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CHEM 472 Biochem > Final: Chapter 9 - Membrane Structure > Flashcards

Final: Chapter 9 - Membrane Structure Flashcards

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1
Q

What are the two main functions of a membrane?

A

1) Define inside and outside of the cell or organelle
2) Control permeability of ions and small molecules

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2
Q

What are membranes primarily composed of?

A

lipids and proteins

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3
Q

What are three common lipids that are found in cell membranes?

A

Glycerophospholipids, sphingolipids, and sterols

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4
Q

What percentage of protein content in membranes?

A

15-80%

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5
Q

What is the purpose of proteins in cell membranes?

A

to add function

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6
Q

What are the three types of proteins based on their association with a membrane?

A

1) Peripheral 2) Integral 3) Lipid-anchored

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7
Q

What is a peripheral membrane protein?

A

One that does not penetrate the lipid bilayer and is mainly associated to the polar groups on the exterior of the membrane via H-bonds and ionic bonds

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8
Q

What is an integral membrane protein?

A

One that penetrates into or through the lipid bilayer, associating with the hydrophobic interior with its own hydrophobic portions

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9
Q

What is a lipid-anchored membrane protein?

A

One that covalently linked to lipids in the membrane

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10
Q

How is a peripheral protein cleaved from a membrane?

A

Change in pH or salt concentration

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11
Q

How is an integral protein cleaved from a membrane?

A

A nonpolar solvent or detergent must be used to break apart the membrane

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12
Q

How is a lipid-anchored protein cleaved from a membrane?

A

Must selectively cleave protein or destroy membrane to release it

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13
Q

What is the fluid mosaic model?

A

describes how membranes are composed of a dynamic and fluid lipid bilayer containing a diverse array of proteins and molecules that move around within the membrane

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14
Q

Describe the structure of an integral membrane protein

A

The membrane spanning portion is dominated by alpha-helices and beta-sheets

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15
Q

What are two reasons that alpha-helices and beta-sheets are more favorable in the lipid bilayer?

A

1) They are stabilized by H-bonds between AAs and their backbone which prevents interactions with the non-polar inner lipid bilayer
2) alpha-helices are primarily composed of nonpolar amino acids

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16
Q

What does a negative hydropathic index value signify?

A

The AA is hydrophilic (polar)

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17
Q

Whay does a positive hydropathic index value signify?

A

The AA is hydrophobic (nonpolar)

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18
Q

Do transmembrane protein domains exhibit a negative or positive hydropathic index overall?

A

Positive

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19
Q

Do extracellular and intercellular protein domains exhibit a negative or positive hydropathic index overall?

A

Negative

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20
Q

What is a beta-barrel?

A

A pore in the cell membrane formed by beta-sheets

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21
Q

Describe AA orientation in a beta-barrel?

A

Nonpolar AAs point outwards and face the lipid bilayer
Polar AAs point towards the center of the pore

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22
Q

Name 3 characteristics that most membranes have?

A

1) transverse asymmetry
2) lateral heterogeneity
3) lipid movements

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23
Q

What is transverse asymmetry?

A

the two leaflets of a lipid bilayer have different lipid compositions

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24
Q

What is lateral heterogeneity?

A

particular lipids or proteins cluster together within the membrane

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25
What is anti-gauche isomerization?
Switch from **gauche arrangement** (where bulky groups are positioned at a 60-degree angle to each other) **to** an **anti arrangement** (where the bulky groups are positioned directly opposite each other at a 180 degree angle)
26
What is an undulation?
membrane movements up down in a wave like motion
27
What kind of lipid movement do proteins typically assist with?
Flip-flop
28
Why are flip-flop proteins necessary?
To maintain transverse symmetry
29
How is protein assisted lipid movement powered and why?
using free energy from ATP hydrolysis because energy is required to move polar heads across the nonpolar bilayers
30
What is flippase?
A protein that assists in lipid flipflop movement from outside the cell to in
31
What is floppase?
A protein that assists in lipid flipflop movement from inside the cell to outside
32
What is scramblase?
A protein that assists in lipid flipflop movement into the cell and out of the cell
33
Why is remodeling and curvature of membranes necessary?
For cell division, endocytosis, and exocytosis
34
What five ways membranes can be remodeled and curved?
1) changing lipid composition or head group composition 2) Addition of membrane proteins 3) Amphipathic helix insertion 4) Scaffolding 5) Cytoskeleton pushing or pulling of the membrane
35
How do membrane proteins and amphipathic helix insertion cause membrane curvature?
Causes one leaflet to be longer than the other
36
How do scaffolding proteins cause membrane curvature?
Interacts with polar head groups of membrane and enforce curvature with protein structure
37
What are two reoccurring themes of membrane transport?
1) concentration gradients 2) transport proteins to help facilitate
38
What are the three types of membrane transport?
1) passive diffusion 2) facilitated diffusion 3) active transport
39
What is passive diffusion?
When transported species are moved across the membrane in a **thermodynamically favorable** direction **without the help of specific transport proteins**
40
What kinds of molecules undergo passive transport and why?
nonpolar small molecules; can pass through hydrophobic layer and fit between lipids
41
In terms of concentrations, which direction to species move during passive diffusion?
high concentration to low concentration
42
What is facilitated diffusion?
transported species moves across membrane in a **thermodynamically favorable** direction **with the help of specific transport protein**
43
Describe proteins involved in facilitated diffusion?
commonly channel proteins that display an affinity or specificity for the transport molecule
44
How can facilitated diffusion be distinguished from passive diffusion experimentally?
by plotting saturation behavior (velocity vs concentration)
45
How can facilitated diffusion and passive diffusion be differentiated using a saturation curve?
- facilitated diffusion displays a square root function, indictive of saturation kinetics - passive diffusion displays a linear relationship between
46
Why does facilitated diffusion experience saturation kinetics?
because its specificity implies a form of binding interactions; thus, the protein that facilitates diffusion can become saturated
47
What are four themes of channels involved in facilitated diffusion?
1) typically comprised of quaternary structure 2) Contain a selectivity filter 3) Can be gated 4) Width provides selectivity
48
Describe selectivity filters involved in facilitated channel diffusion?
commonly charged and use AAs to select for particular ions/molecules
49
What are the three kinds of gated channels?
1) voltage 2) ligand 3) pH
50
How does width of a channel affect selectivity?
Bigger channels allow more things through
51
In channel proteins, what are two typical arrangements of subunits to form quaternary structure?
1) arrange to form a central pore 2) each subunit has a functional pore
52
What form of transport do potassium channels utilize?
facilitated diffusion
53
What is the function of a potassium channel?
To move K+ ions from the interior of the cell to the exterior
54
Describe the quaternary and tertiary structure of a potassium channel?
Made of four subunits each containing a transmembrane alpha helix that form the central pore
55
Describe the nonselective portion of the pore in a potassium channel
about 10 angstroms wide and filled with water
56
How wide is a potassium channel selectivity filter?
3 angstroms wide
57
Why does the carbonyl backbone face the center of the pore in a potassium channel?
Provides four negatively charged oxygens per pentapeptide fragment that can interact with K+
57
Describe the peptide fragments that facilitate selectivity in potassium channels?
TVGYG fragments with their carbonyl backbone and one OH group (from T) facing the center of the pore
57
Why do potassium channels select for K+ over Na+?
Energy required to desolvate K+ as it enters the potassium channel is less than the energy released when the selectivity filter resolvates K+; is favorable
57
How is potassium channel direction reversed?
Reversing the K+ concentration gradient
58
How do gated potassium channels open and close?
They change between open and closed confirmations
59
What is active transport?
transported species moves across membrane in **thermodynamically unfavorable** direction with help of **specific transport protein** and **energy input**
60
What are three possible energy sources for active transport?
1) ATP 2) ion gradient 3) light
61
What are inhibitors of sodium pumps?
cardiotonic steroids
62
How do cardiotonic steroids inhibit sodium pumps?
They form a stable complex with E2-P confirmation, preventing phosphate hydrolysis necessary to return to E1 confirmation
63
How do cardiotonic steroids increase heart rate?
1) sodium pump in E2P causes K+ to accumulate in the cell 2) Opens voltage-gated calcium channels 3) Ca2+ accumulates in cell and triggers muscle contraction
64
Describe the structure of a cardiotonic steroid
Contains a common steroid core with a lactone ring attached at C17 and a Oh at C14
65
Why does K+ pass through potassium channels rapidly?
binding of additional K+ in the channel repels K+ that are currently in the channel
66
What kind of transport do sodium pumps exhibit?
active transport
67
What is the function of sodium pumps aka Na+/K+-ATPase?
To pump Na+ out of the cell and K+ into the cell using energy provided by ATP hydrolysis
68
Describe the main components of Na+/K+-ATPase structure
1) three unidentical subunits 2) Asp 369 that accepts a phosphate from ATP 3) lots of alpha helices because it is an integral membrane protein
69
What is an example of Na+/K+-ATPase inhibitor?
cardiotonic steroids
70
What are the three primary components of cardiotonic steroid structure?
1) common steroid core 2) lactone ring at C17 3) hydroxyl (OH) at C14
71
What is an ABC transporter?
An ATP binding cassette transporter
72
What is an example of a MDR pump?
ABC transporters
73
What are MDR pumps?
Multi-drug resistance pumps
74
What do MDR pumps do?
pump cellular waste and drugs out of the cell
75
What kinds of cells typically evolve MDR pumps? How do they evolve them?
bacterial and cancer cells; adaptation of pumps that typically expel cellular waste in response to drug stressors
76
Describe the structure of an ABC transporter?
Two transmembrane protein domains form a pore Two nucleotide binding domains bind to and hydrolyze ATP The domains can be part of the same polypeptide chains or different ones
77
What part of an ABC transporter functions as the ATP binding cassette?
nucleotide binding domains
78
What is secondary active transport?
Transport that uses energy from an ion gradient established by primary active transport
79
What is a common example of secondary active transport?
Na+ and H+ gradients transporting other molecules
80
What is a symporter?
A secondary active transporter in which ions and molecules move in the same direction
81
What is a antiporter?
A secondary active transporter in which ions and molecules move in opposite directions
82
In what organism is AcrB found?
E. coli
83
What kind of transport does AcrB undergo?
secondary active transport
84
What kind of secondary active transporter is AcrB?
A antiporter
85
Describe the structure of AcrB
composed of three identical subunits (homotrimer) that each have a pore
86
What powers transport of drug molecules through AcrB?
H+ moving with its gradient through the channel drives subunit confirmational changes
87
Describe the confirmational changes a subunit of AcrB undergoes as a drug molecule passes through it? (2 steps)
1) drug binds to subunit in L and triggers change to T 2) Confirmational change to O releases drug
88
What are the threes confirmations possible for a subunit of AcrB?
L - loosely bound to drug molecule T - tightly bound to drug molecule O - open, not bound to drug molecule
89
How do the subunits of AcrB interact?
cycle independently of one another

CHEM 472 Biochem (12 decks)

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