Lipids and Cell Membranes

Question 1

What is a lipid?

Answer 1

A chemical that is describe as having a low solubility in water.

Question 2

What do lipids do?

Answer 2

They provide a source of energy, form cell membranes are participate in cell signalling

Question 3

Describe some of the features of fatty acids

Answer 3

These are a good store of energy. Naturally occurring fatty acids have even numbers of carbons. They are rarely found freely in the body and are more frequently found as part of the lipid molecule or attached to a carrier protein

Question 4

Describe how short, medium and long fatty chains are taken in?

Answer 4

short and medium are absorbed into the blood stream but long fatty acids are unable to be absorbed so are synthesised by cells.

Question 5

What radio of carbon to double bonds makes a fat polyunsaturated?

Answer 5

20:4

Question 6

How are omega fatty acids names?

Answer 6

Omega then number. This number is the first carbon to carbon double bond from the methyl end.

Question 7

Give some examples of sterols

Answer 7

Bile acids, steroids, vitamins and cell membranes

Question 8

Name some inherited disorders in lipid pathways and what this causes

Answer 8

Gaucher's (most common)
Niemann Pick
Tay-Sachs
Fabry Disease
It causes defects in enzymes that metabolise lipids leading to lipid accumulation. Effects neurological system, liver, spleen and bone marrow

Question 9

Name the three types of membrane lipids and give an example

Answer 9

Phospholipids (Glycerophospholipids and Spingolipids)
Glycolipids (spingolipids)
Sterols (cholesterol)

Question 10

What are the ranger of different phospholipids and what are they defined by?

Answer 10

Defined by their different polar head group. The rage of phospholipids are;
Choline, Ethanoalmine, serine and inositol

Question 11

Define amphipathic

Answer 11

A molecule having both hydrophobic and hydrophilic parts.

Question 12

What are the energetically favourable and unfavourable bilayer formations

Answer 12

Planar phospholipid bilayer is unfavourable as the edges are exposed to water. The more favourable formation is spherical as this is a sealed compartment and no lipids are exposed to water

Question 13

What is membrane fluidity and why is it important?

Answer 13

This means that lipids and proteins can undergo rotational and later movement. It allows for the diffusion of membrane proteins and lipids from the site they are produced

Question 14

How can you measure membrane fluidity?

Answer 14

Measure the fluorescence recovery time after bleaching. It measures how quickly the fluorescent lipids travel to the bleached area.

Question 15

What increases the viscosity of membranes?

Answer 15

Cholesterol

Question 16

How are phospholipids generated?

Answer 16

Synthesised by enzymes at the ER in the cytosol. They use fatty acids available in the cytosol. Phospholipids are released in the cytoplasm and travel to the outer leaflet of the membrane. Flippases transfer them to the inner leaflet. Flippases are specific to certain phospholipids.

Question 17

Describe how membrane is synthesised.

Answer 17

New memebrane synthesis occurs at the ER. The membrane is then transported to other parts of the cell. This occurs via a process of vesicle budding and fusions (vesicle trafficking)

Question 18

What is exocytosis?

Answer 18

Delivery of lipids and membrane proteins to the plasma membrane. Also involved in the release of other molecules.

Question 19

What is endocytosis?

Answer 19

Movement of material into a cell via vesicles.

Question 20

What are lipid rafts?

Answer 20

They are organising centres used in vesicle trafficking and cell signalling.

Question 21

Name some types of membrane proteins

Answer 21

Transmembrane - the hydrophobic amino acid side chain stabilises its presence in hydrophobic regions

Membrane associated - contain domains that selectively bind to phospholipids

Lipid anchored - work through GPI anchors

Protein attached - important in signal transduction