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IB BIOLOGY Topic 1 Cell Biology 1.3-1.6 Membrane Structure • 1915- scientists knew structure of membranes included proteins and lipids. • Davson and Danielli Model 1935 – Lipid bilayer model – Covered on both sides with thin layer of globular protein • Singer and Nicholson 1972 – Proteins are inserted into phospholipid bilayer, not covering it • Current model– Fluid mosaic model Phospholipids • Composed of: – 3C glycerol – 2 glycerol carbons have fatty acid tails – 3rd C attached to highly polar organic alcohol bound to a phosphate – Hydrophobic and hydrophylic regions – Fatty acid tails not strongly attracted to each otherallows for fluidity – Structure maintained by hydrogen bonding among H2O molecules Cholesterol • Membranes consistency of olive oil • Various locations in fatty acid tail region, cholesterol molecules are embedded • Determine fluidity of cell, temperature dependent • Allows function during wide temperature range Proteins • Create extreme diversity in membrane function • Embedded in bilayer • Two Types: – Integral protein • Amphipathic- has both hydrophobic and hydrophylic portions – Peripheral protein • Bound to membrane surface • Can be anchored to integral Membrane Protein Functions • Hormone binding- specific shapes • Enzymatic action- catalyze chemical reactions • Cell adhesion-permanent or temporary connection • Cell-cell communication-many have carbs attached • Channels for passive transport- down the concentration gradient • Pumps for active transportneeds ATP, up the concentration gradient Membrane Transport • Passive transport – No ATP used – Goes with concentration gradient (Hi to lo) • Diffusion: membrane – Gases: O2 diffuses into a cell, CO2 diffuses out • Facilitated diffusion: – Uses carrier proteins • Osmosis: – H2O across semi-permeable membrane – Solute and solvent ratio important Membrane Transport • Size and Charge of Molecules: – Small, non-polar cross easily • CO2, O2, N2, H2O, glycerol – Large, polar cross with difficulty • Cl-, K+, Na+, glucose, sucrose Membrane Transport • Active transport: – Uses ATP – Goes against the concentration gradient • Animal cells have higher K+ concentration inside than outside, and have greater Na+ concentration outside than inside • Balanced maintained by sodium-potassium pump Membrane Transport • Endocytosis – Fluidity dependent – Allows macromolecules to enter cell – Part of plasma membrane pinched off to enclose macromolecule – Changes shape of membrane – Creates vesicle that enters cell Membrane Transport • Exocytosis – Reverse of endocytosis Specialized Transport • Pinocytosis- intake of extracellular fluids • Phagocytosis- intake of large particulate matter – Ex. Macrophage engulfing antigen Cell Division • The Cell Cycle: – Describes the behavior of cells as they grow and divide. – Interphase: G1, S, G2 – G1-smallest cell will ever be, major event is growth – S- replication of cellular DNA – G2-organelles increase in number, DNA begins to condense from chromatin chromosomes, microtubules begin to form. Cell Division • Cyclins: – Proteins that control cell’s progression through cell cycle – Bind to cyclin-dependent protein kinases (CDKs) enabling them to act like enzymes – Cause cell to go from G1S G2M – Can pause during G1 and enter G0- a non-growing phase • Time remaining in this phase varies – Nerve and muscle cells do not progress past G0 Mitosis • M phase: – Replicated chromosomes move to opposite poles of cell – Cytoplasm divides – Result: identical daughter cell • Phases of Mitosis: – – – – Prophase Anaphase Metaphase Telophase Chromosome • Before replication in S phase, cells have 1 molecule of DNA • After- 2 molecules of DNA held on center by centromere • Condensation of DNA: – Super-coiling – DNA wraps around histone proteins- “nucleosome” – Nucleosomes solenoid chromosome Prophase • The chromatin fibers become more tightly coiled • The nuclear envelope distinegrates, nucleoli disappear • Mitotic spindle forms • Centromere of chromosomes attach to spindle fibers by kinetochores • Centrosomes move to opposite poles of cell lengthening the microtubules Metaphase • Chromosomes move to the middle of the cell. • Centromere of chromosomes lie on the plate. • Movement of chromosomes controlled by spindle • Centrosomes at opposite poles Anaphase • Shortest phase of mitosis • Chromosomes move to opposite parts of the cell. • Movement due to shortening of the microtubules of spindle • Centromeres attached to microtubules, so they move first • Result: each pole has complete, identical set of chromosomes. Telophase • Chromosomes are at each pole • Nuclear membrane begins to reform • Chromosomes chromatin • Spindle disappears • Cell elongates, ready for cytokinesis Cytokinesis • Cleavage of animal cell • Cell plate formation in plant cell https://www.youtube.com/watch?v=ofjyw7AR P1c https://www.youtube.com/watch?v=ZEwddr9 ho-4 Cancer • Uncontrolled cell growth • Primary tumor: – Occurs at original site of cancer • Secondary tumor: – Metastatic- has spread from original site to another location – Can be found in many locations Henrietta Lacks and HeLa Cells • http://www.cbsnews.com/news/the-immortalhenrietta-lacks/ • Henrietta Lacks was an African American woman who died in 1951 of cervical cancer. – Her cancerous tumor cells were of interest to doctors, because they were the first cancer cells that would grow under laboratory conditions. The cells have been studied and cultured world- wide for decades without her knowledge, permission, or family compensation. – She is the most important contributor to cancer research to date. Cancer, cont. • Reasons for formation of primary tumors: – Gene mutation – Abnormally high gene expression – Oncogenes: • Section of genes that contributes to conversion of normal cell cancer cell • Oncogenes: – Can mutate in response to environmental trigger • Ex: Cigarette smoke