Membrane Proteins

Question 1

Lipid bilyer vs protines function

Answer 1

Lipid bilayer provides the basic structure of biological membranes,

proteins perform most of the specific tasks (functional properties)

Question 2

Amount of protein in a biological membrane typically reflects function:
plasma membrane vs myelin

Answer 2

Plasma membrane 50% lipid, 50% protein
Myelin 75% lipid, 25% protein

Question 3

Membrane proteins show ____ across the bilayer

Answer 3

asymmetry

Unique orientation set at biosynthesis, kept throughout protein’s lifetime.

Question 4

Membrane protines are synthisised in the

Answer 4

in the ER - made in a cetine way - transported everywhere else - maintain a set orentation

Question 5

Types of Membrane Proteins

Answer 5

Transmembrane Proteins
Membrane Associated Proteins
Lipid Associated Proteins

Question 6

Transmembrane Proteins:

Answer 6

Hydrophobic regions pass through the membrane, hydrophilic groups exposed to water.

Includes single-pass TM (1), multipass TM (2), and β barrel (3).

Question 7

Membrane Associated Proteins location

Answer 7

do not extend into hydrophobic interior of the lipid bilayer; they are bound to either face of the membrane by non covalent interactions with other membrane proteins

Question 8

Lipid-Associated Proteins are attached by

Answer 8

Proteins attached to bilayer by covalent attachment to lipid anchors

Question 9

Transmembrane Domains

portion of __

of ___ ameno acids

form ___

Answer 9

Portion of the integral membrane protein (trans-membrane domain) is embedded within the lipid bilayer.

20-30 NON POLAR amio acids
amost always form a alfa helex .

polar peptide bonds are forced into H bonding in non aqueous enviorment (hydrophobic core of lipid bilayer)
non polar side chains stick out facing hydrofillic lipid bilayer

Question 10

Single-Pass Transmembrane Protein

types __

Answer 10

Polypeptide chain crosses only once

Typed according to topography.
Type 1: N-terminus out, C-terminus in.
Type 2: N-terminus in, C-terminus out.

N - free amino
C - free carboxyl

Question 11

Multipass Transmembrane Proteins

Answer 11

Polypeptide chain crosses multiple times

α helices occupy specific positions in the folded protein structure that are determined by interactions between the neighboring helices, important for function of many channels and transporters

slight conformational change from newly synthiszed to folded

Question 12

Hydropathy Plot

Answer 12

Localize potential α helical membrane spanning segments

If energy is required (+) to transfer from non polar to water - means hydrophobic
determines which arease are hydrophobic - most likely a trans membrane domain
- analizes in segements (20-30) of each alfa helisces

Question 13

β Barrel are more __ than Alda helies because ___

are abundant in ___

Answer 13

More rigid in comparison to multipass proteins with α helices.( α has more flexability - slight conformational changes) because of alighnmens of H bonds in structure

Porins are well studied examples

Abundant in outer membranes of bacteria, mitochondria, and chloroplasts

Question 14

Would a β Barrel require a long strech of hydrophobic ameno acids (~20) in transmembrane portion of a protine?

Answer 14

No
R sides of alfs - stick out
R side of β - alternate

would be an alternating strech of hydrophobic and fillic

Question 15

Can a hydropath plot be used for a β Barrel?

Answer 15

No
because the plot looks at/analized the polypeptide in seggments (20-30 of hydropobic) would not work

(B barrel can be ~10) and alternating fobic and fillic

Question 16

Isolation of Integral Membrane Proteins requires
___

to remain soluble Isolated protein requires ____

Answer 16

disruption of the bilayer by detergents.

detergent.

Question 17

Many Detergents used for isolation of integral membrane proteins

Answer 17

Amphipathic

non-ionic (Triton) - mild - denaturing

ionic (SDS) - harsh - polypeptide is extended/unfolded - react with hydrophobic core (use for western blot, seperate on MW)

Question 18

Mild detergents: Purify protein in ___

Answer 18

active form

Question 19

Steps of mild detergent isolation of inegral membrane protines

Answer 19

add deterngts (mild, if too harsh would not be able to suddy)

Hydrophobic interactions with proteins - soluablizes membrane proteins

Lipid micells (detergents) added

Purfication of protine of intrests

add phospolipids and remove detergent

results in formation of a liposome - just studdy the spcific membrane protine’s functions

Question 20

Peripheral Membrane Proteins are___

assoacated by __

issolated by __

Answer 20

Membrane proteins non-covalently bound to integral proteins or lipid head groups.

Usually associated via electrostatic interactions

Can be isolated without bilayer disruption.

change pH - extremly basic - interfeers with interactions of proteins and bylater membrane.

Question 21

Lipid-Anchored Protein Types

Answer 21

1. Proteins with covalently linked acyl chains (fatty acids) –(cytosolic side only)
2. Proteins with covalently linked polyisoprenoid anchors (cytosolic side only).
3. Proteins with covalently linked (SUGGAR) glycophosphatidylinositol (GPI) anchors (non cytosolic side only). Phosphatidylinositol (PI) is a phosphoglyceride

Question 22

Myristic acid (C=14)

Answer 22

Protine with covalently linked acytl chains (fatty acids) -

stable ancher - made with protine itself

Question 23

palmitic acid (C=16)

Answer 23

Protine with covalently linked acytl chains (fatty acids)

denamic ancher - made in response to signal

Question 24

Lipid anchors Control

Answer 24

Membrane Localization of Some Signaling Proteins

Question 25

Lipid Anchors and Intracellular signaling

Answer 25

help to relay extracellular signals into cell interior, are bound to cytosolic half of membrane with attached lipid group (ie fatty acid chain)

Question 26

Src Kinases:

Answer 26

Fatty acid anchor During its synthesis, myristoyl acid added (attachment to membrane by single anchor not very strong). Second lipid (palmitic acid) added, more firm anchor. This lipid added in response to extracellular signal.

Question 27

GPI-Anchored proteins are invovled in

Answer 27

have been involved in membrane protein transportation, cell adhesion, cell wall synthesis, and cell surface protection

Question 28

Most transmembrane proteins are

Answer 28

glycosylated (noncytosolic side of membrane) a layer of oligosaccharide and polysaccharide chains that are attached to the lipids and protein domains facing the outside. This environment decreases the likelihood that intrachain or interchain disulfide (S–S) bonds will form between cysteines on the cytosolic side of membranes.

Question 29

Carbohydrate layer on cytosolic side purpose

Answer 29

(glycocalyx)-protects cells against mechanical (proteases) and chemical damage, mediate cell adhesion and cell recognition processes differnt kinds of suggars are sued as surface markers Although most of the sugar groups are attached to intrinsic plasma membrane molecules, the carbohydrate layer also contains both glycoproteins and proteoglycans that have been secreted into the extracellular space and then adsorbed onto the cell surface

Question 30

Selections

Answer 30

carbohydrate binding protines (lectins) lucose roling - only veins not arteries immune - search for sites slow immune to cite of injury when large opening - go through cell wall

Question 31

Diffusion of Membrane Proteins

Answer 31

membrane proteins can be mobile

Question 32

FRAP

Answer 32

Floresence Recovery After Fotobleaching Measure of Lateral Diffusion Rates of Membrane Proteins how much time to fill areas - if florsence lable - immoble areas - not fill quickly if mobile - fill quickly

Question 33

Spectrin cytoskeleton enables

Answer 33

red blood cell to withstand stress on its membrane as its forced through narrow capillaries it lies below the plasma membrane, criss crosses, holding membrane in place

Question 34

H3(CH2)7CH=CH(CH2)7COOH (Oleic Acid) has a ____ melting point compared to CH3(CH2)16COOH (Stearic acid).

Answer 34

LOWER High fluidity (ie presence of cis double bonds) = low phase transition temperature Also mentioned in class: It takes less energy to melt unsaturated fats (do not pack tightly) than saturated fats. Since there are more interactions between saturated fatty acids, it takes more energy to melt (pull them apart)

Question 35

A bacterium is suddenly expelled from a warm human intestine into the cold world outside. Which of the following adjustments might the bacterium make to maintain the same level of membrane fluidity? a. produce lipids with hydrocarbon tails that are longer and have fewer double bonds b. produce lipids with hydrocarbon tails that are shorter and have more double bonds c. decrease the amount of cholesterol in the membrane d. decrease the amount of glycolipids in the membrane

Answer 35

B

Question 36

Which of the following is most likely to occur after the lipid bilayer is pierced? a. The membrane reseals. b. The membrane collapses. c.. A tear is formed. d. The membrane expands.

Answer 36

A