101: Cell Membranes, Cell Junctions and Membrane Transport

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What is an amphipathic molecule?
One that has both hydrophilic and hydrophobic regions
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What did Davson & Danielli's theory state?
That the cell membrane is coated on both sides with hydrophilic proteins, like a sandwich
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What did Singer & Nicolson's theory state?
That the cell membrane is studded with proteins, with hydrophilic areas protruding
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What does freeze-fracturing do?
Splits the cell membrane along the middle of the bilayer for microscopy purposes
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Can proteins and lipids shift laterally across a cell membrane?
Yes
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Can proteins and lipids shift vertically across a cell membrane?
No
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What determines the temperature at which a cell membrane will solidify?
The number of saturated and unsaturated fatty acids in its phospholipid bilayer
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Why do unsaturated fatty acids in the phospholipid bilayer affect the temperature at which it will solidify?
Because unsaturated hydrocarbon tails contain kinks from the cis double bond that prevents them from packing together as closely as saturated tails
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What role does cholesterol have in a cell membrane?
It resists changes in membrane fluidity
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How do large molecules affect the fluidity of the cell membrane?
Large molecules reduce the closeness of phospholipids and thus decrease the temperature at which they become solid
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The closer the phospholipids in a cell membrane, the more fluid it is
False; close hydrocarbon tails increase the membrane viscosity
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What are integral proteins?
Proteins that penetrate the hydrophobic interior of the lipid bilayer
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What are peripheral proteins?
Proteins that are not embedded in the lipid bilayer, and are loosely bound to the surface of the membrane
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Describe the hydrophobic part of an integral protein
One or more stretches of nonpolar amino acids that are usually coiled into α helices
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What gives the cell membrane strength?
Connection to the cytoskeleton or fibres of the extracellular matrix
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What functions can membrane proteins play?
Transport, enzymatic activity, signal transduction, cell-cell recognition, intercellular joining, attachment to the cytoskeleton
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How do cells recognise other cells?
By binding to molecules on the extracellular surface of the plasma membrane
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What are some characteristics of membrane carbohydrates?
They are typically short, branched chains of under 15 monosaccharides
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What is the difference between a glycolipid and a glycoprotein?
A glycolipid is a carbohydrate bound to a lipid in the plasma membrane; a glycoprotein is a carbohydrate bound to a protein
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Can polar or non-polar molecules easily pass through the plasma membrane?
Non-polar
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Name channel proteins that facilitate the passage of water.
Aquaporins
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What are carrier proteins?
Proteins that alter their shapes in order to transport molecules across the cell membrane
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What are channel proteins that transport ions called?
Ion channels
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How are many gated channels stimulated?
Electrical stimuli
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What is membrane potential?
The difference in voltage across a cell membrane
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What does an ion diffuse down?
Electrochemical gradient
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When do human cells use receptor-mediated endocytosis?
To take in cholesterol for membrane synthesis and the synthesis of other steroids.
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Card 2

Front

What did Davson & Danielli's theory state?

Back

That the cell membrane is coated on both sides with hydrophilic proteins, like a sandwich

Card 3

Front

What did Singer & Nicolson's theory state?

Back

Preview of the front of card 3

Card 4

Front

What does freeze-fracturing do?

Back

Preview of the front of card 4

Card 5

Front

Can proteins and lipids shift laterally across a cell membrane?

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