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PHGY 209 > 2. Transport Mechanisms > Flashcards

2. Transport Mechanisms Flashcards

1
Q

Cell membrane less permeable to

A
  • larger molecules
  • charged molecules
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2
Q

Cell membrane highly permeable to

A
  • water
  • lipid soluble substances
  • dissolved gases
  • small uncharged molecules
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3
Q

Cell membrane impermeable to

A

very large molecules

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4
Q

Phospholipid bilayer components (4)

A
  • cholesterol
  • integral proteins
  • peripheral proteins
  • glycocalyx
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5
Q

cholesterol function

A

maintains membrane fluidity

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6
Q

glycocalyx function (2)

A
  • contributes to cell-cell recognition, communication, adhesion and protection
  • helps control vascular permeability
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7
Q

integral proteins

A

transmembrane: cross the the membrane

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8
Q

peripheral proteins

A

mostly on cytoplasmic side

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9
Q

functions of plasma membrane proteins (6)

A
  • selective transport
  • enzymatic activity
  • cell surface receptor
  • cell surface identity marker
  • cell adhesion
  • attachment to cytoskeleton
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10
Q

Passive transport mechanisms (3)

A
  • diffusion
  • facilitated diffusion
  • osmosis
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11
Q

Active transport mechanisms (3)

A
  • primary active transport
  • secondary active transport
  • pino/phagocytosis
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12
Q

Diffusion definition

A

movement of molecules down a concentration gradient

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13
Q

diffusion equilibrium, net flux =

A

net flux = 0

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14
Q

Fick’s Law of Diffusion (formula)

A

J = PA(C0 - Ci)

J = flux
P = permeability constant
A = surface area
C0 - Ci = concentration gradient

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15
Q

factors affecting diffusion (6)

A
  • mass of molecule
  • concentration gradient
  • lipid solubility
  • electrical charge
  • ion channels
  • membrane carriers
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16
Q

Diffusion is effective over long distances, True/False?

A

False

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17
Q

ion channel

A

transmembrane protein that show ion selectivity

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18
Q

electrochemical gradient

A

simultaneous existence of electrical and concentration gradient for a particular ion

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19
Q

gating

A

conformational changes that open/close iron channels

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20
Q

3 gating ways:

A
  • ligand gated = compound binds to channel
  • voltage gated
  • mechanically gated = stress
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21
Q

current flow through ion channels depends on: (3)

A
  • channel conductance
  • channel open time
  • frequency of channel opening
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22
Q

Facilitated diffusion (def)

A

use of carriers to transport molecules down concentration gradient

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23
Q

Is facilitated diffusion active or passive?

A

passive

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24
Q

carrier/transporter is an

A

integral membrane protein

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25
Q

facilitated diffusion affected by: (4)

A
  • solute concentration
  • affinity of transporter for solute
  • number of transporters
  • rate of transporter conformational change
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26
Q

3 characteristics of mediated transports

A
  • specificity
  • saturation
  • competition
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27
Q

Transport maximum (Tm)

A

when all binding sites on all transporters are occupied

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28
Q

steps for facilitated diffusion (4)

A
  • solute binds transporter
  • transporter changes configuration
  • solute delivered to other side of membrane
  • transporter resumes its original configuration
29
Q

active transport

A

use of carriers to transport molecules against a concentration gradient using ATP

30
Q

primary active transport

A
  • involves hydrolysis of ATP by a carrier
  • phosphorylation of carrier changes conformation of carrier and its solute binding affinity
31
Q

example of primary active transport

A

Na+/K+ pump (ATPase):
- ATP binds to pump: 3Na+ bind to carrier
- phosphorylation: Na+ released outside membrane
- 2K+ binds to carrier
- dephosphorylation: K+ released inside membrane

32
Q

secondary active transport

A

uses energy stored of electrochemical gradient to move both Na+ and the transported solute against the solute molecule’s concentration gradient

33
Q

secondary active transport: glucose example

A
  1. Na+ binds to transporter outside the cell, allowing glucose to bind to the same carrier
  2. change in configuration: transporter delivers Na+ and glucose into cell
  3. transporter reverts to its original configuration
  4. Na+ removed from cell by ATPase
34
Q

secondary active transport mechanisms (2)

A
  • symport/cotransport
  • antiport/counterport
35
Q

symport/cotransport

A

solute transported in same direction as Na+
-> HCO3, amino acid, glucose

36
Q

antiport/counterport/exchange

A

solute transported in opposite direction to Na+
-> H+, Ca2+

37
Q

endocytosis/exocytosis

A

active transport mechanisms involving participation of cell membrane itself

38
Q

3 types of endocytosis

A
  • pinocytosis
  • phagocytosis
  • receptor-mediated endocytosis
39
Q

endocytosis

A

cell membrane invaginates and pinches off to form a vesicle

40
Q

pinocytosis - cell drinking

A
  • non-specific and constitutive
    1. endocytotic vesicle engulfs extracellular fluid
    2. vesicles travel into cytoplasm and fuse with other vesicles
41
Q

phagocytosis - cell eating

A
  • specific and triggered
    1. extensions of cell membrane (pseudopodia) fold around a particle to engulf it
    2. pseudopodia fuse to form large vesicles that pinch off the membrane
    3. created phagosome migrates to and fuses with lysosomes
    4. phagosome content destroyed
42
Q

receptor-mediated endocytosis

A

molecules in extracellular fluid bind with high affinity to specific protein receptors on plasma membrane

43
Q

2 types of receptor-mediated endocytosis

A
  • clathrin-dependent
  • potocytosis
44
Q

clathrin-dependent receptor-mediated endocytosis (process)

A
  1. ligand binds receptors on cell which undergoes conformational change
  2. adaptor proteins link the ligand-receptor to clathrin, leading to aggregation go ligand-bound receptors
  3. clathrin-coated pit formed and invaginates to form clathrin-coded vesicle
  4. vesicle pinches off, shedding its clathrin coat
  5. receptors and clathrin protein recycled back to cell membrane
45
Q

example of clathrin dependent

A

low density lipoproteins (LDL) –> recognised by PM LDL receptors

46
Q

potocytosis receptor-mediated endocytosis

A
  • process by which molecules are sequestered and transported by tiny vesicles (caveolae)
  • caveolae are clathrin independent: can deliver contents directly into organelles
  • implicated in uptake of smaller molecules (lower Mr)
47
Q

exocytosis

A

process of moving material from inside the cell to outside

48
Q

2 types of exocytosis

A
  • constitutive
  • regulated
49
Q

constitutive exocytosis

A
  • continual and non-regulated

functions:
-replace plasma membrane
- deliver membrane proteins to cell membrane
- getting rid of substances from cell

50
Q

regulated exocytosis

A
  • triggered by extracellular signals and the increase of systolic Ca2+
  • secretes hormones, digestive enzymes and neurotransmitters
51
Q

osmosis

A

net diffusion of water across a semipermeable membrane

52
Q

aquaporins

A

facilitate osmosis by forming water permeable channels

53
Q

osmotic pressure

A

pressure required to prevent the movement of water across a semi-permeable membrane

54
Q

osmotic pressure =

A

difference in hydrostatic pressures of 2 solutions

55
Q

osmotic pressure is proportional to…

A

the number of particles in solution per unit volume

56
Q

osmolarity (osm)

A

total solute concentration of a solution

57
Q

1 osm =

A

1 mol of solute particles = 1 osm/l

58
Q

isosmotic

A

solutions which have the same osmolarity as normal extracellular solution = 300mOsm

59
Q

hyposmotic

A

solutions which have an osmolarity < 300mOsm

60
Q

hyperosmotic

A

solutions which have an osmolarity > 300mOsm

61
Q

non-penetrating

A

particles unable to cross membrane
–> Na+

62
Q

isotonic

A

solution has concentration of non penetrating solute particles = 300mOsm
-> no net shift

63
Q

hypotonic

A

solution has concentration of non penetrating solute particles < 300mOsm
-> water will enter cell: cell swelling

64
Q

hypertonic

A

solution has concentration of non penetrating solute particles > 300mOsm
-> water will leave cell: cell shrinking

65
Q

capillary transport mechanisms (3)

A
  • Diffusion (across membrane or through pores)
  • Transcytosis
  • Bulk flow
66
Q

transcytosis

A

exchangeable proteins are moved across by vesicular transport through endocytosis (to lumen side), then exocytosis (to instertital side)

67
Q

bulk flow

A

distributes extracellular fluid volume between plasma and ISF
-> magnitude is proportional to hydrostatic pressure difference between plasma and ISF

68
Q

Capillary wall allows protein-free plasma to move from capillaries to ISF. True/False?

A

True

PHGY 209 (6 decks)

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