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Cell Bio Test 3 Notes.docx

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Kim Dej

Cell Bio Test 3 Notes Lecture 14  Organelles must have a membrane for separation (compartments)  Ground cytoplasm  Endoplasmic Reticulum - Membrane is continuous with outer nuclear membrane - Has its own cytoplasm  Ribosome is not an organelle  Peroxisomes- enzymatic reactions occur inside and are separated by the membrane  Two types of membranes - Plasma- surrounds cell (has outside contact) - Internal Plasma Membrane  Required  Filter not a barrier  Lipid bilayer  Thermodynamically stable (no energy needed to stay together)  Fatty acid tails are hydrophobic and polar  4-5 nm thick  Lipid backbone but has lots of proteins and carbs - Structural= lipids (50%) - Functional= proteins Lipids  Phospholipids - 3 C sugar alcohol (glycerol) attached to phosphate with polar head group that is charged (choline, serine, ethanolamine, inositol, etc) - Fatty acid component- 14-24 C in length, usually 1 is saturated and the other is not (would put a kink in it) - Vary in polar head group, degree of saturation, and length  Regulation of Fluidity - Membranes need to balance fluidity to filter - Fluidity is balanced with fatty acid length (increase length to interact with the one across from it to slow down fluidity) - Phospholipids spin (increase spin, increase fluidity) - Phospholipids also move laterally - Longer phospholipid tails restrict movement - Kinky fatty acids don’t pack as well and increase fluidity (by decreasing saturation) - Stress proteins (HSP) that bind to membranes when they are too high, decrease fluidity very quickly  Outside is phosphatidyl choline and inside (cytoplasm side) are others and they do not flip flop  Asymmetry causes charge difference (more + outside and – cytoplasm side) Cholesterol  Embeds itself in membrane so that hydrocarbon tail fits with fatty acids (90 turn)  Fluidity: - Restricts movement of phospholipids - Increase cholesterol, decrease fluidity Glycolipids  Oligosaccharides (short chain monomer attached to lipid) 3-15 sugars  Attach on outside (face out)  Most are branched  Take in signals and help detect changes outside (signal transduction, outside to inside)  Ex myelin  Less than 5% of all lipids are glycolipids (associated sugar) Proteins  Nerve- less than 25% of membrane is protein (internal membrane will have 80%)  Decrease fluidity (restrict movement)  Proteins can move (fluid themselves)  Can cross entire membrane (transmembrane proteins) - Regions can extend to inside and outside of cell (weave back and forth) to keep protein in membrane (alpha helix or beta sheets are hydrophobic) - Makes pores/channels for molecules to move because of structure and domains - Signal transduction  Some proteins don’t cross (peripheral proteins) - On one side or another - Hydrophobic and hydrophilic sides keep it in the right orientation - Attach covalently to lipids to form lipoproteins - Binds to another protein  Amino acids are hydrophilic and want to react with other molecules  Proteins with signaling can have oligosaccharide bound to it  50 phospholipids for 1 protein but equal in mass  Proteins can hold cells or proteins together (more proteins, more rigidity)  Some are enzymes, some are transporters  Na K atpase has quarternary structure (proteins interacting with eachother) Lecture 15 Grad student- review of 14  Catadromous- freshwater to marine animals  Anadromous- opposite  Small or nonpolar molecules can move easily by diffusion  Water goes to place of highest solute  Carrier Proteins - Binds to ligand and helps it through membrane by facilitated movement - Uniport- helps molecule through in one direction, specialized - Symport (co-transporter)- transport 2 molecules at same time in same direction (ex Na/glucose) - Antiport- NaKatpase (3 Na out, 2 K in), 2 molecules in opposite directions, most sophisticated with quarternary structure)  Channel Proteins - Diffusion/passive - Most are gated (normally closed) - Types of Gates: o Ligand gated- outer domain is blocking channel; has ligand binding site; ligand is not molecule passing through (ligand opens it); ex immune system o Voltage gated- nerves and muscles; action potential triggers brief opening to let ions readjust  Endocytosis - Molecule coming in - Larger nutrients - Membrane is flipped- outer plasma membrane is inner layer in vesicle - Pinocytosis is small molecules (less than 50 nm) - Phagocytosis is large molecules - Happens all the time (exocytosis occurs in pulses when needed) - Actin microfilaments move vesicles - Bulk transport- exocytosis and endocytosis into tissue layers - Special endocytosis o Not to be digested when it enters the cell o Receptor acquires and protects vesicle (signal to come in) - Applies clathrin- protective coating- 180 kd homotrimer - Receptor mediated endocytosis- so that nutrient is not digested  Cytoplasm - 70% water - 15-25% protein - 10 billion proteins- 10,000 varieties - Cytoskeletal proteins - Ground cytoplasm is around organelles - Matrix cytoplasm is within organelles Lecture 16  Cytoplasm is mostly water and protein Endoplasmic Reticulum  Continuous with outer membrane of nucleus  Material associated with membrane can move (lipid protein could go anywhere in nuclear membrane and ER)  Matrix of ER goes in periplasmic space Rough ER  Ribosomes attached  80s- protein synthesis occurring  Looks like flattened sac/balloon Smooth ER  Tubular balloon/sac  Different processes occur in lumen and membrane  Transition ER is like smooth ER but has different processes Rough ER  Protein synthesis  Glycosylation- adding sugar to protein to make a glycoprotein Protein Synthesis  Initiation and some of elongation must occur before 80s ribosome binds to ER  60s subunits is bound to 2 glycoproteins which affix it to ER membrane  After 20 amino acids are synthesized, elongation stops until ribosome attaches to ER - First 20 AA are hydrophobic and are a leader sequence - Chemical signaling occurs after it is docked  Protein is synthesized and released into ER lumen  Leader sequence gets protein to ER then LS is removed (not part of mature protein)  Some proteins become transmembrane proteins (not released into lumen)  All transmembrane and some peripheral proteins are built in rough ER  Protease removes leader sequence Glycosylation  Most sugars are oligosaccharides (short chain, 3-15, may be branched)  Oligosaccharides are custom made - Made in rough ER - Dolichol- large transmembrane (rough ER) protein with phosphorous linkage) - Enzymes build by adding one monosaccharide at a time to cytoplasm side - Phosphatidyl choline is on lumen side (not cytoplasm) - Sugar is not on cytoplasmic side other than when it is being synthesized - Once synthesized, oligosaccharide is flipped into lumen by dolichol - Then cut and attached to protein - Must attach to asparagine that has serine or threonine two AA down from it (amino acid- ASN) (terminal end of R group has NH2) (middle AA can be anything except proline) - The sugar that is attached with usuall
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