Transport of solutes across membrane

Question 1

What are the ways which molecules can get into a cell? How do they work?

Answer 1

Non-mediated transport: does not directly use a transport protein
Mediated transport: use a transport protein
Passive transport: moves substance down their concentration gradient with only their kinetic energy
Active transport: uses energy to drive substance against their concentration or electrochemical gradients
Vesicular transport: move material across membranes in small vesicles by exo or endocytosis

Question 2

Are passive and active transport mediated or non-mediated?

Answer 2

Passive can be either but active must be mediated

Question 3

What is non-mediated transport important for? What kind of molecules are these? What is needed to move these substance across the membrane?

Answer 3

Important for absorption of nutrient and excretion of waste
Non-polar and hydrophobic molecules
A concentration gradient

Question 4

What are ion channels? What do they do?

Answer 4

Water filled pores that span the hydrophobic core of the lipid bilayer and allow passage of ions and small molecules across membrane

Question 5

What governs the direction which molecules flow in ion channels?

Answer 5

Diffusion

Question 6

How do the molecules moving through the ion channel interact with it? What does this result in?

Answer 6

They don't, they just pass through it
Rapid transport (1million ions/sec)

Question 7

Do all channels allow all types of molecules through it? How does this work?

Answer 7

No, specific amino acids line the inside of the pore and determine the selectivity of the channel to ions

Question 8

What does begin selective to particular molecules allow the channel to do?

Answer 8

Harness the energy stored in the different ion gradients

Question 9

How are ion channels defined?

Answer 9

By the type of ion that can flow through it

Question 10

What are on most ion channels to control ion flow?

Answer 10

Gates

Question 11

What do these gates on ion channels prevent?

Answer 11

Prevents the concentration gradient being removed as the particles diffuse across freely

Question 12

What is used to close the ion channel?

Answer 12

Ball and chain

Question 13

What control the ball and chain on the ion channel?

Answer 13

Change in voltage, ligand binding, cell volume (e.g. stretching, pH, phosphorylation, hormone, peptide

Question 14

When ions diffuse through a channel what does it create?

Answer 14

Creates a measurable current of 10-12 amp (pico amp)

Question 15

How can the current of an ion channel be measured?

Answer 15

By the patch clamp technique where a glass pipette that is fire blasted is used to isolate a single ion channel and measure its current

Question 16

What do the current fluctuations of the ion channel represent?

Answer 16

The opening and closing of the ball and chain

Question 17

What do carrier mediated transporters do? How do they do it?

Answer 17

Help mediate individual proteins across membrane
Proteins that control the movement of substances by opening a gate to one side of the membrane, closing then opening to the other side

Question 18

How does the rate of molecules transport compare with carrier mediated and ion channels?

Answer 18

Carrier mediated transporters are slower because they undergo a conformational change for each molecule, ion channels just open up

Question 19

What properties do carrier mediated transporters exhibit?

Answer 19

Show specificity, inhibition, competition, saturation (maximum rate of flow)

Question 20

What other type of molecules do carrier mediated transporter share properties with? What characteristic is shared?

Answer 20

Properties similar to enzymes
Speeds up the rate compared to without it (in this case it is transporting faster than just by diffusion)
Specificity, inhibition, competition, saturation

Question 21

What is and how does the specificity of carrier proteins affect its behaviour?

Answer 21

Specific for the molecule to be transported
They have a very specific class of molecules that can be transported

Question 22

What type, what is and how does the inhibition of carrier proteins affect its behaviour?

Answer 22

Competitive
An inhibitor is able to bind to the active site of the carrier protein preventing its target molecule to be transported
This reduces the movement of molecules via these channels

Question 23

What is and how does saturation of carrier proteins affect its behaviour? How does this compare to ion channel?

Answer 23

It is when the rate of molecule transport is maximum due to all the carrier proteins bonding with target molecules
Sets a maximum speed which molecules can be transported into the cell
Ion channels are wholly dependent on concentration so a higher concentration results in faster ion movement (no max speed)

Question 24

How do carrier mediated transport proteins different from enzymes?

Answer 24

They do not catalyse chemical reactions

Question 25

Is carrier mediated transport proteins passive or active? Explain what this means for the speed which it occurs and why these are the relative speeds

Answer 25

Can be both
Facilitated means that it will occur faster than what would normally occur (due to energy input) if it was just passive which only operates due to its concentration gradient

Question 26

Give an example of passive carrier mediated transport using glucose, how does this work by concentration gradient only?

Answer 26

Glucose binds to transport protein GLUT which moves into cell membrane by concentration gradient as glucose in the cell is converted into glucose - 6 - phosphate therefore always a lower conc of glucose inside cell that blood

Question 27

How is glucose concentration within the cell reduced?

Answer 27

Kinase enzymes phosphorylate glucose into glucose - 6 - phosphate

Question 28

What is the correct terminology for how glucose is transported and the direction across the plasma membrane?

Answer 28

It is a passive carrier mediated transport with the concentration gradient

Question 29

What is the correct terminology for how Na+ is transported and the direction across the plasma membrane?

Answer 29

It is transported with its electrochemical gradient through an ion channel

Question 30

Is glucose transported with its electrochemical gradient? Why/Why not?

Answer 30

No

It is not charged so cell voltage does not affect it

Question 31

What is active transport? What does it achieve?

Answer 31

A process that moves molecules and ions against their concentration or electrochemical gradients

Question 32

What are the two methods of active transport?

Answer 32

Primary active transport

Secondary active transport

Question 33

How does primary active transport work?

Answer 33

Energy is derived from the hydrolysis of ATP and causes conformational changes of enzymes

Question 34

What is an example of a primary active transporter? What does it transport? What does it do?
What is it important for?

Answer 34

Na/K pump
Pumps 2K+ in for every 3 Na+ pumped out
Generates a net current and is electrogenic (generates a voltage)
This is important for: maintenance of resting membrane potential (V), electrical excitability (basis of neural activity), contraction of muscle (influx of Ca FYI), maintenance of steady state cell volume, uptake of nutrients via secondary act transporters, maintenance of intracellular pH

Question 35

How does the hydrolysis of ATP create a conformational change in the Na/P pump?

Answer 35

A phosphorus molecules is cleaved off the ATP which then attached to the pump, P is highly negative which causes molecule to change shape

Question 36

How are ion pumps able to maintain a concentration difference against the concentration gradient?

Answer 36

These ions are unable to move through the cell membrane unless there is a membrane channel

Question 37

Are the ion pumps a fast process? Why/why not?

Answer 37

No
There are a lot of steps which must be done sequentially (e.g. ions go into channel, phosphorous bonds, confirmation change, ions detach etc.)

Question 38

Is the Na/K pump action continuously? Why/why not? What is this called? How much of a cells energy is used to maintain this?

Answer 38

Yes
Na and K are continually leaking back into/out of the cell down their concentration gradients
Pump - leak hypothesis
30%

Question 39

Where does secondary active transport directly gets its energy from?

Answer 39

From the energy stored in ion gradients created by primary transporters

Question 40

What is the main concentration gradient used to power secondary transporter? Why?

Answer 40

Na+ concentration gradient
More energy is stored than in a K+ for example because the concentration and electrical gradient is acting downwards into the cell (high conc outside cell and (-) charge inside cell attracts positive ion)

Question 41

What are the two types of secondary active transporters?

Answer 41

Anti-porter/exchangers and symporters/co-transporters

Question 42

How do anti-porters/exchangers work

Answer 42

Na+ flows with its electrochemical gradient (passive) which then pushes another ion out against its electrochemical/concentration gradient (e.g. Ca2+, H+ etc.)

Question 43

How do symporter/co-transporters work?

Answer 43

Na+ rush into the cell with its electrochemical gradient helping other molecules move against their electrochemical/concentration gradient (e.g. glucose, amino acids etc.)

Question 44

What is the process of water diffusion called? How are concentration gradients set up in aqueous solutions?

Answer 44

Osmosis

Between semi-permeable membranes

Question 45

What makes cell membranes semi-permeable?

Answer 45

Water can freely flow through cell membrane but ions cannot

Question 46

How can water move through a cell membrane? How does most of the water move in/out of a cell?

Answer 46

Either directly through bilayer or through water channels called aquaporins
Most water moves in/out through aquaporins

Question 47

What are the properties of water movement through the lipid bilayer?

Answer 47

It is small (not much movement), it is mercury insensitive and temperatures dependent (higher membrane fluidity= more water movement)

Question 48

What are the properties of water movement through aquaporins?

Answer 48

Large water movement, it is mercury sensitive (indicates that it is a protein channel FYI) and is temperature independent

Question 49

How many iso forms of aquaporins are there? How do these affect membrane permeability to water in different cells?

Answer 49

9 iso forms

Different iso forms have different iso forms on them and the different iso form have different fluidity properties

Question 50

If you don’t want water movement into/out of a cell how can you affect it?

Answer 50

Remove the aquaporins