Cellular Biology ICellular Biology I

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Cell TheoryCell Theory

ConceptsConcepts::11 . .Cells are the functional and structural units ofCells are the functional and structural units of

living organismsliving organisms22 . .The activity of organism is dependent on bothThe activity of organism is dependent on both

individual and collective activity of the cells thatindividual and collective activity of the cells thatcomprise that organismcomprise that organism

33 . .Subcellular structures determine the biochemicalSubcellular structures determine the biochemicalactivities of cells (i.e., activities of cells (i.e., principle of complementarityprinciple of complementarity))

44 . .Continuity of life has a cellular basisContinuity of life has a cellular basis

Generalized CellGeneralized CellPlasma MembranePlasma Membrane

Fluid mosaic modelFluid mosaic model1. Membranes are mosaic of different proteins 1. Membranes are mosaic of different proteins are embedded in a phospholipid bilayerare embedded in a phospholipid bilayer2. Hydrophilic portions of proteins& phospho-2. Hydrophilic portions of proteins& phospho-ipids are maximally exposed to wateripids are maximally exposed to water3. Hydrophobic portions are in nonaqueous 3. Hydrophobic portions are in nonaqueous environment inside membraneenvironment inside membrane

Types of proteins:Types of proteins:1. Integral: transmembrane proteins; span the 1. Integral: transmembrane proteins; span the hydrophobic interior (channels & carriers)hydrophobic interior (channels & carriers)2. Peripheral: not embedded; attach surface 2. Peripheral: not embedded; attach surface (enzymatic activity & structure)(enzymatic activity & structure)

Carbohydrates associated with the exterior Carbohydrates associated with the exterior surface of the membranesurface of the membrane1. Glycolipids1. Glycolipids2. Glycocalyx: attached to proteins in contact 2. Glycocalyx: attached to proteins in contact with extracellular matrixwith extracellular matrix

Function of membrane proteins:Function of membrane proteins:1. Transport1. Transport2. Enzyme2. Enzyme3. Receptor sites3. Receptor sites4. Intercellular junctions4. Intercellular junctions5. Cell-cell recognition5. Cell-cell recognition6.Cytoskeletal&extracellular matrix 6.Cytoskeletal&extracellular matrix attachmentattachment

Specialized Structures and FunctionsSpecialized Structures and Functions1. Microvilli: Increase surface area; absorption1. Microvilli: Increase surface area; absorption2. Membrane junctions: 2. Membrane junctions: a.a. Tight junctions: Tight junctions: Impermeable junctions, Impermeable junctions, b.b. Desmosomes: Desmosomes: Anchoring junctions; plaques & linkers; Anchoring junctions; plaques & linkers; intermediate filaments & intermediate filaments & c.c. Gap junctions: Gap junctions: Movement of chemicals between adjacent Movement of chemicals between adjacent cells; connexonscells; connexons

Membrane transportMembrane transport1.1. Membranes are selectively permeable Membranes are selectively permeable2.2. PassivePassive & & activeactive processes processes3.3. Passive movement: Passive movement: DiffusionDiffusion: : a.a. Movement Movement of substance down concentration gradient: of substance down concentration gradient: Changes over distance in particular direction, Changes over distance in particular direction, b.b. Results from intrinsic kinetic energy: Results from intrinsic kinetic energy: Temperature & molecular size, Temperature & molecular size, c.c. Random Random molecular movement, molecular movement, d.d. Dynamic equilibrium Dynamic equilibrium

4.4. Types of diffusion: Types of diffusion:a.a. Simple:Nonpolar substances Simple:Nonpolar substances (lipid soluble) pass directly through lipid bilayer (lipid soluble) pass directly through lipid bilayer (polar &charged particles can diffuse if they can fit (polar &charged particles can diffuse if they can fit through pores),through pores),b.b. Osmosis: Diffusion of solvent via Osmosis: Diffusion of solvent via selectively permeable membrane (hypertonic, hypo-selectively permeable membrane (hypertonic, hypo-tonic, isotonic, osmolarity & osmotic pressure), tonic, isotonic, osmolarity & osmotic pressure), c.c. Facilitated diffusion: Lipid insoluble molecules too Facilitated diffusion: Lipid insoluble molecules too large to diffuse through membrane pores can move large to diffuse through membrane pores can move passively with carrier molecules: Selective (specific) passively with carrier molecules: Selective (specific) & limited by number of carriers (saturation)& limited by number of carriers (saturation)

5.5. FiltrationFiltration: Water and solutes are forced : Water and solutes are forced through a membrane or capillary by through a membrane or capillary by hydrostatic pressure: Pressure gradient hydrostatic pressure: Pressure gradient pushes solute-containing fluid outpushes solute-containing fluid out

6.6. Active Processes: Active Processes: Active TransportActive Transport: : a.a. Cell uses Cell uses energy to move substances across the membrane, energy to move substances across the membrane, b.b. Transport molecules utilize energy from ATP to Transport molecules utilize energy from ATP to pump molecules against concentration gradients, pump molecules against concentration gradients, c.c. Coupled systems(symport&antiport)Coupled systems(symport&antiport)d.d.Na+-K+ pump: Na+-K+ pump: Na+ binding stimulates ATP formation, phosphoryla-Na+ binding stimulates ATP formation, phosphoryla-tion causes conformational change which releases tion causes conformational change which releases Na+, K+ binding causes phosphate release, pump Na+, K+ binding causes phosphate release, pump returns to original conformation & K+ is releasedreturns to original conformation & K+ is released

7.7. Bulk TransportBulk Transport (Active): (Active): a.a. Exocytosis: sub- Exocytosis: sub-stance is released from vesicle (membranous stance is released from vesicle (membranous sac: Fuses with membrane&releases contents sac: Fuses with membrane&releases contents to outside), to outside), b.b. Endocytosis: Large substances Endocytosis: Large substances enclosed by membrane&taken into cell: Phag-enclosed by membrane&taken into cell: Phag-ocytosis, pinocytosis & receptor-mediated ocytosis, pinocytosis & receptor-mediated endocytosis (coated pit & clathrin)endocytosis (coated pit & clathrin)

Cell-Environment InteractionsCell-Environment Interactions

Cell-adhesion molecules (CAMS)Cell-adhesion molecules (CAMS)1. Anchor cell to EC matrix & to each other1. Anchor cell to EC matrix & to each other2. Cell migration2. Cell migration3. Cell signaling3. Cell signaling

Membrane receptorsMembrane receptors1. Contact signaling1. Contact signaling2. Electrical signaling: Voltage-gated channels2. Electrical signaling: Voltage-gated channels3. Chemical signaling: 3. Chemical signaling: a.a. Neurotransmitter & Neurotransmitter & hormone receptors act as ligands, hormone receptors act as ligands, b.b. Binding Binding causes conformational change (creates force causes conformational change (creates force “muscle”, opens or closes channel, activates “muscle”, opens or closes channel, activates enzyme),enzyme), c. c. G protein-linked receptors(second G protein-linked receptors(second messenger, signaling cascade is initiated)messenger, signaling cascade is initiated)

Cytoplasmic OrganellesCytoplasmic Organelles

Cytoplasm: Cellular material inside cellCytoplasm: Cellular material inside cell1. Most cellular activities occur here1. Most cellular activities occur here2. Comprised of:2. Comprised of:a. Cytosol: Fluid in which other components a. Cytosol: Fluid in which other components are suspendedare suspendedb. Organelles b. Organelles c. Inclusions: Non-functioning chemicals sub-c. Inclusions: Non-functioning chemicals sub-stances that may be unique to given cell typestances that may be unique to given cell type

Mitochondria: Transduce energy into useable Mitochondria: Transduce energy into useable cellular work. Double membrane structure cellular work. Double membrane structure similar to PM, similar to PM, a.a.Outer membrane (permeable), Outer membrane (permeable), b.b. Inner membrane contains embedded prn.s Inner membrane contains embedded prn.s involved in cellular work with cristae (folds of involved in cellular work with cristae (folds of the inner membrane), the inner membrane), c.c. Inner membrane Inner membrane space, space, d.d. Mitochondrial matrix: Contains enz.s Mitochondrial matrix: Contains enz.s for metabolic steps of cellular respirationfor metabolic steps of cellular respiration

Ribosomes: Site of protein synthesisRibosomes: Site of protein synthesis1. Complexes of RNA and protein1. Complexes of RNA and protein2. Free in cytosol or bound to ER2. Free in cytosol or bound to ER

Endomembrane System: Interactive system of Endomembrane System: Interactive system of membranes that interact directly through membranes that interact directly through physical contact or indirectly through vesiclesphysical contact or indirectly through vesicles1.1. Vesicle: Membrane-enclosed sacs that are Vesicle: Membrane-enclosed sacs that are pinched off portions of membranes moving pinched off portions of membranes moving from one membrane to anotherfrom one membrane to another2.2. Endomembrane system includes: Endomembrane system includes: a.a. Nuclear envelope, Nuclear envelope, b.b. ER, ER, c.c. Golgi apparatus, Golgi apparatus, d.d. Lysosomes & Lysosomes & e.e. Vacuoles Vacuoles

3.3. Endoplasmic reticulum: Network of memb- Endoplasmic reticulum: Network of memb-ranous tubules & sacs (cisternae) within the ranous tubules & sacs (cisternae) within the cytoplasm: Continuous with nuclear envelopecytoplasm: Continuous with nuclear envelope,two regions: ,two regions: smooth ERsmooth ER and and rough ERrough ER, , SER lacks ribosomes (synthesis of lipids, SER lacks ribosomes (synthesis of lipids, phospholipids & steroids, CHO metabolism, phospholipids & steroids, CHO metabolism, detoxifies drugs & calcium storage)detoxifies drugs & calcium storage)

4.4. RERRER: Protein synthesis (has ribosomes to : Protein synthesis (has ribosomes to synthesize secretory proteins), growing poly-synthesize secretory proteins), growing poly-peptide is threaded through ER membrane peptide is threaded through ER membrane (receptor site) into cisternal space, protein (receptor site) into cisternal space, protein folds into native conformation, in glycopro-folds into native conformation, in glycopro-tein; oligosaccharides enzymatically added to tein; oligosaccharides enzymatically added to the secretory protein, protein departs in the secretory protein, protein departs in transport vesicle pinched off from the ERtransport vesicle pinched off from the ER

5.5. Golgi apparatus: Modifies, concentrates & Golgi apparatus: Modifies, concentrates & packages RER products packages RER products a. Organelle of stacked, flat membranous sacs a. Organelle of stacked, flat membranous sacs (cisternae)(cisternae)b. Has polarity (cis face: receives transport b. Has polarity (cis face: receives transport vesicles from RER & trans face: pinches off vesicles from RER & trans face: pinches off vesicles)vesicles)c. The rough ER products are modified as c. The rough ER products are modified as they move through Golgi apparatusthey move through Golgi apparatus

6.6. Lysomes: Digestive compartments; memb- Lysomes: Digestive compartments; memb-ranous sac containing hydrolytic enzymesranous sac containing hydrolytic enzymesa.a. Digest all major classes of macromolecules Digest all major classes of macromoleculesb.b. Acidic (pump H+ in from cytosol), Acidic (pump H+ in from cytosol), c.c. Seque- Seque-sters destructive enzymes from the cytosolsters destructive enzymes from the cytosold.d. Functions: Intracellular digestion (phagocy- Functions: Intracellular digestion (phagocy-tosis), recycle cellular organic material (auto-tosis), recycle cellular organic material (auto-phagy) & programmed cell death (autolysis) phagy) & programmed cell death (autolysis) e.e. Role in disease: Storage diseases(lack of specific Role in disease: Storage diseases(lack of specific enzymes causes substrate accumulation: Pompe’s: enzymes causes substrate accumulation: Pompe’s: glycogen in liver & Tay-Sachs: lipids in brainglycogen in liver & Tay-Sachs: lipids in brain

CytoskeletonCytoskeleton

Network of fibers throughout cytoplasm that Network of fibers throughout cytoplasm that form a framework for support, movement & form a framework for support, movement & regulationregulationFunctions:Functions:1. Mechanical support to maintain shape1. Mechanical support to maintain shape2. Allows cell to change shape 2. Allows cell to change shape 3. Associated with motility 3. Associated with motility 4. Regulatory role in transmitting signals from 4. Regulatory role in transmitting signals from cell’s surface to its interiorcell’s surface to its interior

Three types of fibers: Three types of fibers: 1. Microtubules (thickest)1. Microtubules (thickest)2. Microfilaments (thinnest)2. Microfilaments (thinnest)3. Intermediate filaments3. Intermediate filaments

1. Microtubules: Radiate from cell’s center, 1. Microtubules: Radiate from cell’s center, determine cell shape, provide tracks for determine cell shape, provide tracks for organelle movement & invovled in separation organelle movement & invovled in separation of chromosomes during cell divisionof chromosomes during cell division2. Microfilaments (thinnest): Made up of cont-2. Microfilaments (thinnest): Made up of cont-ractile protein (actin), attach cytoplasmic side ractile protein (actin), attach cytoplasmic side of PM, help muscle& localized cell contractionof PM, help muscle& localized cell contraction3. Intermediate filaments: Most stable & act as 3. Intermediate filaments: Most stable & act as guy wires to resist pulling forces on the cell & guy wires to resist pulling forces on the cell & fix organelle positionfix organelle position

NucleusNucleus

Control center for cellular function; contains Control center for cellular function; contains genetic material, most cells have single genetic material, most cells have single nucleus, large cells (those with large amount nucleus, large cells (those with large amount of cytoplasm) have to be multinucleate, RBC of cytoplasm) have to be multinucleate, RBC is the only cell lacking nucleusis the only cell lacking nucleus

StructuresStructures1. Nuclear envelope1. Nuclear envelopea.a. Double membrane: Inner & outer: outer Double membrane: Inner & outer: outer

membrane is continuous with ER with membrane is continuous with ER with nuclear pores (selectively permeable)nuclear pores (selectively permeable)

b. Perinuclear cisterna: Fluid between b. Perinuclear cisterna: Fluid between membranesmembranes

2. Nucleoli2. Nucleolia. No membranea. No membraneb. Ribosomes subunits are assembled here b. Ribosomes subunits are assembled here (large in growing cells)(large in growing cells)c. Associated with chromatin region associa-c. Associated with chromatin region associa-ted with DNA coding for rRNA: Nuclear ted with DNA coding for rRNA: Nuclear organizing regions (DNA regions)organizing regions (DNA regions)

3. Chromatin—DNA + globular histone3. Chromatin—DNA + globular histonea.Nucleosome: Fundamental unit of chromatina.Nucleosome: Fundamental unit of chromatin(units of eight wrapped by DNA molecule)(units of eight wrapped by DNA molecule)b. Chromosomes: prior to cell division, b. Chromosomes: prior to cell division, chromatin condenses to form chromosomeschromatin condenses to form chromosomes