Ch 12 Lecture Cards
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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
electrically polarized: charge differential
Lipids are composed of __
fatty acids and glycerol
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
What is the composition of phosphoglycerides? and the simplest?
two fatty acids; glycerol backbone; phosphate attached to alcohol
simplest is phosphatidate
What do unsaturated fatty acids affet?
MP; point at which fluidit increases for a gorup of fatty acids
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
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
What is a cerebroside?
simplest glycolipid with glucose or galactose attached
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
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
If you are a conformer, what will your body do?
introduce more unsaturated fatty acids into the membranes if the temperature lowers
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
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
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
__ is the most common transmembranemotif.
How can you predict if you have a transmembrane motif?
hydrophobic amino acids come in big chunks
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
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
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
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)
Alpha helices are __
20 amino acids long (most are hydrophobic in nature)
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...
Does the hydropathy plot work for all transmembrane domains?
no; ebta sheets don't apply to this
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
What are the two types of diffusion?
What would you like to do?
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