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Cell Molec > Transmembrane Transport > Flashcards

Transmembrane Transport Flashcards

1
Q

what is facilitated diffusion done via

A

channel or carrier proteins

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2
Q

what is active transprot done via

A

pumps

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3
Q

Concentration gradients move from what

A

high to low

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4
Q

What determines how well a substance can diffuse through a lipid bilayer

A

hydrophobicity of substance
size
steepness in concentration gradient
lipid/protein composition in the bilayer
Charge difference between the 2 compartments

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5
Q

what can diffuse through the membrane

A 
small gasses (O2, CO2, N2)
nonpolar molecules 
some small uncharged polar molecules
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6
Q

what does hydrophobicity have to do with rate of diffusion

A

more hydrophobic = faster diffusion

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7
Q

What cant diffuse through the bilayer

A

ions
large uncharged polar molecules (sugar)
Charged polar molecules (amino acids, proteins, ATP)

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8
Q

four main classes of ATP powered transport proteins

A 
P-class pumps 
v-class pumps
F-class pumps 
ABC
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9
Q

What are active transport pumps

A

transmembrane proteins that have ATP binding site in cytoplasmic domain

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10
Q

Why do we need active transport

A

cells want to bring in nutrients from environment even if cytoplasm has high concentration of that nutrient

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11
Q

How to active pumps function

A

to strictly control the pH and ionic composition of the cytosol

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12
Q

What ionic gradients exist between the cytosol and extracellular fluid

A

pH
Na+
K+
Ca2+

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13
Q

What do P class pumps transport

A

ions only

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14
Q

What is special about the P class pumps

A

it is the only pump to get phosphorylated

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15
Q

what are the subunits of P pumps

A

alpha catalytic subnuit- binds to ATP and transports ions

beta- regulatory unit

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16
Q

what gets phosphorylated in the p class pumps

A

the alpha sub unit

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17
Q

Where is Ca2+ stored

A

sarcoplasmic reticulum

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18
Q

What is the sarcoplasmic reticulum

A

smooth ER of muscle cells

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19
Q

How does Ca effect muscles

A

release of Ca into cytosol triggers muscle contraction

in order for muscle to relax Ca must be pumped back in

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20
Q

Examples of P class pumps

A

Sarcoplasmic reticulum Ca2+ pump

Na+/K+ pump

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21
Q

How do sarcoplasmic reticulum Ca2+ pumps work

A
  1. cytoplasmic portion of alpha subunit binds to two Ca ions and a molecule of ATP
  2. ATP is hydrolyzed into ADP +P
  3. this phosphorylation causes a conformational change in the pump
  4. Ca ions come off and go into lumen
  5. the phosphate is removed and the protein goes back to its original conformation
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22
Q

What do the Na+/K+ pumps help

A

keep high K+/ low Na+ in cytosol and high Na+/low K+ in the extracellular

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23
Q

How do Na+/K+ pumps work

A
  1. 3Na+ ions and ATP bind to the alpha subunit
  2. ATP hydrolyzed and P is transferred as before
  3. Conformational changes allow Na+ to be released outside
  4. 2 K+ ions bind to the other sites in the alpha subunit
  5. phosphate removed, protein reverted back to original conformation
  6. bound K+ ions are released into cytosol
    END RESULT: 3 Na+ out and 2K+ in
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24
Q

what do V class proton pumps pump

A

protons only

primary function to pump protons into lysosomes, endosomes and plant vacuoles

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25
Q

Why is a pump needed to pump protons into a lysosome

A

it is very acidic in a lysosome so protons are pumped in against a concentration gradient

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26
Q

what are the two v class pump domains

A

V1 hydrophilic cytosolic domain

V0 hydrophobic transmembrane domain

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27
Q

How V class pumps work

A

ATP is bound and hydrolyzed by the V1 subunit
provides power to pump H+ through the V0 domain
Nothing is phosphorylated

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28
Q

why must a Cl- must be pumped when a H+ is transported into lysosome

A

to keep the charge balance neutral

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29
Q

What is the structure of ABC pumps

A

2 transmembrane domains (T) and 2 cytosolic domains (A) that function to bind to ATP

comes together where two T units meet also where it opens

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30
Q

What do ABC pumps pump

A

various dif substances

sugars, amino acids, toxins not just ion

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31
Q

where are ABC pumps found

A

all over bacterial and eukaryotic plasma membranes

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32
Q

what are the ABC pumps in bacteria called

A

permeases

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33
Q

type of mammal ABC pumps

A

MDR1 (multidrug resistance transport protein)
pumps various toxins and drugs from cytosol to outside

CFTR = chloride pump that when mutated leads to cystic fibrosis, Cl required to keep mucus thin and moving through lungs

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34
Q

what is a hydrophilic passageway

A

channel proteins create them and water ions and small organic molecules move across

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35
Q

what makes up a hydrophilic passageway

A

single polypeptide folded

complex dif polypeptides

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36
Q

what is the difference between gated and non gated channels

A

gated open and close in response to stimuli of changes in voltage while non gated are unaffected by these factors

37
Q

What channel proteins does water diffuse through

A

aquaporins

38
Q

Is there ever a difference in water concentration

A

no but there can be a difference in amount of free water molecules

39
Q

what are free water molecules

A

not bound to anything

capable of diffusing as they are not associated to an ion or something else

40
Q

high solute concentrations will have what levels of water

A

low

41
Q

Water diffuses in what way

A

area of low solute to area of high solute

42
Q

Hypotonic

A

environment containing less solute

43
Q

Hypertonic

A

environment contain more solute

44
Q

Isotonic

A

when solute concentration is equal in the 2 environments

45
Q

What would happen if osmosis went unchecked

A

water would constantly rush into the cell as there is an enormous amount of solute in the cytoplasm
cause osmotic lysis

46
Q

How is osmotic lysis prevented in plant fungal cells

A

cell walls allow for cell swelling

the swelling causes turgor pressure which prevents more water from coming in

47
Q

How is osmotic lysis prevented in animal cells

A

they do not contain a cell wall so they constantly ship out ions into the extracellular fluid in an attempt to make fluid isotonic with respect to cytoplasm

48
Q

How is osmotic lysis prevented in protozoans

A

contractile vacuole that is constantly collecting extra water from cytoplasm and shipping it out

49
Q

What are aquaporins made of

A

4 identical subunits containing 6 membrane spanning alpha helices

50
Q

what provides specificity in aquaporins

A

hydrogen binding- hydrophilic R groups extend in middle of channel and perfectly hydrogen bond with water molecules

51
Q

Non-gated ion channels are

A

highly selective

52
Q

Structure of non gated ion channels

A

must contain 4 subunits arranged around a central pore

each subunit contains a loop that extends into the pore

each loop perfectly takes place of water shell that forms around ion

53
Q

membrane potential

A

difference in charge between two sides of the membrane

54
Q

which side is more negative in plasma membrane of eukaryotic cells

A

more negative on the inside

55
Q

Why is the inside more negative then the outside

A

cytoplasm contains high concentration of large anionic molecules that are unable to exit the cell

K+ is allowed to move down its concentration gradient and diffuse out of the cell

56
Q

Why is K+ being allowed to move down its concentration gradient make it more negative within the cell

A

makes it more positive outside of the cell as Na+ and Ca2+ are not allowed to diffuse into the cell easily

57
Q

What is normal resting membrane potential

A

-70 mV

58
Q

What is the patch clamp technique used to measure

A

ion flow through channels

measure inward or outward flow of ions through a single ion channel complex

59
Q

How does the patch clamp technique work

A

utilizes 2 electrodes

  1. one attached to membrane that should only contain a few ion channels
  2. one inserted into the cytoplasm

use frogs as they have huge cells

60
Q

Patch clamp technique with Na+ ions

A

if measuring how many Na+ ions leave the cell, the intracellular electrode will remove an e-

measures how long these channels stay open and how many ions move through the channel in that time

61
Q

What is oocyte expression

A

frog eggs cotnain few or no ion channels so can inject mRNA encoding ion channel into egg, thus ion channel will be made and inserted into plasma membrane

62
Q

Stimuli that trigger ion channels to open/close

A
  1. voltage
  2. ligands- NT and hormones bind to ion channel causing them to change conformation
  3. activated g proteins
  4. light
  5. many others
63
Q

Structure of voltage gated ion channels

A

4 polypeptides or 1 polypeptide with 4 separate domains arranged in cylinder with central pore

voltage sensing alpha helices that contain lots of lysine and arginines (+ charge)

64
Q

When and what blocks the pore of voltage gated ion channels

A

after alpha helices return to their original position

channel inactivating protein

65
Q

Structure of neuron

A

cell body - nucleus and other organelles
dendrites- receive signals from environment or from other neurons
axon- send electrical impulses to another cell
axon termini - contact these other cells

66
Q

Steps of impulse generation on a neuron

A
  1. small depolarization (Na+ into cell causing a more positive)
  2. depolarization triggers opening of Na+ voltage gated channels
  3. Na+ rush into cytoplasm which causes K+ channels to open
  4. Na+/K+ pumps send Na+ back out and K+ back in
67
Q

Ligand gated ion channels

A

channel that open following binding of a specific environmental chemical ligand

68
Q

What is nicontinic acetylcholine receptor (NAR)

A

prototypical ligand gated ion channel

involved in transfer of electrical impulse from neuron to muscle cell

receptor and channel in one

69
Q

How is NAR activated

A

secretion of acetylcholine triggered from arrival of action potential at end of axon

binds to NAR on muscle cell, triggers Na+ to flow into cell

action potential is initiated

70
Q

What does a G protein do

A

regulates opening of some ion channels

71
Q

How does a G protein work

A

binding of a ligand to its receptor signals for the recruitment and activation of G protein

G leaves receptor and binds to nearby plasma membrane ion channel

bind to channel and induce conformational change

channel opens and allows for the diffusion of some ion

72
Q

What is special about G protein binding

A

it is delayed

73
Q

What are transporters

A

integral membrane proteins that grab various ions/nutrients undergo conformational change and transport cargo across membrane

74
Q

types of transporters

A

uniporters- bind to single substance

symporters- 2 or more in same direction

antiporters- 2 or more in opposite directions

75
Q

How a cotransporter works

A

one moves with gradient thus causing release of energy and this energy is used to transfer second agains the gradient

76
Q

example of uniporter

A

GLUT1 with 2 conformational states

77
Q

example of cotransporters

A

Na+/ glucose symporter - Na+ moves into cell with gradient and the energy released is used to bring glucose in with it against its gradient

Na+/ amino acid symporter

Na+/Ca+ antiporter

pH controlling antiporter

78
Q

what would increase rate of glucose update in liver cells

A

increase glucose in medium

transfect cells with wild type GLUT-1 gene

79
Q

What does the CO2 transport in blood transport require

A

Cl-/ HCO3- antiporter

80
Q

CO2 and O2 in systematic capillaries

A

High CO2

Low O2

81
Q

CO2 and O2 in pulmonary capillaries

A

low CO2 and High O2

82
Q

What forms of transport require a protein

A

facilitated, active, cotransport

83
Q

What forms of transport has solute against gradient

A

active, cotransport

84
Q

What forms of transport couple to ATP hydrolysis

A

Active

85
Q

What forms of transport is driven by movement of another ion down its gradient

A

cotransport

86
Q

Example of molecules transported in simple diffusion

A

O2, CO2, steroid hormones, many drugs

87
Q

Example of molecules transported in facilitated

A

glucose and amino acids (uniporters) ion and water (channels)

88
Q

Example of molecules transported in active transport

A

ions, small hydrophilic molecules, lipids

89
Q

Example of molecules transported in cotransport

A

glucose, amino acids (symporters) various ions and sucrose (antiporters)

Cell Molec (5 decks)

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