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Biochem Test 2 > Membrane Transport 1 > Flashcards

Membrane Transport 1 Flashcards

1
Q

What do you have to use to remove integral proteins from the plasma membrane?

A

Salts or detergents or else will destroy the whole plasma membrane

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2
Q

Finish the sentence: Transport proteins are mostly ____________________________________.

A

Polytopic, transmembrane, integral membrane proteins

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3
Q

Describe some of the properties of the plasma membrane.

A
  • semi-permeable
  • permeable to lipophilic molecules (move by diffusion) (ex. Steroid hormones)
  • impermeable to hydrophilic/ polar molecules - need a specific transport mechanism
  • membrane proteins facilitate the transport of specific molecules across the plasma membrane
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4
Q

What determines the ionic composition of the cell?

A

The activity and protein levels of specific transporters determines the ionic composition of the cell

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5
Q

What determines the biochemical/ metabolic characteristics of a cell?

A

Expression of specific transporters

-can execute only those reactions whose substrates can be taken up

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6
Q

Alteration in expression levels of transporters may be one way of ___________________.

A

Regulating metabolism

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7
Q

What are the intracellular and extracellular relationships of

  1. Sodium
  2. Calcium
  3. Potassium
  4. Chlorine
A
  1. Sodium is high outside and low inside cell
  2. Calcium is high outside cell, very low inside the cell
  3. Potassium is low outside of the cell and high inside of the cell
  4. Chlorine is high outside of the cell and low inside of the cell
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8
Q

What are the two types of transport?

A

Active and passive

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9
Q

What is passive transport?

A

Molecules move down a concentration gradient by using energy stored in the gradient (ion channels)

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10
Q

What is active transport?

A

Molecules move against the concentration gradient by using energy stored in ATP (pumps/ATPases)

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11
Q

What is simple diffusion?

A
  • Passive, unaided diffusion
  • molecules that are very small,non-polar and uncharged diffuse freely across the membrane via simple diffusion
  • the steeper the gradient the faster the diffusion
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12
Q

What is facilitated diffusion?

A
  • Passive transport with the assistance of proteins
  • molecules that are large and charged are unable to cross the membrane
  • these molecules need a facilitator (protein) that can facilitate the movement
  • proteins can function as channels or transporters
  • these proteins increase the rate of transport
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13
Q

Describe free energy

A
  • Unequal distribution of molecules is associated with free energy
  • energy is used to set up an ion gradient across a semi-permeable membrane
  • ion gradients are made by membrane transporters
  • these use energy from ATP and store it as free energy of the gradient
  • energy is minimum when concentration across a semi-permeable membrane is equal
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14
Q

What happens when you increase the gradient or difference in concentration on side 1 and side 2?

A

Energy also increases

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15
Q

What are the type types of proteins that can do active transport?

A

P type ATPases and ATP binding cassette transporters

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16
Q

What are examples of P type ATPases?

A

Na+K+-ATPase
Plasma membrane Ca +2 ATPase (PMCA)
Sarcoplasmic reticulum Ca+2-ATPase (SERCA)
H+K+-ATPase

17
Q

What is an example of a ATP binding cassette transporter?

A

Multi-drug resistant protein

18
Q

Describe in general characteristics of P type ATPases.

A
  • integral membrane proteins
  • use energy from ATP hydrolysis to drive transport against gradient
  • transporter forms a covalent bond with the phosphate to form an enzyme-phosphate intermediate
  • phosphorylation occurs on a conserved aspartate residue
  • undergoes conformational change that facilitates the transport of ions across the membrane
19
Q

What is the stoichiometry of a sodium pump?

A

3 Na+ in and 2K+ out takes a mole of ATP

20
Q

What inhibits the sodium pump?

A

Plant steroids like digitoxigenin and ouabain

  • inhibit dephosphoyrlation of E2P (prevents the transport of the ion by locking it in the E2P state)
  • called cardio tonic steroids due to strong effect on heart
21
Q

What is the mechanism of action of digitoxigenin or ouabain?

A
  • increases Na levels in the cell
  • reduces the activity of the antiporter (Na/Ca exchanger)
  • increase in calcium concentration
  • elevated calcium increases the contractile force of cardiac muscle
  • used in treatment of congestive heart failure
22
Q

Describe the Plasma membrane Ca+2-ATPase (PMCA) pump and how it works.

A
  • protein with 10 transmembrane domains
  • transports calcium from cytosol to extracellular side
  • uses ATP to pump calcium uphill
  • stimulated by the calcium binding protein calmodulin (CaM) which masks the active site when the enzyme is not active
23
Q

Describe the SERCA pump.

A
  • protein with 10 transmembrane domains
  • transports calcium from cytosol to ER (no calmodulin)
  • makes up 80% of SR membrane protein
  • uses ATP
  • plays role in relaxation of contracted muscle
24
Q

Describe the function of ABC transporters.

A
  • multi drug resistance protein
  • pump wide range of small molecules out of cells
  • various conformations
25
Q

Describe the mechanism of action of ABC transporters

A
  1. Protein is free of substrate and ATP
  2. Channel faces intracellular site
  3. Binding of substrate
  4. Conformation changes in the ATP binding cassettes
  5. Increased affinity of ATP
  6. ATP binds
  7. Conformational change in the ATP binding cassettes
  8. Reorientation of the membrane spanning domains
  9. Expulsion of substrate to extracellular side
  10. ATP hydrolysis resets transporter to its original state
26
Q

True or false:

Active transport mediator are not directly driven by ATP

A

True

27
Q

What are antiporters?

A

Ions move in opposite direction

Secondary active transporter

28
Q

What are symporters?

A

Ions move in the same direction

Secondary active transporter

29
Q

What is a uniporter?

A

Ions can move in both directions, depending upon the concentration

30
Q

Describe lactose permease structure and function.

A
  • symporters
  • uses proton gradient generated by oxidation of fuel molecules to drive lactose and other sugars against concentration gradient
  • N terminus and C terminus and the pore in the center is where the sugar binds
31
Q

Describe the mechanism of lactose permease.

A
  1. H+ comes in and binds to COO- molecule which increases affinity for lactose to bind (now in protonated form)
  2. Lactose comes in and binds
  3. Causes a conformational change - eversion now instead of transporter open to the extracellular side, now open to intracellular
  4. Lactose is released into the cell
  5. H+ comes off of the COOH to go back to COO- (deprotonated)
  6. Conformational change- eversion so that the transporter now opens back up to the extracellular side to bind more H+ (reset)

Biochem Test 2 (5 decks)

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