Cellular Biology I

1. Cellular Biology I Generalized Cell Cytoskeleton Cytoplasmic Organelles Nucleus Cell Theory Cell-Environment Interactions Plasma Membrane 6. Lysomes: Digestive compartments; memb-ranous sac containing hydrolytic enzymes a. Digest all major classes of macromolecules b. Acidic (pump H+ in from cytosol), c. Seque-sters destructive enzymes from the cytosol d. Functions: Intracellular digestion (phagocy-tosis), recycle cellular organic material (auto-phagy) & programmed cell death (autolysis) e.Role in disease: Storage diseases(lack of specific enzymes causes substrate accumulation: Pompe’s: glycogen in liver & Tay-Sachs: lipids in brain Endomembrane System: Interactive system of membranes that interact directly through physical contact or indirectly through vesicles 1. Vesicle: Membrane-enclosed sacs that are pinched off portions of membranes moving from one membrane to another 2. Endomembrane system includes: a. Nuclear envelope, b. ER, c. Golgi apparatus, d. Lysosomes & e. Vacuoles 1. Microtubules: Radiate from cell’s center, determine cell shape, provide tracks for organelle movement & invovled in separation of chromosomes during cell division 2. Microfilaments (thinnest): Made up of cont-ractile protein (actin), attach cytoplasmic side of PM, help muscle& localized cell contraction 3. Intermediate filaments: Most stable & act as guy wires to resist pulling forces on the cell & fix organelle position 4. Types of diffusion:a. Simple:Nonpolar substances (lipid soluble) pass directly through lipid bilayer (polar &charged particles can diffuse if they can fit through pores),b. Osmosis: Diffusion of solvent via selectively permeable membrane (hypertonic, hypo-tonic, isotonic, osmolarity & osmotic pressure), c. Facilitated diffusion: Lipid insoluble molecules too large to diffuse through membrane pores can move passively with carrier molecules: Selective (specific) & limited by number of carriers (saturation) Membrane transport 1. Membranes are selectively permeable 2.Passive & active processes 3. Passive movement: Diffusion: a. Movement of substance down concentration gradient: Changes over distance in particular direction, b. Results from intrinsic kinetic energy: Temperature & molecular size, c. Random molecular movement, d. Dynamic equilibrium 3. Endoplasmic reticulum: Network of memb-ranous tubules & sacs (cisternae) within the cytoplasm: Continuous with nuclear envelope ,two regions: smooth ER and rough ER, SER lacks ribosomes (synthesis of lipids, phospholipids & steroids, CHO metabolism, detoxifies drugs & calcium storage) 4.RER: Protein synthesis (has ribosomes to synthesize secretory proteins), growing poly-peptide is threaded through ER membrane (receptor site) into cisternal space, protein folds into native conformation, in glycopro-tein; oligosaccharides enzymatically added to the secretory protein, protein departs in transport vesicle pinched off from the ER 5. Golgi apparatus: Modifies, concentrates & packages RER products a. Organelle of stacked, flat membranous sacs (cisternae) b. Has polarity (cis face: receives transport vesicles from RER & trans face: pinches off vesicles) c. The rough ER products are modified as they move through Golgi apparatus Network of fibers throughout cytoplasm that form a framework for support, movement & regulation Functions: 1. Mechanical support to maintain shape 2. Allows cell to change shape 3. Associated with motility 4. Regulatory role in transmitting signals from cell’s surface to its interior Specialized Structures and Functions 1. Microvilli: Increase surface area; absorption 2. Membrane junctions: a. Tight junctions: Impermeable junctions, b. Desmosomes: Anchoring junctions; plaques & linkers; intermediate filaments & c. Gap junctions: Movement of chemicals between adjacent cells; connexons 6. Active Processes: Active Transport: a. Cell uses energy to move substances across the membrane, b. Transport molecules utilize energy from ATP to pump molecules against concentration gradients, c. Coupled systems(symport&antiport)d.Na+-K+ pump: Na+ binding stimulates ATP formation, phosphoryla-tion causes conformational change which releases Na+, K+ binding causes phosphate release, pump returns to original conformation & K+ is released Concepts: 1. Cells are the functional and structural units of living organisms 2. The activity of organism is dependent on both individual and collective activity of the cells that comprise that organism 3. Subcellular structures determine the biochemical activities of cells (i.e., principle of complementarity) 4. Continuity of life has a cellular basis 7.Bulk Transport (Active): a. Exocytosis: sub-stance is released from vesicle (membranous sac: Fuses with membrane&releases contents to outside), b. Endocytosis: Large substances enclosed by membrane&taken into cell: Phag-ocytosis, pinocytosis & receptor-mediated endocytosis (coated pit & clathrin) Membrane receptors 1. Contact signaling 2. Electrical signaling: Voltage-gated channels 3. Chemical signaling: a. Neurotransmitter & hormone receptors act as ligands, b. Binding causes conformational change (creates force “muscle”, opens or closes channel, activates enzyme), c. G protein-linked receptors(second messenger, signaling cascade is initiated) Cytoplasm: Cellular material inside cell 1. Most cellular activities occur here 2. Comprised of: a. Cytosol: Fluid in which other components are suspended b. Organelles c. Inclusions: Non-functioning chemicals sub-stances that may be unique to given cell type 2. Nucleoli a. No membrane b. Ribosomes subunits are assembled here (large in growing cells) c. Associated with chromatin region associa-ted with DNA coding for rRNA: Nuclear organizing regions (DNA regions) Mitochondria: Transduce energy into useable cellular work. Double membrane structure similar to PM, a.Outer membrane (permeable), b. Inner membrane contains embedded prn.s involved in cellular work with cristae (folds of the inner membrane), c. Inner membrane space, d. Mitochondrial matrix: Contains enz.s for metabolic steps of cellular respiration Fluid mosaic model 1. Membranes are mosaic of different proteins are embedded in a phospholipid bilayer 2. Hydrophilic portions of proteins& phospho-ipids are maximally exposed to water 3. Hydrophobic portions are in nonaqueous environment inside membrane Function of membrane proteins: 1. Transport 2. Enzyme 3. Receptor sites 4. Intercellular junctions 5. Cell-cell recognition 6.Cytoskeletal&extracellular matrix attachment Types of proteins: 1. Integral: transmembrane proteins; span the hydrophobic interior (channels & carriers) 2. Peripheral: not embedded; attach surface (enzymatic activity & structure) 3. Chromatin—DNA + globular histone a.Nucleosome: Fundamental unit of chromatin (units of eight wrapped by DNA molecule) b. Chromosomes: prior to cell division, chromatin condenses to form chromosomes Control center for cellular function; contains genetic material, most cells have single nucleus, large cells (those with large amount of cytoplasm) have to be multinucleate, RBC is the only cell lacking nucleus • Structures • 1. Nuclear envelope • Double membrane: Inner & outer: outer membrane is continuous with ER with nuclear pores (selectively permeable) • b. Perinuclear cisterna: Fluid between membranes Cell-adhesion molecules (CAMS) 1. Anchor cell to EC matrix & to each other 2. Cell migration 3. Cell signaling Carbohydrates associated with the exterior surface of the membrane 1. Glycolipids 2. Glycocalyx: attached to proteins in contact with extracellular matrix Three types of fibers: 1. Microtubules (thickest) 2. Microfilaments (thinnest) 3. Intermediate filaments 5.Filtration: Water and solutes are forced through a membrane or capillary by hydrostatic pressure: Pressure gradient pushes solute-containing fluid out Ribosomes: Site of protein synthesis 1. Complexes of RNA and protein 2. Free in cytosol or bound to ER Home Exit BASIM ZWAIN LECTURE NOTES