water and small ions to pass through the plasma membrane?
© 2011 Pearson Education, Inc. Module 3.3: Cytoskeleton Cytoskeleton (cellular framework) components 1. Microfilaments <6 nm in diameter Typically composed of actin Commonly at periphery of cell Microvilli Finger-shaped extensions of cell membrane Has core of microfilaments to stiffen and anchor Enhance surface area of cell for absorption Terminal web (layer inside plasma membrane in cells forming a layer or lining)
© 2011 Pearson Education, Inc. Module 3.3: Cytoskeleton Cytoskeleton (cellular framework) components (continued) 2. Intermediate filaments 7–11 nm in diameter Strongest and most durable cytoskeletal elements 3. Microtubules ~25 nm in diameter Largest components of cytoskeleton Extend outward from centrosome (near nucleus)
© 2011 Pearson Education, Inc. Figure Structures of the cytoskeleton Microvilli Microfilaments Plasma membrane Terminal web Intermediate filaments Microtubule Secretory vesicle Endoplasmic reticulum Mitochondrion MicrovilliSEM X 30,000
© 2011 Pearson Education, Inc. Module 3.3: Cytoskeleton Centrioles Cylindrical structures Composed of microtubules (9 groups of triplets) Two in each centrosome Control movement of DNA strands during cell division Cells without centrioles cannot divide Red blood cells Skeletal muscle cells
© 2011 Pearson Education, Inc. Figure The structure of centrioles Microtubules in centriole
© 2011 Pearson Education, Inc. Module 3.3: Cytoskeleton Cilia Long, slender plasma membrane extensions Common in respiratory and reproductive tracts Also composed of microtubules Nine groups of pairs surrounding a central pair Anchored to cell surface with basal body Beat rhythmically to move fluids or secretions across cell
© 2011 Pearson Education, Inc. Figure The structure of cilium Basal body Plasma membrane Microtubules
© 2011 Pearson Education, Inc. Figure The action of a beating cilium Power stroke Return stroke
© 2011 Pearson Education, Inc. Module 3.3 Review a. List the three basic components of the cytoskeleton. b. Which cytoskeletal component is common to both centrioles and cilia? c. What is the function of cilia?
© 2011 Pearson Education, Inc. Module 3.4: Ribosomes Ribosomes Protein synthesis Two subunits (1 large, 1 small) containing special proteins and ribosomal RNA (rRNA) Must join together before synthesis begins Free ribosomes Throughout cytoplasm Manufactured proteins enter cytosol
© 2011 Pearson Education, Inc. Figure The two subunits of a functional ribosome Small ribosomal subunit Large ribosomal subunit
© 2011 Pearson Education, Inc. Module 3.4: Ribosomes Endoplasmic reticulum (ER) Network of intracellular membranes attached to nucleus Forms hollow tubes, sheets, and chambers (cisternae, singular, cisterna, reservoir for water)
© 2011 Pearson Education, Inc. Module 3.4: Ribosomes Endoplasmic reticulum (ER) Two types 1. Smooth (SER) Lacks ribosomes Tubular cisternae 2. Rough (RER) Has attached (fixed) ribosomes Modification of newly synthesized proteins Export to Golgi apparatus Proportion of SER to RER depends on the cell and its functions
© 2011 Pearson Education, Inc. Figure – 3 The structure of the endoplasmic reticulum (ER) Nuclear envelope Cisternae Tubular cisternae Smooth endoplastic reticulum (SER)
© 2011 Pearson Education, Inc. Figure 3.4 3
© 2011 Pearson Education, Inc. Module 3.4: Ribosomes Functions of SER Synthesis of phospholipids and cholesterol Synthesis of steroid hormones Synthesis and storage of glycerides in liver and fat cells Synthesis and storage of glycogen in skeletal and liver cells
© 2011 Pearson Education, Inc. Figure mRNA strand Ribosome Transport vesicles Fixed ribosomes Growing polypeptide Enzyme Protein Glycoprotein As a polypeptide is synthesized on a ribosome, the growing chain enters the cisterna of the RER. The polypeptide assumes its secondary and tertiary structure. The complete protein may become an enzyme or a glycoprotein. Transport vesicles deliver proteins, enzymes, and glycoproteins to the Golgi apparatus. The structure and function of rough endoplasmic reticulum (RER) Glycoproteins, proteins, and enzymes are packaged in transport vesicles.
© 2011 Pearson Education, Inc. Module 3.4: Ribosomes Function of RER Polypeptide synthesized on attached ribosome Growing chain enters cisterna Polypeptide assumes secondary/tertiary structures Completed protein may become enzyme or glycoprotein Products not destined for RER are packaged into transport vesicles Deliver products to Golgi apparatus
© 2011 Pearson Education, Inc. Module 3.4 Review a. Describe the immediate cellular destinations of newly synthesized proteins from free ribosomes and fixed ribosomes. b. Describe the structure of smooth endoplasmic reticulum. c. Why do certain cells in the ovaries and testes contain large amounts of smooth endoplasmic reticulum (SER)?
© 2011 Pearson Education, Inc. Module 3.5: Golgi apparatus Golgi apparatus Functions 1.Renews or modifies plasma membrane 2.Modifies or packages secretions for release from cell (exocytosis) 3.Packages special enzymes within vesicles for use in cytosol Typically consist of 5–6 flattened discs (cisternae) May be more than one in a cell Situated near nucleus Animation: Golgi Apparatus
© 2011 Pearson Education, Inc. Module 3.5: Golgi apparatus Golgi apparatus Steps of function 1.Products from RER arrive at the forming face in transport vesicles 2.Transport vesicles fuse with Golgi apparatus and empty contents into cisternae Enzymes modify products 3.New vesicles move material between cisternae 4. Product arrives at maturing face
© 2011 Pearson Education, Inc. Module 3.5: Golgi apparatus Golgi apparatus Products Membrane renewal vesicles Add to plasma membrane Secretory vesicles Contain products to be discharged from the cell Fuse with plasma membrane and release contents into extracellular environment Enzymes for cytosol Contained within lysosomes (lyso-, a loosening + soma, body) Isolate damaging chemical reactions
© 2011 Pearson Education, Inc. Module 3.5: Golgi apparatus Lysosomes Isolated intracellular location for toxic chemicals involved in breakdown and recycling of large organic molecules Three basic functions 1.May fuse with another organelle to activate digestive enzymes 2.May fuse with another vesicle containing fluid or solid extracellular materials 3.May break down with cell injury or death causing autolysis (enzymes destroy cytoplasm) “Suicide packets”
© 2011 Pearson Education, Inc. Figure The three basic functions of lysosomes Waste products and debris are ejected from the cell when the vesicle fuses with the plasma membrane. Vesicles containing fluids or solids may form at the surface of the cell. Extracellular solid or fluid Lysosomal enzymes are activated by fusion with another vesicle or organelle As digestion occurs, nutrients are reabsorbed for recycling. Lysosomes initially contain inactive enzymes. As the materials or pathogens are broken down by lysosomal enzymes, released nutrients are absorbed. Golgi apparatus Function 1: A lysosome may fuse with the mem- brane of another organelle, such as a mitochondrion. This activates the enzymes and begins the digestion of the lysosomal contents. Function 2: A lysosome may also fuse with a vesicle containing fluid or solid materials from outside the cell. Function 3: The lysosomal membrane may break down following injury to, or death of, the cell. The digestive enzymes become active and then attack the cytoplasm in a destructive process known as autolysis. For this reason, lysosomes are sometimes called “suicide packets.”
© 2011 Pearson Education, Inc. Module 3.5: Golgi apparatus Membrane flow Continuous movement and exchange of materials between organelles using vesicles Can replace parts of cell membrane to allow cell to grow, mature, or respond to changing environment
© 2011 Pearson Education, Inc. Module 3.5 Review a. List the three major functions of the Golgi apparatus. b. The Golgi apparatus produces lysosomes. What do these lysosomes contain? c. Describe three functions of lysosomes.
© 2011 Pearson Education, Inc. Module 3.6: Mitochondria Mitochondria (mitos, thread + chondrion, granule) Produce energy (ATP) for cells through the breakdown of carbohydrates (glucose) Vary widely in shape and number Red blood cells have none Cardiac muscle cells are 30% mitochondria by volume Animation: Mitochondria
© 2011 Pearson Education, Inc. Figure The role of mitochondria in the production of the high-energy compound ATP Although most ATP production occurs inside mitochodria, the first steps take place in the cytosol. In this reaction sequence, called glycolysis (glycos, sugar + -lysis, a loosening), each glucose molecule is broken down into two molecules of pyruvate. The pyruvate molecules are then absorbed by mitochondria. In the mitochondrial matrix, a CO 2 molecule is removed from each absorbed pyruvate molecule; the remainder enters the citric acid cycle, of TCA (tricarboxylic acid) cycle, an enzymatic pathway that systematically breaks down the absorbed pyruvate remnant into carbon dioxide and hydrogen atoms. The hydrogen atoms are delivered to enzymes and coenzymes of the cristae which catalyze the synthesis of ATP from ADP and phosphate. At the end of this process, oxygen combines with the hydrogen atoms to form water molecules. The energy released during a series of steps performs the enzymatic conversion of ADP to ATP, which leaves the mitochondrion. CYTOPLASM Glucose 2 Pyruvate Citric acid cycle Enzymes and coenzymes of cristae MITOCHONDRION MATRIX ADP + phosphate
© 2011 Pearson Education, Inc. Module 3.6: Mitochondria Mitochondria Double membrane Outer (surrounds organelle) Inner (contains numerous folds called cristae) Encloses liquid (matrix) Cristae increase surface area for energetic reactions
© 2011 Pearson Education, Inc. Figure Matrix Cristae Cytoplasm of cell A colorized TEM of a mitochondrion TEM x 50,000
© 2011 Pearson Education, Inc. Module 3.6: Mitochondria Steps of ATP production 1. Glycolysis (glycos, sugar + -lysis, a loosening) Occurs in cytosol 1 glucose 2 pyruvate Pyruvate absorbed into mitochondria 2. In mitochondrial matrix CO 2 removed from pyruvate Enters citric acid (or TCA, tricarboxylic acid) cycle Systematically removes CO 2 and hydrogen atoms
© 2011 Pearson Education, Inc. Module 3.6: Mitochondria Steps of ATP production (continued) 3.Enzymes and coenzymes use hydrogen atoms to catalyze ATP from ADP Also forms H 2 O 4.ATP leaves mitochondrion
© 2011 Pearson Education, Inc. Module 3.6 Review a. Describe the structure of a mitochondrion. b. Most of a cell’s ATP is produced within its mitochondria. What gas do mitochondria require to produce ATP? c. What does the presence of many mitochondria imply about a cell’s energy requirements?
© 2011 Pearson Education, Inc. Section 2: Nucleus Learning Outcomes 3.7 Explain the functions of the cell nucleus, and discuss the nature and importance of the genetic code. 3.8 Summarize the process of protein synthesis. 3.9 Summarize the process of transcription Summarize the process of translation.
© 2011 Pearson Education, Inc. Section 2: Nucleus Nucleus Usually largest cellular structure Control center for cellular operations Can direct synthesis of >100,000 different proteins Coded in sequence of nucleotides Determines cell structure/function Usually only one per cell Exceptions: Multiple: skeletal muscle cell None: mature red blood cells
© 2011 Pearson Education, Inc. Section 2: Nucleus The nucleus directs cellular responses to environmental (ECF) changes Short-term adjustments Enzyme activity changes Long-term adjustments Changes in enzymes produced Changes in cell structure from changes in structural proteins Often occur as part of growth, development, and aging
© 2011 Pearson Education, Inc. Figure 3 Section 2 The role of the nucleus in preserving homeostasis at the cellular level Changes in the composition of the ECF Binding to membrane receptors Diffusion through membrane channels EXTRACELLULAR FLUID (ECF) Plasma membrane SHORT-TERM ADJUSTMENTS LONG-TERM ADJUSTMENTS CYTOPLASM Binding to nuclear receptors that alter genetic activity DNA in nucleus Enzyme activation or inactivation Changes in the bio- chemical processes under way in the cell resulting from the synthesis of additional enzymes, fewer enzymes, or different enzymes Changes in the physical structure of the cell due to altera- tions in the rates or types of structural proteins synthesized
© 2011 Pearson Education, Inc. Module 3.7: Nuclear structure Nuclear structures and functions Nuclear envelope Separates nucleus from cytoplasm Double membrane Perinuclear space (peri-, around) Space between layers Nuclear pores Allow passage of small molecules and ions
© 2011 Pearson Education, Inc. Module 3.7: Nuclear structure Nuclear structures and functions (continued) Nucleoplasm Fluid contents of nucleus Fine filaments Ions Enzymes RNA and DNA nucleotides Small amounts of RNA DNA
© 2011 Pearson Education, Inc. Module 3.7: Nuclear structure Nuclear structures and functions (continued) Nucleoli (singular, nucleolus) Transient, clear nuclear organelles Composed of: RNA Enzymes Proteins (histones) Form around DNA instructions for forming proteins/RNA Assemble RNA subunits Many found in large, protein-producing cells Liver Nerve Muscle
© 2011 Pearson Education, Inc. Figure The structure of the nucleus Nuclear envelope Perinuclear space Nuclear pores Nucleoplasm Nucleolus
© 2011 Pearson Education, Inc. Module 3.7: Nuclear structure DNA Instructions for protein synthesis Strands coiled Wrap around histone molecules forming nucleosomes Loosely coiled (chromatin) in nondividing cells Tightly coiled (chromosomes) in dividing cells To begin, two copies of each chromosome held together at centromere 23 paired chromosomes in somatic (general body) cells One each from mother/father Carry instructions for proteins and RNA Also some regulatory and unknown functions
© 2011 Pearson Education, Inc. Figure The coiled structure of DNA in the nucleus of a nondividing cell Nucleus of nondividing cell Chromatin Nucelosome Histones DNA double helix
© 2011 Pearson Education, Inc. Figure The tighter coiling of DNA to form chromosomes in dividing cells Dividing cell Centromere Visible chromosome Supercoiled region
© 2011 Pearson Education, Inc. Module 3.7 Review a. What molecule in the nucleus contains instructions for making proteins? b. Describe the contents and the structure of the nucleus. c. How many chromosomes are contained within a typical somatic cell?
© 2011 Pearson Education, Inc. Module 3.8: Protein synthesis DNA Long parallel chains of nucleotides Chains held by hydrogen bonds Four nitrogenous bases 1. Adenine (A) 2. Thymine (T) 3. Cytosine (C) 4. Guanine (G) Genetic code (sequence of nucleotides) Triplet code (three nucleotides specify single amino acid)
© 2011 Pearson Education, Inc. Figure 3.8 2
© 2011 Pearson Education, Inc. Module 3.8: Protein synthesis DNA (continued) Gene Functional unit of heredity All the DNA nucleotides needed to produce a specific protein Size varies (~300 3000 nucleotides)
© 2011 Pearson Education, Inc. Module 3.8: Protein synthesis Gene activation Removal of histones and DNA uncoiling Messenger RNA (mRNA) Assembled by enzymes Connecting complementary RNA nucleotides (A, G, C, U) Contains information in triplets (codons) Leaves nucleus through pores Transfer RNA (tRNA) Contains triplets (anticodons) that bind to mRNA codons Each type carries a specific amino acid linked to form a polypeptide
© 2011 Pearson Education, Inc. Module 3.8: Protein synthesis Animation: Protein Synthesis: RNA Polymerase Animation: Protein Synthesis: Transcription and Translation
© 2011 Pearson Education, Inc. Figure – 6 The key events of protein synthesis Uncoiling of the portion of DNA molecule containing an activated gene Assembly of an mRNA strand by enzymes Binding of transfer RNA (tRNA) molecules carrying a specific amino acid Linking of amino acids to form a polypeptide Polypeptide methionine-proline-serine-leucine mRNA strand tRNA attaches to mRNA Amino acid Anticodon Codon Codon on mRNA The mRNA strand containing the complementary codons passes through a nuclear pore and enters the cytoplasm. Enzyme Paired DNA strands DNA triplets are exposed to the nucleoplasms
© 2011 Pearson Education, Inc. Figure A summary of how DNA codes for a protein The DNA triplets determine the sequence of mRNA codons. The mRNA codons determine the sequence of tRNAs. The sequence of tRNAs determines the sequence of amino acids in the polypeptide or protein.
© 2011 Pearson Education, Inc. Module 3.8 Review a. List the three types of RNA involved in protein synthesis. b. What is a gene? c. Why is the genetic code described as a triplet code?
© 2011 Pearson Education, Inc. Module 3.9: Transcription Transcription (“to copy” or “rewrite”) Production of RNA from DNA template All three types of RNA are formed Example: mRNA (information for synthesizing proteins)
© 2011 Pearson Education, Inc. Module 3.9: Transcription Steps of transcription 1. Gene activation Occurs at control segment (1st segment of gene) Template strand (One DNA strand used to synthesize RNA) 2. RNA polymerase (enzyme) Binds to promoter Assembles mRNA strand Complementary to DNA Example: (DNA triplet TAC = mRNA AUG) Hydrogen bonds between nucleotides
© 2011 Pearson Education, Inc. Figure Events in the process of transcription of mRNA Gene DNA Gene activation, which results in temporary disruption of the hydrogen bonds between the nitrogenous bases of the two DNA strands The template strand is the DNA strand that will be used to synthesize RNA. The segment at the start of the gene is known as the control segment. Triplet 1 Triplet 2 Triplet 3 Triplet 4 Complementary triplets Adenine Guanine Cytosine Uracil (RNA) Thymine (DNA) The enzyme RNA polymerase binds to the exposed control segment and, using the triplets as a guide, assembles a strand of mRNA.
© 2011 Pearson Education, Inc. Module 3.9: Transcription Steps of transcription (continued) 3. Transcription ends Stop codon reached mRNA detaches Complementary DNA strands reassociate (hydrogen bonding between complementary base pairs)
© 2011 Pearson Education, Inc. Figure – 3 Hydrogen bonding between the nitrogenous bases of the template strand and complementary nucleotides in the nucleoplasm Conclusion of transcription when stop codon is reached RNA polymerase RNA nucleotide Codon 1 RNA polymerase works only on RNA nucleotides—it can attach adenine, guanine, cytosine, or uracil, but never thymine. If the DNA triplet is TAC, the corresponding mRNA codon will be AUG. mRNA strand Codon 1 Codon 2 Codon 3 Codon 4 (stop codon) RNA polymerase The production of functional mRNA from immature mRNA Immature mRNA Introns removed Exons spliced together to from mature mRNA Adenine Guanine Cytosine Uracil (RNA) Thymine (DNA) Events in the process of transcription of mRNA (continued)
© 2011 Pearson Education, Inc. Module 3.9: Transcription Immature RNA Contains triplets not needed for protein synthesis “Edited” before leaving nucleus through pores Introns (removed nonsense regions) Exons (remaining coding segments) Creates shorter, functional mRNA Changing “edits” can produce mRNAs for different proteins
© 2011 Pearson Education, Inc. Figure The production of functional mRNA from immature mRNA Immature mRNA Introns removed Exons spliced together to form mature mRNA
© 2011 Pearson Education, Inc. Module 3.9 Review a. Define DNA template strand. b. What is transcription? c. What process would be affected if a cell could not synthesize the enzyme RNA polymerase?
© 2011 Pearson Education, Inc. Module 3.10: Translation Translation (translate nucleic acids to proteins) Uses mRNA created in nucleus Leaves via nuclear pores Occurs in cytoplasm Animation: Protein Synthesis: Translation Initiation
© 2011 Pearson Education, Inc. Module 3.10: Translation Steps of translation 1.mRNA binds to small ribosomal subunit Binding between mRNA and tRNA mRNA codons with tRNA anticodons 2.Small and large ribosomal subunits assemble around mRNA strand Additional tRNAs arrive More than 20 kinds At least one for each amino acid
© 2011 Pearson Education, Inc. Figure – 2 The process of translation NUCLEUS Entry of mRNA into cytoplasm Adenine Guanine Cytosine Uracil Binding of mRNA strand to a small ribosomal subunit and arrival of the first tRNA Small ribosomal subunit Start codon mRNA strand tRNA binding sites Anticodon tRNA Amino acid Joining of small and large ribosomal subunits around the mRNA strand and arrival of additional tRNAs Large ribosomal subunit
© 2011 Pearson Education, Inc. Module 3.10: Translation Steps of translation (continued) 3.Ribosome attaches to next complementary tRNA 4.Ribosome links amino acids forming dipeptide More tRNAs arrive and continue forming polypeptide 5.Stops once stop codon is reached on mRNA Ribosomal subunits detach Leaves intact mRNA and new polypeptide Animation: Protein Synthesis: Sequence of Amino Acids in the Newly Synthesized Polypeptide
© 2011 Pearson Education, Inc. Figure – 5 Stop codon Attachment of tRNA with anticodon that is complementary to codon on RNA strand Formation of a depeptide, release of first tRNA, and arrival of another tRNA Peptide bond Completion of polypeptide and detachment of ribosomal subunits Completed polypeptide Large ribosomal subunit Small ribosomal subunit Adenine Guanine Cytosine Uracil The process of translation (continued)
© 2011 Pearson Education, Inc. Module 3.10: Translation Translation Produces a typical protein in ~20 seconds mRNA can interact with other ribosomes and produce more proteins Multiple ribosomes can attached to a single mRNA strand to quickly produce many proteins Animation: Transcription Translation
© 2011 Pearson Education, Inc. Module 3.10 Review a. What is translation? b. The nucleotide sequence of three mRNA codons is AUU-GCA-CUA. What is the complementary anticodon sequence for the second codon? c. During the process of transcription, a nucleotide was deleted from an mRNA sequence that coded for a protein. What effect would this deletion have on the amino acid sequence of the protein?
© 2011 Pearson Education, Inc. Section 3: Membrane Transport Learning Outcomes 3.11 Explain the process of diffusion, and identify its significance to the body Explain the process of osmosis, and identify its significance to the body Describe carrier-mediated transport and its role in the absorption and removal of specific substances Describe vesicular transport as a mechanism for facilitating the absorption or removal of specific substances from cells.
© 2011 Pearson Education, Inc. Section 3: Membrane Transport Plasma membrane Acts as a barrier separating cytosol and ECF Must still coordinate cellular activity with extracellular environment Permeability (determines which substances can cross membrane) Freely permeable (any substances) Selectively permeable (some substances cross) Impermeable (none can pass) No living cell is impermeable
© 2011 Pearson Education, Inc. Figure 3 Section 3 1 Permeability characteristics of membranes Freely permeable membranesSelectively permeable membranesImpermeable membranes Freely permeable membranes allow any substance to pass without difficulty. Selectively permeable membranes, such as plasma membranes, permit the passage of some materials and prevent the passage of others. Nothing can pass through impermeable membranes. Cells may be impermeable to specific substances, but no living cell has an impermeable membrane. Protein Lipids Ions —— — Water Carbohydrates
© 2011 Pearson Education, Inc. Section 3: Membrane Transport Selectively permeable membranes Selective based on: 1. Characteristics of material to pass Size Electrical charge Molecular shape Lipid solubility Other factors 2. Characteristics of membrane What lipids and proteins present How components are arranged
© 2011 Pearson Education, Inc. Section 3: Membrane Transport Selectively permeable membranes Types of membrane transport 1. Passive (do not require ATP) Diffusion Carrier-mediated transport 2. Active (require ATP) Vesicular transport Carrier-mediated transport
© 2011 Pearson Education, Inc. Figure 3 Section 3 2 Characteristics of selectively permeable membranes EXTRACELLULAR FLUID CYTOPLASM Materials may cross the plasma membrane through active or passive mechanisms. Passive mechanisms do not require ATP. Active mechanisms require ATP. Diffusion is movement driven by concentration differences. Carrier-mediated transport involves carrier proteins, and the movement may be passive or active. Vesicular transport involves the formation of intracellular vesicles; this is an active process. Plasma membrane
© 2011 Pearson Education, Inc. Module 3.11: Diffusion Diffusion Continuous random movement of ions or molecules in a liquid or gas resulting in even distribution Gradient Concentration difference or when molecules are not evenly distributed At an even distribution, molecular motion continues but no net movement Slow in air and water but important over small distances Animation: Membrane Transport: Diffusion
© 2011 Pearson Education, Inc. Figure
© 2011 Pearson Education, Inc. Module 3.11: Diffusion In ECF Water and solutes diffuse freely Across plasma membrane Selectively restricted diffusion Movement across lipid portion of membrane Examples: lipids, lipid-soluble molecules, soluble gases Movement through membrane channel Examples: water, small water-soluble molecules, ions Movement using carrier molecules Example: large molecules
© 2011 Pearson Education, Inc. Figure Large molecules that cannot fit through the membrane channels and cannot diffuse through the membrane lipids can only cross the plasma membrane when transported by a carrier mechanism. Lipids, lipid-soluble molecules, and soluble gases (O 2 and CO 2 ) can diffuse across the lipid bilayer of the plasma membrane. The effects of the plasma membrane, a selectively permeable membrane, on the diffusion of various substances Plasma membrane Channel protein EXTRACELLULAR FLUID CYTOPLASM Water, small water-soluble molecules, and ions diffuse through membrane channels that vary in shape, size, and specificity.
© 2011 Pearson Education, Inc. Module 3.11: Diffusion Factors that influence diffusion rates: Distance (inversely related) Molecule size (inversely related) Temperature (directly related) Gradient size (directly related) Electrical forces Attraction of opposite charges (+,–) Repulsion of like charges (+,+ or –,–)
© 2011 Pearson Education, Inc. Module 3.11 Review a. Define diffusion. b. Identify factors that influence diffusion rates. c. How would a decrease in the oxygen concentration in the lungs affect the diffusion of oxygen into the blood?
© 2011 Pearson Education, Inc. Module 3.12: Osmosis Osmosis (osmos, a push) Net diffusion of water across a membrane Maintains similar overall solute concentrations between the cytosol and extracellular fluid Osmotic flow Movement of water driven by osmosis Osmotic pressure Indication of force of pure water moving into a solution with higher solute concentration Hydrostatic pressure Fluid force Can be estimate of osmotic pressure when applied to stop osmotic flow
© 2011 Pearson Education, Inc. Figure Osmotic flow, the movement of water driven by osmosis Water molecules Solute molecules Selectively permeable membrane A selectively permeable membrane separates these two solutions, which have different solute concentrations. Water molecules (small blue dots) begin to cross the membrane toward solution B, the solution with the higher concentration of solutes (larger pink circles). At equilibrium, the solute concentrations on the two sides of the membrane are equal. Note that the volume of solution B has increased at the expense of that of solution A. Pushing against a fluid generates hydrostatic pressure. The osmotic pressure of solution B is equal to the amount of hydrostatic pressure, indicated by the weight, required to stop the osmotic flow. Applied force Volumes equal Volume increased Volume decreased Original level
© 2011 Pearson Education, Inc. Module 3.12: Osmosis Osmolarity (osmotic concentration) Total solute concentration in an aqueous solution Tonicity Effect of osmotic solutions on cell volume Three effects 1. Isotonic (iso-, same + tonos, tension) Solution that does not cause osmotic flow across membrane
© 2011 Pearson Education, Inc. Module 3.12: Osmosis Tonicity Three effects (continued) 2. Hypotonic Causes osmotic flow into cell Example: hemolysis (hemo-, blood + lysis, loosening) 3. Hypertonic Causes osmotic flow out of cell Example: crenation of RBCs
© 2011 Pearson Education, Inc. Module 3.12: Osmosis Importance of tonicity vs. osmolarity: Example Administering large fluid volumes to patients with blood loss or dehydration Administered solution has same osmolarity as ICF but higher concentrations of individual ions/molecules Diffusion of solutes may occur across cell membrane Water will follow through osmosis Cell volume increases Normal saline 0.9 percent or 0.9 g/dL of NaCl Isotonic with blood
© 2011 Pearson Education, Inc. Module 3.12 Review a. Describe osmosis. b. Contrast the effects of a hypotonic solution and a hypertonic solution on a red blood cell. c. Some pediatricians recommend using a 10 percent salt solution to relieve nasal congestion in infants. Explain the effects this treatment would have on the cells lining the nasal cavity. Would it be effective?
© 2011 Pearson Education, Inc. Module 3.13: Carrier-mediated transport Carrier-mediated transport Hydrophilic or large molecules transported across cell membrane by carrier proteins Many move specific molecules through the plasma membrane in only one direction Cotransport (>1 substance same direction) Countertransport (2 substances in opposite directions) Carrier called exchange pump
© 2011 Pearson Education, Inc. Module 3.13: Carrier-mediated transport Carrier-mediated transport Three types 1. Facilitated diffusion Requires no ATP (= passive) Movement limited by number of available carrier proteins (= can become saturated) 2. Active transport Requires energy molecule or ATP (= active) Independent of concentration gradient Examples: Ion pumps (Na +, K +, Ca 2+, and Mg 2+ ) Sodium–potassium ATPase
© 2011 Pearson Education, Inc. Module 3.13: Carrier-mediated transport Animation: Membrane Transport: Facilitated Diffusion Animation: Membrane Transport: Active Transport
© 2011 Pearson Education, Inc. Figure Facilitated diffusion EXTRACELLULAR FLUID Glucose molecule Carrier protein Receptor site CYTOPLASM Facilitated diffusion begins when a specific molecule, such as glucose, binds to a receptor site on the integral protein. The shape of the protein then changes, moving the molecule across the plasma membrane. The carrier protein then releases the transported molecule into the cytoplasm. Note that this was accomplished without ever creating a continuous open channel between the extracellular fluid and the cytoplasm. Glucose released into cytoplasm
© 2011 Pearson Education, Inc. Figure On average, for each ATP molecule consumed, three sodium ions are ejected and the cell reclaims two potassium ions. The energy demands are impressive: Sodium- potassium ATPase may use up to 40 percent of the ATP produced by a resting cell! Sodium ion concentrations are high in the extracellular fluids, but low in the cytoplasm. The distribution of potassium in the body is just the opposite: low in the extracellular fluids and high in the cytoplasm. As a result, sodium ions slowly diffuse into the cell, and potassium ions diffuse out through leak channels. Homeostasis within the cell depends on the ejection of sodium ions and the recapture of lost potassium ions. The sodium–potassium exchange pump is a carrier protein called sodium–potassium ATPase. It exchanges intracellular sodium for extracellular potassium. EXTRACELLULAR FLUID Sodium– potassium exchange pump CYTOPLASM Active transport
© 2011 Pearson Education, Inc. Module 3.13: Carrier-mediated transport Carrier-mediated transport (continued) Three types (continued) 3. Secondary active transport Transport mechanism does not require ATP Cell often needs ATP to maintain homeostasis associated with transport
© 2011 Pearson Education, Inc. Figure A sodium ion and a glucose molecule bind to receptor sites on the carrier protein. CYTOPLASM Glucose molecule Sodium ion Secondary active transport The carrier protein then changes shape, opening a path to the cytoplasm and releasing the transported materials. It then reassumes its original shape and is ready to repeat the process. To preserve homeostasis, the cell must then expend ATP to pump the arriving sodium ions out of the cell by using the sodium–potassium exchange pump. It thus “costs” the cell one ATP for every three glucose molecules it transports into the cell. Na + –K + pump + +
© 2011 Pearson Education, Inc. Module 3.13 Review a. Describe the process of carrier-mediated transport. b. What do the transport processes of facilitated diffusion and active transport have in common? c. During digestion, the concentration of hydrogen ions (H + ) in the stomach contents increases to many times that in cells lining the stomach. Which transport process could be responsible?
© 2011 Pearson Education, Inc. Module 3.14: Vesicular transport Vesicular transport Materials move across cell membrane in small membranous sacs Sacs form at or fuse with plasma membrane Two major types (both require ATP) 1. Endocytosis 2. Exocytosis
© 2011 Pearson Education, Inc. Module 3.14: Vesicular transport Vesicular transport (continued) Two major types (both require ATP) 1. Endocytosis (into cell using endosomes) a. Receptor-mediated endocytosis 1)Ligand binds to receptor 2)Plasma membrane folds around receptors bound to ligands 3)Coated vesicle forms 4)Vesicle fuses with lysosomes 5)Ligands freed and enter cytosol 6)Lysosome detaches from vesicle 7)Vesicle fuses with plasma membrane again
© 2011 Pearson Education, Inc. Figure Receptor-mediated endocytosis Receptors bound to ligands cluster together. Once an area of the plasma membrane has become covered with ligands, it forms grooves or pockets that move to one area of the cell and then pinch off to form an endosome. The endosomes produced in this way are called coated vesicles, because they are “coated” by a protein-fiber network on the inner membrane surface. The coated vesicles fuse with lysosomes filled with digestive enzymes. The lysosomal enzymes then free the ligands from their receptors, and the ligands enter the cytosol by diffusion or active transport. The vesicle membrane detaches from the secondary lysosome. After the vesicle membrane detaches, it returns to the cell surface, where its recep- tors become available to bind more ligands. EXTRACELLULAR FLUID Ligands Ligand receptors Ligands binding to receptors Exocytosis Endocytosis CYTOPLASM Coated vesicle Ligands removed Lysosome Fusion Detachment Receptor-mediated endocytosis begins when materials in the extracellular fluid bind to receptors on the membrane surface. Most receptor molecules are glycoproteins, and each binds to a specific target molecule, or ligand, such as a transport protein or a hormone.
© 2011 Pearson Education, Inc. Module 3.14: Vesicular transport Vesicular transport (continued) Two major types (both require ATP) 1. Endocytosis (into cell using endosomes) (continued) b. Pinocytosis (“cell drinking”) Formation of endosomes with ECF No receptor proteins involved c. Phagocytosis (“cell eating”) Produces phagosomes containing solids Phagocytes or macrophages perform phagocytosis 2. Exocytosis Vesicle discharges materials into ECF
© 2011 Pearson Education, Inc. Figure Endosome Plasma membrane Pinocytosis begins with the formation of deep grooves or pockets that then pinch off and enter the cytoplasm. The steps are similar to those of receptor-mediated endocytosis, but they occur in the absence of ligand binding. Pinocytosis TEM 20,000 Cytoplasm Surrounding tissue Bloodstream
© 2011 Pearson Education, Inc. Figure Bacterium Pseudopodium Phagocytosis Lysosome Golgi apparatus Exocytosis Phagocytosis begins when cytoplas- mic extensions called pseudopodia (soo-dō-PŌ-dē-ah; pseduo-, false podon, foot; singular pseudopodium) surround the object. The pseudopodia then fuse at their tips to form a phagosome containing the targeted material. This vesicle then fuses with many lysosomes, whereupon its contents are digested by lysosomal enzymes. Released nutrients diffuse into the surrounding cytoplasm. The residue is then ejected from the cell through exocytosis. The vesicular events linking phagocytosis and exocytosis
© 2011 Pearson Education, Inc. Module 3.14 Review a. Describe endocytosis. b. Describe exocytosis. c. When they encounter bacteria, certain types of white blood cells engulf the bacteria and bring them into the cell. What is this process called?
© 2011 Pearson Education, Inc. Section 4: Cell Life Cycle Learning Outcomes 3.15 Describe interphase, and explain its significance Describe the process of mitosis, and the cell life cycle Discuss the relationship between cell division and cancer.
© 2011 Pearson Education, Inc. Section 4: Cell Life Cycle Cell division Production of daughter cells from single cell Important in organism development and survival Cells have varying life spans and abilities to divide Often genetically controlled death occurs (apoptosis) Two types 1. Mitosis (2 daughter cells, each with 46 chromosomes) 2. Meiosis (sex cells, each with only 23 chromosomes) Animation: Cell Life Cycle
© 2011 Pearson Education, Inc. Section 4: Cell Life Cycle Mitosis Pair of daughter cells half the size of parent cell Grow to size of original cell before dividing Identical copies of chromosomes in each Ends at complete cell separation (= cytokinesis) Followed by nondividing period (= interphase) Cell performs normal activities OR Prepares to divide again Chromosomes duplicated Associated proteins synthesized
© 2011 Pearson Education, Inc. Figure 3 Section 4 1 The production of a pair of daughter cells from a single cell division Original cell Cell division Daughter cells
© 2011 Pearson Education, Inc. Module 3.15: Interphase Phases G 0 (performing normal cell functions) Examples: Skeletal muscle cells (stay in this phase forever) Stem cells (never enter G 0 ; divide repeatedly) G 1 (normal cell function plus growth and duplication of organelles) S (duplication of chromosomes) G 2 (last minute protein synthesis and centriole replication)
© 2011 Pearson Education, Inc. Module 3.15: Interphase DNA replication Strands unwind DNA polymerase binds Assembles new DNA strand covalently linking nucleotides Works only in one direction One polymerase works continuously along one strand toward “zipper” One polymerase works away from “zipper” As “unzipping” occurs, another polymerase binds closer point of unzipping Two new DNA segments bound with ligases Two identical DNA strands formed
© 2011 Pearson Education, Inc. Figure The events in DNA replication, which occurs during the S phase of interphase DNA replication beings when enzymes unwind the strands and disrupt the hydrogen bonds between the bases. As the strands unwind, molecules of DNA polymerase bind to the exposed nitrogenous bases. This enzyme (1) promotes bonding between the nitrogenous bases of the DNA strand and complementary DNA nucleotides dissolved in the nucleoplasm and (2) links the nucleotides by covalent bonds. As the two original stands gradually separate, DNA polymerase binds to the strands. DNA polymerase can work in only one direction along a strand of DNA, but the two strands in a DNA molecule are oriented in opposite directions. The DNA polymerase bound to the upper strand shown here adds nucleotides to make a single, continuous complementary copy that grows toward the “zipper.” DNA polymerase on the lower strand can work only away from the zipper. So the first DNA polymerase to bind to this strand must add nucleotides and build a complementary DNA strand moving from left to right. As the two original strands continue to unzip, additional nucleotides are continuously being exposed to the nucleoplasm. The first DNA polymerase on this strand cannot go into reverse; it can only continue to elongate the strand it already started. Thus, a second DNA polymerase must bind closer to the point of unzipping and assemble a comple- mentary copy (segment 2) that grows until it “bumps into” segment 1 created by the first DNA polymerase. The two segments are then spliced together by enzymes called ligases (LĪ-gās-ez; liga, to tie). Adenine Guanine Cytosine Thymine Segment 2 Segment 1 DNA nucleotide
© 2011 Pearson Education, Inc. Figure Duplicated DNA double helices
© 2011 Pearson Education, Inc. Module 3.15 Review a. Describe interphase, and identify its stages. b. What enzymes must be present for DNA replication to proceed normally? c. A cell is actively manufacturing enough organelles to serve two functional cells. This cell is probably in what phase of interphase?
© 2011 Pearson Education, Inc. Module 3.16: Mitosis Mitosis Division and duplication of cell’s nucleus Phases 1. Prophase (pro-, before) Paired chromosomes tightly coiled Chromatid (each copy) Connected at centromere with raised area (kinetochore) Replicated centrioles move to poles Astral rays (extend from centrioles) Spindle fibers (interconnect centriole pairs)
© 2011 Pearson Education, Inc. Figure – 2 The events in mitosis Centrioles in centrosome Nucleus Interphase, which precedes mitosis Prophase, the first phase of mitosis The nuclear membrane disintegrates during this period. The centrioles have replicated, and the pairs now move to opposite sides of the nucleus. Microtubules extend outward from each pair of centrioles: astral rays extend into the cytoplasm, whereas spindle fibers interconnect the centriole pairs. Chromatids Kinetochore The kinetochore of each chromatid becomes attached to a spindle fiber.
© 2011 Pearson Education, Inc. Module 3.16: Mitosis Mitosis (continued) Phases (continued) 2. Metaphase (meta, after) Chromosomes align at metaphase plate 3. Anaphase (ana-, apart) Chromatids separate Drawn along spindle apparatus 4. Telophase (telo-, end) Cells prepare to enter interphase Cytoplasm constricts along metaphase plate (= cleavage furrow) Nuclear membranes re-form Chromosomes uncoil
© 2011 Pearson Education, Inc. Figure – 6 Metaphase Anaphase Metaphase plate The two chromatids are now pulled apart and drawn to opposite ends of the cell along the spindle apparatus (the complex of spindle fibers). Anaphase ends when the chromatids arrive near the centrioles at opposite ends of the cell. As the chromatids approach the ends of the spindle apparatus, the cytoplasm constricts along the plane of the metaphase plate, forming a cleavage furrow. Daughter cells CYTOKINESIS Telophase, the final phase of mitosis Cytokinesis The events in mitosis (continued)
© 2011 Pearson Education, Inc. Module 3.16: Mitosis Cytokinesis (cyto-, cell + kinesis, motion) Begins with formation of cleavage furrow Continues through telophase Completion marks end of cell division
© 2011 Pearson Education, Inc. Module 3.16 Review a. Define mitosis, and list its four stages. b. What is a chromatid, and how many would be present during normal mitosis in a human cell? c. What would happen if spindle fibers failed to form in a cell during mitosis?
© 2011 Pearson Education, Inc. Module 3.17: Tumors and cancer Cancer Illness that disrupts normal rates of cell division Characterized by permanent DNA sequence changes (= mutations) Most common in tissues with actively dividing cells Examples: skin, intestinal lining Compete with normal cells for resources
© 2011 Pearson Education, Inc. Module 3.17: Tumors and cancer Cancerous tumor (neoplasm; mass of cells) types 1. Benign Remain in original tissue 2. Malignant Accelerated growth due to blood vessel growth and supply to the area Invasion (cells migrating into surrounding tissues) Metastasis (formation of secondary tumors)
© 2011 Pearson Education, Inc. Module 3.17 Review a. Define metastasis. b. What is a benign tumor? c. Define cancer.
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