Cell Theory (3-1) Four basic concepts of the cell theory Cells are the building blocks of all plants and animals. Cells are the smallest functioning units of life. Cells are produced through division of preexisting cells. Each cell maintains homeostasis.

Cells in the Human Body (3-1) Trillions of cells in the human body Homeostasis of body maintained by coordinated action of cells Cells come in variety of shapes and sizes Figure 3-1 The Diversity of Cells in the Human Body.

The Study of Cells (3-1) Cytology Studied using microscopes Study of the structure and function of cells Studied using microscopes Light microscopy (LM) Electron microscopy (EM) Transmission electron microscopy (TEM) Allows to see through a specimen Scanning electron microscopy (SEM) Allows to see the external structures of a specimen

Overview of Cell Anatomy (3-1) Wide variety of cell anatomy All cells have a plasma membrane, or cell membrane Separates cell contents (cytoplasm) from surrounding environment (extracellular fluid) Figure 3-2.

The Plasma Membrane Functions (3-2) Four key functions Provides cell with physical isolation from extracellular fluid Regulation of exchange with the environment Allows for sensitivity to the environment Provides for structural support

The Plasma Membrane Structure (3-2) Extremely thin (6 nm–10 nm) Components Lipids Phospholipids Cholesterol Proteins Carbohydrates Figure 3-3 The Plasma Membrane.

Figure 3-3 The Plasma Membrane.

Membrane Lipids (3-2) Phospholipids are major component of plasma membrane Cholesterol gives “stiffness” to plasma membrane Makes it less fluid and less permeable Lipid-soluble (non-polar) materials cross membrane easily Ions and water-soluble (polar) compounds do not cross lipid portion

Phospholipid Bilayer (3-2) Chemical properties of phospholipids results in formation of phospholipid bilayer Hydrophilic non-lipid “head” in each layer faces watery environment (extracellular fluid on outside or intracellular fluid on inside of cell) Hydrophobic “tails” of phospholipids move away from watery environment and face each other Figure 3-3 The Plasma Membrane.

Membrane Proteins (3-2) Most common are transmembrane proteins that span width of membrane Proteins can “drift” within membrane or remain in specific position Membrane composition can change over time

Membrane Protein Functions (3-2) Six major functions Table 3.1

Membrane Carbohydrates (3-2) Join with proteins and lipids to form complex molecules on outer surface of membrane Combine with lipids to form glycolipids Combine with proteins to form glycoproteins Function as lubricants and adhesives, receptors, and part of immune system “self” recognition

Permeability (3-3) Ease with which substances can cross a membrane Impermeable membrane = nothing can cross Freely permeable membrane = anything can cross Selectively permeable membrane = some things can cross; others cannot Describes plasma membranes Lipid-soluble (non-polar) materials cross membrane easily Ions and water-soluble (polar) compounds do not cross lipid portion

Movement across the Membrane (3-3) Passive processes Require no energy Examples: diffusion, osmosis, facilitated diffusion Active processes Require energy, usually from ATP Examples: active transport, vesicular transport

Diffusion (3-3) Molecules are in constant motion Random collisions spread out molecules This movement from area of high concentration to area of low concentration called diffusion Difference between concentrations called concentration gradient Diffusion proceeds “down concentration gradient” Molecules eventually uniformly distributed

Figure 3-4 Diffusion.

Diffusion across Plasma Membranes (3-3) Plasma membrane selectively restricts diffusion Diffusion possible through: Crossing lipid portion of membrane Lipid-soluble drugs, alcohol, fatty acids, steroids, and dissolved gases (e.g., oxygen and carbon dioxide) Passing through channel proteins Small water-soluble compounds, water, ions Large water-soluble molecules will require a protein carrier

Figure 3-5 Diffusion across the Plasma Membrane. EXTRACELLULAR FLUID Figure 3-5 Diffusion across the Plasma Membrane.

Characteristics of Osmosis (3-3) Three characteristics of osmosis Diffusion of water molecules across a selectively permeable membrane Occurs across a selectively permeable membrane that is freely permeable to water but not freely permeable to solutes (dissolved materials) Water flows from low solute concentration to high solute concentration

Osmotic Pressure (3-3) Osmotic pressure Indication of the force of the water movement into a solution as a result of solute concentration Increase in solute concentration = increase in osmotic pressure Can be measured as amount of hydrostatic pressure required to oppose flow of water Water moves toward the higher concentration of solutes, until equilibrium is reached

Figure 3-6 Osmosis.

Tonicity (3-3) The effect of solute concentrations on the shape or tension of the cell membrane Isotonic solution Does not cause net movement of water into or out of cell Water molecules move in and out at equal rate Cell retains normal appearance

Hypotonic and Hypertonic Solutions (3-3) Hypotonic solution Net flow of water into the cell Causes cell to swell and perhaps burst (lyse) In red blood cells, this is called hemolysis Hypertonic solution Net flow of water out of the cell Causes cell to shrivel and dehydrate In red blood cells, shrinking is called crenation

Figure 3-7 Osmotic Flow across a Plasma Membrane.

Carrier-Mediated Transport (3-4) Process using membrane proteins to move specific ions or organic substrates across plasma membrane Can be passive (no ATP required) or active (ATP dependent) Carrier proteins Are specific to a substrate (e.g., glucose carrier will not carry other simple sugars) Can be used repeatedly

Types of Carrier-Mediated Transport (3-4) Cotransport Carrier moves two substances in same direction Countertransport Carrier moves two substances in opposite directions Examples of carrier-mediated transport Facilitated diffusion Active transport

Facilitated Diffusion (3-4) Uses carrier proteins to passively move larger compounds down concentration gradient Compound binds to receptor site on carrier protein Protein changes shape and moves compound across membrane Limited number of carriers prevents diffusion rate from indefinite increase No further increase in rate once all carriers are bound

Figure 3-8 Facilitated Diffusion.

Active Transport (3-4) Requires energy from ATP Can move substances against concentration gradient Ion pump transports essential ions across plasma membranes Exchange pump is an ATP-driven countertransport mechanism Best example is sodium–potassium exchange pump

Figure 3-9 The Sodium-Potassium Exchange Pump.

Vesicular Transport (3-4) Moves materials into or out of cell in small membrane-enclosed sacs called vesicles Vesicles fuse with plasma membrane Two major categories Endocytosis Exocytosis

Endocytosis (3-4) Packages extracellular materials in vesicles at cell surface and moves them into the cell Active process that requires energy Three major types Receptor-mediated endocytosis Pinocytosis Phagocytosis

Receptor-Mediated Endocytosis (3-4) Begins when receptors on plasma membrane surface bind to specific target molecules (ligands) In-pouching of plasma membrane forms coated vesicle Ligands are removed from the vesicle Receptors recycled to be used again

Figure 3-10 Receptor-Mediated Endocytosis.

Pinocytosis (3-4) Pinocytosis or “cell drinking” Pocket forms in plasma membrane Forms small vesicles filled with extracellular fluid No receptors involved Process common to most cells

Phagocytosis (3-4) Phagocytosis or “cell eating” Produces vesicles containing solid objects Cytoplasmic extensions (pseudopodia) surround an object outside the cell Membrane fuses to form vesicle around object Vesicle fuses with lysosomes inside the cell and contents are digested Process unique to specialized cells that protect tissues

Exocytosis (3-4) Reverse of endocytosis Vesicle created inside the cell Vesicle fuses with plasma membrane Contents discharged to extracellular environment

Figure 3-11 Phagocytosis.

Inside the Cell (3-5) Cytoplasm General term for material between plasma membrane and membrane surrounding nucleus Contains cytosol (intracellular fluid) and organelles

The Cytosol (3-5) Contains dissolved nutrients, ions, proteins, and waste products Differs from extracellular fluid (ECF) in that cytosol: Contains higher K+ and lower Na+ concentrations than ECF Contains higher concentration of dissolved proteins than ECF Gives cytosol a thicker, more viscous consistency Usually contains small reserves of amino acids and lipids along with carbohydrates

The Organelles (3-5) Internal structures that perform specific functions Membranous (membrane-enclosed) organelles are isolated from the cytosol Allow storage and manufacture of substances Nonmembranous organelles are in direct contact with cytosol

The Cytoskeleton (3-5) Internal protein framework Threadlike filaments and hollow tubules give strength and flexibility Most important cytoskeletal elements in most cells Microfilaments Intermediate filaments Microtubules

Microfilaments and Intermediate Filaments (3-5) Thinnest strands of the cytoskeleton Usually composed of actin Attach plasma membrane to underlying cytoplasm Intermediate filaments Intermediate in size Varying protein composition Strengthen and stabilize the cell

Microtubules (3-5) Microtubules Largest component of cytoskeleton Hollow tubes built from globular protein tubulin Give cell strength and rigidity Anchor organelles Form spindle apparatus during cell division

Microvilli (3-5) Small, finger-shaped projections of the plasma membrane on exposed surface of some cells Have internal core of microfilaments for support Provide additional surface area of membrane Found on cells that are absorbing lots of materials from the extracellular fluid Figure 3-12 The Cytoskeleton.

Centrioles (3-5) Centrioles Cylindrical in shape Composed of triplets of microtubules Move DNA strands during cell division

Cilia and Flagella (3-5) Cilia Flagella Relatively long, slender extensions of plasma membrane Formed by microtubules arranged in pairs Multiple motile cilia use ATP to move substances across cell surface Single, nonmotile primary cilium acts as signal sensor Flagella Look like long cilia, but are used to move the cell through its environment

Ribosomes and Proteasomes (3-5) Manufacture proteins Consist of small and large subunits Two major types Free ribosomes that are spread throughout cytosol Fixed ribosomes attached to endoplasmic reticulum (ER) Proteasomes Organelles containing protein-breaking (proteolytic) enzymes, or proteases Remove and recycle damaged proteins from cytoplasm

Endoplasmic Reticulum (3-5) Network of intracellular membranes Continuous with nuclear envelope Forms hollow tubes, flattened sheets, and chambers (cisternae) Two types Smooth endoplasmic reticulum (SER) Rough endoplasmic reticulum (RER)

Endoplasmic Reticulum Functions (3-5) Four key functions Synthesis of proteins, carbohydrates, and lipids Storage of materials, isolating them from the cytosol Transport of materials through the cell Detoxification of drugs or toxins

Smooth Endoplasmic Reticulum (3-5) Smooth endoplasmic reticulum (SER) Has no ribosomes Synthesizes lipids and carbohydrates, such as: Phospholipids and cholesterol for membranes Steroid hormones Glycerides (especially triglyceride) Glycogen in skeletal muscles and liver cells

Rough Endoplasmic Reticulum (3-5) Rough endoplasmic reticulum (RER) Has fixed ribosomes on the membrane Location of protein synthesis Some proteins packaged into membrane-bound sacs Sacs (transport vesicles) pinch off from tips of ER and deliver proteins to Golgi apparatus

Figure 3-13 The Endoplasmic Reticulum.

Golgi Apparatus (3-5) Made of flattened membranous discs called cisternae Three major functions Modifies and packages secretions for release Renews or modifies plasma membrane Packages enzymes within vesicles (lysosomes)

Figure 3-14 The Golgi Apparatus.

Figure 3-15 Protein Synthesis, Processing, and Packaging

Lysosomes (3-5) Vesicles filled with digestive enzymes Functions Cleanup and recycling of materials within the cell Example: removing damaged organelles Defense against disease Fuse with vesicles containing pathogens and breaks them down Autolysis, or self-destruction, of damaged cells

Peroxisomes (3-5) Formed from existing peroxisomes Most abundant in metabolically active cells (e.g., liver cells) Carry different group of enzymes than lysosomes Enzymes absorb and break down fatty acids and other organic compounds By-product is hydrogen peroxide (H2O2), a free radical that is highly reactive and can be destructive to cells Free radicals = ions or molecules that contain unpaired electrons

Mitochondria (3-5) Provides 95% of energy for the cell Have a double membrane The outer surrounds the organelle The inner is folded to form the cristae Cristae increase surface area exposed to fluid matrix Enzymes in this matrix catalyze energy-producing reactions

Mitochondrial Energy Production (3-5) First step of breaking down glucose (glycolysis) occurs in cytosol Remaining steps of aerobic cellular respiration, occur in the mitochondria

The Nucleus (3-6) Control center of the cell Nuclear envelope Dictates cell function and structure by controlling protein synthesis Nuclear envelope Double membrane that surrounds the nucleus Separates nucleoplasm from cytosol Nuclear pores Allow movement of substances into and out of the nucleus

Nuclear Structure and Contents (3-6) Nucleoli Synthesize ribosomal RNA (rRNA) Assemble small and large ribosomal subunits Chromosomes Contain DNA, which stores instructions for protein synthesis Human body cells contain 23 pairs of chromosomes Chromatin Loosely coiled DNA found in cells that are not dividing

Figure 3-17 The Nucleus.

Information Storage in the Nucleus (3-6) Genetic code Chemical “language” of the cell Contains information for protein synthesis in form of nitrogenous base sequence on DNA Arranged in sequence of three bases each representing a single amino acid Gene The functional unit of heredity Each protein-coding gene contains all the triplets needed to produce a specific protein

DNA Control of Cell Function (3-7) Genes are normally tightly coiled with histones, keeping them inactive To activate, enzymes must break bonds and remove histone, revealing the promoter segment Protein synthesis occurs in two stages Transcription Translation

Transcription (3-7) Production of single strand of messenger RNA (mRNA) from single strand of DNA Process required to get DNA blueprint for protein synthesis from the nucleus out to the cytosol

Three Steps of Transcription (3-7) Two DNA strands separate, and RNA polymerase binds to promoter gene New mRNA strand is formed using complementary RNA nucleotides Uracil in RNA strand is paired with adenine in DNA strand Sequence of three nitrogenous bases in RNA represents a codon (complementary to DNA triplet) At DNA “stop” signal, RNA polymerase and mRNA detach, and the original DNA strands reattach

Figure 3-19 Transcription.

Translation (3-7) Uses new mRNA codons to signal the assembly of specific amino acids in series to synthesize a protein mRNA leaves the nucleus and binds to a ribosome in cytoplasm Transfer RNA (tRNA) delivers amino acids to ribosomes Each tRNA has a complement to the codon called an anticodon

Table 3.3

Translation Process (3-7) Three phases of translation Initiation Elongation Termination

Initiation of Translation (3-7) “Start” codon of mRNA combines with small ribosomal subunit and first tRNA Coding for methionine with the base sequence AUG Small and large ribosomal subunits enclose the mRNA

Figure 3-20a-b Translation.

Elongation in Translation (3-7) 2nd tRNA brings another amino acid Its anticodon binds to 2nd codon of mRNA Ribosomal enzymes remove 1st amino acid and attach it to the 2nd with a peptide bond Ribosome moves along the codons repeating these steps

Figure 3-20a-b Translation.

Termination of Translation (3-7) Amino acids continue to be added until ribosome reaches the “stop” codon at end of mRNA Ribosome detaches leaving the strand of mRNA and a newly completed polypeptide Figure 3-20c-e Translation.

Stages of a Cell’s Life Cycle (3-8) Stages include interphase, mitosis, and cytokinesis Cell division Form of cellular reproduction Increases numbers of cells Replaces old and damaged cells Requires duplication of genetic material (DNA replication)

Types of Cell Division (3-8) Mitosis Nuclear division of somatic (body) cells Cells differ in frequency of mitosis Stem cells divide rapidly Some cells programmed to self-destruct Apoptosis is genetically controlled death of cells Meiosis The production of sex cells—the sperm and ova

Interphase (3-8) The period of time between cell divisions Cell spends majority of life here, performing normal functions G1 phase is when the cell duplicates organelles and adds cytosol S phase is when DNA is replicated in the nucleus G2 phase is when centrioles are replicated and protein synthesis continues

Figure 3-21 Stages of a Cell’s Life Cycle. INTERPHASE S DNA replication, synthesis of histones G1 G2 Normal Protein synthesis cell functions plus cell growth, THE CELL CYCLE duplication of organelles, protein synthesis MITOSIS AND CYTOKINESIS (see Fig. 3-23) Figure 3-21 Stages of a Cell’s Life Cycle.

Figure 3-22 DNA Replication.

Mitosis (3-8) Process that separates duplicated chromosomes into two new nuclei Occurs in four stages Prophase Metaphase Anaphase Telophase

Prophase (3-8) Chromosomes become visible under light microscope Each of two copies of DNA is called a chromatid Chromatids are connected to each other at a point called the centromere Nucleoli disappear Two pairs of centrioles move to opposite poles Spindle fibers appear Nuclear envelope disappears Chromatids attach to spindle fibers

Figure 3-23a Interphase, Mitosis, and Cytokinesis. 1b INTERPHASE STAGE EARLY PROPHASE STAGE LATE PROPHASE Nucleus (contains replicated DNA) Spindle fibers Centriole Chromosome with two sister chromatids MITOSIS BEGINS Centrioles (two pairs) Centromeres Figure 3-23a Interphase, Mitosis, and Cytokinesis.

Metaphase (3-8) Chromatids move to narrow central zone called metaphase plate Paired chromatids line up along the plate

Anaphase (3-8) Centromere of each chromatid splits creating daughter chromosomes Daughter chromosomes are pulled apart and move toward the centrioles

Telophase (3-8) New nuclear membranes form Nucleoli reappear DNA uncoils Cell is preparing to enter interphase again

Cytokinesis (3-8) Cytoplasmic division that forms two daughter cells Usually begins in late anaphase Continues throughout telophase Is usually completed after a nuclear membrane has re-formed around each daughter nucleus

Figure 3-23b Interphase, Mitosis, and Cytokinesis. 4 STAGE METAPHASE STAGE ANAPHASE STAGE TELOPHASE INTERPHASE Daughter chromosomes Daughter cells Cleavage furrow CYTOKINESIS Metaphase plate

Tumors (3-9) Tumor or neoplasm is mass produced by abnormal cell growth and division Benign tumors Usually encapsulated and rarely life threatening Malignant tumors Spread from original location or primary tumor through a process called invasion May also spread to distant tissues forming secondary tumors Migration called metastasis

Cancer (3-9) Characterized by gene mutations leading to malignant cells and metastasis Form extremely active secondary tumors Stimulates additional blood vessel growth into area Additional nutrients to cancer cells accelerate tumor growth and metastasis Cancer cells take nutrients and energy away from healthy tissues

Cellular Differentiation (3-10) All somatic cells in the body have the same chromosomes and genes Yet develop to form a wide variety of cell types Differentiation Occurs when specific genes are turned off, leaving the cell with limited capabilities A collection of cells with specific functions is called a tissue