Bio Ch. 8
Terms
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- fluid mosiac model
- proteins are dispersed throughout the phospholipid bilayer with the hydrophobic parts embedded and the hydrophilic parts protruding.
- hydrophobic interactions
- weak, hold the membrane together
- low temperatures
- phospholipids solidify, which effects the ability of the membrane to function
- unsaturated hydrocarbons
- tails have kinks due to double bonds which disallow solidification
- cholesterol
- in animal cells only, wedged between phospholipids to stabilize the membrane. Makes it less fluid at warm temperatures, but also hinders close packing, lowering solidification temperature
- membrane molecules
-
phospholipids- main structure
cholesterol- maintain fluidity
carbohydrates- attached to outside
proteins- control function - Endoplasmic Reticulum
- synthesizes membranes and their proteins
- integral proteins
- span the membrane, strands of amino acids in alpha helixes are hydrophobic and in the interior. maybe attached to cytoplasm or extracellular fibers to give more stability.
- peripheral proteins
- not trans membrane, often bound to intergral proteins
- enzymatic activity
- membrane protein may be an enzyme with active site exposed to substances in the adjacent solution. form an enzymatic pathway.
- signal transduction
- binding site fits a chemical messenger which causes the protein to change shape and relay the message to the other side
- cell-cell recognition
- glyco (short branched carbohydrates)-proteins serve as identification tags that are specifically recognized by other cells
- intercellular joining
- membrane proteins of adjacent cells may hook together in gap junctions or tight junctions
- attachment to cytoskeleton or extracellular matrix
- microfilaments or other elements may bond to the protein which maintains cell shape and protein position
- hydrophilic things (DO NOT ENTER)
- large polar molecules (glucose, other sugars), ions with their shell of water
- hydrophobic (FREE PASS)
- water, ethanol, hydrocarbons, oxygen, carbon dioxide
- diffusion of two solutes
- each solute diffuses down its own concentration gradient
- osmosis
- selectively permeable membrane will not let the solute diffuse so water must. passive transport of water determined by TOTAL solute concentration.
- plant, protist, fungi and prokaryotic cells
- plant cells have elastic walls and only allow a certain amount of water to enter before they become turgid. cells live in hypotonic environments= turgid. isotonic= flaccid. hypertonic= plasmolysis (plasma membrane pulls away from cell wall)
- facilitated diffusion
- transport proteins allow hydrophilic molecules (ions or polar molecules) to pass. each protein is specific for what it moves
- transport protein
- similar to enzyme. specific binding site for its protein, can be saturated, and can be inhibited by imposters
- gated channels
- electrical or chemical stimulus causes protein to open or close
- active transport
- pumps against gradient and cell must expend metabolic energy
- sodium-potassium pump
- 3 NA+ in the cytoplasm bind to the protein and a phosphorous is added (phosphorylation) from ATP. This causes the protein to change shape and dispense the 3 NA+ outside of the cell. Then two K+ bind from the outside, triggering the release of a phosphorous. This restores the original conformation and dispenses the 2 K+ to the inside. Net loss of 1+
- membrane potential
- voltage across a membrane. cytoplasm is negative so anions are favored to enter cell, and cations to exit.
- electrochemical gradient
- two forces that drive the diffusion of ions. chemical force (concentration grad.) and electrical (membrane potential)
- electrogenic pump
-
a transport protein that generates voltage across a membrane
(sodium-potassium in animals)
(proton pump in plants) - cotransport
- ATP actively transports a substance across a membrane. as the substance leaks back through passive tranport, it takes another substance into the cell with it, even though the substance is moving UP the concentration gradient.
- exocytosis
- the cell secretes macromolecules by the fusion of vesicles with the plasma membrane
- phagocytosis
- pseudopodia reach out and engulf the particle and package it in a vacuole which is consumed by a lysosome.
- pinocytosis
- droplets of extracellular fluid are incorportaed into the cell in small vesicles (non specific)
- receptor mediated endocytosis
- coated pits form vesicles when specific molecules (ligand)bind to receptors on the cell surgace. This allows the cell to get the specific things it needs from the outside even if they are not in abundance. Other things are taken in as well.