Membrane Basics and Lipids

Question 1

What is the composition of a membrane?

Answer 1

Proteins, lipids, carbohydrates

Question 2

Functions of lipids

Answer 2

Energy storage, Insulation, water repellent, membrane structure, cofactors for enzymes, signaling molecules, pigments, antioxidants.

Question 3

How are lipids classified?

Answer 3

Based on structure and function. Whether they have fatty acids or not.

Question 4

What’s special about unsaturated cis fatty acids?

Answer 4

• Unsaturated cis fatty acids pack less orderly due to the kink – less-extensive favorable interactions
(Creates space in membrane that can harbor proteins)
Lower melting point.

Question 5

How are unsaturated trans fatty acids formed and why are they used?

Answer 5

Formed by partial dehydrogenation of unsaturated fatty acids

– Done to increase shelf life or stability at high temperature of oils used in cooking (especially deep frying)

Question 6

How do we store fat?

Answer 6

Triacylglycerols

Question 7

What is the major component of cell membranes ?

Answer 7

Phosphatidylcholine

Question 8

Why is it advantageous that most prokaryotes cant synthesize phosphatidylcholine?

Answer 8

Many prokaryotes, including E. coli, cannot synthesize this lipid; their membranes do not contain phosphatidylcholine. Advantageous bc eukaryotic membrane triggers immune response if exposed to them.

Question 9

A fatty acid is joined to sphingosine to form sphingolipids via a what linkage?

Answer 9

Amide linkage

Question 10

Where is sphingomyelin abundant?

Answer 10

Myelin sheath that surrounds some nerve cells

Question 11

Changing the length of the carbon chain changes what?

Answer 11

Membrane thickness.

Question 12

What is a vesicle or liposome?

Answer 12

Small bilayers will spontaneously seal into spherical vesicles. They contain artificially inserted proteins. Vesicles fuse readily with cell membranes or with each other.

Question 13

How do membranes form spontaneously?

Answer 13

Form spontaneously in aqueous solution and are stabilized by noncovalent forces, especially hydrophobic effect

Question 14

Difference between integral and peripheral proteins?

Answer 14

• Integral proteins are firmly associated with the membrane, often spanning the bilayer.
• Peripheral proteins are weakly associated and can be removed easily – Some are noncovalently attached – Some are linked to membrane lipids

Question 15

Serine is a what?

Answer 15

Alcohol

Question 16

What does it mean that the membrane layers are asymmetric?

Answer 16

Two leaflets have different lipid compositions
Outer leaflet is often more positively charged

• Phosphatidylserine outside has a special meaning:
– Platelets: Activates blood clotting
– Other cells: Marks the cell for destruction

Question 17

Membrane needs to be in what phase for proper function?

Answer 17

Fluid-like rather than gel-like.

Question 18

What do the membranes need to maintain integrity and fluidity of the membrane at diff temps?

Answer 18

• At higher temperatures cells need more saturated fatty acids – To maintain integrity
• At lower temperatures cells need more unsaturated fatty acids – To maintain fluidity

Question 19

Flippases do what?

Answer 19

Flippases—catalyze transverse diffusion
• Some flippases use energy of ATP to move lipids against the concentration gradient

Flippase - in ( moves from outer to side of cytosol)
Floppase- out ( from cytosol to outer leaflet)
Scamblase - moves lipids in either direction toward equilibrium

Question 20

How does cholesterol in the membrane move?

Answer 20

moves from one place to another in lipid rafts.

Question 21

What are lipid drafts?

Answer 21

membrane subdomains enriched in certain lipids and proteins

Question 22

Proteins and lipids in the membrane are held together by what interactions?

Answer 22

non covalent interactions