Membrane Transport Part 2

Question 1

Osmosis is the

Answer 1

Movement of water

Question 2

__ allow water to move more rapidly across the membrane

Answer 2

Water channels (small amounts of water can pass through membrane because small enough but need channel for larger volume)

Question 3

Net water movement is baised on

Answer 3

which has solute
ALWAYS low to high (or hypo to hyper)

Question 4

fluid and electrolyte balance

Answer 4

(electrolytes are Cl Na K)
maintaining flow of fluid

Question 5

hypotonic

Answer 5

low concentration of solute

Question 6

Hypersonic

Answer 6

high concentration of solute

Question 7

Aquaporin is a ____

Answer 7

not an actual porin - is not betta pleated stands
is a water channel (of alfa helices)

Question 8

Aquaporin Allows

Answer 8

rapid passage of water, while blocking passage of ions

Question 9

water movement with aquaporin

Answer 9

water must move in a single file line

Pore is too narrow for hydrated ions to enter
(Na+, K+, Cl-, Ca2+) (interact with water - bulky - fully hydrated)

Question 10

how aquaporin Blocks Hydronium Ion

Answer 10

Hydronium ions (H3O+) diffuse through water fast, relay mechanism requires making and breaking of bonds between adjacent water molecules

polar inner lining (hydrophilic)

two Asparagene ameno acids in center of channel - blocks H from going all the way through/block H bonding relay

Question 11

Net water movement is always

Answer 11

low to high
hyop to hyper

Question 12

hyponatremia

Answer 12

level of Na+ in blood is too low

water rushes into cells and they swell, skull bocks from expanding and they burst

treat by giving electrolytes to offset imbalance

Question 13

Ion chanels

and selectivity

Answer 13

do not have binding sites inside of the chanel
must interact with wall itself

ions must be dehydrates and they energy used to remove can be valced out if favorable interaction with slelectivity filter (if too small, not balance interactions)

Question 14

voltage gated

Answer 14

sences change in voltage and opens/closes

Question 15

ligand gated

Answer 15

interacellular ligand - often ions themselves

extracellular ligand - any molecule that binds to the chanel

(both not going through channel, binds and then confromational change)

Question 16

mechanicaly gated

Answer 16

strssor
ex. streching of lipid bilayer, sound, light etc.

Question 17

gating of ion channels

Answer 17

voltage gated
ligand gated (intra and extracellular)
Mechanically gated

Question 18

charge of neuron membrane

Answer 18

inside is more negatively charged than the outside.

This is largely due to negatively charged proteins inside the cell and greater permeability of membrane to K+ (leaky K+ channels, K+ ions move down gradient out of cell, without simulation).

Question 19

resting membrane potental

Answer 19

Steady voltage difference across the neuron’s plasma membrane

Question 20

Voltage gated Na+Channels

Answer 20

How detects differences of charge across membrane

Tetramer of 4 identical polypeptide chains

Each domain has a voltage sensor (contains unusual transmembrane helix with many positively charged amino acids)- interact with more negatively charged extracllular matrix

Question 21

Na channel activation

Answer 21

Voltage gated Na+ channels open in response to a stimulus

A small amount of Na+ enters cell down its electrochemical gradient.

Influx of positive charge depolarizes membrane further, opens more Na+ channels (self amplification, positive feedback), from -70mV to +40 mV.

At this point, net electrochemical driving force for Na+ is zero, cell would come to new resting state (with all Na+ channels open). - Na chnnel incativation prevents this

Question 22

Na+ Channel Inactivation

Answer 22

VG Na+ Chanels have three conformaitons

inactivated - gate closes - prevents cell from going through spasm - is more energeticly favorable

Question 23

Action ptental

Answer 23

Na chanels closed, gets to threshold, na open, na inactivated
repolarization vg K channels open - during this time Na cannot open
Na closes, hyperpolarazation vg k channels close
vg na k pump restores Na and K gradeitnds (from hyperpolarized)

Question 24

Repolarization

Answer 24

Voltage gated K+ channels open, K+ move out of cell-. Restoration of negative membrane potential is called repolarization.

Efflux of K+ causes an overshoot of resting membrane potential, hyperpolarizing the neuron.

K channels are very slow to close

Question 25

Absolute regractory period

Answer 25

no ammount of simulation can caue anoterh AP

Na channels are inactivated and cannnot open, durring repolarization

Question 26

Relative refractory period

Answer 26

must be a greater than normal stimulation to cause an AP

durring hyperpolarization Na is closed so it can open but need greater stimulation to reach threshold

Question 27

Channelrhodopsins

Answer 27

Photosensitive ion channels: Open in response to light

Can be expressed in almost any cell type: introduced in neurons. When neurons exposed to blue light, channelrhodopsin channels open, depolarizing (Na in) and activating cells

Optogenetic control of aggression in a living mouse

Question 28

Chemical Synapse

Answer 28

When action potential arrives at presynaptic site, depolarization of membrane opens voltage gated Ca2+ channels

Ca2+ influx triggers release of neurotransmitters, which are stored in synaptic vesicles and released by exocytosis

Question 29

Differences between ion channels and aquaporin

Answer 29

1. Ion selectivity
2. ion channels are not conounously open.