Lecture 2 bio: Membranes

Question 1

So how do transmembrane proteins help the membrane?

Answer 1

The transmembrane proteins form a protein-lined path across the membrane which helps to transport polar and charged molecules.

Question 1

What substances does artificial membrane or liposome is permeable to and not permeable to?

Answer 1

Liposomes are most permeable to small uncharged polar molecules (water, ethanol and glycerol), and small non-polar molecules (O2, CO2, N2 steroid hormones)

Liposomes are not permeable to larger uncharged polar molcules such as amino acids, glucose and nucleosides and also impermeable to Ions such as H+, K+ etc.

Question 2

What are the two main classes of transport proteins?

Answer 2

Channel and Transport proteins

Question 3

What are the characteristics of channel proteins?

Answer 3

Binds loosely to the transported molecule and does not undergo conformational changes.

These are selective to charge and size of the molecules

Question 4

What are characteristics of transporter proteins?

Answer 4

They bind strongly to the transported molecule and undergo conformational changes

These are selective whether the solute fits the binding site or not

Question 5

What are the two types of transporter proteins?

Answer 5

A pump and a normal carrier protein

Question 6

What are the two types of transports possible?

Answer 6

1. Passive Transport: Does not require direct energy and the solute goes down/ along the energy gradient
2. Active Transport: Requires direct energy and the solute goes against the energy gradient Like a pump protein which is also a transporter protein

Question 7

What two add up to give the electrochemical gradient?

Answer 7

conc gradient + membrane potential = Electrochemical gradient

Question 8

What is membrane potential?

Answer 8

It is the difference in charge from the outside of the membrane compared to the inside of the membrane.

Question 9

What is an example of channel protein?

Answer 9

Ion channels

Question 10

What are the types of ion channels?

Answer 10

Non-gated Ion channels like K+ leak channel
- always open and help to generate the resting membrane potential in the plasma membrane of animal cells.

Ion gated: These need some signal for channel opening and only specific ions are transported.

Question 11

What are the four types of gated ion channels?

Answer 11

1. Mechanically-gated: need mechanical signal to open (like stretch receptors or hearing)
2. Ligand Gated (extracellular ligand): signal is neurotransmitter or nutrients
3. Ligand Gated (intracellular): Signal is ions or nucleotides
4. Voltage-gated : Signal is change in voltage membrane

Question 12

What is an example of passive transporter protein?

Answer 12

GLUT Uniporter:

Question 13

What are ways solute can be transported in transporter proteins in passive transport?

Answer 13

1. Uniport: Only one solute at a time and always goes down the electrochemical gradient. However the direction can be reversible. Like GLUT uniporter

Question 14

What are ways solutes can be transported via active transport using transporter proteins?

Answer 14

1. Gradient driven: One solute goes down the energy gradient and releases energy for the other molecule to move up the energy gradient
2. ATPases: ATP driven pump, it hydrolyses ATP and moves the solute against its energy gradient
3. Light driven pump (bacteria): Uses light energy to move solute against its gradient

Question 15

Is ATP always needed in active transport?

Answer 15

No, recall that only ATPases uses ATP to transport the solute aganist the electrochemical gradient.

Question 16

What are the two movements taking place in gradient-driven pumps which are transporter proteins used in active transport.

Answer 16

Symport: Both the solutes move in the same direction (one is facing electrochemical gradient and the other is against it)

Anti-port: One solute is pumped in while the other solute is pumped out.

Question 17

What are the steps for Na/Glu pump? for symport?

Answer 17

Functioning of the Na+-Glucose symport (transporter protein in active transport):

Occluded closed: Both the binding sites are closed
Outward Open: Glucose binds and also sodium binds
Occluded occupied: Both glucose and sodium are in
Inward Open: Both glucose and sodium are in the cell
Occluded closed: Nothing in the binding site.

Question 18

Can the symport oscillate between conformational changes?

Answer 18

yes, however both na+ and glucose have to be in cooperative binding.

Question 19

In which direction do na and glucose move in symport in terms of their electrochemical gradients?

Answer 19

Na moves towards its electrochemical gradient, and glucose moves against its electrochemical gradient.

Question 20

What is an example of an antiport in transporter protein in active transport?

Answer 20

Na + — H+ exchanger.

na moves towards its electron gradient while H moves out of its electrochemical gradient

Question 21

Why is H pumped against its electrochemical gradient in Na-H exchanger ?

Answer 21

Cytosolic Ph needs to be regulated for optimal enzyme function (about 7.2)

but excess H+ occurs in the cytosol from acid forming reactions, leaks out of lysosomes (making ph 5)

So the transporters maintain cytosolic pH.

Question 22

Under what conditions does the transporter protein’s activity increase? in Na+ - H exchanger

Answer 22

When the environment becomes more acidic, the activity increases.

Question 23

What is the role of Na+/K+ pump?

Answer 23

It helps to push the sodium out of the cell to use that sodium as solute in the Na+-glucose symport and Na+- H exchanger.

This pump is a plasma membrane ATP-driven pump.

Question 24

What are the 3 types of ATP driven pumps?

Answer 24

1) P-type pumps
2) V-type pumps
3) ABC transporter

Question 25

What is an example of P type pump and how can you recognise P type pumps?

Answer 25

Flippase is an example of P-type pump as it transports phospholipids. Or even sodium potassium pumps, in whwich they both are moved against their gradients. 3Na move out and 2 K move in

You can remember this using the acronym - it Pees itself.

It phosphorylates itself. and uses ATP. May P-type pumps transport IONS.

Question 26

Why are P-type pumps generally used?

Answer 26

they function in generating and maintaining electrochemical gradients

Question 27

How many ATP’s does ABC pump use?

Answer 27

2, and this pumps out toxins

Question 28

What is the role of V-type pumps?

Answer 28

They use ATP to pump H+ into lumen to make it acidifying.

Question 29

V-Type pump vs F-Type ATP synthase

Answer 29

V-types uses atp and makes adp and p and uses that energy to push H against its electron gradient

F type ATP syntahse uses H and makes ATP.

Question 30

Which side does apical domain face on an epithelial cell?

Answer 30

It faces the gut lumen, faces out

Question 31

Which side does lateral domain face on an epithelial cell?

Answer 31

It faces the plasma membrane of other cells

Question 32

Which side does basil lamina domain face on an epithelial cell?

Answer 32

It faces the extra cellular fluid.

Question 33

What is the role of tight junctions?

Answer 33

They stop things from flowing laterally into other cells. And they also restrict proteins from coming in.

Question 34

How does glucose flow gut to the blood stream?

Answer 34

the gut lining has epithelium cells which together form the villis.

Now the top of the cell called apical domain face the gut lumen and the lteral domian faces other cells while the basil lamina faces the extra cellular matrix or the blood stram.

Now glucose is really low in the gut, so it uses a sodium-glucose pump and pumps the stuff into the cytosol. Now the high conc of glucose in the cytosol leads to using the GLUT-uniporter via passive transport into the blood stream.

Question 35

What type of pump does plant cell use?

Answer 35

Its a P-type pump, and it pumps out h+ and generates H+ electrochemical gradient. it carries out active transport, electrical signaling and regulates the pH.