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Biochemistry > Transport I&II > Flashcards

Transport I&II Flashcards

1
Q

List the components of a plasma membrane.

A

integral membrane proteins

intracellular proteins

extracellular components

lipid bilayer - amphipathic

extracellular matrix

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2
Q

What facilitates movement of specific molecules across the plasma membrane?

A

membrane transport proteins

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3
Q

True or False, the plasma membrane is semi-permeable.

A

True

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4
Q

True or False, transport proteins are mostly polytopic, transmembrane, integral membrane proteins.

A

True

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5
Q

What is the plasma membrane permeable to and how do they move through the membrane?

A

lipophilic molecules (steroids); via simple diffusion

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6
Q

What is the plasma membrane impermeable to and how do they move through the membrane?

A

hydrophilic (polar) molecules; via specific transport mechanism

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7
Q

What determines the ionic composition of the cell?

A

the activity and protein levels of specific transporters

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8
Q

What is one way of regulating metabolism?

A

alteration in expression levels of transporters

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9
Q

Which ion has a 10,000 fold difference between the extracellular and intracellular matrix of cells?

A

Calcium ion

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10
Q

True or False, ATP consumption per gram per minute used for signaling in the brain is equal to the energy used by a human leg muscle running a marathon.

A

True

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11
Q

What are the 2 types of transport?

A

passive and active

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12
Q

Define passive transport.

A

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

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13
Q

Define active transport.

A

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

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14
Q

List and describe the 2 types of passive transport.

A

simple diffusion: (unaided) molecules that are small, non-polar, and uncharged diffuse freely across the membrane; the steeper the gradient the faster the diffusion

facilitated: (with assistance of proteins) molecules that are large and charged are unable to cross the membrane alone, they need a facilitator (protein); proteins function as channels or transporters

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15
Q

True or False, the energy across a semi-permeable membrane is minimum when the concentration is equal.

A

True

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16
Q

What are the 2 types of ATP utilizing proteins?

A

P type ATPases and ATP binding cassette transporters

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17
Q

List examples of P type ATPases.

A

Na+/K+/ATPase

Plasma Membrane Ca2+ ATPase (PMCA)

Sarcoplasmic reticulum Ca2+ ATPase (SERCA)

H+/K+/ATPase

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18
Q

Describe P type ATPases.

A

use energy form ATP hydrolysis to drive transport against gradient

transporter forms a covalent bond with the phosphate to form an enzyme-phosphate intermediate (E1P)

phosphorylation on a conserved aspartate residue

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19
Q

Describe the sodium pump.

A

sets up Na+ and K+ gradients across plasma membrane

stoichiometry: 3Na+: 2K+/mole ATP

Makes neurons and muscle cells electrically excitable, controls cell volume, drives the active transport of sugars and amino acids

25-40% of brain ATP used by Na+ pump

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20
Q

List some inhibitors of the Na+ pump.

A

digitoxigenin and ouabain

inhibit dephosphorylation of E2P

called cardiotonic steroids due to strong effect on heart

used in treatment of congestive heart failure

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21
Q

What is the function of calcium pumps?

A

to reduce cystosolic calcium concentration

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22
Q

Describe PMCA.

A

transports calcium from cytosol to extracellular side

maintains 10,000 fold gradient across PM

uses ATP to pump Ca2+ uphill

stimulated by the calcium binding protein calmodulin

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23
Q

Describe SERCA.

A

transports calcium from cytosol to ER

80% of SR membrane protein

uses ATP

plays a role in relaxation of contracted muscle

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24
Q

List an example of an ATP binding cassette transporter.

A

ABC transporter

25
Q

Describe ABC transporters.

A

Have common architecture

multi-drug resistance protein/P glycoprotein

pumps a wide range of small molecules out of cells

uses ATP as energy source

when broken, pump molecules in then right back out

discovered through the use of tumor cells

26
Q

Describe secondary transporters.

A

active transport mediators not directly driven by ATP

thermodynamically unfavorable flow of one species of ion against a gradient coupled to favorable flow of another species down a gradient

27
Q

List and describe the types of secondary transporters.

A

Antiporters - ions move in opposite directions
(Sodium calcium exchanger)

Symporters - ions move in same direction
(lactose permease)

Uniporter - ions can move in both directions, depending upon the concentration
(mitochondrial calcium transporter)

28
Q

Describe lactose permease.

A

is a symporter

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

29
Q

A researcher mutated a critical domain on the Na+/K+ - ATPase gene. When expressed in cells, the mutated protein was unable to form the E-P intermediate in the reaction cycle of the enzyme. Which of the following amino acids was most likely altered in the mutant protein?

A

Aspartate

30
Q

A 60 year old man arrived to the Emergency Room complaining of chest pain, shortness of breath, and swelling of the legs. Echocardiography results showed evidence of congestive heart failure. The attending physician immediately started him on Digitalis. Which ion transporter/channel is the primary target of this drug?

A

Na+/K+ ATPase

31
Q

Describe ion channels.

A

integral, polytopic membrane proteins

mediate facilitated passive transport

transport ions 1000X faster than pumps

highly selective and specific for ions

respond to physical and chemical changes in their environment and undergo precisely timed conformational changes

opening and closing of channels shapes the membrane potential

32
Q

List and describe the types of ion channels.

A

voltage gated: respond to change in membrane potential

chemically gated: responds to ligands such as neurotransmitters

mechanically gated: respond to mechanical stimuli, found in sensory neurons

33
Q

What is the purpose of patch clamping?

A

measure conductance across membrane

34
Q

During his summer vacation in Hawaii, Dr. OshKosh was bit on his left arm by a puffer fish as he was swimming in the beautiful blue waters. His entire left arm was immediately numb. Which type of transport protein was impacted by the toxin in the puffer fish?

A

sodium channel

35
Q

What does lidocaine do?

A

pain blocker - inhibits sodium channel

36
Q

Through what animal was the sodium channel discovered?

A

electric eel

37
Q

How was the structure of the potassium channel studied?

A

gene cloning; used structural biochemistry to predict function

38
Q

What is the amino acid signature selectivity filter for the potassium channel?

A

TVGYG

39
Q

What area is the voltage sensor in the potassium channel?

A

S1-S4

40
Q

What is the pore in the potassium channel?

A

S5-S6

41
Q

What unit is the “switch” for the potassium channel?

A

S4

42
Q

Why does the ion selectivity work for the potassium channel?

A

K+ gain energy bound to channel; favorable reaction;
net negative delta G

Na+ loses energy when bound to channel;
unfavorable reaction
net positive delta G

43
Q

How does the potassium channel transport molecules?

A

due to repulsion of like charges

44
Q

Which step in the function of the K+ channel is controlled by the ball and chain mechanism?

A

Inactivation

45
Q

Describe acetylcholine receptor.

A

ligand is the neurotransmitter

present on post-synaptic side

binding of Ach to its receptor opens the channel

channel equally permeable to K+ and Na+

Pentamer of 4 kinds of membrane spanning subunits arranged in the form of a ring that creates a pore through the membrane

46
Q

In what animal was acetylcholine observed?

A

electric rays

47
Q

What are the subunits of Ach?

A

2 alphas, 1 beta, gamma, delta

48
Q

Describe neurotransmission.

A

most important manifestation of membrane transport - the basis for communication in the nervous system

nerve impulse is an electrical signal produced by the flow of current across the plasma membrane of a neuron

inside of neuron has high K+ and low Na+

generated by Na+/K+ ATPase

49
Q

Describe an action potential.

A

arises from large transient changes in the permeability of the axonal membrane to ions

the conductance for Na+ changes first due to opening of sodium channels

depolarization increases permeability to Na+ which begin to flow in via the Na+ channel due to high concentration outside

depolarization then opens the K+ channels and K+ move out

50
Q

List the 9 steps of an action potential.

A
  1. resting membrane potential (-60mV)
  2. depolarizing stimulus
  3. Na+ channels open
  4. rapid Na+ entry - further depolarization
  5. Na+ channels close, K+ open
  6. K+ move out
  7. membrane hyperpolarization
  8. K+ channels close
  9. cells return to resting potential
51
Q

List steps in synaptic transmission.

A
  1. action potential reaches presynaptic terminal
  2. depolarization opens up the VGCC
  3. calcium enters cell
  4. Causes fusion of synaptic vesicles
  5. exocytosis - release NT in synaptic cleft
  6. NT bind to receptor on post-synaptic side
  7. opens up a ligand-gated channel
52
Q

Describe gap junctions.

A

special form of ion channels

called cell to cell channels

passages between contiguous cells

important role in cell to cell communication

53
Q

List the properties of gap junctions.

A

small hydrophilic molecules and ions can pass through these channels

sugars, amino acids and nucleotides can pass through

proteins, polysaccharides and nucleic acids cannot pass through

54
Q

Describe the structure of gap junctions.

A

each channel is made up of 12 molecules of a transmembrane protein = connexin

6 connexin molecules are hexagonally arrayed to form a half channel called connexon

2 connexons join end to end in the intercellular space to form a functional channel

55
Q

What is the physiological relevance of gap junctions?

A

very important in cardiac tissue as it ensures a synchronous response to stimuli

induction of labor, all muscle cells contract in synchrony

important in lens and bone tissue - distribute nourishment

sealed by high Ca2+ and H+

regulated by membrane potential and hormone-induced phosphorylation

56
Q

What is the difference between ion channels and gap junctions?

A

traverse 2 membranes

connect cytoplasm to cytoplasm

synthesized by 2 different cells

remain open for seconds to minutes

57
Q

Describe water channels (aquaporins).

A

increase rate of water flow across membranes

found in rbc, kidney, cornea

have 6 transmembrane alpha helical domains

58
Q

What does digitalis inhibit?

A

Na+ K+ ATPase pump

Biochemistry (13 decks)

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