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Cell Biology Exam 2 > Membrane Proteins > Flashcards

Membrane Proteins Flashcards

1
Q

Lipid bilyer vs protines function

A

Lipid bilayer provides the basic structure of biological membranes,

proteins perform most of the specific tasks (functional properties)

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2
Q

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

A

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

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3
Q

Membrane proteins show ____ across the bilayer

A

asymmetry

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

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4
Q

Membrane protines are synthisised in the

A

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

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5
Q

Types of Membrane Proteins

A

Transmembrane Proteins
Membrane Associated Proteins
Lipid Associated Proteins

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6
Q

Transmembrane Proteins:

A

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

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

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7
Q

Membrane Associated Proteins location

A

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

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8
Q

Lipid-Associated Proteins are attached by

A

Proteins attached to bilayer by covalent attachment to lipid anchors

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9
Q

Transmembrane Domains

portion of __

of ___ ameno acids

form ___

A

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

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10
Q

Single-Pass Transmembrane Protein

types __

A

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

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11
Q

Multipass Transmembrane Proteins

A

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

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12
Q

Hydropathy Plot

A

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

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13
Q

β Barrel are more __ than Alda helies because ___

are abundant in ___

A

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

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14
Q

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

A

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

would be an alternating strech of hydrophobic and fillic

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15
Q

Can a hydropath plot be used for a β Barrel?

A

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

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16
Q

Isolation of Integral Membrane Proteins requires
___

to remain soluble Isolated protein requires ____

A

disruption of the bilayer by detergents.

detergent.

17
Q

Many Detergents used for isolation of integral membrane proteins

A

Amphipathic

non-ionic (Triton) - mild - denaturing

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

18
Q

Mild detergents: Purify protein in ___

A

active form

19
Q

Steps of mild detergent isolation of inegral membrane protines

A

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

20
Q

Peripheral Membrane Proteins are___

assoacated by __

issolated by __

A

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.

21
Q

Lipid-Anchored Protein Types

A
  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
22
Q

Myristic acid (C=14)

A

Protine with covalently linked acytl chains (fatty acids) -

stable ancher - made with protine itself

23
Q

palmitic acid (C=16)

A

Protine with covalently linked acytl chains (fatty acids)

denamic ancher - made in response to signal

24
Q

Lipid anchors Control

A

Membrane Localization of Some Signaling Proteins

25
Q

Lipid Anchors and Intracellular signaling

A

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

26
Q

Src Kinases:

A

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.

27
Q

GPI-Anchored proteins are invovled in

A

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

28
Q

Most transmembrane proteins are

A

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.

29
Q

Carbohydrate layer on cytosolic side purpose

A

(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

30
Q

Selections

A

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

31
Q

Diffusion of Membrane Proteins

A

membrane proteins can be mobile

32
Q

FRAP

A

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

33
Q

Spectrin cytoskeleton enables

A

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

34
Q

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

A

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)

35
Q

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

A

B

36
Q

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.

A

A

Cell Biology Exam 2 (6 decks)

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