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Physiology > Principles - Membranes > Flashcards

Principles - Membranes Flashcards

1
Q

What is a plasma membrane?

A

Fluid lipid bilayer embedded with proteins

Mostly phospholipids and cholesterol

Proteins

Small amount of carbohydrate

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2
Q

What is the structure of a phospholipid molecule?

A

Negatively charged, polar, hydrophilic head

Uncharged, nonpolar, hydrophobic tail

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3
Q

What effect does cholesterol have on the membrane?

A

It contributes to fluidity and stability

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4
Q

How can proteins in the bilayer be classified?

A

Integral - embedded in the bilyar (receptors)

Transmembrane - extend through the membrane (transporters, channels)

Peripheral - most common intracellularly, don’t penetrate membrane

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5
Q

What is the glycocalyx?

A

Small amount of carbohydrate located on outer surface of cells

Often bound to membrane protein, or to a lesser extent, lipids forming glycoproteins or glycolipids

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6
Q

What are docking-marker acceptors?

A

Proteins located on inner membrane surface

They interact with secretory vesicles leading to exocytosis of the vesicle contents

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7
Q

What are desmosomes?

A

Adhering junctions anchoring cells together.

Particularly common in tissues that can stretch.

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8
Q

What are tight junctions?

A

Join the lateral edges of epithelial cells near their lumenal (apical) membranes

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9
Q

What are gap junctions?

A

Communicating junctions allowing movement of charge carrying ions between two adjacent cells

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10
Q

What properties influence whether a particle can permeate the plasma membrane unassisted?

A

Solubility of particle in lipid

Size of particle

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11
Q

How can molecules and ions passively cross the membrane?

A

Diffusion down concentration gradient

Movement along electrical gradient

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12
Q

Which factors influence the rate of net diffusion (Fick’s Law)?

A

Magnitude of concentration gradient

Surface area of membrane

Lipid solubility of substance

Molecular weight of substance

Thickness of membrane

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13
Q

What is osmosis?

A

Net diffusion of water down its own concentration gradient

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14
Q

Why can water molecules permeate the plasma membrane more easily than would be expected?

A

Because of aquaporins - water channels

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15
Q

What is osmolarity?

A

Concentration of osmotically active particles present in solution

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16
Q

What is tonicity?

A

The effect a solution has on cell volume

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17
Q

What happens in hypotonic conditions?

A

Cells swell

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18
Q

What happens in hypertonic conditions?

A

Cells shrink

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19
Q

What three characteristics define carrier mediated transport?

A

Specificity

Saturation

Competition

20
Q

How does the transport rate between simple diffusion and facilitated diffusion compare?

A

Simple diffusion - straight line

Facilitated diffusion - hyperbolic

21
Q

What are the two types of carrier-mediated transport?

A

Facilitated diffusion - passive

Active transport - requires energy

22
Q

What are the two types of active transport?

A

Primary active transport - ATP is used as energy source

Secondary active transport - secondhand energy stored in the form of an ion concentration gradient is used

23
Q

Na+K+ pump (Na+-K+ ATPase) transports how many ions in each direction?

A

3 Na+ out of the cell

2 K+ in to the cell

24
Q

What are the three important roles of the Na+-K+ pump?

A

Helps establish Na+ and K+ concentration gradients

Helps regulate cell volume by controlling solute concentration

Energy used to drive pump serves indirectly as energy source for secondary active transport

25
Q

What is symport?

A

Co-transport of a solute and ion (usually Na+) across the membrane in the same direction

(e.g. glucose absorption at apical membrane of enterocytes)

26
Q

What is antiport?

A

Solute and ion (usually Na+) move in opposite directions across the cell membrane

27
Q

What are the functions of exocytosis?

A

Secretion of enzymes, protein hormones

Method of adding carriers, channels or receptors to plasma membrane, e.g. GLUT4

28
Q

What is the membrane potential?

A

Potential difference between extracellular and intracellular fluid

29
Q

What causes the membrane potential?

A

Difference in concentration and permeability of key ions

30
Q

What direction is the concentration gradient for K+?

A

Outwards

31
Q

What is the direction of concentration gradient for Na+?

A

Inwards

32
Q

What direction is the electrical gradient for both Na+ and K+?

A

Towards the negatively charged side of the membrane

33
Q

What is the difference in permeability of the membrane to Na+ and K+?

A

The membrane is about 100x more permeable to K+ than Na+

34
Q

What is the equilibrium potential of K+?

A

-90mV

35
Q

What is the equilibrium potential for Na+?

A

+61mV

36
Q

What is the resting membrane potential?

A

-70mV

37
Q

What is the effect of the Na+-K+ pump on the membrane potential?

A

Generates a hyperpolarizing current

38
Q

How do nerve and muscle cells rapidly change their membrane potentials?

A

Altering their membrane permeabilities in response to stimulation

39
Q

What external factor is linked to a change of membrane potential in nerve and muscle cells?

A

Release of insulin by β cells of pancreas

40
Q

What do the terms hyperpolarization and depolarization mean?

A

Hyperpolarization - membrane potential becomes more negative

Depolarization - membrane potential becomes less negative or positive

41
Q

What sort of stimuli control ion channels?

A

voltage-gated

ligand-gated

mechanical

thermal

42
Q

What type of ion channels are responsible for the action potential in neurones?

A

Voltage-gated Na+ channels - depolarization

Voltage-gated K+ channels - hyperpolarization

43
Q

How do voltage-gated Na+ channels exhibit positive feedback?

A

Opening of a few channels causes further channels to open causing further depolorization

44
Q

How do voltage-gated K+ channels exhibit negative feedback?

A

Outward movement of K+ causes repolarization, therefore turning off the stimulus for channel opening.

45
Q

What causes the refractory period?

A

Na+ channels enter a non-conducting, inactivated state during maintained depolarization

This allows the channel to enter the closed state again, ready for a further action potential

46
Q

How does the myelin sheath of a neuronal axon contribute to the conduction of the action potential?

A

Action potentials just along the nodes of Ranvier

Physiology (8 decks)

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