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I've got kidney disease > Lecture 4: Protein transporters > Flashcards

Lecture 4: Protein transporters Flashcards

1
Q

Solutes diffuse from an area of _______ concentration to an area of _______ concentration. What is this called?

A

high
low
Flux

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2
Q

What is osmosis?

A

When water flows of areas of where water is in high concentration to where water is in low concentration across a semipermeable membrane

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3
Q

The cell membrane limits free movement, to varying degrees. This is because the membrane is a _______ __________

A

selective barrier

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4
Q

Membrane spanning proteins provide an alternative, regulated mechanism to what?

A

passive diffusion

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5
Q

What is the net flux?

A

the sum of the total number of opposing fluxes

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6
Q

The larger the concentration difference, the bigger the what?

A

flux

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7
Q

What do membrane proteins allow?

A

they allow more solutes to be moved through the membrane, even at low concentrations of solutes

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8
Q

What is a limitation of membrane proteins?

A

The solute has to interact with the membrane protein which means that only one protein can go in at a time and therefore there is a saturation point

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9
Q

What is upreulation?

A

Adding more proteins into the membrane which increases the flux

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10
Q

Describe protein mediated membrane transport. What two types are there?

A

Proteins span the membrane. These proteins function as enzymes and they catalyse the transport of solutes across the membrane
The two types are:
1. passive transport
2. active transport

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11
Q

What is involved in passive protein mediated membrane transport?

A

This involves channels and carriers (facilitated diffusion) it is dependent on concentration gradient

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12
Q

What is involved in active protein mediated membrane transport?

A

Primary active transport which is ATP dependent or secondary active transport which uses carriers and transporters and use the downhill gradient for one solute to transport another solute uphill

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13
Q

Channels and carriers are very _______. What do they require and what do they have?

A

selective
they require interaction between substrate and protein
they have a binding site/selectivity filter in the protein

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14
Q

What is the main difference between channels and carriers?

A

The rate of transport

  • channels are very fast
  • carriers are much slower
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15
Q

Channels have a ______ and when that opens, you have a _______

A

gate

pore

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16
Q

Why are carriers much slower than channels?

A

because there has to be an interaction between and protein and the solute and it requires conformational change in the protein to move the solute across the membrane

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17
Q

What is another name for a channel that participate in facilitated diffusion? Define this

A

gated pore or non-gated pore

this is a small, selective tunnel through which molecules can move rapidly

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18
Q

What three things do channels move via facilitated diffusion?

A

ion
water
small solutes

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19
Q

Is the movement of ions, water and small solutes a passive or active process?

A

this is a passive mechanism: the movement of a solute via a channel is determined by the gradient for the solute (both concentration and electrical gradients)

20
Q

Naming of channels can vary. What are some of the ways they are named after?

A
  • they are named after the things that go through them
  • they are named after a disease state (eg. cystic fibrosis transmembrane regulatory protein)
  • they are named after an inhibitor (eg. Ryanodine receptor)
21
Q

What two states can gated channels exist in?

A

open or closed state

22
Q

When gated channels open, they open to the _________ extent every time. What does this mean?

A

same

therefore a channel is either nothing when it is closed or maximum when it is open

23
Q

Do gated channels open spontaneously?

A

yes

however propensity of opening can be modified by other agent

24
Q

Are channels prone to competition? How is this dealt with?

A

Yes

  • If you (for eg.) wanted Cl- to go through the CFTR channel but CO32- can also go through, the concentration of Cl- would have to be really high on one side so that the chance of Cl- bumping into the protein is higher (has a greater flux).
  • you can also have selectivity eg. have a positively charge in the pore so only negatively charged ions can go through
25
Q

As well as selectivity and competition, how else can a pore have reduced activity?

A
  • inhibition: sometimes an inhibitor will block the channel, sometimes it will lock the channel open
26
Q

Chanel open to the same extent every time. Because of this, the permeability of membrane to a solute that crosses the membrane can only be determines by two things. What are these?

A
  1. the number of channels (N) for that solute that are in the membrane
  2. the open probability (Po) of the channels that are in the membrane
27
Q

What is open probablilty?

A

this is the fraction of time the channel stays open

28
Q

Proteins in the membrane are always being ___________ and ________.

A

Proteins in the membrane are always being inserted and removed.

29
Q

If you increase the number of transporters in the membrane, you increase the _________ of that ion

A

permeability

30
Q

The fraction of time that channels stay open for and the number of channels is modified by what three things?

A
  1. specific molecules
  2. the membrane potential
  3. mechanical deformation
31
Q

How do specific molecules modify the fraction of time that channels stay open for and the number of channels in the membrane? Give examples?

A

ACh, cAMP, [Ca2+]i

they can cause the opening of more channels eg. calcium induced calcium release causes the activation of calcium release channels in the SR

ACh can bind to gated channels which causes the open probability to increase

32
Q

How does the membrane potentials modify the fraction of time that channels stay open for and the number of channels in the membrane? Give examples?

A

Voltage gated Na+ opens and the membrane potential changes which is how you get propagation of action potentials.
A change in membrane potential activates things that will further alter the membrane potential

33
Q

How does mechanical deformation modify the fraction of time that channels stay open for and the number of channels in the membrane? Give examples?

A

Touch receptors respond to pressure and mechanical changes which cause the opening of calcium channels

34
Q

What is secondary active transport and what are the two types? What do these mean?

A

Uses the downhill gradient of one solute to transport another solute “uphill”

  • cotransporter: both solutes are moving in the same direction
  • counter-transporter: both solutes moving in the opposite direction
35
Q

What do carriers normally transport?

A

ions and something else (eg, glucose or amino acids), or two different ions

36
Q

What do carriers contain?

A

a binding site that determines the selectivity

37
Q

What is the type of system that carriers are?

A

they are a turn-style type system

38
Q

Describe a turn-style type system

A

Binding site(s) is only accessible from one side of the membrane at a time. It binds 1-2 molecules and then it changes conformation transporting solute across the membrane

39
Q

Explain carriers transporting a molecule

A

The carrier is open to the outside and the molecule enters from the outside and binds at a binding site. The outer gate closes and the molecule becomes occluded, still attached to its binding site. The inner gate opens with the molecule still bound. The molecules exits and enters the inside of the cell. The outer gate closes, occluding an empty binding site. This cycle can also flow in reverse order.

40
Q

Carriers are prone to _______ and ______-

A

competition

inhibition

41
Q

Carriers have _______ kinetics

A

saturation (there is only a limited number of molecules that can bind per second)

42
Q

The types of carriers are defined in terms of their what?

A

substrate whether it is the solute transported against electrochemical gradient or the binding of substrates

43
Q

Explain the na+/glucose cotransporter

A

2 Na+ molecules and a glucose and then it will open

44
Q

What is the purpose of the Na+/H+?

A

to maintain charge difference and to control acid secretion

45
Q

Where can a summary of gated channels and carriers are found?

A

slide 26

46
Q

What is the purpose of NKCC1?

A

Cl- transporting into the cell coupled to Na+ so when CFTR opens, Cl- can exit the membrane
Na+ is pumped out through Na+/K+ ATPase, and a K+ channel so K+ can leave the cell

I've got kidney disease (43 decks)

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