Unit 1: Membrane Proteins

Question 1

What type of molecules interact with integral membrane proteins?

Answer 1

Integral membrane proteins interact
extensively with the hydrophobic region of
membrane phospholipids.

Question 2

What type of R groups do peripheral membrane proteins have and where are they located?

Answer 2

Peripheral membrane proteins have
hydrophilic R groups on their surface and are
bound to the surface of membranes, mainly
by ionic and hydrogen bond interactions
Many peripheral membrane proteins interact
with the surfaces of integral membrane
proteins

Question 3

What is facilitated diffusion?

Answer 3

Facilitated diffusion is the passive transport
of substances across the membrane through
specific transmembrane proteins

Question 4

What does the phospholipid bilayer act as a barrier towards?

Answer 4

The phospholipid bilayer is a barrier to ions
and most uncharged polar molecules

Question 5

What molecules can pass through the phospholipid bilayer?

Answer 5

Some small molecules, such as oxygen and
carbon dioxide, pass through the bilayer by
simple diffusion

Question 6

What is the function of transporter proteins?

Answer 6

Transporter proteins bind to the specific
substance to be transported and undergo a
conformational change to transfer the solute
across the membrane

Question 7

How is the binding site made available on each side of the bilayer by transporter proteins?

Answer 7

Transporters alternate between two
conformations so that the binding site for a
solute is sequentially exposed on one side of
the bilayer, then the other.

Question 8

what type of proteins does active transport use?

Answer 8

Active transport uses PUMP PROTEINS that
transfer substances across the membrane
against their concentration gradient
Pumps that mediate active transport are
transporter proteins coupled to an energy
source.

Question 9

What type of proteins use facilitated diffusion?

Answer 9

Channel proteins and transporter proteins.

Question 10

What are channel proteins?

Answer 10

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

Question 11

How selective are channel proteins?

Answer 11

Most channels are highly selective

Question 12

What types of gated channels are there?

Answer 12

Voltage gated
Ligand gated
Transporter proteins (passive)
Protein Pumps (active process)

Question 13

How do ligand gated channels work?

Answer 13

Ligand-gated channels are controlled by the
binding of signal molecules. When the correct signal molecule binds, the gate opens and allows ions to flow through

Question 14

How do voltage gated channels work?

Answer 14

Voltage-gated channels are controlled by changes in
ion concentration

Question 15

Describe a membrane potential

Answer 15

A membrane potential (an electrical potential
difference) is created when there is a
difference in electrical charge on the two
sides of the membrane.

Question 16

What is an example of an ion pump?

Answer 16

Sodium-potassium pump

Question 17

Describe the direction of sodium ions and potassium ions in the pump?

Answer 17

The pump actively transports sodium ions out of the
cell and potassium ions into the cell

Question 18

How does the sodium potassium pump source its energy?

Answer 18

The sodium-potassium pump transports ions
against a steep concentration gradient using
energy directly from ATP hydrolysis

Question 19

Describe the process of the sodium potassium pump?

Answer 19

1. Pump has a high affinity for sodium ions within the cell, therefore binding of sodium ions to the pump occurs within the cell.
2. Phosphorylation by ATP occurs, causing a conformational change of the protein
3. Pump loses affinity for sodium ions, causing sodium ions to be released outside of the cell.
4. pump has high affinity for potassium ions outside of the cell, causing binding of potassium ions outside of the cell occurs
5. Dephoshorylation occurs, causing conformational change of the protein
6. Pump loses affinity for potassium ions, causing potassium ions to be released into the cell. Affinity returns to the start

Question 20

Describe the movement of sodium ions and potassium ions in the pump for one ATP that is hydrolysed?

Answer 20

For each ATP hydrolysed, three sodium ions
are transported out of the cell and two
potassium ions are transported into the cell.
This establishes both concentration gradients
and an electrical gradient.

Question 21

What is the name of the protein that is directly responsible for hydrolysing ATP?

Answer 21

ATPases