Membranes and lipids

Question 1

Why is the membrane referred to as the fluid mosaic

Answer 1

Lipids can move laterally in membrane and proteins can be integral

Question 2

What kind of proteins can be in membrane

Answer 2

• membrane spanning

- Peripheral (attached to membrane)

Question 3

What is the layer of the membrane associated with carbs

Answer 3

GLycocalyx

Question 4

What are micelles formed from

Answer 4

Lipids

Question 5

What determines whether bilayer is formed instead of micelles

Answer 5

If cross-sectional areas of head group and acyl side chains are similar

Question 6

What is the glyocalyx and carbohydrates attached via?

Answer 6

Glycoproteins and glycolipids

Question 7

Properties of membrane

Answer 7

• flexible
• self-sealing
• selectively permeable

Question 8

Why do lipids aggregate in presence of water

Answer 8

• Clustering reduces hydrophobic surface exposed to water
• MInimises number of molecules no. in water shell
• results in increase in entropy
• Therefore hydrophobic interactions provide them with thermodynamic drive

Question 9

How are vesicles formed?

Answer 9

If edges are exposed of lipids, then vesicles form

Question 10

3 classes of membrane lipids

Answer 10

• PHosphoglycerides (form of phospholipid)
• Sphingolipids (some are phospholipids, others are glycolipids)
• Cholesterol (sterol)

Question 11

Structure of phosphoglycerides

Answer 11

Alcohol attached to a phosphate which is attached to a glycerol which has two fatty acids attached to it

Question 12

Examples of phosphoglycerides

Answer 12

PH

Question 13

What bonds do glycolipids have

Answer 13

Contains covalently attached carbohydrate

Question 14

Example of phosphoglycerides

Answer 14

PHosphotidylcholine
PHosphatidylethanolamine
PHosphatidylserine

Question 15

What can sphingolipids be

Answer 15

phospholipids

glycolipids

Question 16

Structure of sphingolipids in membrane

Answer 16

• 2 hydrophobic tails
• one is fatty acid residue (situated at ‘R’)
• one is hydrocarbon tail of sphingosine

Question 17

What are the two hydrophobic tails in a sphingolipid which is in a membrane

Answer 17

• fatty acid residue

- hydrocarbon tail of sphingosine

Question 18

What are sterols characterized by

Answer 18

4 rigid, fused hydrocarbon rings

Question 19

What is cholesterol like compared to other membrane lipids and why

Answer 19

More rigid because has only one hydroxyl group and so not very water soluble

Question 20

What does cholesterol do in bilayer

Answer 20

Helps maintain membrane fluidity

Question 21

What forms ‘pockets’ for cholesterol within bilayer

Answer 21

Cis conformation fatty acids

Question 22

What do associations of sphingolipids and cholesterol produce and their roles

Answer 22

A microdomain enriched with proteins (lipid Rafts and also has roles in signaling)

Question 23

What is the Golgi membrane made of

Answer 23

PHosphatidycholine

Question 24

What are transport vesicles made of

Answer 24

Sphingolipids and cholesterol

Question 25

What does flippase do

Answer 25

Moves phospholipids from outer to cytosolic leaflet

Question 26

What does floppase do

Answer 26

Moves phospholipids from cytosolic to outer leaflet

Question 27

What does scramblase do

Answer 27

Moves lipids in either direction-towards equilibrium

Question 28

What do integral membrane proteins contain and what do the hydrophilic portions do?

Answer 28

Contain transmembrane domains

-Hydrophilic portions protrude into extracellular environment or cytoplasm

Question 29

How can peripheral proteins be released from membrane

Answer 29

by ionic solvents

Question 30

What is the orientation of proteins in membrane

Answer 30

Asymmetric

Question 31

What are some functions of membrane proteins

Answer 31

• transporters and channels
• provide anchors to cell cytoskeleton and extracellular matrix
• act as receptors to extracellular signal (e.g. hormones)
• may be enzymes

Question 32

What are bacterial plasma membranes of mitochondria like

Answer 32

Sites of enzyme catalysed processes contain more protein than lipid

Question 33

What is the role of the glycocalyx

Answer 33

• protects cell from digestion
• restricts uptake of hydrophobic compounds
• cell recognition modulators

Question 34

Structure of glycocalyx

Answer 34

Short chains of oligosaccharides on surface proteins and lipids extend into aqueous medium

Question 35

What does the glycocalyx contain?

Answer 35

branched 15 sugar residues

Question 36

What are the sugar residues in the glycocalyx attached via?

Answer 36

N-glycosidic or O-glycosidic bonds