[2] Class 4: Transport Through Membrane 2

Question 1

Integral, polytopic membrane proteins

400 genes in human genome

Mediates Facilitated passive transport

Highly selective and specific for ions

1000X faster than pumps

Opening and closing channels shapes membrane potential

Answer 1

Ion channels

Question 2

Why are transport ions 1000x faster than pumps?

Answer 2

They have efficient gates that can be voltage gated and not require the sequential steps of waiting for ATP binding and hydrolysis for the action to occur.

Question 3

3 types of ion channels:

Answer 3

Voltage
Ligand
Mechanical

Question 4

Respond to change in membrane potential

Answer 4

Voltage-gated

Question 5

Respond to ligand such as neurotransmitters

Answer 5

Chemically gated

Question 6

Respond to mechanical stimuli, detect vibration, pressure. Stretch, touch, sounds, tastes, smell, heat, volume, and vision. Found in sensory neurons:

Answer 6

Mechanically gated

Question 7

How was ion channeling proven by experiment?

Answer 7

Patch clamping

Question 8

Who was involved in first patch clamping experiment?

Answer 8

Erwin neher and Bert Sakmann

Question 9

How long are ion channels open?

Answer 9

Msec ‘s

Question 10

Current applied to patch clamping

Answer 10

4 pA

Question 11

S5 and S6 form:

Answer 11

The pore of the ion channel

Question 12

S1-S4 form the:

Answer 12

Voltage sensor

Question 13

Sequence homology:

Answer 13

Sodium, Ca+, K+ all homologous seem to be handed down in evo.

Question 14

Model organism for Na+ channel testing:

Answer 14

Electric eel

Question 15

260 kDa protein
4 terminal repeats
6 transmembrane domains
TM 4-voltage sensor

Answer 15

Na+ channel

Question 16

What is the basis of topical anesthetics:

Answer 16

Block sodium channels

Question 17

Toxic substance from pufferfish that acts to inhibit Na+ channels:

Answer 17

Tetrodotoxin

Question 18

Voltage sensor for K + channel

Answer 18

S1-s4

Question 19

S5-s6 K+ channel:

Answer 19

Pore

Question 20

Who determined structure of K+ channel and when?

Answer 20

Robert mackinnon; 1998

Question 21

K+ direction of movement in tissue:

Answer 21

Move from inside out

Question 22

HOw does selectivity filter work for K+ channel?

Answer 22

Hydrated K+ dehydrated when going through selectivity filter. Carbonyl bonds are forms w/ AA’s in channel. Rehydrated exiting channel.

Question 23

What is the signature of potassium channel?

Answer 23

TVGYG

Question 24

Which is larger? Na+ or K+

Answer 24

Na+ = 0.95 å

K is 1.33å

Question 25

Why cant Na+ pass through K+ channel if it is smaller than K+?

Answer 25

Na+ is rejected b/c of higher energetic cost of dehydrating sodium would not be recovered when passing through channel. K+ resolvation energy > desolvation energy

Question 26

How many binding sites for K+ channel?

Answer 26

4

Question 27

Describe the fundamental reason that K+ ions continue through channel as opposed to remaining bonded to carbonyl of AA in pore:

Answer 27

D/t repulsion of like charges- K+ ions push each other along as more come into pore

Question 28

Na+/ K+ channels are gated by:

Answer 28

membrane potential or voltage

Question 29

What happens in voltage gated channels in response to changes in membrane potential?

Answer 29

Conformational change

Question 30

Voltage gated sponsors

Answer 30

S1-s4

Question 31

Pore of voltage gated channels:

Answer 31

S5-s6

Question 32

The duration of the open state can be controlled by length and flexibility of this part of the channel:

Answer 32

Ball and chain

Question 33

The ball and chain model inactivation domain is the:

Answer 33

Ball

Question 34

What creates a binding site for the + charged ball in the mouth of the pore?

Answer 34

Depolarization

Question 35

What happens when the ball binds to the mouth of the pore:

Answer 35

It is inactivated by occlusion.

Question 36

How many AA units make up ball:

Answer 36

20; Zaidia talked about 1st 40 AA important for closing the channel

Question 37

Ex of ligand gated ion channel

Answer 37

Acetylcholine receptor

Question 38

Present on post-synaptic side Binds acetylcholine and open channel Equally permeable to Na+ and K+ Pentamer of 4 kinds of membrane spanning (a2ßdelta) arranged in the form of a ring that creates a pore through the membrane

Answer 38

Ligand gated Acetylcholine receptor

Question 39

5 subunits come together to form a pore

Answer 39

Ach receptor

Question 40

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

Answer 40

Neurotransmission

Question 41

Nerve impulse is an ______ _______ produced by the flow of current across the plasma membrane of a neuron.

Answer 41

Electrical signal

Question 42

K+ and Na+ content inside of neuron

Answer 42

High [K+] and low [Na+]

Question 43

How is the K+/Na+ gradient generated?

Answer 43

Na+/K+ ATPase

Question 44

This is used to calculate membrane potential

Answer 44

Nernst equation

Question 45

Action potential rise from large transient

Answer 45

Changes in the permeability of axonal membrane to ions

Question 46

Conduction for _____ changes first d/t opening of ____channels

Answer 46

Na+; Na+

Question 47

__________ increases permeability to Na+ which begin to flow in via the Na+ chanel d/t high [ ] outside

Answer 47

Depolarization

Question 48

After Na+ rush in ________ then opens K+ channels and K+ move out

Answer 48

Depolarization

Question 49

Sequence of AP

Answer 49

1. resting pot. -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

Question 50

Synaptic transmission steps:

Answer 50

1. AP reaches presynaptic terminal 2. Depolarization opens up the VGCC 3. Ca++ enters cell 4. Causes fusion of synaptic vesicles 5. exocytosis- release of NT in synapse 6. NT binds to receptor on post-synaptic side 7. opens up ligand gated Na+ channel

Question 51

Special form of ion channel Called "cell to cell' channels Passages btw contiguous cells Important role in cell to cell communication

Answer 51

Gap junctions

Question 52

Packed in hexagonal array Lumen ~20å Distance btw gap junctions of 2 adjacent cells is ~35å

Answer 52

Structure of gap junctions

Question 53

Properties of gap junctions:

Answer 53

Small hydrophilic molecules and ions pass through < 1 kDA molecules can pass: sugars, AA, and nucleotides can pass thru Proteins, polysaccharides and nuclei acids cant pass

Question 54

Allow direct communication

Answer 54

Gap junctions

Question 55

Structure of gap junctions

Answer 55

12 molecules of transmembrane protein= connexin 6 connexin molecules hexagonally arrayed to form a half channel= connexon 2 connexons join end to end in the intercellular space to form functional channel.

Question 56

Physiological relevance gap junctions in cardiac tissue:

Answer 56

Synchronous response to stimuli - contraction in synchrony

Question 57

Significance of gap junctions in lens and bone

Answer 57

Distribute nourishment: Sealed by high Ca+ and H+: protect norm cells from injured or dying cells b/c too much inside of too little outside can be fatal

Question 58

The induction of biological effects in cells that are not directly traversed by a charged particle

Answer 58

The bystander effect

Question 59

Differ Ion channels and GAP junctions membrane location:

Answer 59

Gap junctions: transverse 2 membranes Ion: 1 membrane

Question 60

Differ Ion channels and GAP junctions connections:

Answer 60

GAP: connect cytoplasm to cytoplasm Ion: Cytoplasm to ECM

Question 61

Differ Ion channels and GAP junctions synthesis:

Answer 61

GAP: synthesized by 2 different cells Ion:

Question 62

Differ Ion channels and GAP junctions duration of acticity:

Answer 62

GAP: remain open for sec to min Ion: open for only msec

Question 63

Water channels

Answer 63

Aquaporins

Question 64

Increase rate of water flow across membranes Found in RBC, kidney, cornea 24 kDa protein Have 6 transmembrane alpha helical domains

Answer 64

Aquaporins

Question 65

Structure of aquaporins

Answer 65

6 transmembrane alpha helical domains