Chpt 4 Biology of the Cell I PDF

BlackBoard Lecture pt I Chapter 4: Biology of the Cell 1 4.1c What are Common Features of Cells? Plasma membrane Forms outer, limiting barrier separating internal contents from external environment Modified extensions of plasma membrane o Cilia, flagellum, microvilli...

BlackBoard Lecture pt I Chapter 4: Biology of the Cell 1 4.1c What are Common Features of Cells? Plasma membrane Forms outer, limiting barrier separating internal contents from external environment Modified extensions of plasma membrane o Cilia, flagellum, microvilli Fig 4.4 2 4.1c What are Common Features of Cells? Nucleus Largest structure in cell; enclosed by a nuclear envelope Contains genetic material, DNA Nucleoplasm—inner fluid Cytoplasm Cellular contents between plasma membrane and nucleus Includes: cytosol, organelles, and inclusions Fig 4.4 3  4.1c What are Common Features of Cells? Cytosol (intracellular fluid ) o Viscous fluid of cytoplasm o High water content o Contains dissolved macromolecules and ions Fig 4.4 4  4.1c What are Common Features of Cells? Organelles (“little organs”) o Complex, organized structures within cells o Unique shapes and functions o Two categories ˗ Membrane-bound organelles ˗ Non-membrane-bound organelles Fig 4.4 5  4.1c What are Common Features of Cells? o Membrane-bound organelles ˗ Enclosed by a membrane ˗ Separates contents from cytosol ˗ Includes endoplasmic reticulum, Golgi apparatus, lysosomes, peroxisomes, mitochondria Fig 4.4 6  4.1c What are Common Features of Cells? o Non-membrane-bound organelles ˗ Not enclosed within a membrane ˗ Composed of protein ˗ Includes ribosomes, cytoskeleton, centrosome, proteasomes Fig 4.4 7  4.1c What are Common Features of Cells? Inclusions Temporary cytosol stores Not considered organelles Molecules added to and removed from continuously E.g., pigments, glycogen, triglycerides Fig 4.4 8 The Structure of a Cell Figure 4.4 9 Chapter 4: Biology of the Cell 10  4.2a What is the Plasma Membrane? Separation of cytosol from interstitial fluid Intracellular (ICF) vs. extracellular (ECF) fluids Regulates movement of most substances in and out of cell Effective nonpolar barrier to most substances Small and nonpolar substances able to penetrate without assistance Establishes and maintains electrochemical gradient Functions in cell communication Figure 4.5 11  What is the composition of the Plasma Membrane? Fluid mixture composed of equal parts lipid and protein by weight Small and nonpolar substances able to penetrate without assistance Contains several different types of lipids o Phospholipids o Cholesterol o Glycolipids Figure 4.5 12 What are Phospholipids? Polar and hydrophilic “head”; two nonpolar and hydrophobic “tails” Form two parallel sheets of molecules lying tail to tail o Hydrophobic tails form internal environment of membrane o Hydrophilic polar heads directed outward toward fluids Phospholipid bilayer is the basic structure of the framework o Ensures cytosol remains inside the cell o Ensures interstitial fluid remains outside Figure 4.5 13 4.2a What are the other Lipid Components of the Plasma Membrane? Cholesterol Scattered within phospholipid bilayer Strengthens membrane Stabilizes membrane against temperature extremes Glycolipids Lipids with attached carbohydrate groups Helps form glycocalyx—“coating of sugar” on cell’s surface Important in cell recognition Figure 4.5 14  Membrane Carbohydrates Glycocalyx APR 15 Structure and Functions of the Plasma Membrane Figure 4.5 16 What are characteristics of Membrane Proteins? Float and move in fluid bilayer Integral proteins Embedded within, and extend across, phospholipid bilayer Hydrophobic regions interact with hydrophobic interior Hydrophilic regions are exposed to aqueous environments Many are glycoproteins with carbohydrate portion Peripheral proteins − Not embedded in lipid bilayer − Loosely attached to external or interior surfaces Figure 4.5 17 What are the functional categories of Membrane Proteins? Transport proteins o Regulate movement of substances across membrane o E.g., channels, carriers, and pumps, symporters, antiporters Cell surface receptors o Bind molecules called ligands o E.g., neurotransmitters released from a nerve cell that binds to a muscle cell to initiate contraction Figure 4.6 18 What are the functional categories of Membrane Proteins? Identity markers o Communicate to other cells that they belong to the body o These markers are used to distinguish healthy cells from cells to be destroyed Enzymes o May be attached to either internal or external surface of a cell o Catalyze chemical reactions Figure 4.6 19 What are the functional categories of Membrane Proteins? Anchoring sites o Secure cytoskeleton to plasma membrane Cell-adhesion proteins o Perform cell-to-cell attachments Figure 4.6 20  Membrane Transport Concept Map Figure 4.7 21 What are the two main categories of Membrane Transport? Passive processes of membrane transport Do not require energy Depend on substances moving down concentration gradient o Move from area of more substance to area of less Two types: diffusion, osmosis Active processes of membrane transport Require energy Substance must be moved up its concentration gradient (active transport) Membrane-bound vesicle must be released (vesicular transport) Concentration Concentration ENERGY Gradient Gradient 22 Passive Active 4.3a What is the Passive Processes of Diffusion? Net movement of a substance from area of greater concentration to area of lesser concentration Molecules and ions in constant motion due to kinetic energy If unopposed, diffusion continues until substance reaches equilibrium o Molecules evenly distributed throughout a given area Figure 4.8 23 4.3a What effects the rate of Diffusion? Rate of diffusion depends on “Steepness” of concentration gradient Measure of the difference in concentration between two areas Steeper gradient causes faster rate of diffusion Temperature Reflects kinetic energy or random movement Higher movement with higher temperature Faster rate of diffusion Concentration Gradient Concentration Gradient Passive 24 Passive 4.3a What is Simple Diffusion? Molecules pass between phospholipid molecules Small and nonpolar solutes Include: O2 , CO2, some fatty acids, ethanol, urea Not regulated by plasma membrane Movement dependent on concentration gradient Continues to move as long as gradient exists Figure 4.9 25  4.3a What is Facilitated Diffusion? Transport process for small charged or polar solutes requires assistance from plasma membrane proteins Two types o Channel-mediated diffusion o Carrier-mediated diffusion Figure 4.10 26 4.3a What is Channel-Mediated Diffusion? Movement of ions through water-filled protein channels Channels specific for one ion type Leak channels o Continuously open Gated channel o Usually closed o Opens in response to stimulus for fraction of second Important in normal function of muscle and nerve cells Figure 4.10 27  4.3a What is Carrier-Mediated Diffusion? Small polar molecules assisted across membrane by carrier protein Binding of substance causing change in carrier protein shape Moves substances down their gradient Uniporter—carrier transporting only one substance Diffusion Figure 4.10 28  4.3b What is Osmosis? Movement of water, not solutes Passive movement of water through selectively permeable membrane o Membrane allows passage of water o Membrane prevents passage of most solutes Differences in water concentration on either side of a membrane Figure 4.11 29  4.3b What is Osmosis? Two ways water crosses membrane Slips between molecules of phospholipid bilayer Moves through integral protein water channels— aquaporins Figure 4.11 30  4.3b What is Osmotic Pressure? Pressure exerted by movement of water across semipermeable membrane Steeper gradient, more water moved by osmosis and greater osmotic pressure Hydrostatic pressure—pressure exerted by a fluid on the inside wall of its container Figure 4.12 31  4.3b What is Tonicity? Tonicity—ability of a solution to change the volume or pressure of a cell by osmosis Osmosis Figure 4.13 32  4.3c What is Primary active transport? Uses energy directly from breakdown of ATP Ion pumps Cellular protein pumps that move ions across membrane Factor in maintaining internal concentrations of ions Figure 4.14 33  What is the Sodium-potassium (Na+/K+) pump? Exchange ion pump Continuously exports Na+ out of the cell and moves K+ into the cell Plasma membrane preserves steep gradient differences Figure 34  4.3c What is Secondary active transport? Moves substance against concentration gradient Uses energy from movement of second substance down its gradient Symport o Two substances moved in same direction—symporters Antiport o Two substances move in opposite directions—antiporters Active tra nsport Figure 35 4.3c What is Vesicular Transport? Involves energy input to transport substances by a vesicle o Membrane-bounded sac filled with materials Organized into processes of o Exocytosis o Endocytosis  Phagocytosis  Pinocytosis  Receptor-mediated endocytosis 36  4.3c What is Exocytosis? Macromolecules too large to be moved across membrane Vesicle and plasma membrane fusion requires ATP Contents released to outside of cell following fusion o E.g., release of neurotransmitters from nerve cells Figure 37  4.3c What is Endocytosis? Uptake of substances from external environment Severing new vesicle from plasma membrane requires ATP Used for o Uptake of materials for digestion o Retrieval of membrane regions from exocytosis o Regulation of membrane protein composition to alter cellular processes 38 Endocytosis types - Endocytosis - Wi kipedia  4.3c What is Phagocytosis? Cellular eating Only a few cell perform this E.g., when a white blood cell engulfs and digests a microbe Figure 39  4.3c What is Pinocytosis? Cellular drinking Internalization of droplets of interstitial fluid with dissolved solutes Multiple, small vesicles formed Performed by most cells Figure 40  4.3c What is Receptor-mediated endocytosis? Uses receptors on plasma membrane to bind molecules within interstitial fluid and bring the molecules into cell Enables the cell to obtain bulk quantities of substances Fusion of lipid bilayers requiring ATP E.g., transport of cholesterol from blood to a cell o Cholesterol is bound to low- density lipoproteins (LDL) o LDL receptors on the plasma membrane o LDLs are then internalized Figure 4.18 41  What is Familial Hypercholesteremia? Inherited genetic disorder Defects in LDL receptor or proteins of LDLs Interfere with normal receptor-mediated endocytosis of cholesterol Results in greatly elevated cholesterol Causes atherosclerosis Greatly increased risk of heart attack Familial Hypercholesterolemia - Atherosclerosis and Lipid Genomics Laboratory - Mayo Clinic 42 Research  4.4 What is the Resting Membrane Potential? Plasma membrane establishes and maintains electrochemical gradient —resting membrane potential Essential for muscle and nerve cell function Electrical charge difference at plasma membrane Membrane potential—potential energy of charge difference Resting membrane potential (RMP)—potential when a cell is at rest Fig 4.20 43 What are Driving Forces creating Electrochemical gradient? Include chemical and electrical forces Both forces = electrochemical force Passive Movement down the force Active Movement against the force What is the Chemical Driving Force? Figure: Pearson Education What is the Electrical Driving Force? Direction of force depends on Polarity charge on particle Opposite charges attract Figure: Pearson Education What is the Membrane Potential? What is the Electrochemical Driving Force? Electrochemical gradient - is the combination of the electrical and chemical gradients and is the driving force responsible for the movement of charged particles through the membrane 4.4b What are the roles of ions in Establishing and Maintaining RMP? The role of K+ K+ moves down steep concentration gradient through leak channels from cytosol to interstitial fluid Negatively charged proteins remain inside cell Electrochemical gradient o Positive charge outside repels movement of K+ out o Negative charge on inside attracts K+ inward o Equilibrium reached when two forces become equal Fig 4.20 49 4.4b What are the roles of ions in Establishing and Maintaining RMP? The role of Na+ Na+ diffuses into cells from interstitial fluid to cytosol simultaneous to the loss of K+ Enters through Na+ leak channels Down concentration gradient Pulled by electrical gradient The limited number of Na+ leak channels allow less Na+ into the cell as K+ out Fig 4.20 50 4.4b What are the roles of ions in Establishing and Maintaining RMP? RMP= -70 mV Equilibrium from K+ moving out and Na+ moving in. Maintaining an RMP Na+/K+ pumps significant o Maintains K+ and Na + gradients following their diffusion o Na + pumped out o K + pumped in o Opposite directions o Against concentration gradient Fig 4.20 51 4.5a How do Cells Communicate? Direct Contact Between Cells Immune system cells Direct contact between cells important for functioning Need to destroy unhealthy and foreign cells Determine if contacted cells exhibit normal glycocalyx Unhealthy and foreign cells express different glycocalyx pattern o Subsequently destroyed Sperm and oocyte Egg with unique glycocalyx Allows for recognition by sperm during fertilization Cellular regrowth following injury Damaged tissue replaced by cell division in epidermis Cellular contact prevents overgrowth 52  4.5b How do Cells Communicate? Ligand-Receptor Signaling Most cell communication occurs through specific chemical signal molecules (ligands) binding to specific receptors Neurotransmitters from nerve cells and hormones from endocrine cells Important for controlling growth, reproduction, and other cellular processes 3 types of receptors that bind ligands o Channel-linked receptors o Enzymatic receptors o G protein-coupled receptors 53  4.5b How do Cells Communicate? Channel-linked receptors Permit ion passage into or out of cells Occurs in response to neurotransmitter binding Help initiate electrical changes to RMP in muscle and nerve cells 54 Figure 4.21a  4.5b How do Cells Communicate? Enzymatic receptors Protein kinase enzymes Activated to phosphorylate other enzymes within the cell Provides mechanism for altering enzymatic activity Figure 4.21b 55  4.5b How do Cells Communicate? G protein-coupled receptors Indirectly activate protein kinase enzymes G Protein Receptors Figure 4.21c 56 lackBoard Lecture pt II Chapter 4: Biology of the Cell 57  4.6a What are Membrane-Bound Organelles? Membrane-bound organelles Surrounded by membrane Allows activities in isolated environment Differ in shape, membrane composition, enzymes Include o Endoplasmic reticulum o Golgi apparatus o Lysosomes o Peroxisomes o Mitochondria Fig 4.4 58  4.6a What is the Endoplasmic Reticulum (ER)? Extensive interconnected membrane network Varies in shape, but one continuous lumen Extends from nuclear envelope Composes about half of membrane within cell Point of attachment for ribosomes o With ribosomes—rough ER o Without ribosomes—smooth ER Fig 4.22 59  4.6a What is the Endoplasmic Reticulum (ER)? The Endoplasmic Reticulum (ER) Figure 4.22 60  4.6a What is the Rough ER? Rough ER Protein production by ribosomes Proteins inserted into membrane as synthesized Transported out in enclosed membrane sacs o Transport vesicles shuttle proteins from rough ER lumen to Golgi apparatus Fig 4.22 61  4.6a What is the Smooth ER? Diverse metabolic processes vary by cell Functions o Synthesis, transport, and storage of lipids o Carbohydrate metabolism o Detoxification of drugs and poisons Fig 4.22 62  4.6a What is the Golgi Apparatus? Composed of elongated saclike membranous structures; stack of pancakes Functions of Golgi apparatus Modification, packaging, and sorting of proteins Molecules are modified within lumen Formation of secretory vesicles o Some vesicles become part of plasma membrane o Others release contents outside cell o Golgi apparatus is extensive in cells specializing in protein secretion Fig 4.23 63  4.6a What is the Golgi Apparatus? Figure 4.23 64 4.6a What are Lysosomes? Small, membranous sacs Contain digestive enzymes formed by Golgi Participate in digestion of unneeded substances Digest contents of endocytosed vesicles Figure 4.24 65 4.6a What are Peroxisomes? Membrane-enclosed sacs, smaller than lysosomes Metabolic functions include o Role in chemical digestion o Beta oxidation o Lipid synthesis o Note: functions include both digestion and synthesis APR 66 What can happen if Lysosomes are nonfunctioning? Lysosomal Storage Diseases Group of heritable disorders Accumulation of incompletely digested molecules within lysosomes Mutation in genes for lysosomal enzymes E.g., Tay-Sachs disease ̶Lack enzyme needed to break down complex membrane lipids ̶Lipids accumulate within nerve cells ̶Paralysis, blindness, deafness, followed by death by age 4 Tay – Sachs Disease – Dentowesome 67 4.6a What is Endomembrane System? Extensive array of membrane-bound structures Includes ER, Golgi apparatus, vesicles, lysosomes, peroxisomes, plasma membrane and nuclear envelope Connected directly or through vesicles moving between them Provides means of transporting substances within cells Fig 4.23 68 4.6a What are Mitochondria? Oblong shaped organelles with double membrane Genes produce mitochondrial proteins Aerobic cellular respiration Complete digestion of fuel molecules to synthesize ATP “Powerhouses” of cell Multiply through fission Figure 4.26 69  4.6b What are Ribosomes? Non-membrane bound organelle Contain protein and ribonucleic acid (RNA) Arranged into large and small subunit Large subunit with A, P, and E sites Made within nucleolus and assembled in cytoplasm Bound ribosomes attached to external surface of ER membrane Free ribosomes suspended within cytosol Seeley’s Anatomy and Physiology e11; Fig 3.30 70  What are Ribosomes? Figure 4.27 71  4.6b What is the Cytoskeleton? Plays roles in o Intracellular support o Organization of organelles o Cell division o Movement of materials Extends throughout interior of cell Anchors proteins in plasma membrane Includes microfilaments, intermediate filaments, microtubules Figure 4.30 72 4.6b What are Microfilaments? Smallest components of cytoskeleton Actin protein monomers in two twisted filaments Functions of microfilaments o Help maintain cell shape o Form internal support of microvilli o Separate two cells during cytokinesis Figure 4.30 73 4.6b What are Intermediate Filaments? Intermediate-sized components of cytoskeleton More rigid than microfilaments Support cells structurally Stabilize cell junctions Varied protein composition between cells o E.g., keratin in skin, hair, and nails o Another type forms neurofilaments of nerve cells Figure 4.30 74 4.6b What are Microtubules? Largest components of cytoskeleton Hollow cylinders Long chains of globular protein—tubulin Impermanent structures that may be elongated or shortened as needed Function to o Maintain cell shape o Organize and move organelles o Separate chromosomes during cell division Figure 4.30 75 4.6b What is the Centrosome? Centrosome Pair of perpendicularly oriented cylindrical centrioles Primary function: organizes microtubules within cytoskeleton Functions in cellular division Figure 4.28 76 4.6b What are Proteasomes? Large, barrel-shaped protein complexes Protein-digesting organelles o E.g., damaged proteins, incorrectly folded proteins, proteins no longer needed Proteins marked with ubiquitin tag for disposal Figure 4.29 77 4.6c What structures are on the Cell’s External Surface? Cilia Extensions of plasma membrane involved in moving substances over the surface of the cell Flagella Propel the cell; Sperm Microvilli Increase surface area of plasma membrane Smaller than Cilia and lack powered movement Cili Microvi a lli APR 78  4.6d What are Membrane Junctions? Membrane junctions connect and support cells Often called cell-junctions Located between adjacent cells Three types ̶Tight junctions ̶Desmosomes ̶Gap junctions Figure 4.32 79  4.6d What are Tight Junctions? At apical surfaces around adjacent cells Prevent substances from passing between cells o Requires materials to move through, rather than between cells Figure 4.32 80  4.6d What are Desmosomes? Composed of proteins that bind neighboring cells Provides integrity to cells exposed to stress o E.g., external layer of skin Hemidesmosomes o Anchor basal layer of cells of epidermis to underlying components Figure 4.32 81  4.6d What are Gap Junctions? Composed of transmembrane proteins called connexons Form pores between cells Provide direct passageway for substances to travel between cells o E.g., flow of ions between cells in cardiac muscle Figure 4.32 82 Chapter 4: Biology of the Cell 83  4.7 What are the structures of the Nucleus? The nucleus is the cell’s control center Nuclear envelope Double phospholipid membrane enclosing nucleus Nuclear pores o Open passageways formed by proteins o Allow passage of large molecules into and out of nucleus Figure 4.34 84  4.7a What is the Nucleolus? Nucleolus Produces small and large ribosome subunits Not present in all cells o E.g., more than one in nerve cells due to production of many proteins o E.g., absent in sperm cells because no proteins are produced Figure 4.34 85  4.7b What is Deoxyribonucleic Acid (DNA)? Most housed in nucleus Composed of repeated monomers (nucleotides) Each deoxyribonucleotide composed of o Five-carbon sugar deoxyribose o A phosphate o One of four nitrogenous bases ˗ Adenine ˗ Cytosine ˗ Guanine ˗ Thymine Figure 2.21 86 4.7b What is DNA? Each molecule has two complementary strands of nucleotides Spiral ladder Sugar and phosphates form “struts” of ladder Pairs of nucleotide bases form “rungs” Connected by hydrogen bonds Human has 46 separate double-stranded DNA Figure 4.34 molecules 87 4.7b What is DNA? When not dividing, DNA are in form of finely filamented mass called chromatin When dividing, DNA chromatin becomes tightly coiled mass called chromosomes Figure 4.34 88 4.7b What is a Gene? Segmental units of nucleotides Provide instructions for synthesis of specific proteins Promoter region—“start” signal Terminator region—“stop” signal Figure 4.34c 89 How are Genes Expressed? Cellular activities are dependent upon protein synthesis Directed by DNA DNA mRNA protein TRANSCRIPTION TRANSLATION Central Dogma of Molecular Biology  4.8 How are Genes Expressed? Transcription Synthesis of complementary messenger RNA (mRNA) Single strand Copy of a gene formed from DNA in nucleus Translation Uses mRNA for synthesis of protein by ribosomes in cytosol Figure 4.35 91  4.8 How is the information Encoded? DNA mRNA TRANSCRIPTION TRANSLATION protein DNA’s “language” = triplet A triplet is a three-base sequence on DNA specifying a particular amino acid The corresponding three-base sequence on mRNA is called a codon RECALL……….. DNA’s bases = A,T,C,G RNA’s bases = A,U,C,G The form is different, but the same information is being conveyed 92  4.8 What are the Steps of Transcription? Initiation RNA uses promoter region as start point for gene transcription Elongation Free ribonucleotides are base-paired with template strand A with U C with G RNA polymerase catalyzes formation of bonds between ribonucleotides forming mRNA Termination Figure 4.36 mRNA released at terminal region of gene Transcription 93 4.8a How is mRNA modified after Transcription? 94 4.8b What happens during Translation? mRNA TRANSLATION protein Synthesis of a new protein Language of nucleic acids (base sequence) is “translated” into the language of proteins (amino acid sequence) Codons (mRNA) are “translated” into amino acids with the help of ribosomes and tRNA. tRNA anticodons match with mRNA codons Seeley’s Anatomy and Physiology e11; Fig 3.43 95  4.8b What are required structures for Translation? Ribosomes, mRNA, tRNA, amino acids Ribosomes Large subunit—A site, P site, E site Small subunit Figure 4.37 96  4.8b What are required structures for Translation? mRNA Start codon—AUG, signal to begin protein synthesis Codons following start and before stop, direct assembly Stop codon—where mRNA reading ends Figure 4.37 97  4.8b What are required structures for Translation? tRNA o Brings specific amino acids to a specific mRNA codon o Amino acid acceptor region provides attachment site for specific amino acid o Anticodon region determines the specific amino acid to which tRNA attaches o 20 amino acids found in proteins of living things Figure 4.37 98 4.8b What are the steps of Translation? 1. Initiation Figure 4.38 99 4.8b What are the steps of Translation? 2. Elongation Figure 4.38 100 4.8b What are the steps of Translation? 3. Termination Translation Figure 4.38 101  Ricin Castor Beans (5% of dry weight) Minimal amount of 500 micrograms can kill (via inhalation, injection, or ingestion) Ricin A (cytoxic portion) which inactivates ribosomes and prevents protein synthesis One single Ricin A can inactivate close to 50,000 ribosomes No know cure!  4.9 What is Cell Division? Cell division One cell divides to produce two cells Necessary for development, tissue growth, replacement of old cells, tissue repair, reproduction Mitosis Cell division that occurs in somatic cells (all cells other than sex cells) Meiosis Cell division in sex cells (cells that give rise to sperm or oocytes): covered in Bio 145 A&P II. 103  4.9b What is the Cell Cycle? G0 phase Figure 4.40 104  4.9b What are the events of Mitosis? Prophase: Metaphase: Interphase: -Chromosomes form. Chromosomes align DNA and Organelles -Centrioles migrate. attached to spindle duplicate. -Nucleus fibers. disappears. Figure 4.42 3-105  4.9b What are the events of Mitosis? Mitosis ends with completion Anaphase: Telophase: of cytokinesis and formation -Chromosomes separate and Chromosomes unravel. migrate to centrioles. of two daughter cells each Nucleus reforms. with DNA identical to parent -Cytokinesis begins with cleavage furrow. cell. Mitosis Figure 4.42 106