Membrane Proteins

Question 1

What hold integral membrane proteins within the phospholipid bilayer?

Answer 1

Regions of hydrophobic R groups allow for strong interactions

Question 2

What do integral membrane protein’s interact with?

Answer 2

Interact extensively with the hydrophobic region of the membrane phospholipids

Question 3

What are peripheral membrane proteins?

Answer 3

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.

Question 4

What molecules can pass through the phospholipid bilayer by simple diffusion?

Answer 4

Small molecules such as oxygen and carbon dioxide

Question 5

What is facilitated diffusion?

Answer 5

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

Question 6

What are most channel proteins in animal and plant cells?

Answer 6

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

Question 7

Why are some membrane channel proteins gated and change conformation?

Answer 7

To allow or prevent diffusion

Question 8

What controls Ligand- gated channels?

Answer 8

By the binding of signal molecules

Question 9

What are voltage gated channels controlled by?

Answer 9

By changes in ion concentration.

Question 10

What is the function of a transporter protein?

Answer 10

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

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 11

What does active transport use to to transport molecules across the bilayer?

Answer 11

Uses pump proteins that transfer substances across the membrane against their concentration gradient.

Pumps that meditate active transport are transporter proteins coupled with an energy source.

Question 12

What is required for active transport?

Answer 12

A source of Metabolic energy

Question 13

What do some active transport proteins do to provide the the energy for the conformational change required to move substances across the membrane?

Answer 13

Some active transport proteins hydrolyze ATP directly to provide the energy required.

Question 14

What hydrolyze ATP?

Answer 14

ATPases

Question 15

When is a membrane potential ( an electrical potential difference) created?

Answer 15

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

Question 16

What do ion pumps such as the sodium potassium pump use to establish and maintain ion gradients?

Answer 16

The energy from the hydrolysis of ATP

Question 17

What does the sodium potassium pump transport in and out of the cell?

Answer 17

Sodium ions out of the cell and potassium ions into the cell

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

Question 18

Explain what happens with sodium ions and the sodium potassium pump

Answer 18

• The pump has a high affinity for sodium ions inside the cell; binding of three sodium ions to the binding sites stimulates ATP to phosphorylate the transport protein.
  Addition of negative phosphate causes a conformational change in the shape of the protein.
  The opening changes to the extracellular side of the plasma membrane.
  Affinity for Na is reduced and Na ions are released to outside of the cell two potassium binding sites form.

Question 19

What does the sodium potassium pump establish?

Answer 19

Both a sodium ion concentration gradient and a electrical gradient

Question 20

Explain what the process of potassium binding to the sodium potassium pump.

Answer 20

K ions from the extracellular fluid, move towards and bind with the binding sites.
Binding sites fill with potassium ions (2).
Filling of the binding sites causes release of the phosphate.
Loss of phosphate changes conformation of proteins, it now opens on the cytosolic side of the plasma membrane. Affinity for k ions is lost.
Potassium ions are released into the cell.
Shape and affinity for Na ions returns to the start.