Chapter 12Transport Across Cell Membrane

Whats the difference between lipid bilayer vs cell membrane

Cell membrane have channels/transporters that span the membrane to regulate passage

What can permeate through (most to least permeable and end with non permeable)

Small nonpolar molecules (steroids, hormones)
Small uncharged polar molecules (Ethanol, glycerol)
large uncharged polar molecules (glucose, amino acids)

Ions

How does a cell membrane move things in and out of cell

a channel, and a transporter

What is a channel

Selective channel that may open and close

What is a transporter and how does it work

One side is open and the other side is close the protein changes conformation to allow solutes to move

Channels can only be ___

passive

Transporters can be ___ and ___

passive and active

Simple diffusion is only_____

passive

Do passive transport need energy

no, its’ provided by the concentration gradient

What is aquaporins

a channel that allows H2O to move along it’s graident

What’s the orientation of aquaporins

4 protein channels that go near each other

Do organelles have their own channel/transporters

Yes!

Whats cool about transporters

Transporters go through an equalibrium where they can spit the molecule back out for where it came from

How does a transporter regonize it’s specific molecule

H-bonding/ionic bonding

The site the molecule of a transporter binds to is called

binding site

What causes transporter to go through conformational change

molecule binding

What’s the voltage gradient of a cell

more negative inside then outside

What is a voltage graident

a separation of charge

K+ is found more

inside

Na+ is found more

10 times higher outside

Most negative ions/molecules are found inside the cell except

Cl-

What is electrochemical graident

where chemicals wants to flow towards it’s opposite charge

What is very cool about electrochemical gradient

when things move down it’s electrochemical gradient it can power unfavorable things

What are the 3 different types of transporters

symport, antiport, and uniport

What is unique about symport and antiport

the transport molecule moves down it’s chemical gradient and allows co/anti-transport ion to move against chemical gradient

What is symport

When transport molecule and co-transport ion move in the same direction

What is anti-port

When transport molecule and anti-transport ion move in opposite direction

What is uniport

When one thing is moved along it’s concentration gradient

What are the 3 ways a transporter can be energized

gradient pump, atp pump, light pump, electrochemical gradient

Na/K atpase is

a pump that pumps 3 Na+ out for 2K+ in via ATP

(pushes these ions against concentration gradient)

How does Na/K ATPase work

It has a kinase domain to turn ATP→ ATP and phosphorylate a domain of the pump

Give me the detailed mechanism of Na/K ATPase

3 Na binds to pump, then the pump phosphorylates it self

3 Na is ejected and the 2K+ binds

Phosphate leaves and K+ is spit out

Where are the ‘tails’ of the Na/K ATPase that hydrolysizes ATP

cytosol

Why isn’t that Na+ or K+ cant rebind to the pump once it’s spit out

theres a conformational change that only picks up the opposite molecule

How does Ca+2 ATP pump work

2 calcium binds to transporter, aspartic acid found within the transporter holds onto phosphate and now there’s conformational change where it can’t bind to Ca+

Are symports and anti-symports reversable

yes

What is the formation of an ion channel

a channel entrance has a vestibule which gets rids of water molecule that surrounds an ion after that then there is the selective filter

How does the vestibule work

it has specific amino acids it that pulls away water

What is something that constantly setups up a concentration gradient/electrostatic gradient

K+ Leak channel

How does K+ leak channel work

it pushes K+ one way, which is down concentration gradient so there is less positive charge within the cell

When does K+ leak stop

when there is a balance between concentration gradient and electrostatic gradient because when K+ leaves it creates - charge that it’s attracted to

When the K+ leak channel close whats it membrane potential

0

What are the 4 types of ion channels

mechanically gated channels, ligan-gated channels (intracellular and extracellular), and voltage gated channel

What’s the difference between ligan-gated extracellular vs intracellular

where ligands bind

When a ligan bond what happens to do channel

increases probability of channels opening

What’s found in cell body of a neuron

organelles and normal thing we expect a cell to have

What technique is used to observe a channel

patch clamp

How does patch clamp work

a small pipette pricks a channel from a cell and then you put a metal wire in the same median to measure current

True or false there is a max current of a channel, in which channels only run at max current

True

Does a ligand in solution makes a channel stay open

no, it increases probability of channel opening

What is the resting membrane potential of a neuron

-60 mv

What is the threshold value of action potential

-40 mV

What is peak depolarization value

+40 mV

How does an action potential work

Na+ are open which depolarizes the surrounding area and open more Na+ channels now membrane is more positive

K+ then opens after a little delay to make K+ leave and make cell more negative

How does Na+ channel work

1) During resting potential the gate is closed,
2) during action potential the sodium gate opens,
3)voltage sensory domain twist to have an open channel with a ball stock in the pore channel to maintain a charge balance and block Na
4) repolarization goes back to original conformation

Whats cool about K+ channel

they restore the resting potential, Na+ and K+ are supposed to open at the same time but K+ has a delayed response

What is open longer K+ or Na+

K+

What opens first actually

Na+

What does PET scan measuer

glucose consumption

What causes synaptic vesicle to fuse to membrane

Ca+2