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What are the six features of the membrane
sheetlike: extend in two dimesions and close in at teh ends
made of lipids and proteins (mediate function); together they form a barrier
hydrophilic and hydrophobic: both are amphipathic so that they can form a barrier as well as react with water
noncovalent bonds: held togetehr by them to maintain fluidity and movement through teh membrane; mostly v.d.W.
asymmetric: not the same inside and outside; proteins need to face the proper direction; lipids too
fluid
electrically polarized: charge differential
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Lipids are composed of __
fatty acids and glycerol
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Explain fatty acids
- hydrophobic hydrocarbon chains with carboxylic acid groups at the end
- long chains are even in number with 16-18 carbons eing the most common
- to break down fats, it's easier to do two at a time
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What is the composition of phosphoglycerides? and the simplest?
two fatty acids; glycerol backbone; phosphate attached to alcohol
simplest is phosphatidate
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What do unsaturated fatty acids affet?
MP; point at which fluidit increases for a gorup of fatty acids
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what must happen to lower MP?
double the bonds or shorten the chain
less bonds to break with shorter chain; double bond prevents tight packing
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What is a sphingosine?
What is a sphingomyelin?
shingosine is an amino alcohol; long unstturated fatty acid tail
sphingomyelin: add phsophorylcholine and antoher fatty acid tail
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What is a cerebroside?
simplest glycolipid with glucose or galactose attached
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What is cholesterol?
- big hydrophobic ring structure
- only hydrophilic portion is the hydroxyl group
- only in euk. membranes, not in organelles
rigid--> adds to the rigidity of the membrane; extreme case is one cholesterol per phospholipid
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When a single layer of phospholipids (such as what is present in detergents) is placed in aq. environments, what forms?
micelles, which are circular and single layer
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If you are a conformer, what will your body do?
introduce more unsaturated fatty acids into the membranes if the temperature lowers
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What can we do to test permeability?
create lipid vesicles via sonificatoin: probe sonicates sound waves through the liquid to get things moving rapidly; then, filter the surrounding solution and measure the rate at whcih glycine leaves
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Experiments testing permeability do what?
allow the formatin of a permeability scale
if you carry a charge, you can't get through with ese; hydrohobic have an easier time
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What are the three types of proteins in the membrane and how do you isolate them?
transmembrane: reuires disruption of the membrane
integral: can be completely in the membrane; must disrupt membrane
peripheral: located at the membrane surface and require high salt concentration to isolate
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__ is the most common transmembranemotif.
How can you predict if you have a transmembrane motif?
alpha helix
hydrophobic amino acids come in big chunks
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What else, besides alpha helices, can span the helix?
- beta sheets; they form a barrel through
- they are interspersed because the side chains stick out on one side
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Explain prostaglandin H2 synthase?
lodged in the membrane and detects damage to membrane
2 step reaction: converts fatty acid tail and converts it to hydrophilic molecule that signals pain and welling associated with damage
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Third type of proteins?
grey area protiens
addition of hydrophobic group to asociate the protein to the membrane (prenyl groups keep anchor_
fatty acid tail anchors it into teh memrbane; cysteine and whole protein is anchored
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Why are values of energy assigned to amino acids?
used as a test to find transmembrane regions in a protein
values assigned to each individual amino acid--> hydropathy vllues and hydropathy plots
positive indicates an input of energy
negative is an output of energy (spontaneous)
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Alpha helices are __
20 amino acids long (most are hydrophobic in nature)
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What is a window?
a stretch of twenty amino acids; twenty are needed to span the membrane (add up trnsfer free energy for all 20 amino acids)
if you reach a criterion level, then it is highly likely that an alpha helix is present. Not always a transmembrane helix, but ya know...
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Does the hydropathy plot work for all transmembrane domains?
no; ebta sheets don't apply to this
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What is FRAB
fluorescent recovery after bleaching; labeled entire surface with fluorescent dye; bleached some out and waited to see fi it would turn green again
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What are the two types of diffusion?
lateral: rapid
transerse: flip-flop
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