biol213 exam 2

Diffusion of molecules across a synthetic lipid bilayer is dependent on

their size and solubility

Charged molecules

rarely diffuse across a bilayer no matter how small they are

Small nonpolar molecules

diffuse easily

Small uncharged polar molecules

diffuse half the time

Large uncharged polar molecules

do not diffuse easily

Ions

cannot diffuse across the bilayer

Small nonpolar molecules include

O2, CO2, N2, steroids, hormones

Small uncharged polar molecules include

H2O, ethanol, glycerol

Larged uncharged polar molecules include

amino acids, glucose, nucleosides

Ions include

H+, Na+, K+, Cl-, HCO3-

Membrane transport proteins are responsible for

selective transfer of soluble molecules across the membrane

Na+ concentration inside and outside cell

5-15mM in cell and 145mM outside

K+ concentration inside and outside cell

140mM in and 5mM out

Ca2+ concentration inside and outside cell

10⁻⁴mM inside and 1-2mM outside

Cl- concentration inside and outside cell

5-15mM inside and 110mM outside

Simple diffusion

movement of molecules from high to low concentration, downhill movement

Membrane transport proteins are classified by

their mechanisms of selectivity

Mechanisms of selectivity

carrier proteins, channels, transport energetics

Carrier proteins are

transporters

Transport energies can be

passive or active

Transporters work by

binding specific molecules and ungeroing physical shape changes to shift molecules across the membrane

Channels are

like gates that let specific ions go through without changing their shape

Channels are ____ than transporters

faster

Passive transport

aka facilitated diffusion, move things down their concentration gradient

Channels and transporters are ____ transport

passive

Simple diffusion

just passing through the membrane

facilitated diffusion is ____ than simple diffusion

faster

Active transport

moving up the concentration gradient by using an input of energy

Uniport

moves in either direction depending on gradient, reversible, is not coupled to other substances

Symport

moves two molecules in the same direction

Antiport

moves two molecules in opposite directions

Membrane potential

voltage across the cell membrane that exerts force on charged molecules

The driving force for membrane potential is the

electrochemical gradient

The electrochemical gradient has two components

concentration difference (chemical) and charge difference (electrical)

Animal cells typically have a ____ charge along the inner membrane and ____ charge along the outer membrane

negative, positive

Membrane potential is about ___mV

60

ATP driven pump

Na-K pump uses ATP hydrolysis to drive Na+ out and let K+ in and moving against their concentration gradients

ATP driven pumps contribute to membrane potential T/F

T

How the Na-K pump works

Na+ binds to the pump from inside the cell, it consumes ATP and the phosphorylation changes the shape of the binding site and pushes Na+ out of the cell. K+ can bind to this new binding site, which causes dephosphorylation, and changes the binding site back and pushes K+ into the cytosol, Na+ can now bind again

The Na-K pump brings in _ K+ and out _ Na+

2, 3

Coupled transporters include

symport and antiport

Na-Glucose symport

Na+ gradient is generated by the Na-K pump, this energy source drives the transport of many coupled solutes, like glucose and Na+, glucose is able to go up its concentration gradient paired to Na+ which is going down

Ion channels can be

selective, gated, and passive

Ion channels have ___ transport rates compared to carriers

higher

Open and closing of an ion channel is caused by

stimulus from a charge or messenger

Voltage gated channels

controlled by changes in charge across the membrane

Ligand gated channels

controlled by the binding of a substrate/messenger

Stress gated channels

controlled by physical forces pushing open and closed

Patch clamp

they took a piece of membrane off with some transporters on it, they put it in water and showed that when electricity was added the channels opened and water could flow through, it showed that electrical current was passing through the membrane channels

Defects in ___ can be cause of inherited diseases like migraines and myasthenia gravis

ion channels

Exact balance of charges on either side of the membrane means potential is

0

K+ leak channels help _____ membrane potential

maintain

The Na-K pump establishse a high concentration of ___ inside the cell

K+

In a resting cell the K+ leak channels are ____ and K+ moves ___ its gradient ____ the cell

open, down, outside

As K+ leaves the cell it leaves behind a ____ charge

negative

Neurons are

nerve cell structural components

Neurons are made of

dendrites and axons

Signals are received at the ___ of the neuron

cell body

Signals are transmitted across ____ to the ____

the axons, nerve terminals

At the nerve terminals there are ____ and signals are ____

terminal branches, released

A stimulus causes a ____

localized membrane depolarization

Resting membrane potential is

-60mV

Membrane polarized is

-60mV

The increase in membrane potential is ____

depolarization

Na+ channels are open at

-40mV

Threshold potential is

-40mV

Membrane potential reaches ___ when it is fully depolarized

+40mV

Depolarization is

when membrane potential is negative and changes towards positive

mV =

voltage inside-voltage outside

Once the membrane is fully depolarized Na+ channels are

inactivated

Once the cell reaches -60mV Na+ channels are

closed

To get the cell back to -60mV ___ open

K+ leak channels

Action potential moves

forward down the axon

Neurons in vertebrates have

a myelin sheath that allows faster propagation of action potentials

When action potential reaches the end of the axon

a signal is communicated at the nerve terminal

Synaptic cleft

the separation between target cells and the nerve terminal, about 20nm

A ___ signal is converted into a ___ signal by ___ gated channels

chemical, electrical, transmitter

The neurotransmitters attach to the receptor and

that opens the channels and ions enter the cell

The ions entering the cell from the neurotransmitter changes membrane potential which is a ____ signal

electrical

Action potential activates voltage gated ___ channels in the nerve terminal to allow synaptic vesicles to exit

Ca2+

Excitatory neurotransmitters ____ an action potential

initiate

Inhibitory neurotransmitters _____ an action potential

inhibit

Excitatory neurotransmitters cause an influx of ___ to ____ the membrane

Na+, depolarize

Inhibitory neurotransmitters cause an influx of ___ to ___ the membrane

Cl-, polarize

Excitatory neurotransmitters ____ the likelihood of firing an action potenial

increase

Inhibitory neurotransmitters ____ the likelihood of firing an action potenial

decrease

Excitatory neurotransmitters are located in the

dendrites

Inhibitory neurotransmitters are located in the

cell body near axon hillock

Hyperpolarizing means the cell is more ____ than its resting potential so it is ____

negative, far less likely to far an action potential

Acetylcholine and glutamate

Excitatory neurotransmitters

GABA and glycine

inhibitory neurotransmitters

When acetylcholine activates

Na+ channels open and depolarize the membrane, then calcium can come in and in the muscle this causes a muscle contraction

Neurotransmitters gated ion channels make the ____ run in your brain

nervous system

Tranquilizers

bind to GABA Cl- channels and make them easier to open to hyperpolize the cell and make it harder for it to activate

Antidepressants

block reuptake of serotonin so less can be used and prolong the response to it

Dendrites have ___ of synapses/neurons making for ____ of spots for contacts

thousands, trillions

Gylcolysis happens in the ____

cytoplasm

Gylocylsis net yields ___ per glucose molecule

2 ATP, 2 NADH

First step of glycolysis

hexokinase is used to add a phosphate to glucose to make it G6P, which traps it in the cycle

Second step of glycolysis

G6P is turned to fructose-6P, the carbonyl group is shifted