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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
channel mechanism
when open, forms a pore across the bilayer through which specific inorganic ions or polar organic molecs can diffuse
26
which is faster channel or transporter?
channels!
27
passive transport
no energy required solute moves down concentration gradient spontaneously this occurs to keep equilibrium all channels and many transporters facilitate passive transport
28
active transport
drives flow against conc gradient by coupling it to a process to provides input of energy uses pumps to harness an energy source
29
energy sources for active transport
ATP hydrolysis, transmembrane ion gradient, sunlight
30
what influences passive transport of charged solutes
BOTH conc gradient AND membrane potential
31
what influences passive transport of uncharged solutes
conc gradient ONLY
32
cytosolic side of membrane charge?
negative
33
extracellular membrane charge
positive
34
positively charged solutes are typically brought
into the cell since the interior is more negative
35
electrochemical gradient
net force of conc gradient and membrane potential determines direction of solutes for passive transport
36
steep electrochemical gradient
when voltage and conc gradients run in same direction EX: Na+
37
small electrochemical gradient
when voltage and conc gradient have opp effects EX: K+ little movement even when channels are open
38
osmosis
passive movement of water down its conc gradient
39
which direction does water typically move?
into the cell bc solute is usually more concentrated outside the cell
40
aquaporins
specialized channel proteins that speed up flow of water hourglass shaped
41
what happens if osmosis occurs without constraint?
the cell swells
42
how do animal cells resist osmotic swelling?
gel-like cytoplasm
43
transporter
move small, water-soluble, organic molecules (and some inorganic ions) across cell membranes highly selective
44
glucose charge
uncharged chemical part of electrochemical gradient is 0 ONLY conc gradient drives glucose
45
glucose transporter
in plasma membrane switches conformation to expose glucose binding sites to exterior, interior, whatever is needed highly selective
46
transmembrane pumps
actively transport a solute against its electrochemical gradient
47
why do we need active transport?
1) maintain appropriate intracellular ionic composition of cells 2) import solutes that are at a lower concentration outside the cell than inside
48
3 active transport methods
1) ATP-driven pumps 2) coupled pumps 3) light-driven pumps
49
ATP-driven pumps
hydrolyze ATP to drive uphill transport
50
coupled pumps
link uphill transport of one solute across a membrane to the downhill transport of another
51
light-driven pumps
mainly in bacteria use energy from sun to drive uphill transport
52
symport
pump that moves both solutes in same direction across the membrane
53
antiport
pump that moves both solutes in opposite direction across the membrane
54
uniport
A transporter that ferries only one type of solute across the membrane (and is therefore not a coupled transporter)
55
electrochemical Na+ gradient drives
coupled pumps in plasma membrane Na+ flows in drives other solutes into animal cells EX: epithelial cells in the gut
56
why do we need the glucose-Na+ symport?
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
why do we need glucose-Na+ symport
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
how does glucose-Na+ symport work?
electrochemical gradient for Na+ is steep, so when Na_ moves into the cell (down its gradient), glucose is dragged into the cell
59
binding of Na+ and glucose is...
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
What would happen if gut epithelial cells only had glucose-Na+ symport?
they could never release glucose for use by other cells of the body SO, we need two types of symporters
61
2 types of glucose transporters
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
glucose transporters in apical domain
face gut lumen take up glucose actively, create high glucose conc in cytosol
63
basal and lateral glucose transporters
passive glucose uniports release glucose down its conc gradient for use by other tissues
64
how are 2 types of glucose transporters kept in place
segregated in their proper domains of plasma membrane by a diffusion barrier formed by tight junction around apex of the cell
65
why do we need to keep glucose transporters apart
to prevent mixing of membrane components between the two domains

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

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