1Chapt. 10 Cell Biology and BiochemistryChapt. 10 Cell Biology and BiochemistryStudent Learning Outcomes:• Describe basic features of typical human cell• Explain plasma membrane structure/ function• Describe different transport proteins that permit compounds to cross the membrane• Explain the structure and unique function of each organelle• Describe the structure of the cytoskeletonCellFig. 10.1 typical animal cell The cell:• Lipid bilayer membrane• Integral transport proteins• Membrane-bound organellessequester enzymes• Cytoskeleton• Different cell types have different amounts of organelles, enzymesPhospholipid bilayer membranePhospholipid bilayer membrane:Separates contents from external environmentFig. 10.2 typical lipid bilayerMobility of phospholipids (Figure 2.23 Cooper et al)• Lipid bilayers behave as 2-dimensional fluids: individual molecules can rotate and move laterally• Fluidity determined by temperature, lipid composition.• Asymmetric distribution of specific phospholipids2PhospholipidsGlycerol lipids:2 fatty acids, glycerol, phosphate;often polar group attached to phosphateSphingolipids:2 fatty acids, serine, phosphateFig. 10.3 phospholipids and different head groupsFigure 2.9 Cholesterol and steroid hormones Animal cell membranes contain cholesterolHydrocarbon rings very hydrophobic, but -OH group is weakly hydrophilic, so cholesterol is amphipathicCholesterol comes from diet or bodysynthesizessteroid hormones (e.g., estrogens andtestosterone) are derived fromcholesterol.Insertion of cholesterol in a membraneRing structure of cholesterol helps determine membrane fluidity:• Interactions between hydrocarbon rings and fatty acid tails makes membrane more rigid.• Inserts near unsaturated fatty acids• Cholesterol reduces interaction between fatty acids, maintains fluidity at lower temperatures.Fig. 10.4 Membrane proteins anchored to protein meshRed blood cell is model membrane:no nucleus, organelles• Integral proteins: (hydrophobic & hydrophilic regions)• oftenTransmembrane• Channels• Transporters• Receptors• Peripheral proteins:• Bound to integral• Signaling• StructuralFig. 10.53ABO, Structure of glycolipidsMany cell membranes contain glycolipids:Sugar, fatty acids, no phosphateAlso amphipathicCholera toxin binds glycolipidsABO blood groups are glycolipids:Lipids & carbohydratesGPI anchors some extracellular proteins:Glycophosphatidyl inositolhas sugar inositol on phospholipidOther lipids anchor proteins inside membrane Fig. 10.6 Phospholipid bilayer membraneMany carbohydrates are found on external surface of plasma membrane (glycocalyx) - protectiveFig. 10.2 typical lipid bilayerPermeability of phospholipid bilayers• Selective permeability of membrane allows cell to control its internal composition.• Some molecules diffuse across bilayer: CO2, O2, H2O,• Steroid hormones.• Ions, larger uncharged, or polar molecules cannot diffuse across.4Proteins carry specific componentsProteins transport most compounds across hydrophobic barrier of membranesFig. 10.7 Facilitative diffusion and transporter proteinsFig. 10.8 Glucose transporter: • Facilitative diffusion: • Glucose moves down concentration gradient• Insulin increases number of transportersGated channels regulated by stimuliGated channels are regulated by stimuli: voltage, ligand binding, phosphorylationCFTR (cystic fibrosis transmembrane conductance regulator) is a Cl- channel • ATP binding domains regulated by phosphorylation• mutated in cystic fibrosis• Still passive transport since many Cl- for 1 ATPFig. 10.9Active transport uses ATP to transport itemsActive transport: energy is used to transport items independent of concentration Primary: Na+, K+ATPase sets up major ion gradient(also Ca+2/ATPase pump)Secondary: gradient is used to concentrate item(antiport, symport or cotransport)Fig. 10.10 Na+/K+/ATPase5Active transport – cotransporter/antiportFig. 10.11 Active transport:Symport: Glucose cotransporter• let in Na+, glucose• Intestinal cellsAntiport:Band 3 of red blood cell:• Exchanges Cl- (in) for bicarbonate (out)Fig. 4.9, partLysosomes recycle componentsLysosomes have acid hydrolases:• digest components, eliminate, recycle• defects -> storage diseases (ex. Tay-Sachs)Fig. 10.12 PhagocytosisEndocytosis: cells take up macromolecules, fluids, and particles such as bacteria. Area of plasma membrane buds off inside cell to form vesicle with ingested materialPhagocytosis (cell eating) occurs in specialized cell types.Autophagy recycles damaged organellesPinocytosis (cell drinking) is a property of all eukaryotic cells.Receptor-mediated EndocytosisReceptor-mediated endocytosis: mechanism for selective uptake of specific macromolecules.• Cell surface receptors in regions (clathrin-coated pits).• Pits bud as clathrin-coated vesicles, fuse to form lysosome6EndocytosisReceptor-mediated endocytosis first elucidated in patients with familial hypercholesterolemia• lack LDL receptors on cell surface• very high blood levels of cholesterol• Cholesterol transported inbloodstream mostly aslow-density lipoprotein, LDL.• 1500 cholesterols• 800 phospholipids• 1 proteinMitochondriaMitochondria: powerhouses• Have DNA, divide• Two membrane layers• Oxidative phosphorylation• enzymes to make ATPFig. 10.13 One mitochondrion,Two mitochondriaPeroxisomesPeroxisomes:• Single-membrane-enclosed organelles contain diverse metabolic enzymes (peroxins) • Oxidative reactions, as fatty acid degradation• Generate hydrogen peroxide (H2O2)• No genome NucleusNucleus: DNA, genome• 2-layer membrane• Nuclear pores for transportFig. 10.147Endoplasmic reticulumEndoplasmic reticulum:RER (rough): ribosomesmake proteins destined for modification, transport to Golgi, vesicles, secretedSER (smooth): enzymes make lipids, detoxify drugsFig. 10.15 The Golgi ApparatusDistinct regions of Golgi: cis Golgi network—receives molecules from ER medial and trans Golgi stacks— most modifications here  trans Golgi network—sorting and distributionCytoskeletonFig. 10.16 Cytoskeleton:• Strength, shape, movement• Microtubules α, β heterodimers• Intermediate filaments• Actin filamentsDynamic microtubules move organelles, vesicles, chromosomesActin filamentsActin fibers: • Dynamic• G-actin subunits (bound ATP) add to the F-actin polymer• Provide shape• Ex. under rbc membrane bound to spectrin (fig. 10.5)• Muscle movement