Membrane Proteins

Question 1

What are integral membrane proteins ?

Answer 1

They are proteins found in the cell membrane within the phospholipid bilayer.

Question 2

What allow these integral proteins to hold to the phospholipid bilayer ?

Answer 2

Regions of hydrophobic R groups allow strong hydrophobic interactions that hold the proteins within the phospholipid bilayer , integral proteins interact extensively with the hydrophobic regions of the membrane phospholipids.

Question 3

What are some integral proteins ?

Answer 3

Transmembrane proteins

Question 4

What are peripheral membrane proteins ?

Answer 4

They are proteins which are found on the the surface of the membranes.

Question 5

How are peripheral membrane proteins bond there ?

Answer 5

Peripheral membrane proteins have hydrophilic R groups on their surface and are bound to he surface of membranes mainly by ionic and hydrogen bond interactions .

Question 6

What do they bind to ?

Answer 6

Many peripheral membrane proteins interact with the surfaces of integral memberane proteins .

Question 7

What is the phospholipid bilayer?

Answer 7

It is a barrier to ions and most uncharged polar molecules

Question 8

What can pass the phospholipid bilayer and how ?

Answer 8

Some small molecules such as oxygen and c02 can pass the bilayer by diffusion.

Question 9

What is facilitated diffusion?

Answer 9

Is the passive transport of substances across the membrane through specific transmembrane proteins

Question 10

How do they preform specific functions ?

Answer 10

To perform specialised functions, different cell types have different channel and transporter proteins

Question 11

How selective are channel proteins?

Answer 11

They are highly selective.

Question 12

What are channels ?

Answer 12

Channels are multi-subunit proteins with the subunits arranged to form water-filled pores that extend across the membrane. They are highly selective

Question 13

What can some channel proteins do ?

Answer 13

Some channel proteins are gated and change confirmation to allow of prevent diffusion

Question 14

What are ligand gated channels ?

Answer 14

Ligand-gated channels are controlled by the binding of signal molecules, when a molecule binds a gate opens and ions are allowed to flow through. and voltage- gated channels are controlled by changes in ion concentration

Question 15

What are transporter proteins ?

Answer 15

They bind to the specific substance to be transported and undergo a confirmational change to transfer the solute across the membrane.

Question 16

Why do transporters alternate between 2 conformations ?

Answer 16

So that the binding sight for a solute is sequentially exposed on one side of the bilayer , then on the other

Question 17

What are protein pumps ?

Answer 17

Active transport uses proteins that transfers substances across the membrane against their concentration gradient. Pumps mediate active transport are transporter proteins

Question 18

What is required for active transport ?

Answer 18

A source of metabolic energy

Question 19

What do some transport proteins hydrolyse ?

Answer 19

ATP . this directly provides the energy for the conformational change required to move the substances across the membrane.

Question 20

What hydrolyses ATP

Answer 20

ATPases

Question 21

What is an ion gradient and how is it come by ?

Answer 21

For a solute carrying a net charge , the concentration gradient and electrical potential difference combine to form The electrochemical gradient that determines the transport of the solute

Question 22

What are ion pumps ?

Answer 22

Examples - sodium potassium pump

They use energy from hydrolysis of atp to establish and maintain ion gradients.

Question 23

How are membrane potentials made ?

Answer 23

When there is a difference in electrical charge and the two sides of the membrane

Question 24

What does the sodium potassium pump do ?

Answer 24

They transport ions against the concentration gradient using energy from hydrolysis

It actively transports 3 sodium’s out and 2 potassium in, This establishes both concentration gradients and an electrical gradient.

Question 25

The process of the sodium potassium pump.

Answer 25

The pump has high affinity for sodium ions inside the cell; binding occurs; phosphorylation by ATP; conformation changes; affinity for sodium ions decreases; sodium ions released outside of the cell; potassium ions bind outside the cell; dephosphorylation; conformation changes; potassium ions taken into cell; affinity returns to start

Question 26

What do sodium potassium pumps account for .

Answer 26

The sodium potassium pump is found in most animal cells and it accounts for m the basal metabolic rate in many organisms

Question 27

What happens in the small intestine

Answer 27

In the small intestine, the sodium gradient created by the sodium-potassium pump drives the active transport of glucose

In intestinal epithelial cells the sodium- potassium pump generates a sodium ion gradient across the plasma membrane.

Question 28

What is a glucose transporter responsible for in the small intestine?

Answer 28

Active transport of glucose (glucose symport ), this transports sodium ions and glucose at the same time in the same direction

Answer 29

Sodium goes down a gradient and simultaneous transport of glucose pumps glucose in against its concentration gradient .