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Biochemistry > Week 9 - Membrane Transport Pt II > Flashcards

Week 9 - Membrane Transport Pt II Flashcards

1
Q

What does K ion channel coming of?

A

4 subunits

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2
Q

What does each subunit comprise of?

A

M1 and M2 helixes joined by a P (pore) segment consisting of a short helix and non helical portion that lines the channel through which ions pass

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3
Q

What does a portion of each P segment contain?

A

Conserved pentapeptide (GYGVT) whose residues kind the selectivity filter that screen for K+ ions

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4
Q

What does the selectivity filter contain?

A

4 rings of carbonyl O atoms and one ring of threonyl O atoms

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5
Q

Why is the diameter of ring large enough?

A

8 O atoms can coordinate a single K ion, replacing it’s normal water of hydration

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6
Q

Voltage-gated channels

A

Conformation depends on the difference in ionic charge on two sides of membrane

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7
Q

Ligand gated channels

A

Conformation depends on binding of a ligand to channel

ACH binds on outside and CAMP binds on inside

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8
Q

Mechano-gated channels

A

Conformation depends on mechanical forces applied to membrane

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9
Q

What are voltage-gated K+ channel from Eukaryotes known as?

A

Kv channels

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10
Q

What is the structure of KV channel?

A

Four identical/ homologous subunit

Each subunit: 6 transmembrane alpha helices

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11
Q

What are 2 functionally distinct domain of KV channel?

A

Pore domain

Voltage sensing domain

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12
Q

What is pore domain?

A

Helices S5, S6 and P segment homologous to helices M1, M2 and P segment in Kcsa

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13
Q

What is voltage sensing domain?

A

Consist of helices S1 to S4

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14
Q

How many subunits do all channels have?

A

4

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15
Q

Prokaryotic channel

A

4 subunits and 2 helices each=8

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16
Q

What is the role of transmembrane portion?

A

Voltage gating?

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17
Q

What is the role of cytoplasmic portion?

A

Regulation

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18
Q

What does amino acid sequence of S4 helix show?

A

A number of positively charged amino acid residues

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19
Q

What does S4 segment show?

A

A series of positively charged amino acids (Lysine and arginine) and every 2 residues, +ve side chain going down

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20
Q

Where does helix face when there’s an active membrane potential?

A

Cytoplasmic

More negative inside cell than outside

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21
Q

Why is S4 rotates?

A

Positive residues face electronegative area in cytosol

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22
Q

When does helix face outside of cell?

A

Losing negative charge on inside

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23
Q

What is transfixed to open channel?

A

Structural change

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24
Q

What does moving S4 helix transducer?

A

Movement of two helices (S4-S5) that forms channel for opening and closing of channel

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25
Q

What connects the voltage sensing and pore domain?

A

S4-S5 linker helix

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26
Q

What is the inner surface of channel below pore domain lined by?

A

S6 helix

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27
Q

Resting condition, negative potential

A

S4 helix exposed to cytoplasm

Channel closed

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28
Q

Depolarisation

A

S4 helix exposed to the outside of cell

Channel open

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29
Q

Once the channel is open, how many K+ ions can pass through per second?

A

10 million K+ ions

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30
Q

What is the conformational states of Kv channel?

A

Rest
Open
Inactivated

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31
Q

Conformational state: rest

A

Membrane potential is there

Pore is closed

32
Q

Conformational state: open

A

Depolarising membrane

Flux of sodium

33
Q

Conformational change: inactivated

A

Milliseconds after K+ channel shut down

34
Q

Why do we need so many voltage gated K+ channel?

A

Depending on the charges on the S4 helix, it will rotate channel at higher potentials/lower potentials
Channel to detect subtle changes in membrane potential (differentiate to transduce lots of signals)
Switched on and off through: phosphorylation, PTM etc

35
Q

What requires a facultative transporter to cross Membranes?

A

Large or hydrophilic substances

36
Q

What is facilitative diffusion?

A 
Passive 
Specific 
Saturable 
Regulated 
Much slower than ion channels
37
Q

Faciliative transporters can move how much solute molecules per second across the membrane?

A

Hundred to thousands

38
Q

What is a gradient favouring the continued diffusion of glucose into the cell maintained by?

A

Phosphorylating the sugar after it enters the cytoplasm

Lowers the intracellular glucose concentration

39
Q

Transport

A
  1. Glucose binds to transporter
  2. Transporter changes shape
  3. After binding, active site now exposed to cytosolic side
  4. Transport
40
Q

Recovery

A

Active site closed to cytosol

41
Q

How many glucose transporters in human body?

A

5

42
Q

Which glucose transporter is most important?

A

GLUT 4

43
Q

Why is hexokinase phosphorylation?

A

Concentration gradient to drive glucose in

44
Q

What happens when you eat a lot of sugar?

A

Pancreas produces insulin

45
Q

Vesicles full of GLUT4 transporters on surface of cells

A

Vesicular fusion

Glucose import from bloodstream to cells (skeletal muscle and adipocytes)

46
Q

Where are transporters present?

A

Membrane of cytoplasmic vesicles

47
Q

What is nitrate central in?

A

Nitrogen metabolism

48
Q

How is nitrite rapidly removed from the cell?

A

Channels

Transporters

49
Q

What do assimilatory enzymes do?

A

Reduce nitrite to ammonium it dinitrogen

50
Q

What is the structure of Nark?

A

Positively charged substrate-translocation pathway lacking protonable residues

51
Q

What does Nark function as?

A

Nitrate/nitrite exchanger

Protons are unlikely to be co-transported

52
Q

How does Nark exchange nitrate for nitrite by?

A

Rocker switch mechanism

Facilitated by: inter-domain hydrogen bond networks

53
Q

Active Transport

A

Energetically unfavourable so needs to be coupled to a favourable reaction

54
Q

What does active transport do?

A 
Maintain gradients for:
Potassium 
Sodium 
Calcium 
Other ions across cell membrane
55
Q

Active transport

A

Couples the movement of substances against gradients to ATP hydrolysis

56
Q

What is the ratio of Na+ : K+ pumped?

A

3:2

The Na+/K+ ATPase is electrogenic

57
Q

What is ATPase?

A

P-type pump

Phosphorylation causes change in structure and affinity that allow transport against gradients

58
Q

Where is Na+/K+ ATPase found only in?

A

Animals

59
Q

What does hydrolysing ATP give?

A

Structural change in ATPase protein

60
Q

Define electrogenic?

A

Producing a change in the electrical potential of a cell

61
Q

What does Na+/K+ ATPase have high affinity for?

A

Na+ in the cytoplasm

K+ in the extracellular space

62
Q

What does Na+/K+ ATPase have lower affinity for?

A

Na+ in the extracellular space

K+ in the cytoplasm

63
Q

E1 —> E2

A

Phosphorylated and release ADP

64
Q

E2 —> E1

A

Dephosphorylated and binds ATP

65
Q

Where does sodium ions bind protein?

A

Inside of membrane

66
Q

When ATP is hydrolysed andphosphate transferred to protein what does it allow?

A

Sodium ions to be expelled to external space

67
Q

What happens to the phosphate group when potassium ions bind to the protein

A

Subsequently lost

68
Q

Where is cation binding site located?

A

Deep within transmembrane domain

Consist of 10 membrane spanning helices

69
Q

What does V-type pump actively transport?

A

Hydrogen ions across the walls of cytoplasmic organelles and vacuoles

70
Q

Where does V type pump occur?

A

Membrane that line:
Lysosomes
Secretory granule
Plant cell vacoules

71
Q

V type pump in the plasma membrane of kidney tubules

A

Maintain body’s acid-base balance by secreting protons into forming urine

72
Q

What is active transport coupled to?

A

Existing ion gradient

73
Q

What is symport?

A

Pump gradient up on inside
Move sodium with other compounds to create smaller gradients of other molecules
The molecules will travel in same direction in relation to each other

74
Q

What is antiport?

A

Integral membrane transport protein that simultaneously transport two different molecules in opposite directions

75
Q

Sodium glucose transporter

A

High sodium concentration outside

Low concentration of glucose

76
Q

What is secondary transport?

A

The use of energy stored in an ionic gradient

Biochemistry (15 decks)

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