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3 Cellular Level of Organization.

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1 3 Cellular Level of Organization

2 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.

3 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.

4 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

5 Section 1: An Introduction to Cells
Cell theory Cells are building blocks of all plants and animals All new cells come from division of preexisting cells Cells are smallest unit that perform all vital physiological functions

6 The differentiation of the four tissue types from a single cell:
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. Nutrients O2 Division Wastes CO2 Cell Growth New cells The cell theory Epithelial tissue Connective tissue Figure 3 Section 1 An Introduction to Cells Muscle tissue The differentiation of the four tissue types from a single cell: the fertilized ovum Neural tissue Figure 3 Section 1 6

7 Section 1: An Introduction to Cells
Each cell maintains homeostasis Coordinated activities of cells allow homeostasis at higher organizational levels

8 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

9 Section 1: An Introduction to Cells
Extracellular fluid Watery medium surrounding cells Called interstitial fluid (interstitium, something standing between) in most tissues

10 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 Cytosol Intracellular fluid Organelles (“little organs”) Intracellular structures with specific functions

11 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

12 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

13 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

14 Module 3.1: Smallest living units of life
Organelles Ribosomes STRUCTURE: RNA and proteins Fixed: attached to endoplasmic reticulum Free: scattered in cytoplasm

15 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 Removal of damaged organelles or pathogens

16 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

17 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

18 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

19 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.

20 Module 3.2: Plasma membrane
Selectively permeable membrane that controls: Entry of ions and nutrients Elimination of wastes Release of secretions

21 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

22 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

23 Integral (transmembrane) proteins
Structure of the plasma membrane EXTRACELLULAR FLUID Glycocalyx (extracellular carbohydrates) Integral protein with channel Glycolipid Figure The plasma membrane isolates the cell from its environment and performs varied functions Integral glycoproteins = 2 nm CYTOPLASM Integral (transmembrane) proteins Peripheral proteins Cytoskeleton (microfilaments) Figure 23

24 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

25 The phospholipid bilayer that forms the plasma membrane
Hydrophilic heads Hydrophobic tails Figure The plasma membrane isolates the cell from its environment and performs varied functions Cholesterol Figure 25

26 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

27 Figure The plasma membrane isolates the cell from its environment and performs varied functions Figure 27

28 Figure The plasma membrane isolates the cell from its environment and performs varied functions Figure 28

29 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?

30 Module 3.3: Cytoskeleton Cytoskeleton (cellular framework) components
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)

31 Module 3.3: Cytoskeleton Cytoskeleton (cellular framework) components (continued) Intermediate filaments 7–11 nm in diameter Strongest and most durable cytoskeletal elements Microtubules ~25 nm in diameter Largest components of cytoskeleton Extend outward from centrosome (near nucleus)

32 Structures of the cytoskeleton
Microvilli Microfilaments Plasma membrane Terminal web Microvilli SEM X 30,000 Figure The cytoskeleton plays both a structural and a functional role Intermediate filaments Microtubule Secretory vesicle Mitochondrion Endoplasmic reticulum Figure 32

33 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

34 The structure of centrioles
Microtubules in centriole Figure The cytoskeleton plays both a structural and a functional role Figure 34

35 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

36 The structure of cilium
Plasma membrane Figure The cytoskeleton plays both a structural and a functional role Microtubules Basal body Figure 36

37 The action of a beating cilium
Power stroke Figure The cytoskeleton plays both a structural and a functional role Return stroke Figure 37

38 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?

39 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

40 The two subunits of a functional ribosome Small ribosomal subunit
Large ribosomal subunit The two subunits of a functional ribosome Figure Ribosomes are responsible for protein synthesis and are often associated with the endoplasmic reticulum Figure 40

41 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)

42 Module 3.4: Ribosomes Endoplasmic reticulum (ER) Two types
Smooth (SER) Lacks ribosomes Tubular cisternae 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

43 The structure of the endoplasmic reticulum (ER)
Nuclear envelope Tubular cisternae Cisternae Smooth endoplastic reticulum (SER) Figure Ribosomes are responsible for protein synthesis and are often associated with the endoplasmic reticulum Figure – 3 43

44 Figure Ribosomes are responsible for protein synthesis and are often associated with the endoplasmic reticulum Figure 44

45 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

46 The structure and function
of rough endoplasmic reticulum (RER) Fixed ribosomes mRNA strand Ribosome Transport vesicles Enzyme Figure Ribosomes are responsible for protein synthesis and are often associated with the endoplasmic reticulum Growing polypeptide 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. Glycoproteins, proteins, and enzymes are packaged in transport vesicles. Transport vesicles deliver proteins, enzymes, and glycoproteins to the Golgi apparatus. Figure 46

47 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

48 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)?

49 Module 3.5: Golgi apparatus
Functions Renews or modifies plasma membrane Modifies or packages secretions for release from cell (exocytosis) 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

50 Module 3.5: Golgi apparatus
Steps of function Products from RER arrive at the forming face in transport vesicles Transport vesicles fuse with Golgi apparatus and empty contents into cisternae Enzymes modify products New vesicles move material between cisternae Product arrives at maturing face

51 Module 3.5: 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

52 Module 3.5: Golgi apparatus
Lysosomes Isolated intracellular location for toxic chemicals involved in breakdown and recycling of large organic molecules Three basic functions May fuse with another organelle to activate digestive enzymes May fuse with another vesicle containing fluid or solid extracellular materials May break down with cell injury or death causing autolysis (enzymes destroy cytoplasm) “Suicide packets”

53 Figure 3.5.2 The Golgi apparatus is a packaging center
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 the materials or pathogens are broken down by lysosomal enzymes, released nutrients are absorbed. Lysosomes initially contain inactive enzymes. As digestion occurs, nutrients are reabsorbed for recycling. Golgi apparatus Figure The Golgi apparatus is a packaging center 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.” Figure 53

54 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

55 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.

56 Animation: Mitochondria
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

57 Figure 3.6.2 Mitochondria are the powerhouses of the cell
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. Glucose CYTOPLASM The energy released during a series of steps performs the enzymatic conversion of ADP to ATP, which leaves the mitochondrion. 2 Pyruvate MITOCHONDRION ADP + phosphate Enzymes and coenzymes of cristae Citric acid cycle Figure Mitochondria are the powerhouses of the cell MATRIX In the mitochondrial matrix, a CO2 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. Figure 57

58 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

59 Cytoplasm of cell Matrix Cristae A colorized TEM of a mitochondrion
Figure Mitochondria are the powerhouses of the cell A colorized TEM of a mitochondrion TEM x 50,000 Figure 59

60 Module 3.6: Mitochondria Steps of ATP production
Glycolysis (glycos, sugar + -lysis, a loosening) Occurs in cytosol 1 glucose  2 pyruvate Pyruvate absorbed into mitochondria In mitochondrial matrix CO2 removed from pyruvate Enters citric acid (or TCA, tricarboxylic acid) cycle Systematically removes CO2 and hydrogen atoms

61 Module 3.6: Mitochondria Steps of ATP production (continued)
Enzymes and coenzymes use hydrogen atoms to catalyze ATP from ADP Also forms H2O ATP leaves mitochondrion

62 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?

63 Section 2: Nucleus Learning Outcomes
Explain the functions of the cell nucleus, and discuss the nature and importance of the genetic code. Summarize the process of protein synthesis. Summarize the process of transcription. 3.10 Summarize the process of translation.

64 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

65 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

66 EXTRACELLULAR FLUID (ECF)
The role of the nucleus in preserving homeostasis at the cellular level Plasma membrane Binding to membrane receptors SHORT-TERM ADJUSTMENTS Changes in the composition of the ECF Enzyme activation or inactivation Diffusion through membrane channels LONG-TERM ADJUSTMENTS Changes in the bio- chemical processes under way in the cell resulting from the synthesis of additional enzymes, fewer enzymes, or different enzymes Binding to nuclear receptors that alter genetic activity Figure 3 Section 2 Structure and Function of the Nucleus Changes in the physical structure of the cell due to altera- tions in the rates or types of structural proteins synthesized DNA in nucleus CYTOPLASM Figure 3 Section 2 66

67 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

68 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

69 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

70 The structure of the nucleus
Perinuclear space Nuclear envelope Nuclear pores Figure The nucleus contains DNA, RNA, organizing proteins, and enzymes Nucleoplasm Nucleolus Figure 70

71 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

72 The coiled structure of DNA in the nucleus of a nondividing cell
Chromatin Nucelosome Histones DNA double helix Nucleus of nondividing cell Figure The nucleus contains DNA, RNA, organizing proteins, and enzymes Figure 72

73 The tighter coiling of DNA to form chromosomes in dividing cells
Centromere Supercoiled region Figure The nucleus contains DNA, RNA, organizing proteins, and enzymes Dividing cell Visible chromosome Figure 73

74 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?

75 Module 3.8: Protein synthesis
DNA Long parallel chains of nucleotides Chains held by hydrogen bonds Four nitrogenous bases Adenine (A) Thymine (T) Cytosine (C) Guanine (G) Genetic code (sequence of nucleotides) Triplet code (three nucleotides specify single amino acid)

76 Figure 3.8.2 Protein synthesis involves DNA, enzymes, and three types of RNA
76

77 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)

78 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

79 Module 3.8: Protein synthesis
Animation: Protein Synthesis: RNA Polymerase Animation: Protein Synthesis: Transcription and Translation

80 methionine-proline-serine-leucine
The key events of protein synthesis Uncoiling of the portion of DNA molecule containing an activated gene DNA triplets are exposed to the nucleoplasms Paired DNA strands Enzyme Assembly of an mRNA strand by enzymes The mRNA strand containing the complementary codons passes through a nuclear pore and enters the cytoplasm. Codon on mRNA Binding of transfer RNA (tRNA) molecules carrying a specific amino acid Amino acid Figure Protein synthesis involves DNA, enzymes, and three types of RNA tRNA attaches to mRNA Anticodon mRNA strand Codon Linking of amino acids to form a polypeptide Polypeptide methionine-proline-serine-leucine Figure – 6 80

81 acids in the polypeptide
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. Figure Protein synthesis involves DNA, enzymes, and three types of RNA Figure 81

82 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?

83 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)

84 Module 3.9: Transcription
Steps of transcription 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

85 Events in the process of transcription of mRNA
The template strand is the DNA strand that will be used to synthesize RNA. The enzyme RNA polymerase binds to the exposed control segment and, using the triplets as a guide, assembles a strand of mRNA. The segment at the start of the gene is known as the control segment. Triplet 1 1 1 Gene Triplet 2 2 Complementary triplets 2 3 Triplet 3 3 4 Figure Transcription encodes genetic instructions on a strand of RNA Triplet 4 4 Gene activation, which results in temporary disruption of the hydrogen bonds between the nitrogenous bases of the two DNA strands Adenine DNA Guanine Cytosine Uracil (RNA) Thymine (DNA) Figure 85

86 Module 3.9: Transcription
Steps of transcription (continued) Transcription ends Stop codon reached mRNA detaches Complementary DNA strands reassociate (hydrogen bonding between complementary base pairs)

87 Immature mRNA Events in the process of transcription of mRNA (continued) 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. Introns removed Exons spliced together to from mature mRNA The production of functional mRNA from immature mRNA mRNA strand Codon 1 Codon 2 Codon 1 Codon 3 Codon 4 (stop codon) RNA nucleotide Figure Transcription encodes genetic instructions on a strand of RNA RNA polymerase RNA polymerase Hydrogen bonding between the nitrogenous bases of the template strand and complementary nucleotides in the nucleoplasm Conclusion of transcription when stop codon is reached Adenine Guanine Cytosine Uracil (RNA) Thymine (DNA) Figure – 3 87

88 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

89 Exons spliced together The production of functional mRNA
Immature mRNA Introns removed Exons spliced together to form mature mRNA Figure Transcription encodes genetic instructions on a strand of RNA The production of functional mRNA from immature mRNA Figure 89

90 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?

91 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

92 Module 3.10: Translation Steps of translation
mRNA binds to small ribosomal subunit Binding between mRNA and tRNA mRNA codons with tRNA anticodons Small and large ribosomal subunits assemble around mRNA strand Additional tRNAs arrive More than 20 kinds At least one for each amino acid

93 The process of translation
NUCLEUS Amino acid tRNA Anticodon tRNA binding sites Entry of mRNA into cytoplasm Start codon mRNA strand Small ribosomal subunit Large ribosomal subunit Binding of mRNA strand to a small ribosomal subunit and arrival of the first tRNA Joining of small and large ribosomal subunits around the mRNA strand and arrival of additional tRNAs Figure Translation builds polypeptides as directed by an mRNA strand Adenine Guanine Cytosine Uracil Figure – 2 93

94 Module 3.10: Translation Steps of translation (continued)
Ribosome attaches to next complementary tRNA Ribosome links amino acids forming dipeptide More tRNAs arrive and continue forming polypeptide 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

95 The process of translation (continued)
Small ribosomal subunit Peptide bond Large ribosomal subunit Completed polypeptide 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 Completion of polypeptide and detachment of ribosomal subunits Figure Translation builds polypeptides as directed by an mRNA strand Adenine Guanine Cytosine Uracil Figure – 5 95

96 Animation: Transcription Translation
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

97 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?

98 Section 3: Membrane Transport
Learning Outcomes 3.11 Explain the process of diffusion, and identify its significance to the body. 3.12 Explain the process of osmosis, and identify its significance to the body. 3.13 Describe carrier-mediated transport and its role in the absorption and removal of specific substances. 3.14 Describe vesicular transport as a mechanism for facilitating the absorption or removal of specific substances from cells.

99 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

100 Permeability characteristics of membranes
Freely permeable membranes Selectively permeable membranes Impermeable membranes Ions Carbohydrates Ions Carbohydrates Ions Carbohydrates Protein Protein Protein Water Water Water Lipids Lipids Lipids 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. Figure 3 Section 3.1 How Things Enter and Leave the Cell Figure 3 Section 100

101 Section 3: Membrane Transport
Selectively permeable membranes Selective based on: Characteristics of material to pass Size Electrical charge Molecular shape Lipid solubility Other factors Characteristics of membrane What lipids and proteins present How components are arranged

102 Section 3: Membrane Transport
Selectively permeable membranes Types of membrane transport Passive (do not require ATP) Diffusion Carrier-mediated transport Active (require ATP) Vesicular transport

103 Characteristics of selectively permeable membranes
EXTRACELLULAR FLUID Materials may cross the plasma membrane through active or passive mechanisms. Plasma membrane 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. Figure 3 Section 3.2 How Things Enter and Leave the Cell CYTOPLASM Figure 3 Section 103

104 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

105 Figure 3.11.1 Diffusion is movement driven by concentration differences
105

106 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

107 The effects of the plasma membrane, a selectively permeable membrane, on
the diffusion of various substances Lipids, lipid-soluble molecules, and soluble gases (O2 and CO2) can diffuse across the lipid bilayer of the plasma membrane. Water, small water-soluble molecules, and ions diffuse through membrane channels that vary in shape, size, and specificity. EXTRACELLULAR FLUID Channel protein Plasma membrane Figure Diffusion is movement driven by concentration differences 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. CYTOPLASM Figure 107

108 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 –,–)

109 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?

110 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

111 Osmotic flow, the movement of water driven by osmosis
Volume increased Applied force Volume decreased Original level Volumes equal Water molecules Solute molecules Selectively permeable membrane Figure Osmosis is the passive movement of water 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. Figure 111

112 Module 3.12: Osmosis Osmolarity (osmotic concentration) Tonicity
Total solute concentration in an aqueous solution Tonicity Effect of osmotic solutions on cell volume Three effects Isotonic (iso-, same + tonos, tension) Solution that does not cause osmotic flow across membrane

113 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

114 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

115 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?

116 Module 3.13: 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

117 Module 3.13: Carrier-mediated transport
Three types Facilitated diffusion Requires no ATP (= passive) Movement limited by number of available carrier proteins (= can become saturated) Active transport Requires energy molecule or ATP (= active) Independent of concentration gradient Examples: Ion pumps (Na+, K+, Ca2+, and Mg2+) Sodium–potassium ATPase

118 Module 3.13: Carrier-mediated transport
Animation: Membrane Transport: Active Transport Animation: Membrane Transport: Facilitated Diffusion

119 Facilitated diffusion
EXTRACELLULAR FLUID Glucose molecule Receptor site Glucose released into cytoplasm Carrier 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. CYTOPLASM Figure In carrier-mediated transport, integral proteins facilitate membrane passage Facilitated diffusion begins when a specific molecule, such as glucose, binds to a receptor site on the integral protein. Figure 119

120 Active transport 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 Figure In carrier-mediated transport, integral proteins facilitate membrane passage CYTOPLASM 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! Figure 120

121 Module 3.13: Carrier-mediated transport
Carrier-mediated transport (continued) Three types (continued) Secondary active transport Transport mechanism does not require ATP Cell often needs ATP to maintain homeostasis associated with transport

122 Secondary active transport
Glucose molecule Sodium ion + Na+–K+ pump 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. CYTOPLASM + Figure In carrier-mediated transport, integral proteins facilitate membrane passage 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. A sodium ion and a glucose molecule bind to receptor sites on the carrier protein. Figure 122

123 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?

124 Module 3.14: 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) Endocytosis Exocytosis

125 Module 3.14: Vesicular transport
Vesicular transport (continued) Two major types (both require ATP) Endocytosis (into cell using endosomes) Receptor-mediated endocytosis Ligand binds to receptor Plasma membrane folds around receptors bound to ligands Coated vesicle forms Vesicle fuses with lysosomes Ligands freed and enter cytosol Lysosome detaches from vesicle Vesicle fuses with plasma membrane again

126 Receptor-mediated endocytosis
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. 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. After the vesicle membrane detaches, it returns to the cell surface, where its recep- tors become available to bind more ligands. EXTRACELLULAR FLUID Ligands Ligands binding to receptors Exocytosis Endocytosis Ligand receptors 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 vesicle membrane detaches from the secondary lysosome. Coated vesicle CYTOPLASM Figure In vesicular transport, vesicles perform selective membrane passage The lysosomal enzymes then free the ligands from their receptors, and the ligands enter the cytosol by diffusion or active transport. Detachment Fusion The coated vesicles fuse with lysosomes filled with digestive enzymes. Lysosome Ligands removed Figure 126

127 Module 3.14: Vesicular transport
Vesicular transport (continued) Two major types (both require ATP) Endocytosis (into cell using endosomes) (continued) Pinocytosis (“cell drinking”) Formation of endosomes with ECF No receptor proteins involved Phagocytosis (“cell eating”) Produces phagosomes containing solids Phagocytes or macrophages perform phagocytosis Exocytosis Vesicle discharges materials into ECF

128 Pinocytosis begins with the formation of deep grooves
Bloodstream 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. Cytoplasm Endosome Figure In vesicular transport, vesicles perform selective membrane passage Plasma membrane Surrounding tissue Pinocytosis TEM  20,000 Figure 128

129 Phagocytosis Exocytosis The vesicular events linking
Bacterium Pseudopodium Phagocytosis begins when cytoplas- mic extensions called pseudopodia (soo-dō-PŌ-dē-ah; pseduo-, false podon, foot; singular pseudopodium) surround the object. The vesicular events linking phagocytosis and exocytosis Phagocytosis The pseudopodia then fuse at their tips to form a phagosome containing the targeted material. Lysosome This vesicle then fuses with many lysosomes, whereupon its contents are digested by lysosomal enzymes. Figure In vesicular transport, vesicles perform selective membrane passage Released nutrients diffuse into the surrounding cytoplasm. Golgi apparatus Exocytosis The residue is then ejected from the cell through exocytosis. Figure 129

130 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?

131 Section 4: Cell Life Cycle
Learning Outcomes 3.15 Describe interphase, and explain its significance. 3.16 Describe the process of mitosis, and the cell life cycle. 3.17 Discuss the relationship between cell division and cancer.

132 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 Mitosis (2 daughter cells, each with 46 chromosomes) Meiosis (sex cells, each with only 23 chromosomes) Animation: Cell Life Cycle

133 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

134 Original cell Cell division Daughter cells
The production of a pair of daughter cells from a single cell division Original cell Cell division Figure 3 Section 4.1 The Cell Life Cycle Daughter cells Figure 3 Section 134

135 Module 3.15: Interphase Phases G0 (performing normal cell functions)
Examples: Skeletal muscle cells (stay in this phase forever) Stem cells (never enter G0; divide repeatedly) G1 (normal cell function plus growth and duplication of organelles) S (duplication of chromosomes) G2 (last minute protein synthesis and centriole replication)

136 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

137 Figure 3.15.2 During interphase, the cell prepares for cell division
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.” Segment 2 DNA nucleotide Segment 1 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. Figure During interphase, the cell prepares for cell division Adenine 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). Guanine Cytosine Thymine Figure 137

138 Duplicated DNA double helices
Figure During interphase, the cell prepares for cell division Figure 138

139 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?

140 Module 3.16: Mitosis Mitosis
Division and duplication of cell’s nucleus Phases 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)

141 The events in mitosis Chromatids 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. Kinetochore The kinetochore of each chromatid becomes attached to a spindle fiber. The nuclear membrane disintegrates during this period. Centrioles in centrosome Nucleus Figure Mitosis distributes chromosomes before cytokinesis separates the daughter cells Interphase, which precedes mitosis Prophase, the first phase of mitosis Figure – 2 141

142 Module 3.16: Mitosis Mitosis (continued) Phases (continued)
Metaphase (meta, after) Chromosomes align at metaphase plate Anaphase (ana-, apart) Chromatids separate Drawn along spindle apparatus Telophase (telo-, end) Cells prepare to enter interphase Cytoplasm constricts along metaphase plate (= cleavage furrow) Nuclear membranes re-form Chromosomes uncoil

143 The events in mitosis (continued)
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 Metaphase plate Figure Mitosis distributes chromosomes before cytokinesis separates the daughter cells Metaphase Anaphase Telophase, the final phase of mitosis Cytokinesis Figure – 6 143

144 Module 3.16: Mitosis Cytokinesis (cyto-, cell + kinesis, motion)
Begins with formation of cleavage furrow Continues through telophase Completion marks end of cell division

145 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?

146 Module 3.17: Tumors and 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

147 Module 3.17: Tumors and cancer
Cancerous tumor (neoplasm; mass of cells) types Benign Remain in original tissue Malignant Accelerated growth due to blood vessel growth and supply to the area Invasion (cells migrating into surrounding tissues) Metastasis (formation of secondary tumors)

148 Module 3.17 Review a. Define metastasis. b. What is a benign tumor?
c. Define cancer.


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