Cell Surface

Question 1

What are the functions of the cell surface membrane

Answer 1

• Barrier between the cell and its environment
• Maintaining different intracellular and extracellular environments
• Site of chemical reaction
• Protect vital components
• Allow cell communication

Question 2

What are the predominant phospholipids in biological membranes

Answer 2

• phosphatidylcholine
• phosphatidylserine
• phosphatidylethanolamine
• sphingomyelin

Question 3

What effect does cholesterol have on the fluidity of the membrane and how does it do this

Answer 3

• Makes the membrane less fluid and more rigid.
• Intercalates between the phospholipids, a tighter packed bilayer

Question 4

What 3 processes does the fluidity of biological membranes allow

Answer 4

• Signalling - lipids and membrane proteins are able to diffuse rapidly to interact.
• Ensure membranes are shared equally between daughter cells
• Allows membranes to fuse together (endo and exocytosis)

Question 5

What do transmembrane regions of integral proteins contain and what is their significance

Answer 5

• Mainly contain hydrophobic amino acids.
• These amino acids interact with phospholipid tails

Question 6

What are the 6 functions of membrane proteins

Answer 6

• Transport
• Catalysis (enzymes)
• Signal transduction
• Cell recognition
• Intercellular joining
• Attachment (to cytoskeleton or intracellular matrix)

Question 7

List the 4 Intracellular signal transduction lipids

Answer 7

• Phosphatidylinositol
• Diacylglycerol
• Ceramide
• Sphingosine-1-phosphate

Question 8

Where do Intracellular signal transduction lipids come from and what proportion of phospholipids do they make up

Answer 8

• Derived from lipids in the plasma membrane.
• Minor proportion of phospholipid content

Question 9

Give some features of Intracellular signal transduction lipids due to their specificity

Answer 9

• Rapidly generated and destroyed by enzymes
• Spatially and temporally generated depending on when and where they are needed
• Bind to specific regions

Question 10

What drives passive transport across biological membranes

Answer 10

• Concentration gradients

Question 11

What is the difference between facilitated and simple diffusion

Answer 11

• Facilitated involves membrane proteins, simple does not

Question 12

What 3 factors affect the ability of a solute to cross the membrane in simple diffusion

Answer 12

• Hydrophobicity
• Size - Large uncharged polar molecules cannot pass through whereas smaller ones can
• Charged - Ions are too polar to pass through

Question 13

What are the 2 classes of proteins involved in facilitated diffusion

Answer 13

• Channel proteins-
• Uniporter carrier proteins

Question 14

What factors do channel proteins discriminate based on

Answer 14

• Size
• Charge

Question 15

What are channels (proteins)

Answer 15

• Hydrophilic pores through the membrane
• Non-directional ion channels
• Gated channels (more control than simple pore)
• Fast

Question 16

What factors do uniporter proteins discriminate based on

Answer 16

• Solute must be complimentary to the binding site. Highly selective

Question 17

How do uniporter carrier proteins work

Answer 17

-Substrate binds and induces conformational shape change.
- The shape change moves the substrate across membrane and releases into the cell
- Slow

Question 18

Why do cells maintain electrochemical gradients

Answer 18

• Drive transport across membranes
• Maintains osmotic balance
• Electrical forces inside and outside the cell must be balanced)

Question 19

Why is ATP required in active transport

Answer 19

• Solutes are moved against their electrochemical gradients, this requires energy

Question 20

What are the 3 ways that active transport occurs

Answer 20

• ATP- driven pumps - Couples hydrolysis of ATP with the transport of solute
• Coupled transporters - Couples movement of a solute with the concentration with the movement of a solute against it
• Light-driven pumps - Couples transport of solute against gradient with the input of energy from light

Question 21

What are the 2 types of ATP- driven pumps active transport

Answer 21

• Symport- When both solutes move in the same direction
• Antiport - When the solutes move in opposite directions

Question 22

Describe the Na+ and K+ example of ATP driven active transport

Answer 22

• 3Na+ moves out of the cell while 2K+ moves in
• Na+ binds to the catalytic unit to activate ATPase, and hydrolysis of ATPase causes a conformational change
• Na+ is released out of the cell and K+ bind extracellularly, dephosphorylation of the subunit causes conformational change.
• K+ released into the cell

Question 23

Describe the Na+/ glucose example of symporter active transport

Answer 23

• Na+ is in high concentration inside the gut whereas glucose concentration is low.
• Binding of glucose is dependent on the binding of Na+
• Glucose becomes more likely to bind to symporter as concentration of Na+ is higher outside the cell

Question 24

Describe the Na+/ Ca2+ example of antiporter active transport (CARDIAC)

Answer 24

• Concentration of Na+ and Ca2+ outside the cell is higher
• Antiporter moves 3Na+ outside the cell (along its gradient), for every 1Ca2+ out (against its gradient).