Lipids in Cell Membranes

Question 1

What are some examples of lipids?

Answer 1

1- Phospholipids
2- Fats
3- Sterols
4- Some vitamins

Question 2

What is the solubility of lipids in water?

Answer 2

Very low

Question 3

What are the roles of lipids?

Answer 3

1- Sources of energy
2- Forming membranes
3- Participating in cell signalling

Question 4

Describe the structure of fatty acids.

Answer 4

1- Carboxyl group with a long hydrocarbon chain
2- CH3(CH2)4-24COOH (CH2 anywhere between 2 to 24)
3- All naturally occuring fatty acids have an even number of carbons

Question 5

How are fatty acids acquired into the body?

Answer 5

1- Short and medium chains are absorbed into the blood stream
2- Long chains cannot be absorbed so they are synthesised

Question 6

In respect to the ratio of carbon bonds to double bonds, what are the three types of fatty acids?

Answer 6

1- Saturated (16:0)
2- Unsaturated (18:1)
3- Polyunsaturated (20:4)

Question 7

What are examples of sterols?

Answer 7

1- Bile acids
2- Steroid hormones
3- Vitamins
4- Cell membranes

Question 8

What type of lipid is cholesterol?

Answer 8

Sterol

Question 9

What is Gaucher’s disease?

Answer 9

1- Inherited disorder
2- Affects lipid pathways
3- Accumulation of glucocerebrocide

Question 10

How do disorders which affect the lipid pathway affect the body?

Answer 10

1- Lipid accumulation
2- Affect neurological system
3- Enlarged liver and spleen
4- Enlarged bone marrow cavities
5- Failure to thrive

Question 11

Which three groups of lipids are found in the membrane?

Answer 11

1- Phospholipids
2- Glycolipids
3- Sterols

Question 12

Describe the structure of a phospholipid.

Answer 12

1- Polar head group
2- Glycerol backbone
3- Fatty acid chains (usually two)

Question 13

What are five examples of phospholipids?

Answer 13

1- Choline
2- Ethanolamine
3- Serine
4- Glyerol
5- Inositol

Question 14

Describe the structure of a glycolipid.

Answer 14

1- Sphingosine backbone
2- Fatty acid chain
3- Attached to CH R group

Question 15

What is an amphipathic compound?

Answer 15

A molecule with a hydrophilic head and a hydrophobic tail

Question 16

Describe the lipid bilayer.

Answer 16

1- Biylayer of phospholipids
2- Hydrophilic heads point outwards and are attracted to water
3- Hydrophobic tails point inwards and seek to aggregate with other, hydrophobic molecules
4- Contain lipids which help contribute to membrane strength and stability

Question 17

Why are membranes important?

Answer 17

1- Compartmentalisation, separating cell from outside
2- Compartmentalisation, separating organelles
3- Have highly selective barriers to control entry and exit
4- Have sensors which respond to internal and external conditions to help the cell act accordingly

Question 18

What are the two classes of proteins in the membrane?

Answer 18

1- Peripheral (extrinsic) proteins

2- Integral (intrinsic) proteins

Question 19

In what ways can phospholipids move within the membrane?

Answer 19

Membrane is extremely fluid
1- Lateral movement: very frequent, 10^7 per second
2- Flip-flop: very rare, may happen ~once per month

Question 20

What is the difference of the structure of phospholipids between fluid and viscous membranes?

Answer 20

1- Fluid membranes have phosphilipids with unsaturated hydrocarbon tails with kinks
2- Viscous membranes have phospholipids with saturated hydrocarbon tails with no kinks

Question 21

Describe the structure of cholesterol.

Answer 21

1- Polar head group
2- Rigid, planar steroid ring structure
3- Nonpolar hydrocarbon tail

Question 22

How does the cholesterol molecule fit in the phospholipid membrane?

Answer 22

1- Polar head next to hydrophobic phospholipid heads
2- Rigid, planar steroid ring structure next to proximal tail to stiffen the region
3- Nonpolar hydrocarbon tail next to distal tail, more fluid than proximal tail

Question 23

Where does membrane synthesis take place?

Answer 23

Endoplasmic reticulum

Question 24

How is new membrane transported to other parts of the cell?

Answer 24

1- Vesicle trafficking
2- Bits of membrane pinch off from the ER to form vesicles
3- These travel in the cytosol and fuse with other membranes, releasing their content

Question 25

How is asymmetry generated in the membrane?

Answer 25

1- Newly synthesised phospholipids are released into the outer leaflet of the ER bilayer
2- Lipids are transferred to other side by flippases
3- This created asymmetry

Question 26

What are lipid rafts?

Answer 26

1- Subdomain of membranes
2- Organising centre
3- Contain high concentrations of cholesterol and glycophingolipids
4- Regulate vesicle trafficking
5- Responsible for cell signalling

Question 27

In regards to their position in the membrane, what are the four types of membrane proteins?

Answer 27

1- Transmembrane
2- Membrane-associated
3- Lipid-linked
4- Protein-attached

Question 28

How are transmembrane proteins positioned in relation to phospholipids?

Answer 28

Transmembrane proteins have hydrophobic amino acid side chains, which interact with the hydrophobic tails

Question 29

How are membrane-associated proteins positioned in relation to phospholipids?

Answer 29

1- Attached to only one side of the membrane and not across

2- Contain domains that selectively bind to phospholipids

Question 30

How are lipid-linked proteins attached to the phospholipid membrane?

Answer 30

1- Attached via GPI anchors

2- GPI: glycosylphosphatidylinositol