The Cell Surface

Question 1

4 major phospholipids

Answer 1

• Phosphatidylethanolamine
• Phosphatidylserine
• Phosphatidylcholine
• Sphingomyelin

Question 2

What does cholesterol do?

Answer 2

• Increases rigidity
• Decreases permeability to small molecules

Question 3

What do intracellular signal transduction lipids do?

Answer 3

• Bind specifically to certain regions of proteins
• Cause conformational, localization and/or activity change(s)

Question 4

What does fluidity of membranes allow?

Answer 4

• Signalling lipids and membrane proteins to rapidly diffuse laterally
• Membrane to be shared equally by daughter cells
• Membranes to fuse with other membranes

Question 5

Integral and peripheral membrane proteins

Answer 5

• Single-pass
• Multi-pass
• Beta-barrel
• Lipid-linked
• Peripheral membrane

Question 6

Functions of membrane proteins

Answer 6

• Transport
• Enzymatic activity
• Signal transduction
• Cell-cell recognition
• Intercellular joining
• Attachment to cytoskeleton and extracellular matrix

Question 7

Factors affecting ability of solute to simply diffuse across a membrane

Answer 7

• Concentration gradient
• Hydrophobicity/charge
• Size

Question 8

2 classes of membrane proteins involved in facilitated diffusion

Answer 8

• Channels
• Uniporter carrier proteins

Question 9

What do channel proteins form in the membrane?

Answer 9

Hydrophilic pores

Question 10

Speed of channel proteins

Answer 10

10^7 ions per second

Question 11

How do uniporter carrier proteins work?

Answer 11

Solute binds to the binding site

Question 12

Speed of uniporter carrier proteins

Answer 12

<1000 molecules per second

Question 13

Why do cells maintain electrochemical gradients?

Answer 13

• Drive transport
• Maintain osmotic balance
• Electrical forces inside and out must be balanced

Question 14

What protein is used to maintain Na+ electrochemical gradient?

Answer 14

Na+/K+ ATPase

Question 15

Why is Na+/K+ ATPase both a carrier and enzyme?

Answer 15

Also hydrolyses ATP to ADP

Question 16

Na+/K+ ATPase mechanism of action

Answer 16

1. 3x Na+ bind and pump is phosphorylated by hydrolysing ATP
2. Conformational change transfers Na+ and it is released
3. 2x K+ bind and pump dephosphorylated
4. Conformational return transfers K+ and releases them

Question 17

3 ways active transport happens

Answer 17

• ATP-driven pumps
• Coupled transporters
• Light-driven pumps

Question 18

How do ATP-driven pumps work?

Answer 18

Transport of solute coupled with hydrolysis of ATP (primary AT)

Question 19

How do coupled transporters work?

Answer 19

Transport of one solute down gradient with to another against gradient (secondary AT)

Question 20

Types of coupled transporters

Answer 20

• Symport (both solutes same way)
• Antiport (solutes in opposite directions)

Question 21

How do light-driven pumps work?

Answer 21

Transport of solute coupled with input of energy from light