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Whitney - Biochem Test 2 > Lecture 18 Membrane Transport 1 > Flashcards

Lecture 18 Membrane Transport 1 Flashcards

1
Q

What are the majority of transport proteins?

A

Most are polytopic, transmembrane integral membrane proteins

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2
Q

What is the plasma membrane permeable to?

A

Lipophilic molecules

e.g. steroid hormones

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3
Q

What is the plasma membrane impermeable to?

A

Hydrophilic/Polar molecules

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4
Q

What is the function of membrane proteins?

A

Facilitate the transport of specific molecules across the membrane

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5
Q

Since hydrophilic/polar molecules are impermeable, how do they pass the membrane?

A

They need specific transport mechanisms

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6
Q

What determines the ionic composition of the cell?

A

The activity and protein levels of specific transporters

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7
Q

What governs the biochemical/metabolic characteristics of a cell?

A

The expression of specific transporters

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8
Q

What might be one way of regulating metabolism?

A

Alteration in expression levels of transporters

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9
Q

Passive Transport

A

Molecules move down a concentration gradient by using energy stored in the gradient
e.g., ion channels

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10
Q

Active Transport

A

Molecules move against a gradient by using biochemical energy stored in ATP
e.g., pumps/ATPase

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11
Q

What are the two types of energy independent movement of molecules down a gradient?

A

Simple Diffusion

Facilitated Diffusion

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12
Q

Simple Diffusion

A

Molecules that are small, non-polar and uncharged polar diffuse freely across the membrane via simple diffusion
Unaided

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13
Q

Facilitated Diffusion

A

Molecules that are large and charged are unable to cross the membrane so they need a facilitator (i.e. proteins - function as channels or transporters)

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14
Q

When is energy at a minimum?

A

When concentration across a semi-permeable membrane is equal

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15
Q

Equation for Free Energy of an Uncharged Molecule

A

ΔG = 2.303 RT log(c2/c1)

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16
Q

Equation for Free Energy of a Charged Molecule

A

ΔG = 2.303 RT log(c2/c1) + ZFΔV
Z is the electrical charge of the transported species
F is the Faraday’s constant
Δ V is the membrane potential

17
Q

What does a positive free energy mean in terms of transport?

A

Active transport

18
Q

What are the two types of ATP utilizing proteins?

A

P type ATPases

ATP Binding Cassette Transporters

19
Q

List exaples of P Type ATPases

A

Na+K+-ATPase
Plasma Membrane Ca2+-ATPase (PMCA)
SR Ca2+-ATPase (SERCA)
H+-K+-ATPase

20
Q

Give an example of ATP Binding Cassette Transporters

A

Multi drug resistance protein

21
Q

Why are P type ATPases considered P type?

A

Transporter forms a covalent bond with the phosphate (cleaved from ATP) to form an enzyme-phosphate intermediate

22
Q

In P Type ATPases, where does the energy come from?

A

Uses energy from ATP hydrolysis to drive transport against gradient

23
Q

In P type ATPases, what residue of the transporter is phosphorylated?

A

Aspartate

24
Q

What are the functions of the Sodium Pump?

A

Set up Na+ and K+ gradients across PM
Makes neurons and muscle cells electrically excitable, controls cell volume, drives the active transport of sugars and AAs
3 Na+ out, 2 K+ in

25
Q

How much of brain ATP is used by the Na+ pump?

A

25 to 40%

26
Q

Give an example of a Na pump inhibitor

A

Plant steroids (digitoxigenin and ouabain)
Strong effect on heart
Can be used in treatment of cardiotonic steroids

27
Q

How do plant steroids inhibit the Na+ pump?

A

By inhibiting dephosphorylation of E2P

28
Q

Mechanism of action of Cardiac Glycosides

A 
Inhibition of Na+K+-ATPase activity 
Increase Na+ levels in cell
Reduce activity of Na+-Ca2+ antiporter
Increase in [Ca2+]i
Elevated Ca2+ increases contractile force of cardiac muscle
29
Q

Name the two Calcium Pumps

A

Plasma membrane Ca2+-ATPase (PMCA)

Sarco-endoplasmic reticulum Ca2+-ATPase (SERCA)

30
Q

Describe PMCA

A

10 transmembrane domains
Transports Ca from cytosol to extracellular side
Uses ATP
Stimulated by Ca binding protein calmodulin (CaM)

31
Q

Describe SERCA

A

10 transmembrane domains
Transports Ca from cytosol to ER
Uses ATP
Plays role in relaxation of contracted muscle

32
Q

Describe ABC Transporters

A

Human genome has ~150
Have common architecture
Multi-drug resistance protein/P glycoprotein
Pump wide range of small molecules out of cell
Use ATP

33
Q

Describe Mechanism of Action of ABC Transporters

A

See slide 32

34
Q

Describe Secondary Transporters

A

Not directly driven by ATP
Thermodynamically unfavorable flow of one species of ion against a gradient coupled to a favorable flow of another species down a gradient

35
Q

Three types of Secondary Transporters

A

Antiporters
Symporters
Uniporters

36
Q

Lactose Permease

A

Symporter
Uses proton gradient generated by oxidation of fuel molecules to drive lactose and other sugars against concentration gradient

Whitney - Biochem Test 2 (6 decks)

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