What is a membrane?

Question 1

Describe the structure of the cell membrane. (4)

Answer 1

• Phospholipid bilayer which is a primary barrier to diffusion
• Fluid mosaic
• Membrane proteins perform membrane specific functions
• Carbohydrates play a role in “self recognition” and cell-to-cell interactions.

Question 2

What is meant by the membrane having a trilaminer appearance?

Answer 2

The membrane appears to have three layers.

Question 3

Describe a phospholipid molecule.

Answer 3

• Negatively charged, polar, hydrophilic head group

- Two non polar, hydrophobic tails made of hydrocarbon

Question 4

What is the role of cholesterol in the cell membrane, how does cholesterol achieve this? (2)

Answer 4

• Cholesterol contributes to the fluidity and stability of the membrane.
• They prevent phospholipids by packing tightly together by “tucking in” between phospholipid molecules.

Question 5

What causes the bilayer to be fluid?

Answer 5

Weak bonding between the phospholipid molecules allowing them to move freely.

Question 6

Name and describe the three types of membrane protein.

Answer 6

• Integral proteins: Embedded in the lipid bilayer (e.g receptors)
• Transmembrane protein: Extend through the membrane (e.g transporters/channels)
• Peripheral proteins: Do not penetrate membrane- more common intracellularly. (e.g receptor associated enzymes)

Question 7

What are ion channels?

Answer 7

Transmembrane proteins that form water filled, highly selective ion channels.

Question 8

What are leak channels?

Answer 8

Ion channels that are open all the time.

Question 9

What are voltage-gated channels?

Answer 9

Ion channels that open and close in response to changes in membrane potentials.

Question 10

Describe carrier or transport proteins.

Answer 10

Proteins that transport a specific molecule or ion, or a group of closely related molecules.

Question 11

What are Docking-marker acceptors?

Answer 11

Proteins on the inner membrane that interact with secretory vesicles leading to exocytosis of the vesicle contents.

Question 12

What is the function of protein kinase C

Answer 12

It phosphorylates certain proteins causing a cellular response.

Question 13

Name two types of cell adhesion molecules (CAMs), and describe their function.

Answer 13

• Cadherins: Help hold cells within tissue together.

- Integrins: Span the plasma membrane acting as a link between extra and intra-cellular environments.

Question 14

What are receptors?

Answer 14

Proteins found on the outer membrane surface that bind specific molecules (lock and key theory)

Question 15

Describe the role of membrane carbohydrates.(2)

Answer 15

• Membrane carbohydrates serve as self identity markers, different cells have different markers
• Play a role in tissue growth: Cells do not overgrow their territory

Question 16

What are the three important functions of the lipid bilayer?

Answer 16

• Forms the basic structure of the membrane
• Has a hydrophobic interior that serves as a barrier (especially to water soluble substances like amino acids and glucose.)
• Responsible for the fluidity of the membrane.

Question 17

Name and describe the three types of specialised cell junctions.

Answer 17

• Desmosomes: Adhering junctions that anchor cells together, especially in tissue designed to stretch (e.g skin, uterus, heart)
• Tight junctions: Join lateral edges of epithelial cells near their apical membranes. Classified as tight or leaky. Important in movement of substances across epithelial layers.
• Gap (communicating junctions): Allow movement of charge carrying ions and small molecules between two adjacent cells.