lec 4- The structure and function of the plasma membrane

Question 1

what is the plasma membrane?

Answer 1

The outer boundary of the cell that separates it from the world, is a thin fragile structure

Question 2

what are the 7 things a plasma membrane does?

Answer 2

-compartmentalization (forms continuous sheets that enclose intracellular compartments)
-scaffold for biochemical activities (provide a framework that organizes enzymes for effective interaction)
-selectively permeable barrier
-transporting solutes
-responding to external signals (receptors transduce signals)
-intracellular interactions
-energy transduction (transduce photosynthetic energy)

Question 3

what is the lipid to cell surface area ratio that the lipid bilayer accounted for?

Answer 3

2:1

Question 4

why is the surface tension of membranes lower than that of pure lipids?

Answer 4

due to protein being in the membrane

Question 5

what stabilizes bilayers?

Answer 5

van der waals interactions between acyl chains, and ionic/ hydrogen bonds with polar heads

Question 6

what varies depending on the type of membrane and the type of cell it is?

Answer 6

The ratio of lipid to protein

Question 7

what is the ratio of lipid to protein in the inner mitochondrial membrane?

Answer 7

very high ratio

Question 8

what is the ratio of lipid to protein in the myelin sheath?

Answer 8

low ratio

Question 9

what diseases have defective lipids in membranes?

Answer 9

alzheimers and infant respiratory distress syndrome

Question 10

what are the three major lipids in the membrane?

Answer 10

phosphoglycerides (most common/ AKA phospholipids)
sphingolipids (glycerol backbone)
cholesterol

Question 11

what are the molecules that the phosphate in the head group of the phospholipid links to?

Answer 11

choline, ethanolamine, serine, and inositol

Question 12

how many carbons do phosphoglycerides have?

Answer 12

16-22 carbons

Question 13

what are the steps to lipid biosynthesis in the ER?

Answer 13

step 1: acyl transferases successively add two fatty acids to glycerol-3-phosphate to produce phosphatidic acid
step 2: a phosphotase removes the phosphate leaving Diacylglycerol (DAG)
step 3: the addition of a head group

Question 14

what are the types of sphingolipids?

Answer 14

sphingosine = an amino alcohol that contains a long hydrocarbon chain
ceramide =sphingocine linked to a fatty acid
sphingomyelin = phosphorylcholine added to ceramide (also a phospholipid)
glycolipids = a carbohydrate added to a ceramide instead of a phosphorylcholine

Question 15

what are the two types of glycolipids?

Answer 15

cerebrocide = one sugar added to ceramide
gangliocide = a cluster of sugars added

Question 16

where is sphingolipid synthesis finished after it leaves the ER?

Answer 16

the golgi

Question 17

where are glycolipids found in the membrane?

Answer 17

in the exoplasmic face of the membrane

Question 18

what makes up 50% of the lipids inside the membrane?

Answer 18

cholesterol

Question 19

what are liposomes?

Answer 19

vesicles

Question 20

what does the asymmetry of membrane lipids do?

Answer 20

causes different physical and chemical properties in two different leaflets

Question 21

in which direction do carbohydrates face in the plasma membrane?

Answer 21

face outward

Question 22

what are integral proteins?

Answer 22

proteins that are penetrated and passed through the membrane (aka transmembrane proteins)

Question 23

what are peripheral proteins?

Answer 23

proteins that stick on the outer side of the membrane

Question 24

what are lipid-anchored proteins?

Answer 24

proteins on surface of cell attached to lipids, distinguished both by the types of lipid anchor and their orientation

Question 25

what do integral membrane proteins do?

Answer 25

function as receptors, channels, proteins that transfer electrons

Question 26

what is acylation of a lipid-anchored protein?

Answer 26

when the lipids in the palmitoyl group or myristol group attach to cytosolic proteins

Question 27

what is prenylation of a lipid-anchored protein?

Answer 27

instead of fatty acid, protein is attached to prenyl group

Question 28

what are examples of lipid anchored proteins?

Answer 28

G-proteins, acetylcholinesterase, Ras

Question 29

what are transmembrane domains?

Answer 29

a string of about 20 mostly nonpolar amino acids that span the lipid bilayer as an alpha helix

Question 30

what is glycophorin A?

Answer 30

a major integral protein of erythrocyte plasma membrane, 17 of 20 amino acids are hydrophobic that face the lipid layer

Question 31

what anchors glycophorin A to the membrane?

Answer 31

positively charged arginine and lysine residues near the cytosolic face

Question 32

what protein is one of the two that are exposed on red blood cells?

Answer 32

glycophorin A

Question 33

which protein had its complete amino acid sequence determined first?

Answer 33

glycophorin A

Question 34

what does a hydropathy plot do?

Answer 34

measure the hydrophobicity of amino acids

Question 35

what is bacteriorhodospin?

Answer 35

a seven membrane-spanning alpha helical protein that acts as a transmembrane proton pathway

Question 36

what protein generates gap junctions?

Answer 36

connexin

Question 37

what are lipid rafts and what do they do?

Answer 37

the outer leaflet of plasma membrane has cholesterol and sphingolipids that pack together and form lipid rafts that float in the more disordered environment and they provide a favorable environment for cell surface receptors

Question 38

are lipid bilayer molecules rapidly fluctuating?

Answer 38

yes

Question 39

how long does it take for a phospholipid to move laterally down the same leaflet?

Answer 39

a few seconds

Question 40

how long does it take for a phospholipid to move down to the other leaflet?

Answer 40

hours to days

Question 41

what enzyme moves phospholipids in leaflets?

Answer 41

flippase

Question 42

T or F: membranes in fused cells cannot fuse

Answer 42

no

Question 43

how can protein be labelled and tracked?

Answer 43

by FRAP (fluorescence recovery after photobleaching)

Question 44

what are the steps of FRAP?

Answer 44

unlabelled cell surface gets labelled with fluorescent dye, laser beam bleaches an area on cell surface, dyed molecules diffuse into area, bleached area disappears