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BioChem > Lecture 11 > Flashcards

Lecture 11 Flashcards

1
Q

6 functions of membranes

A

define the boundaries of the cell, regulate import and export, retain meatbolites and ions within/outside the cell, sense external signals and transmit info into the cell, provide compartmentalization with in the cell, and store energy as a proton gradient and support synthesis of ATP

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2
Q

How thick is a typical membrane?

A

30-100 A (3-10 nm) thick

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3
Q

Which leaflet of a membrane is typically positively charged?

A

The outer leaflet.

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4
Q

Phosphatidylserine on the outside for platelets and for other cells?

A

Platelets: activates blood clotting

Other cells: marks the cell for destruction

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5
Q

Phosphatidylenthanolamine where it is found and percentage of total

A

30% of total and found primarily on the inner monolayer. positively charged group head

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6
Q

Phosphatidylcholine where it is found and percentage of total

A

27% of total and found primarily on the outer monolayer. Positively charged group head.

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7
Q

Sphingomyelin where it is found and percentage of total

A

23% of total and found primarily on the outer monolayer. Positively charged group head.

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8
Q

Phosphatidylserine where it is found and percentage of total

A

15% and primarily found on the inner monolayer. Neutral head group

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9
Q

Fluidity and temperature

A

Fluidity is determined by ratio of unsaturated to saturated fatty acids. To maintain constant fluidity, cells need more saturated fatty acids at higher temps

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10
Q

At higher temps you want what in the membrane?

A

longer, saturated fatty acids

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11
Q

At lower temps you want what to keep constant fluidity?

A

More unsaturated fatty acids.

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12
Q

T or F: Lipid composition is different in different organisms and in different tissues of the same organism?

A

True.

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13
Q

Plasma membranes have a high concentration of what?

A

cholesterol.

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14
Q

Integral proteins

A

firmly associated with the membrane, often spanning the bilayer. Helix spans (composed of hydrophobic residues - Ile, Leu, Val)

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15
Q

Peripheral proteins

A

weakly associated and can be easily removed. Some are non-covalently attached, some are linked to membrane lipids

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16
Q

Rho protein is what type of protein and attached how?

A

Peripheral protein and it is a form of isoprenelation.

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17
Q

Lateral diffusion of membranes

A

individual lipids undergo fast lateral diffusion within the leaflet

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18
Q

Transverse diffusion of membranes

A

spontaneous flips from one leaflet to the other is rare and slow. Since energetically unfavorable.

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19
Q

Flippases

A

outside to inside by hydrolyzing ATP

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20
Q

Floppases

A

inside to outside by hydrolyzing ATP

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21
Q

Scramblase

A

moves lipids in either direction toward equilibrium.

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22
Q

Cholesterol acting as a membrane fluidity buffer

A

It will decrease fluidity at lower temps, preventing fatty acids from packing too much. At higher temps, the rigid structure will prevent excess fluidity.

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23
Q

Membrane rafts

A

allow for segregation of lipids and proteins in the membrane. Longer tailed lipids will want to get together.

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24
Q

What regulates membrane fusion?

A

receptor proteins

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25
Q

3 Functions of proteins in membranes

A

receptors - detecting signals from outside; channels, gates, and pumps; and enzymes

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26
Q

Amphitropic proteins

A

same as amphipathic

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27
Q

How do peripheral membranes associate with the membrane?

A

electrostatic interactions (non-covalent) and hydrogen bonding with integral membrane proteins and/or lipid head groups; some contain a covalently attached lipid group that acts as an anchor.

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28
Q

What may peripheral proteins regulate?

A

may regulate membrane-bound enzymes or may limit the mobility of integral proteins by tethering them to intracellular structures.

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29
Q

Lipid anchored proteins

A

insert into membrane and can be stabilized by ionic interactions between the protein and the lipid head groups. Tail is a form of regulation.

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30
Q

GPI anchored proteins

A

glycosylated (sugar) derivatives of phosphatidylinositol. anchors to outer leaflet of membrane.

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31
Q

How many residues for an alpha helix to span the membrane?

A

20-25 helices. Made up of hydrophobic residues.

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32
Q

Most is known about what type of integral membrane protein?

A

Type 7.

33
Q

Hydropathy index. What is negative and what is positive

A

Negative: Lys, ARg (hydrophilic)
Positive: Leu, Ile (hydrophobic)

34
Q

Barrel membrane proteins

A

Often to transfer ions across the membrane. Takes about 7 to 9 amino acid residues to get across the membrane. Often composed of 20 or more strands.

35
Q

Why cant we use a hydropathy plot for barrel membrane proteins?

A

Since the side chains alternate in a beta sheet, it would be difficult to pin point where it was occurring.

36
Q

What type of residues on the inside of a barrel membrane protein?

A

hydrophilic facing the interior of the channel and hydrophobic facing the membrane.

37
Q

Fences in regards to proteins

A

internal protein structures that restrict both protein and lipid movement throughout the membrane. Often by attaching to the cytoskeleton

38
Q

What sort of compound can freely diffuse across the membrane?

A

nonpolar molecules.

39
Q

Chemi-osmotic theory

A

concentration gradient can drive an ion, but if the ion is charged then the electrical gradient (if molecule is charged) can also have an affect

40
Q

Passive and active transport

A

Passive: flow with the electrochemical gradient
Active: flow against the electrochemical gradient (and requires energy)

41
Q

Mediated and non-mediated transport

A

Mediated: requires specific carrier proteins

Non-mediated: occurs through diffusion

42
Q

Transporters or permeases

A

membrane proteins that lower the activation energy for transport by providing an alternative pathway through the membrane

43
Q

Two types of transporters

A

Carriers and channels

44
Q

Carriers

A

stereospecific. Transport at rates below that of diffusion and are saturable. Carry the cargo across the membrane. Usually monomeric

45
Q

Channels

A

less stereospecificity and transport at rates close to diffusion. Similar to gates. Usually made up of one or more protein. No saturable.

46
Q

GLUT1

A

erythrocyte glucose transporter is a passive mediated transporter. (thus a carrier and saturable). Rate of transport depends on relative concentration inside and outside the cell.

47
Q

Kt

A

transport constant. concentration of substrate at 1/2 Vmax

48
Q

GLUT1 structure

A

12 transmembrane alpha helices. Seen to not have all hydrophobic so likely bunches together to put charged and polar residues to interact with glucose in the core.

49
Q

T1 of glucose transporter

A

glucose-binding site exposed to the outer surface

50
Q

T2 of glucose transporter

A

binding site exposed to the inner surface

51
Q

Mechanism for glucose transporter

A

Glucose binds to T1, lowers the activation energy for a conformational change, then glucose is let into the cell when in T2, then it snaps back to T1.

52
Q

Types of mediated transport

A

Uniport, symport, and antiport

53
Q

Uniport

A

movement of a single molecule at a time

54
Q

Symport

A

simultaneous transport of two different molecules in the same direction

55
Q

Antiport

A

simultaneous transport of two molecules in opposite directions

56
Q

Chloride-bicarbonate exchanger

A

passive mediated antiport exchanger. In respiring tissues - bicarbonate out, chloride in.
In lungs - bicarbonate in, chloride out. Enhances ability of blood to carry CO2 by converting it into bicarbonate

57
Q

carbonic anhydrase

A

converts CO2 and water to bicarbonate and vice versa.

58
Q

Primary active transport

A

solute accumulation is directly coupled to a chemical reaction (usually ATP hydrolysis)

59
Q

Secondary active transport

A

solute accumulation is coupled to the favorable transport of a second solute (generally through a symporter and use a primary transporter to make the gradient)

60
Q

Active mediated transport

A

allows accumulation of a solute above its equilibrium point

61
Q

4 types of ATPases

A

P-type, V-type, F-type, and ABC transporters

62
Q

P-type ATPase

A

transport cations and are reversibly phosphorylated by ATP on an Asp residue. Na-K ATPase. Antiporter

63
Q

V-type ATPase

A

proton pumps. Acidify intracellular compartments

64
Q

F-type ATPase

A

catalyze reversible transmembrane passage of protons. During downhill proton flow they catalyze ATP synthesis.

65
Q

ABC transporter

A

remove metabolites and drugs from cells using the energy from ATP hydrolysis. Have two nucleotide binding domains, and two transmembrane domains (different specificities)

66
Q

Na - K ATPase

A

antiporter. Generates the electrical gradient for nerve cells and to control water content. 3 Na out and 2 K in (both against their concentration gradient). Negative inside the cell. Accounts for 25% of our body’s energy

67
Q

Na - K ATPase mechanism

A

3 Na bind to protein, ATP binds with help from Mg, ATP hydrolysis and phosphorylation of protein, sodium exits other side of membrane, potassium binds, hydrolysis of phosphorous atom, then releases potassium onto other side of cell. Sodium can then rebind.

68
Q

High affinity for K and low Na affinity in Na-K ATPase

A

phosphorylated form of the protein.

69
Q

High affinity for Na and low affinity for K in Na-K ATPase

A

non-phosphorylated form of the protein.

70
Q

Digitalis inhibits the Na-K ATPase how?

A

binding to the external portion of the protein and blocking the hydrolysis of the phosphorylated enzyme (occurs outside the cell).

71
Q

What happens with digitalis?

A

causes Na to go up in the cell, which activates a Na-Ca antiport system, this causes Ca to increase intracellular, causing intense muscle contractions

72
Q

MDR1

A

ABC transporter. In some tumor cells, they are upregulated, causing the cells to pump out the chemo drugs.

73
Q

Cystic fibrosis

A

two defective copies of cystic fibrosis transmembrane conductance regulator (CFTR). ABC transporter specific for Chloride. Less efficient at secreting substance that traps and kills bacteria in lungs

74
Q

Solute going against gradient in E.coli and cotransported solute. And type of transport

A

Transported - lactose, proline, and dicarboxylic acids.
Cotransported - hydrogen ions
Symport.

75
Q

Solute going against gradient in intestine and cotransported solute. And type of transport

A

transported - glucose and amino acids
Cotransported - sodium
Symport

76
Q

Sodium glucose symporter in the intestine

A

cotransporter that transports glucose in symport with 2 sodium ions. High concentration of sodium in the intestinal lumen. Na-K ATPase creates gradient for low sodium in cell and acts as primary active transport

77
Q

Potassium Channel structure

A

4 identical subunits that form a cone shape. Entryways are guarded by several negatively charged residues (thus only positive charged ions allowed close)

78
Q

Potassium channel specificity

A

Desolvation of the ion as it enters into the channel. Favorable contacts between carbonyl oxygen atoms of the backbone (Na would be too small). Pass through single file, but 4 binding sites and only 2 in the channel at a time, other 2 are water.

BioChem (14 decks)

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