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Biochemistry > Membranes and Membrane Transport > Flashcards

Membranes and Membrane Transport Flashcards

1
Q

Cholesterol is a precursor to which of the following?

Vit C, NADH, nucleic acids, or steroid hormones?

A

Steroid hormones

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2
Q

True or False: Peripheral membrane proteins are located near the cell membranes, while integral membrane proteins extend through the cell membrane.

A

True

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3
Q

Which statement is true regarding passive/active transport?

a) Passive moves solutes against gradient
b) Passive requires ATP hydrolysis
c) Active requires net input of energy

A

C

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4
Q

Which substance would most easily cross lipid bilayer through passive diffusion?

O2, water, glucose, or Na+?

A

O2

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5
Q

What are isoprenoids? Where are they found

A

Repeating five-carbon units (isoprene units).

Found in terpenes, vit E, vit K, ubiquinone

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6
Q

What are terpenes?

A

Contain a number of isoprene units, found in plant essential oils

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7
Q

What is prenylation?

A

Attachment of isoprene to a protein. Helps tether protein to membrane.

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8
Q

What is cholesterol?

A

4 ring structure with side chain and OH at C3 (sterol).

Membrane component–embedded in lipid bilayer.

Precursor to all steroid hormones, vitamin D, and bile salts.

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9
Q

How is cholesterol stored in cells?

A

Stored as fatty acid esters, to keep it out of the membrane.

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10
Q

Basic steroid structure?

A

3 6-carbon rings and one 5-carbon ring.

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11
Q

What are lipoproteins?

A

Proteins linked to a lipid group. Usually refer to plasma macromolecules.

Transport lipid molecules in blood. Why? Lipids aren’t water soluble.

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12
Q

3 components of lipoprotein?

A

Apolipoprotein- protein component
Phospholipid, cholesterol, other proteins
Cholesteryl esters/triacyl glycerols

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13
Q

How are lipoproteins classified?

A

According to density.

HDL, LDL, VLDL, ULDL.

HDL has more protein relative to the amount of cholesterol than LDL.

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14
Q

Describe the cell membrane.

A

Heterogeneous mixture of lipids and proteins.

Inner and outer leaflets. Fluid mosaic.

Membrane features vary greatly between cell types. E.g. mitochondrial membrane has more protein, red blood cell membrane has more carbohydrates.

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15
Q

What is one function of membranes in cells?

A

Compartmentalization. Hydrophobic barrier and specialized proteins allow micro-environments.

Specialization of function.

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16
Q

Describe membrane fluidity. What affects this?

A

Viscosity depends on composition.

Un/saturated fatty acid and cholesterol content.

Lateral movement of lipids. Lipid transfer between leaflets–flippase, floppase, and scramblase are enzymes that catalyze this.

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17
Q

Describe membrane permeability.

A

Selectively permeable.

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18
Q

What can move across a membrane?

A

Lipophilic molecules, very small and uncharged polar molecules, water (somewhat)

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19
Q

What cannot move across a membrane?

A

Ions, large molecules, charged and polar molecules

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20
Q

What functions are membrane proteins involved in?

A

Transport, catalysis, signal transduction

21
Q

What is the difference between peripheral and integral proteins?

A

Peripheral = located near cell membrane. Non-covalent, prenylation, GPI anchor, etc.

Integral = traverse the membrane, or are embedded.

22
Q

What does cholesterol do in the membrane?

How does it affect fluidity?

A

Cholesterol has a rigid hydrophobic structure and is interspersed among phospholipids.

Acts as a buffer to fluidity. As temperature increases, cholesterol stabilizes neighboring phospholipids. At lower temperature, spaces out phospholipids to prevent solidification.

Generally, more cholesterol = more stability, less fluidity.

23
Q

What are lipid rafts?

A

Segment of the plasma membrane that contains higher proportion of cholesterol and sphingolipids (saturated FA tails). Doesn’t move around as much as typical phospholipids.

24
Q

What do lipid rafts do?

A

Membrane sections–microdomains–form ordered and rigid structure, help stabilize groups of proteins.

25
Q

What happens at the cell membrane?

A

Transport of substances, transduction of signals.

26
Q

What is typically transported across a cell membrane?

A

Ions, nutrients, small molecules, water.

27
Q

How can non-lipophilic molecules be transported?

A

Transporter proteins

28
Q

How can transport types be classified?

A

1) Are proteins needed?

2) Is energy needed?

29
Q

What is passive transport?

A

Transport that does not require direct energy input. Simple and facilitated diffusion. Solute moves down concentration gradient.

30
Q

What is simple diffusion?

A

Substance moves through bilayer on its own.

31
Q

What is facilitated diffusion?

A

Substance requires a transport protein to move.

32
Q

What are channel proteins?

A

Nonspecific facilitated diffusion transport protein. E.g. ion channel. Either open or closed–no binding.

Channels allow passage through a pore.

33
Q

What are carrier proteins?

A

Specific facilitated diffusion transport protein. Changes conformation and binds to solute.

34
Q

What determines rate of simple diffusion of solids?

A

1) concentration gradient
2) lipid solubility
3) molecular weight

The greater the concentration gradient and more solubility in lipids, the faster the rate. High molecular weight = low rate.

35
Q

What determines gas diffusion?

A

Concentration/partial pressure gradient.

36
Q

How is facilitated diffusion regulated?

A

Ligand binding, physical stimuli, phosphorylation, trafficking.

37
Q

What is trafficking?

A

Transporters only expressed when a signal is given/solute is present.

38
Q

What is active transport?

A

Moving solute against concentration gradients. Requires energy input- usually ATP hydrolysis.

Two forms, primary and secondary.

39
Q

What is primary active transport?

A

ATP hydrolysis directly coupled to solute movement.

e.g. Na+/K+ pump.

40
Q

What is secondary active transport?

A

Concentration gradient established by primary transport drives movement of a separate solute.

41
Q

How does the Na/K pump work?

A

Hydrolyze ATP to transport 2 K+ into cell and 3 NA+ out of cell. Primary active transport.

42
Q

How does the sodium-glucose pump work?

A

Movement of Na+ along the concentration gradient established by Na/K pump drives transport of glucose against its concentration gradient.

Secondary active transport.

43
Q

What are aquaporins?

A

Water can diffuse through membrane, but not very well. Aquaportins (AQPs) make diffusion EXPONENTIALLY faster.

Facilitated diffusion of water through a “water channel”–moving a solvent instead of solutes.

Asparagines in protein interact with oxygens of water molecules and allow them to line up single file as they pass through.

44
Q

Why are aquaporins important?

A

Cell volume regulation.

Water transport across epithelial tissues. E.g. absorb water in kidney epithelial cells and help bring it back to the blood.

45
Q

What is ADH? What does it do?

A

ADH = anti diuretic hormone. Acts on GPCR in kidney epithelial cell. That activates adenylate cyclase, and through cascade, causes aquaporins to be inserted into the membranes (both the membrane facing urine and the one facing the blood). Helps water move from urine to blood.

Alcohol inhibits ADH release.

46
Q

What is CFTR? What does it do? What happens when it doesn’t work properly?

A

CFTR = Cystic fibrosis transmembrane conductance regulator.

Chloride ion channel found in various epithelial tissues. Important for electrolyte and water transport.

Chloride secretion to surface of a tissue (from inside to outside of cell) draws sodium and water along, keeping outer mucus layer hydrated. Important inn lung, intestine, sweat gland, and pancreas. This is needed for cilia to beat and remove particles–this is why CF patients often succumb to infection.

47
Q

How does CFTR work? What is its structure?

A

Member of ABC transporters (ABC = ATP binding cassette)

Two intracellular nucleotide binding domains that bind and hydrolyze ATP and drive conformational change to open/close channel.

Regulated by phosphorylation of regulatory (R) domain by cAMP dependent protein kinase A.

48
Q

Is CFTR active or passive transport?

A

Passive. Has to bind and hydrolyze ATP to make a conformational change, but chloride is still moving across its concentration gradient, so not active.

49
Q

How is cholera related to CF?

A

Vibrio cholera infection leads to massive activation of CFTR channels–massive release of chlorine, sodium, water = severe dehydration.

Why? Cholera toxin inhibits GPCR from hydrolyzing GTP. Remember, GTP hydrolysis is the “off mechanism” for GPCR. Because of this G(a) stays bound to adenylate cyclase, cAMP goes up, CFTR channel keeps getting phosphorylated and transporting ions.

Cholera = overactive CFTR channels
CF = underactive CFTR channels

Biochemistry (43 decks)

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