Unit 1 - Membrane Proteins

Question 1

What are integral proteins?

Answer 1

Proteins that have one or more segment embedded in the phospholipid bilayer

Question 2

What are transmembrane proteins?

Answer 2

Proteins which span across the membrane and act as channels or transporters of ions

Question 3

What are peripheral proteins?

Answer 3

Proteins which are temporarily bound to either surface of the membrane

Question 4

What is facilitated diffusion?

Answer 4

The passive transport of substances across the membrane through specific proteins

Question 5

What are transporter proteins?

Answer 5

Membrane proteins involved in the movement of ions, small molecules and macromolecules across a membrane

Question 6

What are gated channel proteins?

Answer 6

Channel-forming proteins controlled by signalling molecules or ion concentration.

Question 7

What are ligand-gated channels?

Answer 7

Transmembrane protein channels controlled by the binding of signal molecules

Question 8

What are voltage-gated proteins?

Answer 8

Transmembrane proteins that form ion channels, activated by the changes in the electrical membrane potential

Question 9

What is the electrochemical gradient?

Answer 9

A gradient of electrochemical potential, consisting of difference in solute concentration and difference in charge

Question 10

What is the membrane potential?

Answer 10

An electrical gradient that forces ions to move passively in one direction

Question 11

What is the sodium-potassium pump?

Answer 11

A protein that removes 3 sodium ions and takes 2 potassium ions into the cell during a cycle of action

Question 12

What is a glucose-symport?

Answer 12

An integral membrane protein involved in transport of glucose and sodium ions across the membrane

Question 13

What does the plasma membrane control?

Answer 13

Entry and exit of materials

Question 14

What is the plasma membrane composed of?

Answer 14

-Phospholipids
-Proteins

Question 15

What are the 2 regions of a phospholipid and what are their properties i.e. charge?

Answer 15

• Head region ( charged, hydrophilic, attracted to water )
• Tail region ( uncharged, hydrophobic, repelled by water )

Question 16

What gives the membrane a fluid quality?

Answer 16

Phospholipids which are constantly changing position

Question 17

Examples of proteins found in the membrane

Answer 17

• Active transport proteins
• Channel forming proteins
• Enzymes
• Receptors

Question 18

Examples of integral proteins

Answer 18

• Channels
• Transporters
• Receptors

Question 19

What do integral proteins interact with?

Answer 19

The hydrophobic region of membrane phospholipids

Question 20

What holds integral proteins within the phospholipid bilayer?

Answer 20

Regions of hydrophobic R groups allow strong hydrophobic interaction, holding them in the membrane

Question 21

How are peripheral proteins bound to the surface of the membrane?

Answer 21

They have hydrophilic R groups on their surface, so can be bound by ionic and hydrogen bonds interactions

Question 22

What molecules does the phospholipid bilayer act as a barrier to?

Answer 22

Ion and most uncharged polar molecules

Question 23

How do oxygen and carbon dioxide pass through the membrane?

Answer 23

Diffusion

Question 24

What are the proteins involved in transporting substances?

Answer 24

• Channel proteins ( ligand-gated, voltage-gated)
• Transporter proteins
• Protein pumps

Question 25

What proteins use the method of facilitated diffusion?

Answer 25

Transporter proteins and channel proteins

Question 26

What are channels?

Answer 26

Multi-subunit proteins with the subunits arranged to form water-filled pores

Question 27

What do gated proteins respond to?

Answer 27

Stimulus ( Chemical, Electrical )

Question 28

How does the ligand-gated channel open?

Answer 28

**When correct signal molecules bind**, gate open allowing ions to flow through

Question 29

How do transporter proteins work?

Answer 29

Transporter proteins **bind to specific substances** which are to be transported and undergo a **conformational change** to transfer the solute across the membrane

Question 30

Why do transporter proteins alternate between 2 conformations?

Answer 30

So that the binding site is sequentially exposed on one side for the bilayer then the other

Question 31

What are transporter proteins coupled to an energy source?

Answer 31

Pumps

Question 32

What is required for protein pumps to transfer substances?

Answer 32

A source of metabolic energy

Question 33

What do some active transport proteins do to provide energy?

Answer 33

Hydrolyse ATP directly

Question 34

What are the proteins that hydrolyse ATP directly?

Answer 34

ATPases

Question 35

How is the electrochemical gradient formed?

Answer 35

The **concentration gradient** and **electrical potential difference** are combined

Question 36

What does the electrochemical gradient determine?

Answer 36

The transport of the solute carrying a net charge

Question 37

What is the concentration gradient?

Answer 37

The difference in concentration of a solute across the plasma membrane

Question 38

When is an electrical potential difference/membrane potential created?

Answer 38

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

Question 39

What does the sodium potassium pump use to **establish and maintain ion gradients**?

Answer 39

Energy from the hydrolysis of ATP

Question 40

How does Na/K-ATPase transport ions?

Answer 40

Transports ions against a steep concentration gradient using energy directly from ATP hydrolysis

Question 41

The process of sodium potassium pump?

Answer 41

- Pump has high affinity for sodium inside the cell, binding occurs - Pump hydrolyses ATP and phosphate attaches to pump - Phosphorylation by ATP causes conformation of the protein to change - Affinity for sodium ions decrease and 3 ions are released outside cell - Pump now has high affinity for potassium outside the cell therefore 2 ions bind to pump - Dephosphorylation occurs which causes conformation of protein to change - Potassium ions taken into cell and affinity returns to start

Question 42

What does the sodium-potassium pump account for a high proportion of?

Answer 42

High proportion of the basal metabolic rate (up to 25% in humans)

Question 43

What does the sodium-potassium pump generate in the small intestine?

Answer 43

A sodium ion gradient across the plasma membrane which drives active transport of glucose

Question 44

What is the glucose transporter called?

Answer 44

Glucose symport

Question 45

What does the glucose symport do?

Answer 45

Transports sodium ions and glucose at the same time and in the same direction.