The plasma membrane

Question 1

Which parts of phospholipids are Hydrophilic and hydrophobic?

Answer 1

• head = hydrophilic (polar)

* tail = hydrophobic (non-polar)

Question 2

How are phospholipids organised?

Answer 2

They organise themselves to keep their hydrophilic “heads wet” and hydrophobic “tails dry”

Question 3

What is the Fluid mosaic model?

Answer 3

• a two-dimensional liquid. Restricts the lateral diffusion of membrane components
• regions within the membrane that contain lipid rafts, proteins, and glycoproteins

Question 4

What does the basic structure of a membrane consist of?

Answer 4

• phospholipids (75%): MAIN COMPONENT
• cholesterol (20%): attached between phospholipids and between layers
• polar glycolipids in the external layer (5%)

Question 5

What is Cholesterol?

Answer 5

Cholesterol is a steroid lipid. It is a useful structural lipid for membranes, lipid rafts.

Question 6

What does membrane fluidity enable?

Answer 6

It allows the movement of membrane components which are required for cell movement, growth, division section and the formation of cellular junctions

Question 7

What is a glycolipid?

Answer 7

• a lipid covalently attached to an oligosaccharide

~ forms part of cell membrane and glycocalyx

Question 8

How is the glycocalyx formed?

Answer 8

• from glycoproteins (a membrane protein) containing associated oligossacharides

Question 9

What is the function of the phospholipid bilayer?

Answer 9

To regulate what enters and exits the cell, altering PH and charge. Involved in cell recognition as well as playing a big role in cell signalling (e.g through hormones)

Question 10

Explain membrane permeability

Answer 10

The cell membrane is selectively permeable.
- lipid bilayer is permeable to non-polar molecules and hormones
(slightly permeable to small uncharged polar molecules like water)
- it is impermeable to ions and large molecules

Question 11

What allows cells to build concentration gradients?

Answer 11

• The selective permeability

Question 12

What are the types of membrane transport?

Answer 12

• Passive transport: e.g diffusion
• Active transport: e.g primary&secondary
• Vesicular: e.g endocytosis

Question 13

What are the types of facilitated transport?

Answer 13

• Channel mediated

- Carrier mediated

Question 14

How does facilitated diffusion allow regulation?

Answer 14

Selective permeability can be regulated to maintain homeostasis. E.g insulin’s hormone through its receptor up-regulates glucose transporters

Question 15

What is osmosis?

Answer 15

Osmosis is the diffusion of water through a semi-permeable membrane.
~ diffusion through the lipid bilayer occurs through transmembrane protein channels called aquaporins

Question 16

Active transport involves the expenditure of energy from….

Answer 16

hydrolysis of ATP

Question 17

What is Active transport used for?

Answer 17

Used to transport essential ions against their concentration gradient (helps maintain tonicity, volume and charge)

Question 18

Compare the two types of active transport

Answer 18

• primary active transport uses energy from the hydrolysis of ATP where as secondary active transport uses energy stored by an ionic concentration gradient

Question 19

What is primary active transport?

Answer 19

Movement against a concentration gradient (mainly ions)

Question 20

What is secondary active transport?

Answer 20

A transporter protein couples the movement of an ion down its electrochemical gradient (grace has been made by primary active transport) to uphill the movement of another molecule or ion

Question 21

What is Symport and Antiport?

Answer 21

Symport is where molecules travel in the same direction and Antiport is where they go in opposite directions.

Question 22

What is vesicular transport used for?

Answer 22

• Used for endocytosis and exocytosis
• Used for inter-organelle transport

~ endocytosis is classified into receptor mediated endocytosis, phagocytosis and pinocytosis