Membrane Proteins

Question 1

Integral membrane proteins

Answer 1

Interact extensively with the hydrophobic region of membrane phospholipids, some are transmembrane proteins.

Question 2

Peripheral membrane proteins

Answer 2

Have hydrophilic r groups on their surface and are bound to the surface of membranes, mainly by ionic and hydrogen band interactions. Many interact with the surfaces of integral membrane proteins

Question 3

What holds integral membrane proteins within the phospholipid bilayer?

Answer 3

Regions of hydrophobic r groups allow strong hydrophobic interactions that hold integral membrane proteins within the phospholipid bilayer..

Question 4

What is the phospholipid bilayer a barrier to?

Answer 4

lons and most uncharged polar molecules

Question 5

What can pass through the bilayer by simple diffusion?

Answer 5

Some small molecules, like oxygen and carbon dioxide

Question 6

Facilitated diffusion

Answer 6

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

Question 7

How do cells use channel and transporter proteins to perform specialised functions?

Answer 7

Different cell types have different channel and transporter proteins.

Question 8

Channels

Answer 8

Multi-subunit proteins with the subunits arranged to form water-filled parts that extend across the membrane

Question 9

How do gated channel proteins work?

Answer 9

They change conformation to allow or prevent diffusion

Question 10

Ligand-gated channels

Answer 10

Controlled by the binding of signal molecules

Question 11

Voltage - gated channels

Answer 11

Controlled by changes in i on concentration

Question 12

How do transporter proteins work?

Answer 12

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

Question 13

Active transport

Answer 13

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 14

How is the energy ter active transport produced?

Answer 14

Some active transport proteins hydrolyse ATP directly to provide the energy needed for the conformational change required to more substances across Te membrane, ATPases hydrolyse ATP.

Question 15

What forms the electrochemical gradient?

Answer 15

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

Question 16

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

Answer 16

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

Question 17

What do Ian pumps do?

Answer 17

Ion pumps, such as the sodium potassium pump, use energy from ty hydrolysis of ATP to establish and maintain i on gradients

Question 18

What does the sodium potassium pump do?

Answer 18

Transports ions against a steep concentration gradient using energy directly from ATP hydrolysis, it actively transports sodium ions out of the cell and potassium ions into the cell.

Question 19

How does the sodium potassium pump work?

Answer 19

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

Question 20

What is the ratio of sodium to potassium for each ATP hydrolysed?

Answer 20

Three sodium ions are transported outside the cell and two potassium ions are transported into the cell, this establishes both concentration gradients and an electrical gradient.

Question 21

Where is the sodium-potassium pump found?

Answer 21

In most animal cells, accounting for a high proportion of the basal metabolic rate in many organisms.

Question 22

How does the sodium potassium pump work in the small intestine?

Answer 22

The sodium gradient created by the pump drives the active transport of glucose, in intestinal epithelial cells the pump creates a sodium ion gradient across the plasma membrane.

Question 23

Glucose transporter

Answer 23

The glucose transporter responsible for this glucose symport transports sodium ions and glucose at the same time and direction. Sodium ions enter the cell down their concentration gradient, the simultaneous transport of glucose pumps glucose into the cell against its concentration gradient.