Seeing Double: Biomembrane Structure

Question 1

What 2 macromolecules are biomembranes composed of in vivo?

Answer 1

lipids and proteins

Question 2

What is the only macromolecule required to make an artificial biomembrane in vitro?

Answer 2

lipids

Question 3

List the four functions of biomembranes.

Answer 3

1. Compartmentalization
2. Insulation
3. Communication
4. Transport

Question 4

Of the four functions of biomembranes, which ones are lipids responsible for?

Answer 4

1. Compartmentalization
2. Insulation
3. Communication

Question 5

Of the four functions of biomembranes, which ones are proteins responsible for?

Answer 5

3. Communication
4. Transport

Question 6

What is the general ratio of protein to lipids in biomembranes?

Answer 6

No set ratio. Varies depending on function.

Question 7

Is there more lipid or protein in the biomembrane of a neuron (myelin sheath)?

Answer 7

More lipid - insulative properties

Question 8

Is there more lipid or protein in the biomembrane of a mitochondrion (myelin sheath)?

Answer 8

More proteins

Question 9

What are the three main roles of lipids in cells?

Answer 9

1. Membrane Structure - compartmentalization
2. Chemical Signals - communication
3. Energy Storage

Question 10

How many different types of lipid molecules does a fungal cell contain at any given time?

Answer 10

Around 1000

Question 11

What are the 3 main classes of lipids in biomembranes?

Answer 11

Sterols
Phosphoglycerides
Sphingolipids

Question 12

Describe cholesterol.

Answer 12

Sterol; generally very hydrophobic; only the hydroxy group is hydrophilic

Question 13

Describe the structure of all phosphoglycerides.

Answer 13

modified glycerol (glyceride)
hydrocarbon chains on carbons 1 and 2
phosphate group on carbon 3 (phosphoester)

Question 14

What is the only thing that varies in the structure of a phosphoglyceride?

Answer 14

head groups can vary

Question 15

Describe the general structure of a sphingolipid.

Answer 15

Long hydrocarbon (acyl) chain
Amide between the acyl chain and a head group

Question 16

Which is hydrophobic in the biomembrane, the head or the tail?

Answer 16

Tail

Question 17

Which is hydrophilic in the biomembrane, the head or the tail?

Answer 17

Head

Question 18

Where do phosphoglycerides come from?

Answer 18

fatty acids and glycerol

Question 19

What is the difference between saturated and unsaturated?

Answer 19

Saturated molecules have all single bonds.
Unsaturated molecules have at least one alkene and are kinked.

Question 20

How do fatty acids attach to glycerol in phosphoglycerides?

Answer 20

a series of hydrolysis reactions

Question 21

How are phosphoglycerides constructed?

Answer 21

1. Fatty acids attach to glycerol with a series of hydrolysis reactions.
2. The side chain is removed from triglycerol and replaced with a phosphate group.
3. A head group (R group) is added to the phosphate.

Question 22

What are the four common phosphoglycerides?

Answer 22

phosphatidylcholine
phosphatidylserine
phosphatidylethanolamine
phosphatidylinositol

Question 23

Describe the solubility of sterols.

Answer 23

Soluble in nonpolar solvents (due to large hydrophobic regions).
Weakly soluble in polar solvents (due to singular hydroxy group).

Question 24

Do all sphingolipids have a phosphate group in their head group?

Answer 24

Some do, some don’t.

Question 25

What does amphipathic/amphiphilic mean?

Answer 25

has a hydrophobic and hydrophilic region

Question 26

How does the hydrophobic effect influence the structure of the biomembrane?

Answer 26

The hydrophobic effect encourages an increase in entropy of the universe and a decrease in order by hiding all the head groups inside, creating a bilayer.

Question 27

Why are the hydrophobic tails inside of the bilayer?

Answer 27

protects from aqueous solution hydrophobic effect

Question 28

What determines the thickness of the bilayer?

Answer 28

length of hydrocarbon chain

Question 29

Which has a longer hydrocarbon tail, a phosphoglyceride or a sphingolipid?

Answer 29

sphingolipid

Question 30

What evidence is there that biological membranes are bilayers?

Answer 30

The Gorter and Grendel experiment took red blood cells, calculated the surface area of them, extracted lipids, put the lipids in the Langmuir trough, and measured the area occupied on top of the trough. The lipid area in the trough and the surface area of a red blood cell had a 2:1 ratio, indicating that cells are surrounded by a lipid bilayer.

Question 31

What evidence is there that hydrocarbon tails aren't touching?

Answer 31

Xray diffraction studies examined the electron density of a membrane. When the density fell sharply, it indicated there was a gap between the tails.

Question 32

What is a lipid.

Answer 32

The functional definition of a lipid is that it is a molecule highly soluble in a non-polar solvent (and weakly soluble in water). No structural definition.

Question 33

How thick is the lipid bilayer?

Answer 33

3.5-5.5 nm thick

Question 34

How many nanometers is one angstrom?

Answer 34

0.1 nm

Question 35

How to distinguish between phosphoglycerides and sphingolipids?

Answer 35

The quick way to distinguish between a phosphoglyceride and a sphingolipid is to determine whether any of the side chains on the first or second carbon centers of the backbone have oxygens. If yes, you are most likely looking at a phosphoglyceride. However, if you see a nitrogen attached to the second carbon of the backbone, then you are most likely looking at a sphingolipid.