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biosci S1 Pt2 > Lec 16 - Membrane proteins > Flashcards

Lec 16 - Membrane proteins Flashcards

1
Q

What is non-mediated transport?

A

When particles can enter the cell without the assistance of membrane proteins. Important for absorption or nutrients

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2
Q

What is mediated transport?

A

The movement of materials with the help of a transport protein

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3
Q

What is passive trasnport?

A

The movement of substances down their concentration or electrochemical gradients with only their kinetic energy

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4
Q

Can passive transport happen when there is not gradient?

A

No

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5
Q

What is active trasnport?

A

The movement of substances against their concentration or electrochemical gradients.

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6
Q

What is vesicular transport?

A

Movement of materials across membranes in small vesicles either by endocytosis or exocytosis

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7
Q

What are examples of things that can go into the cell via non-mediated transport?

A

Oxygen
Carbon dioxide
nitrogen
Fatty acids
Steroids
small alcohols
fat soluble vitamins (A, E, D and K)

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8
Q

What are the main features of diffusion through ion channels?

A

Water-filled pore that shields ions from hydrophobic core
RAPID TRANSPORT since ions do not bind to pore.
Hydrophilic amino acids line the pore.

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9
Q

What are the main properties of ion channels?

A

Have an ionic selectivity filter which allows harnessing of energy stored in different ion gradients
If it has a negative charge, it will only let + through.

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10
Q

What are the main properties of gated channels?

A

Have a ‘plug’ gates that control opening and closing of the pore
Stimuli can control opening/closing:
- Voltage
- ligand
- pH
- cell volume
- phosphorylation

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11
Q

What is the patch clamp technique used for?

A

measures the current flowing through whenever the channel opens. Current fluctuations represent the conformational changes in channel structure that are associated with channel gating.

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12
Q

What is the measurable current that can be identified using the patch clamp technique?

A

~10^-12 Amps

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13
Q

What are the main features of carrier mediated transport?

A

Molecule to be transported binds to protein (directly interacts), protein undergoes conformational change. SLOWER TRANSPORT RATES THAN CHANNELS

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14
Q

How are the properites of carrier mediated transporters similar to enzymes?

A

specificity - key and lock
inhibition - something can prevent ligand binding
competition - for binding site
saturation - all binding sites can be filled- RDS

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15
Q

Is carrier mediated transport passive or active?

A

Can be either

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16
Q

What is the process of facilitated diffusion of glucose?

A
  1. Glucose binds to tranport brotein (GLUT)
  2. Protein changes shape and glucose moves down gradient into cell.
  3. Kinase enzyme converts glucose to glucose-6-phosphate to maintain low glucose concentration inside of the cell
17
Q

How does primary active transport work?

A

Energy is derived directly from hydrolysis of ATP
A typical cell uses 30% of its energy on primary active transport

18
Q

How does secondary active transport work?

A

Energy stored in an ionic concentration gradient is used to drive the active transport.

19
Q

How does Na/KATPase work?

A

3 Na+ ions removed from the cell and 2 K+ brought into the cell. maintains low Na and high K in cytosol.
This pump is electrogenic

20
Q

What are examples of primary active transporters?

A

Ca/KATPase (liver cell - muscle SR)
H/KATPase (stomach)- creates pH of 2

21
Q

What is the difference in Na and K+ concentrations important for?

A

Maintaining resting membrane potential
electrical exitability (nervous system)
Contraction of muscle
Maintenance of cell volume
Uptake of nutrients via secondary active transporters
Maintenance of pH by secondary active transporters (lungs-acid base regulation)

22
Q

What is the pump-leak hypothesis?

A

The fact that Na and K are constantly leaking back down their concentration gradients and so the Na/KATPase has to work continuously

23
Q

How do secondary active transporters use energy?

A

Uses the energy stored in concentration gradients that are created by primary active transporters.

24
Q

What are the two examples of secondary active transporters?

A

Na+ antiporters/exchangers (Na+ rush inwards, Ca2+ or H+ pushed out)
Na+ symporters or co-transporters (glucose rushes inwards with Na+ ions)

25
Q

How do you calculate the membrane permeability to water? Pw

A

Pw = Pd + Pf
Pd = water through lipid bilayer
Pf = water through aquaporins

26
Q

What are the features of Pd?

A

Small
mercury insensitive
temperature dependent (lipid fluidity)

27
Q

What are the features of Pf?

A

Large
Mercury sensitive
temp independent

biosci S1 Pt2 (16 decks)

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