Membrane Proteins

Question 1

What are membranes comprised of?

Answer 1

A bilayer of phospholipid molecules and a patchwork of protein molecules.

Question 2

The head region of the phospholipid?

Answer 2

Charged and therefore hydrophilic.

Question 3

The tail region of the phospholipid molecule?

Answer 3

Uncharged and non polar and therefore, hydrophobic.

Question 4

What gives the membrane its fluid quality?

Answer 4

The phospholipids are constantly changing position.

Question 5

The cell membrane is embedded with ——

Answer 5

Proteins

Question 6

These proteins that the membrane is embedded with form a —— ——

Answer 6

Patchy mosaic

Question 7

Proteins found within the membrane can have many different ——

Answer 7

Functions.

Question 8

Integral membrane proteins - how are they held in the membrane?

Answer 8

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

Question 9

Integral membrane proteins interact extensively with the —— region of the membrane phospholipids

Answer 9

Hydrophobic

Question 10

Some integral membrane proteins are?

Answer 10

Transmembrane proteins.

Question 11

Peripheral membrane proteins - how are they held in the membrane?

Answer 11

Have hydrophilic R groups on their surface and are bound to the surface of membranes, mainly by ionic and hydrogen bond interactions.

Question 12

Many peripheral membrane proteins interact with the —— of integral membrane proteins

Answer 12

Surfaces

Question 13

What is the phospholipid bilayer a barrier to?

Answer 13

Ions and most uncharged polar molecules.

Question 14

What molecules pass through the bilayer by simple diffusion?

Answer 14

Small molecules like oxygen and carbon dioxide.

Question 15

Facilitated diffusion?

Answer 15

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

Question 16

To perform specialised functions, different cell types have different —— and —— proteins

Answer 16

Channel and transporter proteins

Question 17

Most channel proteins in animal and plant cells are —— ——

Answer 17

Highly selective.

Question 18

What are channels?

Answer 18

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

Question 19

What are gated channels?

Answer 19

Some channel proteins are gated and change conformation to allow or prevent diffusion.

Question 20

Ligand gated channels?

Answer 20

Controlled by binding of signal molecules.

Question 21

Voltage gated channels?

Answer 21

Controlled by changes in ion concentration.

Question 22

Transporter proteins bind to… and undergo…

Answer 22

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

Question 23

Transporters alternate between 2 conformations - why?

Answer 23

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

Question 24

Active transport uses —— —— to transfer substances …

Answer 24

Uses pump proteins to transfer substances against their concentration gradient.

Question 25

Pumps that mediate active transport are ?

Answer 25

Transporter proteins coupled to an energy source.

Question 26

What is required for active transport?

Answer 26

A source of metabolic energy

Question 27

Some active transport proteins hydrolyse ATP directly to…

Answer 27

Provide energy for the conformational change required to move substances across the membrane.

Question 28

What is the electrochemical gradient?

Answer 28

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 29

What is a membrane potential (electrical potential difference)?

Answer 29

Created when there is a difference in electrical charge on the 2 sides of the membrane.

Question 30

What energy source do ion pumps such as the sodium potassium pump use to establish ion gradients?

Answer 30

Energy from the hydrolysis of ATP

Question 31

What does the sodium potassium pump do?

Answer 31

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 in.

Question 32

Process of sodium potassium pump (6 steps)?

Answer 32

1) pump has high affinity for Na+ ions inside cell, bonding occurs. 2) Phosphorylation by ATP causes conformation of protein to change 3) Affinity for Na+ ions decreases resulting in Na+ ions released outside cell. 4) K+ ions bind outside cell. 5) Dephosphorylation causes conformation of protein to change. 6) K+ ions taken into cell and affinity returns to start.

Question 33

For each ATP hydrolysed, — Na+ ions are transported — — — cell and — K+ ions are transported — — — cell

Answer 33

3 Na+ ions transported out of the cell 2 K+ ions transported into the cell

Question 34

What is the purpose of the sodium potassium pump?

Answer 34

Establishes both concentration gradients and an electrical gradient

Question 35

Where is the sodium potassium pump found?

Answer 35

In most animal cells.

Question 36

What does the sodium potassium pump account for?

Answer 36

A high proportion of the basal metabolic rate in many organisms.

Question 37

What does the sodium potassium pump do in the small intestine?

Answer 37

The sodium gradient created by the sodium potassium pump drives the active transport of glucose.

Question 38

In intestinal epithelial cells the sodium potassium pump…

Answer 38

Generates a sodium ion gradient across the plasma membrane.

Question 39

The glucose transporter responsible for glucose symport transports Na+ ions and glucose at the…

Answer 39

Same time and in the same direction.

Question 40

Glucose symport?

Answer 40

Sodium ions enter the cell down their concentration gradient; the simultaneous transport of glucose pumps glucose into the cell against its concentration gradient.