W4 - Membrane Lipids

Question 1

Biological membranes are usually 60-100 angstrom thick, describe their polarity, symmetry and fluidity

Answer 1

Polarised (inside cell more -ve than outside), asymmetrical and they’re very fluid (no covalent bonds)

Question 2

When looking at the bilayer using an EM, why is there banding? (inside of bilayer different to outer edges)

Answer 2

Lipid molecules are amphipathic, EM stain cannot reach the middle of the bilayer due to hydrophobic FAs

Question 3

The lipids themselves have one function of structure but the membrane has many functions, list these 5 functions

Answer 3

Selective barrier (defence), transport, energy storage, enzymatic reactions and sensing information

Question 4

What are the 3 main functional groups involved in fatty acids?

Answer 4

Hydrogen, alkyl and carboxyl

Question 5

What does 18:0 and 18:3 mean when naming fatty acid long chain hydrocarbons?

Answer 5

18 - 18C, 0/3 - no. of C=C

Question 6

What is the shorthand for octadecanoic, octadecenoic, octadecadienoic and octadecatrienoic acid

Answer 6

18:0, 18:1, 18:2, 18:3

Question 7

How many C=C do linolenate, arachidonate and laurate have?

Answer 7

Lin - 3, Arach - 4, Laur - 0

Question 8

If a FA is shorter is the membrane more or less fluid?

Answer 8

More

Question 9

If a FA has more C=C is the membrane more or less fluid?

Answer 9

More

Question 10

Thermodynamics always pushes molecules to the lowest energy state, what does this mean when lipids interact?

Answer 10

The lipids dock to form the bilayer as this is the lowest energy state

Question 11

What are 4 components of phospholipids?

Answer 11

1(+) FA chain(s), glycerol/sphingosine, phosphate and an alcohol attached to the phosphate

Question 12

The major phospholipids are derived from phosphatidate, what does the ester bond form between when forming a PL?

Answer 12

Phosphate of phosphatidate and hydroxyl of alcohols

Question 13

Instead of an ester bond, in sphingomyelin there is what bond between the sphingosine backbone and the fatty acid?

Answer 13

Peptide bond

Question 14

What happens to the primary alcohol in sphingomyelin to join it to phosphorylcholine?

Answer 14

Undergoes an esterification reaction

Question 15

What are glycolipids?

Answer 15

Sugar containing lipids derived from sphingosine

Question 16

Glycolipids are asymmetric in terms of where the sugar is, where is the sugar always?

Answer 16

Extracellularly

Question 17

In glycolipids what is the primary alcohol esterified to?

Answer 17

1 or more sugars

Question 18

Cholesterol has a steroid nucleus and is not in prokaryotes, how do the molecules associate with the PLs?

Answer 18

Lie parallel to PL, OH interacts with head of PL

Question 19

Why do PLs and GLs prefer a planar sheet rather than micelles?

Answer 19

The bulkiness of the FA chains makes it unfavourable

Question 20

What are the main, weak bonds that hold lipids together?

Answer 20

Hydrophobic/van der waals

Question 21

After glycine in water is added to a layer of phospholipids, what does sonication do?

Answer 21

The waves of pressure disturb the layer of PLs to create liposomes trapping glycine

Question 22

What is the step after sonification?

Answer 22

Gel filtration to leave the liposomes

Question 23

What are two things that can be studied by creating liposomes?

Answer 23

Study cell permeability and delivering chemicals to cells

Question 24

Liposomes are roughly 500A across, how would you make them larger?

Answer 24

Slowly evaporate organic solvent from suspension of PL in a mixed solvent system

Question 25

Lipid bilayers are highly impermeable to ions and most polar molecules but water is an exception, why?

Answer 25

It’s small, lacks full charges and has very high concentration

Question 26

Give examples of cells/organelles that have high and low membrane protein content

Answer 26

Myelin cells have low protein content as fairly pure lipids tend to be better insulators, mitochondria has lots of proteins for energy transduction processes

Question 27

Membrane proteins can be integral and span the membrane but how else may they associate with the membrane?

Answer 27

They can be peripheral