Biological Membranes

Question 1

Main function of the cell membrane?

Answer 1

Protect the cells and its contents from surroundings and other cells.

Question 2

How does the cell membrane provide cellular integrity?

Answer 2

A number of function and structures work together to allow the membrane to stand strong against extreme changes in environment (pH, temperature etc.)

Question 3

What is the structure of the cell membrane composed of?

Answer 3

• Lipids & proteins (50/50)

- Phospholipid bilayer

Question 4

What type of bonds hold together the structure of the membrane?

Answer 4

Non-covalent bonds

Question 5

What type of proteins are attached and integrated within the membrane?

Answer 5

Structural proteins, transporters, sensors and receptors. These are known as membrane proteins.

Question 6

What allows phospholipids to form a bilayer?

Answer 6

Phospholipids are amphiphilic, meaning they contain both hydrophobic/hydrophilic parts.

Question 7

What is the chemical structure of a phospholipid?

What bond does it have?

Answer 7

Glycerol backbone and a phosphate. They are joined by an ester bond.

Question 8

What group does cholesterol belong to?

Answer 8

Sterols

Question 9

What is the function of cholesterol?

Answer 9

Provides rigidity to the membrane.

Question 10

Which type of group does not contain any cholesterol in their cell membranes?

Answer 10

Bacteria. The cell wall provides rigidity cell wall in their case.

Question 11

How are lipid bilayers formed?

Answer 11

• Hydrophilic lipid head exposed to water.

- Hydrophobic fatty acid tail group together

Question 12

Is the lipid bilayer two-dimensional or three-dimensional?

Answer 12

Two-dimensional.

Question 13

Which factors affect membrane fluidity?

Answer 13

• Lipid composition of membranes
• Temperature
• Cholesterol composition

Question 14

How does an increase in unsaturated lipids affect fluidity?

Answer 14

Double bonds causes a ‘kink’ in the chain which allows less room for phospholipids to bunch together. This leads to a thinner membrane which is more flexible. Fluidity increases.

Question 15

How does length of hydrocarbons affect the fluidity in membranes?

Answer 15

The shorter the hydrocarbons, less interaction so the membrane is thinner. Fluidity increases.

Question 16

Lipid rafts contain…

Answer 16

higher levels of cholesterols and glycosylated sphingolipids.

Question 17

Lipid rafts are involved in…

Answer 17

the organization of specific membrane proteins.

Question 18

Primary function of lipid rafts.

Answer 18

Cellular signalling.

Question 19

What is used as building block for membrane synthesis and as an energy source?

Answer 19

Lipids.

Question 20

What is the role of phosphatidylserine?

Answer 20

It recognized by macrophages in apoptosis (programmed cell death).

Question 21

Phosphatidylinositol is involved in…

Answer 21

cellular signalling.

Question 22

Glycolipids are…

Answer 22

sugar-containing lipids.

Question 23

Functions of glycolipids on the membrane…

Answer 23

• Cell recognition

- processes cell-cell adhesion

Question 24

Extra reading…

Answer 24

Part IV Chapter 10 Membrane Structure.

Question 25

What is the fluid mosaic model?

Answer 25

Fluid combination of phospholipids, cholesterol and proteins.

Question 26

The two types of proteins associated within the membrane are called…

Answer 26

integral and peripheral.

Question 27

Which compounds on the surface of the membrane allow proteins to be attached?

Answer 27

Covalent bound fatty acids, usually weak.

Question 28

Which side is the asymmetry found on the membrane when it comes to membrane proteins?

Answer 28

Non-cytosolic side.

Question 29

Majority of membrane proteins are modified with sugar through…

Answer 29

glycosylation.

Question 30

Function of glycosylation?

Answer 30

Provide cell coat. (carbohydrate layer)
Protects against chemical and mechanical damage.
Prevents unwanted protein-protein interaction.

Question 31

What type of molecules does the cell membrane allow through?

Answer 31

Hydrophobic molecules, H2O.

Question 32

All charged polar molecules (except H2O) and ions are..

Answer 32

not able to pass through the cell membrane passively.

Question 33

Which proteins allow passive transport?

Answer 33

Channels, transporters, electrochemical gradient.

Question 34

Which proteins facilitate active transport?

Answer 34

Carrier proteins as it requires an energy input.