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PHGY209 > TRANSPORT MECHANISMS - DR. SHRIER > Flashcards

TRANSPORT MECHANISMS - DR. SHRIER Flashcards

1
Q

Which compartment are we talking about?

  1. Materials enter the body, can get absorbed, and exit the body
  2. Materials get absorbed from the GI tracht, and can move through lungs, skin and kidneys, and back up to the GI tracht
  3. Materials go through the capillary wall from the plasma, and can cross the cell membrane and back up
  4. Last compartment that is reached by a material entering from the GI tracht
A
  1. Gastro-intestinal tracht
  2. Plasma
  3. ISF
  4. ICF
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2
Q

Cell membranes are highly permeable to__

A

Water, Lipid-soluble substances, Dissolved Gases (O2, CO2), Small uncharged molecules

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3
Q

Cell membranes are less permeable to___

A

Larger molecules, charged particles

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4
Q

Cell membranes are impermeable to__

A

Very large molecules

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5
Q

Whats the cell membrane composed of?

A

Phospholipid bilayer.

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6
Q

What are characteristics of the phospholipid bilayer

A

It’s ampiphatic (polar ends on the outside surface with hydrophilic heads; nonpolar on the inside with the hydrophobic tails)
Phospholipids comprise 40-50% of the plasma membrane by weight

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7
Q

How does Cholesterol act within the phospholipid bilayer? (3 actions)

A

1) Reduces packing of fatty acid tails and tends to increase membrane fluidity.
2) Involved in formation of vesicles that pinch off the plasma membrane and in lipid rafts.
3) Acts to stabilize cell membrane and adds firmness when at high temperatures; Inserts itself into phospholipids and prevents aggregation when at low temperatures

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8
Q

Is Cholesterol hydrophobic, hydrophilic or amphipatic

A

amphipatic

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9
Q

Which proteins are found in cell membranes

A

Integral: closely associated with phospholipids, mostly cross the membrane (transmembrane, amphipatic)

Peripheral: more loosely associated, mostly on the cytoplasmic side

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10
Q

What percentage of weight of the cell membrane do proteins take up

A

25 to 75 per cent

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11
Q

what is glycocalyx and what is it attached to

A

layer of carbohydrate formed by a chain of monosaccharides that extend from the extra cellular surface of the cell membrane. it is bound to proteins.

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12
Q

what is glycocalyx role (3)

A

provides protection from infection, enables cells to identify each other and interact

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13
Q

what are 6 functions of plasma membrane proteins

A

selective transport channel
enzyme
cell surface receptor
cell surface identity marker
cell adhesion
attachment to the cytoskeleton

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14
Q

What is enzymes role in membrane

A

Catalyze membrane associated rx

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15
Q

what is receptors role in cell membrane

A

receiving and transducing chemical signals from the cell environment

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16
Q

what are the two transmembrane transport pathways

A
  1. via phospholipid layer
  2. via interaction with protein cluster (channel or carrier)
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17
Q

What are the two types of transport mechanisms across cell membrane

A

passive and active

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18
Q

what are 3 passive transport mechanisms across cell membrane

A

diffusion, carrier-mediated facilitated diffusion, osmosis

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19
Q

what are 2 active transport mechanisms across cell membrane

A
  1. carrier-mediated active transport (a. primary b. secondary)
  2. pino/phagocytosis
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20
Q

whats the difference between active and passive transport mechanisms

A

active = energy dependant
passive = energy independant

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21
Q

whats diffusion

A

movmt of molecules from one location to another as a result of random thermal motion

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22
Q

what is flux

A

amount of particles crossing a surface per unit time

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23
Q

net flux is from ___ [C] to ___ [C]

A

high to low

24
Q

at equilibrium, diffusion fluxes are ___ and net flux is ___

A

equal, zero

25
Q

At equilibrium, net movement =

A

0

26
Q

When a cell is exposed to a solute in a large extracellular solution, the Ci rises over time and only plateau’s when?

A

when Ci = Co

27
Q

The rate of diffusion may be calculated by Fick’s Law of Diffusion, which is given by

A

J = PA (C0 - Ci)

28
Q

In J = PA (C0-Ci), what do the variables mean

A

J = net flux = rate of diffusion
P = permeability coefficient, constant based on the ease with which a molecule moves through a membrane
A = surface area of the membrane
C0-Ci = concentration gradient of the diffusing molecule across the membrane

29
Q

Diffusion time increases in proportion to the ____________ travelled by the solute molecules. (1 um = 1 msec, 10 um = 100 msec, etc.)

A

square of the distance

30
Q

Diffusion is an effective transport process only over _____ distances.

A

short

31
Q

what are 5 factors that affect diffusion across the cell membrane

A
  1. mass of molecule
  2. concentration gradient across cell membrane
  3. lipid solubility
  4. electrical charge
  5. availability of selective ion channels or membrane carriers
32
Q

Diffusion particles may penetrate either by a) or b)

A

a) dissolving in the lipid component (for non-polar molecules), e.g., o2, co2, fatty acids

b) diffusing through channels (for ions)

33
Q

In either way of penetration, diffusion movement depends upon the existence of a

A

concnetration gradient

34
Q

Ion channels show selectivity based on _____ as well as on ______

A

diameter; distribution of charges lining the channel

35
Q

Movement of ions is affected not only by concentration gradient, but by ______. The simultaneous existence of these two gradients for a particular ion is known as_____.

A

electrical gradient; electrochemical gradient

36
Q

whats the resting membrane potential

A

-90 mV

37
Q

Ion channels may be gated in which 3 ways?

A

1) Ligand-gated
2)Voltage-gated
3)Mechanically-gated

38
Q

What is gating of ion channels

A

Ion channels can exist in open or closed state as they undergo conformational changes

39
Q

Which are the voltage gated ion channels?

A

Na+ channel, K+ channel, Ca+ channel, Cl- channel

40
Q

The total number of ions that flow through these channels generating ionic current depend upon:

A
  1. channel conductance
  2. how often the channel opens
  3. how long the channel stays open
41
Q

Mediated transport is the movement of ions and other molecules (glucose, AA’s) by integral membrane proteins called ____

A

transporters

42
Q

Ion movement across membranes via transporters is much slower than through ion channels. Which two types of movmeent require transporters?

A

Facilitated diffusion (passive) and Active transport (active)

43
Q

what are 3 characteristics of mediated-transport systems

A
  1. specificity
  2. saturation
  3. competition
44
Q

What is specificity, a characteristic of mediated-transport systems

A

system usually transports one particular type of molecule only

45
Q

what is saturation , a characteristic of mediated-transport systems

A

rate of transport reaches a maximum when all binding sites on all transporters are occupied. Thus , a limit - the TRANSPORT MAXIMUM (Tm) - exists for a given substance across a given membrane

46
Q

what is competition - a characteristic of mediated-transport systems

A

occurs when structurally similar substances compete for the same binding site on a membrane carrier

47
Q

how does flux into cell differ between diffusion and mediated transport?

A

mediated transport reaches a maximal flux, at the Tm, whereas diffusion does not

48
Q

which 4 factors determine flux magnitude of mediated-transport systems

A
  1. solute concentration
  2. affinity of transporter for the solute
  3. numbers of transporters
  4. rate of transporter conformational change
49
Q

what is facilitated diffusion

A

involves the presence of a transporter molecule, which enables a solute to penetrate more readily than it would be expected to by simple diffusion.

50
Q

what are 4 steps to facilitated diffusion

A

a) solute binds to transporter
b) transporter changes configuration
c) solute is delivered to other side of membrane
d) transporter resumes original configuration

51
Q

what are 3 characteristics of facilitated diffusion

A

1- transporter mediated
2- passive
3- next flux from high to low concentration

52
Q

what can increase the number or affinity of tansporters in some membrnaes; give an example

A

hormones; ex. insulin increases Glut-4 which transports glucose in muscle

53
Q

what are 4 characteristics of passive transport

A

1- transporter mediated
2- requires supply of chemical energy (usually derived form of enzymatic hydrolysis of ATP)
3- susceptible to metabolic inhibitors
4- can transport solute agaisnt its concnetration gradient

54
Q

What is primary active transport?

A

WHen ATP gives a P group to the transporter as part of phosphorylation, the conformation of the transporter changes and lets the solute cross the membrane agaisnt its gradient of concentration. After it passes, the transporter dephosphoylates and pumps the solute on the other side come across the opposite way. This is how it works with Na+/K+-ATPase.

55
Q

What are other primary active transporters?

A

Ca2+-ATPase: maintain low intracellular Ca2+ levels
H+-ATPase: maintain low lysosomal pH
H+/K+-ATPase: acifification of the stomach

PHGY209 (2 decks)

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