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Biochemistry MCAT > Biological Membranes > Flashcards

Biological Membranes Flashcards

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MCAT flashcards
1
Q

Fluid Mosaic Model

A

Accounts for the presence of lipids, proteins, and carbohydrates in a dynamic, semisolid plasma membrane that surrounds the cell

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2
Q

Plasma membrane

A

The membrane at the boundary of every cell that acts as a selective barrier, thereby regulating the cell’s chemical composition.

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3
Q

Lipid movement in membrane

A

Lipids are free to move in the plane of the membrane and assemble into lipid rafts.

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4
Q

Flippases

A

Specific membrane proteins that maintain the bidirectional transport of lipids between the layers of the phospholipid bilayer.

allows lipids to have lower Ea to cross hydrophobic portion of membrane

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5
Q

Macromolecule movement in membrane?

A

Proteins and carbohydrates are also free to move within membrane, but are slowed by the relatively large size.

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6
Q

glycoprotein coat

A

carbohydrates associated with membrane-bound proteins

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7
Q

cell wall

A

plants, bacteria, and fungi contain higher levels of carbohydrates

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8
Q

Membrane components

A

1) Lipids
2) Proteins
3) Cholesterol
4) Carbohydrates

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9
Q

within the cell membrane, there are large numbers of

A

phospholipids with very few free fatty acids

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10
Q

steroid molecules and cholesterol

A

lend fluidity to the membrane

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11
Q

waxes

A

provide membrane stability, help maintain the structural integrity of the cell

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12
Q

Lipids

A

The primary component of the plasma membrane, both by mass and mole fraction.

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13
Q

fatty acids

A

a carboxylic acid consisting of a hydrocarbon chain and a terminal carboxyl group

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14
Q

Triacylglycerols

A

storage lipids involved in human metabolic processes, contain three fatty acid chains esterified to a glycerol molecule

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15
Q

unsaturated fatty acids

A

“healthier” because tend to have one or more double bonds and exist in liquid form at room temperature

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16
Q

chylomicrons

A

transport triacylglcerols from the intestine (from diet)

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17
Q

two important fatty acids

A

alpha-linolenic acid, linoleum acid

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18
Q

saturated fatty acids

A

main components of animal fats and tend to exist as solids at room temperature, found in processes foods and considered less healthy

decrease membrane fluidity

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19
Q

Glycerophospholipids

A

By substituting one of the fatty acid chains of triacylglycerol with a phosphate group, a polar head group joins the non polar tails, forming a phospholipid

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20
Q

phospholipids roles

A

structural but can also serve as second messengers in signal transduction

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21
Q

phosphate group of phospholipid serves as

A

attachment point for water-soluble groups like choline or inositol

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22
Q

fat soluble proteins

A

can travel through bilayer while large and water-soluble compounds must seek alternative entry

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23
Q

sphingolipids

A

-important constituents of cell membranes
-do not contain glycerol
-contain hydrophilic region and two fatty acid-derived hydrophobic tails
-include ceramide, sphingomyelins, cerebrosides, and gangliosides

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24
Q

classes of sphingolipids

A

ceramide, sphingomyelins, cerebrosides, and gangliosides

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25
Q

Cholesterol

A

Present in large amounts (20 percent of membrane), by mole fraction makes up about half, this large ratio of cholesterol to phospholipid ensures that the membrane remains fluid, and contributes to membrane fluidity and stability.

necessary in the synthesis of all steroids

stabilizes adjacent phospholipids, occupies space between them, prevents formation of crystal structures in the membrane, increases fluidity at lower temperatures

at high temperatures, limits movement of phospholipids in bilayer decreases fluidity and holds membrane intact

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26
Q

Waxes

A

Present in very small amounts, if at all; Most prevalent in plants and function in waterproofing and defense.

long fatty acid and long alcohol chain which contribute to high melting point

provide stability and rigidity within the non polar tail region only when present

very hydrophobic

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27
Q

Lipid rafts

A

Special lipid domains that have high concentration of glycosphingolipids and cholesterol and membrane proteins involved in cell signaling.

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28
Q

plasma membrane lipid components overview

A
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29
Q

plasma membrane Proteins

A

1) Transmembrane proteins
2) Embedded proteins
3) Membrane-associated proteins

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30
Q

Transmembrane proteins

A

Have one or more hydrophobic domains and are most likely to function as receptors or channels. (or transporters)

1) Cross the plasma membrane

31
Q

Embedded proteins

A

Likely to be part of a catalytic complex or involved in cellular communication.

1) Associated with the interior (cytoplasmic) or exterior (extracellular) surface of the cell membrane

32
Q

integral proteins

A

transmembrane and embedded proteins together because association with interior of the plasma membrane which Is usually assisted by one or more membrane associated domains that are partially hydrophobic

33
Q

Membrane-associated proteins

A

May act as recognition molecules or enzymes.
proteins which are bound through electrostatic interactions with the lipid bilayer, particularly at lipid rafts or to other membrane proteins

34
Q

carbohydrates

A

generally attached to protein molecules on the extracellular surface of cells, generally hydrophilic, act as signaling and recognition molecules

35
Q

Glycoprotein coat

A

Carbohydrates generally attach to proteins on extracellular side of plasma membrane and act as signaling or recognition molecules.

36
Q

Cell-cell junctions

A

1) Gap junctions
2) Tight junctions
3) Desmosomes and hemidesmosomes

37
Q

CAM

A

cell adhesion molecules
proteins that allow the cell to recognize each other
they contribute to proper cell differentiation and development
make up cell to cell junctions

38
Q

Gap junctions

A

Allow the rapid exchange of ions and other small molecules between adjacent cells via hydrophilic channels called connexons.

39
Q

Tight junctions

A

Prevent solutes from leaking into the space via paracellular route between cells and create a physical link to limit permeability.

maintain differing concentrations of ions on either side of the epithelium

*membranes of neighboring cells are actually fused forming continuous belts around cell to prevent leakage of extracellular fluid

40
Q

Desmosomes

A

Bind adjacent cells by anchoring to their cytoskeleton .
Join two cells at a single point, attach directly to the cytoskeleton of each cell. Found in tissues that normally experience a lot of stress due to sliding.

41
Q

Hemidesmosomes

A

Anchor cells to connective tissue.

42
Q

passive transport

A

spontaneous do not require energy

43
Q

diffusion, facilitated diffusion, osmosis generally ____ in rate as temperature increases

A

increase in rate as temperature increases

44
Q

is active transport affected by temperature

A

it may or may not be, depending on enthalpy (delta h) of the process

45
Q

primary thermodynamic motivator in most passive transport is an increase in

A

entropy (delta s)

46
Q

Concentration gradients

A

An increase or decrease in the density of a chemical substance in an area. Cells often maintain concentration gradients of ions across their membranes. When a gradient exists, the ions or other chemical substances involved tend to move from where they are more concentrated to where they are less concentrated.

47
Q

Osmosis

A

The net movement of water molecules from regions of low solute concentration (high [H2O]) to high solute concentration (low [H2O]).

Describes the diffusion of water across a selectively permeable membrane.

48
Q

Hypotonic solution

A

More solute on inside of cell than outside, causing water to rush in and lyse cell.

49
Q

Hypertonic

A

More [solute] in solution than in the cell. Water rushes out of the cell and it shrivels.

50
Q

Isotonic

A

Having the same solute concentration as another solution.

51
Q

Osmotic pressure

A

The pressure applied to a pure solvent to prevent osmosis and is used to express the concentration of a solution.

colligative property: physical property of solutions that is dependent on concentration of dissolved particles but not chemical identity

*Often conceptualized as a sucking pressure because water will move toward the compartment with the highest osmotic pressure

pressure to counterbalance the tendency of water to flow across the membrane

52
Q

Passive transport

A

Does not require energy because the molecule is moving down its concentration gradient or from an area of higher concentration to an area of low concentration.

53
Q

Passive transport types

A

1) Simple diffusion
2) Osmosis
3) Facilitated diffusion

54
Q

Simple diffusion

A

Does not require a transporter. Small non polar molecules moving passively from an area of high concentration to an area of low concentration until equilibrium is achieved.

55
Q

Facilitated diffusion

A

Uses transport proteins to move impermeable solutes across a cell membrane. I.e. large polar or charged

requires integral membrane proteins to serve as transporters or channels

56
Q

Carriers

A

open to one side of the cell like a revolving door, substrate binds-> conformational change, finally dissociates on other side

57
Q

Occluded state

A

carrier not open to either side for brief time

58
Q

channels

A

may be open or closed, open–> exposed to both sides and act like tunnel

59
Q

Active transport

A

Requires energy in the form of ATP or an existing favorable ion gradient. May be secondary or primary.

60
Q

Primary active transport

A

Energy from ATP causes shape change in transport protein so that the solutes can be pumped across membrane. The pump is the ‘Sodium-Potassium pump.’

61
Q

Secondary active transport

A

Form of active transport which does not use ATP as an energy source; rather, harnesses the energy released by one particle going down its electrochemical gradient to drive a different particle up its gradient

62
Q

Symport

A

A membrane transport process that carries two substances in the same direction across the membrane.

63
Q

Antiport

A

A membrane transport process that carries one substance in one direction and another in the opposite direction.

64
Q

Uniport

A

A membrane transport process that carries a single substance.

65
Q

Endocytosis

A

The process by which a cell surrounds and engulfs substances. Useful for large, polar molecules.

material is encased in a vesicle-> important because cells sometimes ingest toxic particles

plasma membrane is shortened in the process.

66
Q

Exocytosis

A

a process by which the contents of a cell vacuole are released to the exterior through fusion of the vacuole membrane with the cell membrane.

67
Q

Pinocytosis

A

The ingestion of liquid and dissolved particles into the cell in vesicles formed from the cell membrane.

68
Q

Phagocytosis

A

The ingestion of larger, solid molecules like bacteria.

69
Q

vesicle-coating proteins

A

invagination initiation and carried out (most notably clathrin)

70
Q

Membrane potenial

A

potential difference across a membrane (difference of ions pretty much)

71
Q

leak channels

A

ions may passively diffuse through cell membrane over time, required membrane potential to use energy to restore membrane potential

72
Q

How is membrane potential maintained?

A

The sodium-potassium pump and leak channels.

73
Q
A

Biochemistry MCAT (12 decks)

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