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Cell Bio Exam 2 Questions And Answers
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Cell Bio Exam 2 Questions And Answers Cell Bio Exam 2 Questions And Answers Cell Bio Exam 2 Questions And Answers
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Cell Bio Exam 2Plasma membrane The outer boundary of the cell that separates it from the world is a thin, fragile
structure about 5-10 nm thick
What detects the plasma membrane? Electron microscope, not a light microscope detects it
Membrane Functions Compartmentalization; scaffold for biochemical activities; selectively permeable
barrier; transporting solutes; responding to external signals; intracellular interaction; energy
transduction
Prokaryotes no interior compartments, very complicated external membranes
What makes up an outer membrane in a prokaryote? Lipopolysaccharides
Alterations to the hydrophobic tails of lipids Control of fluidity and permeability of biological membranes
is accomplished through this
Early model of plasma membrane structure Davson-Danielli, 1954; lipid bilayer existws primarily in two
dimensions; contains SOME membrane-embedded proteins; homogeneous in composition
Later model of plasma membrane structure Singer and Nicholson, 1972; lipid bilayer exists primarily in
two dimensions; contains MANY membrane-embedded proteins; heterogeneous in lipid & protein
composition, formation of distinct domains
Fluid-mosaic model core lipid bilayer exists in a fluid state, capable of movement; lipid bilayer exists
primarily in 3D; membrane proteins form a mosaic of particles penetrating the lipids; heterogeneous in
lipid and protein composition, formation of distinct domains
,More than 30 years later the model's characteristics include -overall, mosaicism is high; fluidity/diffusion
is limited for many molecules
-membrane thickness is not uniform
-proteins bind together and function in complexes
-large protein domains on either side of bilayer limit accessibility of bilayer
Proteins perform most of the functions of a cell membrane
Why does membrane thickness vary? Lipids may contort to interact closely with membrane proteins
Membrane lipids -All are amphipathic, three types:
1. Phosphoglycerides
2. Sphingolipids
3. Cholesterol
Phosphoglycerides diacylglycerides with small functional head groups linked to the glycerol backbone by
phosphate ester bonds
Ways phosphoglycerides can differ -Polar head group
-Length of FA chain (16-22 C's long)
-Level of FA saturation (saturated, monounsaturated, polyunsaturated)
Sphingolipids ceramides formed by the attachment of sphingosine to fatty acids
Characteristics of sphingolipids -FA chains tend to be longer and more highly saturated than
phosphoglycerides
-Additional groups can be added to the terminal alcohol of the sphingosine
, Cholesterol Steroid molecule that is amphipathic and only found in animals; carbon rings are flat and
rigid, interfering with movement of phospholipid fatty acid tails
At low temps, what does cholesterol do to a membrane? Makes membrane more fluid
At high temps, what does cholesterol do to a membrane? Make it more ordered
What determines shape of lipids? Chemical structure
Three types of membrane proteins integral, peripheral, lipid-anchored
What gives membranes a distinct "sidedness"? Membrane proteins attach to the bilayer asymmetrically
Integral proteins Penetrate and pass through lipid bilayer; make up 20-30% of all encoded proteins; are
amphipathic; include channel proteins
Channel proteins Integral proteins that have hydrophilic cores that form aqueous channels in the
membrane-spanning region
What makes integral proteins amphipathic? -20-30 non-polar AA forming hydrophobic interactions with
FA tails of PL
-Polar AA, hydrophilic regions forming functional domains outside of the bilayer
Glycophorin A An IMP that carries carboydrate which gives RBC a hydrophilic coat that enables cells to
circulate without adhering to other cells or vessel walls; big carbohydrate strand gives it the
hydrophobic coat to allow them to keep sliding around; example of a glycoprotein
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