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Biochemical and Physiological Basis of Nutrition I: Macronutrients > Chapter 12 > Flashcards

Chapter 12 Flashcards

1
Q

protein-free artificial lipid bilayer (liposome)

A

impermeable to most water-soluble molecules

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2
Q

cell membranes

A

contain transport proteins, each of which transports a specific type of molecule

EX: selective transport includes active pumping of specific molecules into or out of the cell

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3
Q

combined action of transport proteins can…

A

allow solutes to build up inside a membrane enclosed compartment (ex: cytosol or and organelle)

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4
Q

interior of the lipid bilayer is…

A

hydrophobic
creates a barrier that hydrophilic molecules can’t pass

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5
Q

why doesn’t simple diffusion work for hydrophilic molecules?

A

it is way too slow!

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6
Q

how do we accelerate passage of hydrophilic molecules through lipid bilayers?

A

facilitated transport

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7
Q

can all molecules diffuse across a lipid bilayer?

A

YES, but some rates are super slow

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8
Q

what type of molecules diffuse more quickly across the membrane?

A

smaller, more hydrophobic (aka more nonpolar) molecules

fewer favorable interactions with water (less polar) = diffuses more quickly

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9
Q

solutes

A

substances dissolved in water that are polar

need transporters to cross cell membranes

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10
Q

lipid bilayer permeability
small nonpolar molecules

A

O2, CO2
dissolve readily, rapidly diffuse
important for cellular respiration

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11
Q

lipid bilayer permeability
uncharged polar molecules

A

molecules w/ uneven distribution of electric charge
diffuse readily if small enough
H20, ethanol cross quickly
glycerol crosses very slowly
glucose is large and hardly crosses

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12
Q

lipid bilayer permeability
charged molecules

A

highly impermeable!
includes inorganic ions
why?: strong electrical attraction to water inhibits entry into inner hydrocarbon phase of the bilayer

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13
Q

most plentiful ion outside the cell?

A

Na+

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14
Q

most plentiful ion inside the cell?

A

K+

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15
Q

high conc Na+ outside cell is balanced by?

A

Cl- inside cell

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16
Q

high conc K+ inside cell is balanced by?

A

negatively charged ions including nucleic acids, proteins, and cell metabolites

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17
Q

membrane potential

A

electrical imbalances in plasma membrane

generate a voltage difference across the membrane

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18
Q

resting membrane potential

A

cell is unstimulated, exchange of cations and anions across membrane is balanced

resting potential is negative bc inside of cell is more neg than outside

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19
Q

most membrane transport proteins have…

A

polypeptide chains that cross lipid bilayer many times (multipass transmembrane proteins)

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20
Q

how do we use multipass transmembrane proteins?

A

to allow small, hydrophilic molecules to cross the membrane without contacting hydrophobic interior of lipid bilayer

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21
Q

how do transporter and channels differ?

A

in the way they discriminate between solutes

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22
Q

channels discriminate on

A

size and electric charge
open channel = any ion or molecule small enough and with the right charge can pass through

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23
Q

transporter

A

transfers only molecules or ions that fit into specific binding sites on the protein

bind solutes with great specificity (just like enzymes binding substrates)

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24
Q

transporter mechanism

A

undergoes conformational changes to transfer small solutes across lipid bilayer

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25
Q

channel mechanism

A

when open, forms a pore across the bilayer through which specific inorganic ions or polar organic molecs can diffuse

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26
Q

which is faster channel or transporter?

A

channels!

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27
Q

passive transport

A

no energy required
solute moves down concentration gradient spontaneously

this occurs to keep equilibrium

all channels and many transporters facilitate passive transport

28
Q

active transport

A

drives flow against conc gradient by coupling it to a process to provides input of energy

uses pumps to harness an energy source

29
Q

energy sources for active transport

A

ATP hydrolysis, transmembrane ion gradient, sunlight

30
Q

what influences passive transport of charged solutes

A

BOTH conc gradient AND membrane potential

31
Q

what influences passive transport of uncharged solutes

A

conc gradient ONLY

32
Q

cytosolic side of membrane charge?

A

negative

33
Q

extracellular membrane charge

A

positive

34
Q

positively charged solutes are typically brought

A

into the cell since the interior is more negative

35
Q

electrochemical gradient

A

net force of conc gradient and membrane potential

determines direction of solutes for passive transport

36
Q

steep electrochemical gradient

A

when voltage and conc gradients run in same direction
EX: Na+

37
Q

small electrochemical gradient

A

when voltage and conc gradient have opp effects
EX: K+
little movement even when channels are open

38
Q

osmosis

A

passive movement of water down its conc gradient

39
Q

which direction does water typically move?

A

into the cell
bc solute is usually more concentrated outside the cell

40
Q

aquaporins

A

specialized channel proteins that speed up flow of water
hourglass shaped

41
Q

what happens if osmosis occurs without constraint?

A

the cell swells

42
Q

how do animal cells resist osmotic swelling?

A

gel-like cytoplasm

43
Q

transporter

A

move small, water-soluble, organic molecules (and some inorganic ions) across cell membranes

highly selective

44
Q

glucose charge

A

uncharged
chemical part of electrochemical gradient is 0
ONLY conc gradient drives glucose

45
Q

glucose transporter

A

in plasma membrane
switches conformation to expose glucose binding sites to exterior, interior, whatever is needed

highly selective

46
Q

transmembrane pumps

A

actively transport a solute against its electrochemical gradient

47
Q

why do we need active transport?

A

1) maintain appropriate intracellular ionic composition of cells
2) import solutes that are at a lower concentration outside the cell than inside

48
Q

3 active transport methods

A

1) ATP-driven pumps
2) coupled pumps
3) light-driven pumps

49
Q

ATP-driven pumps

A

hydrolyze ATP to drive uphill transport

50
Q

coupled pumps

A

link uphill transport of one solute across a membrane to the downhill transport of another

51
Q

light-driven pumps

A

mainly in bacteria
use energy from sun to drive uphill transport

52
Q

symport

A

pump that moves both solutes in same direction across the membrane

53
Q

antiport

A

pump that moves both solutes in opposite direction across the membrane

54
Q

uniport

A

A transporter that ferries only one type of solute across the membrane (and is therefore not a coupled
transporter)

55
Q

electrochemical Na+ gradient drives

A

coupled pumps in plasma membrane
Na+ flows in
drives other solutes into animal cells
EX: epithelial cells in the gut

56
Q

why do we need the glucose-Na+ symport?

A

if we only had the passive glucose uniport, they would release glucose into the gut after fasting AS freely AS they take it up from the guy after a feast

NO regulation!

57
Q

why do we need glucose-Na+ symport

A

so we can take up glucose from gut lumen even when concentration of glucose is higher in cell’s cytosol than in its gut lumen

58
Q

how does glucose-Na+ symport work?

A

electrochemical gradient for Na+ is steep, so when Na_ moves into the cell (down its gradient), glucose is dragged into the cell

59
Q

binding of Na+ and glucose is…

A

cooperative: binding of one enhances binding of the other

if one solute is missing, the other fails to find

both Na+ and glucose must be present for coupled transport to occur

60
Q

What would happen if gut epithelial cells only had glucose-Na+ symport?

A

they could never release glucose for use by other cells of the body

SO, we need two types of symporters

61
Q

2 types of glucose transporters

A

at opposite ends of cell
1) in apical domain of plasma membrane (faces gut lumen)
2) In basal and lateral domains of plasma membrane

allow gut epithelial cells to transfer glucose across epithelial lining of gut

62
Q

glucose transporters in apical domain

A

face gut lumen
take up glucose actively, create high glucose conc in cytosol

63
Q

basal and lateral glucose transporters

A

passive glucose uniports
release glucose down its conc gradient for use by other tissues

64
Q

how are 2 types of glucose transporters kept in place

A

segregated in their proper domains of plasma membrane by a diffusion barrier formed by tight junction around apex of the cell

65
Q

why do we need to keep glucose transporters apart

A

to prevent mixing of membrane components between the two domains

Biochemical and Physiological Basis of Nutrition I: Macronutrients (12 decks)

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