B2 Chapter 2: Membranes and Transport

Question 1

What does membrane composition differ between?

Answer 1

• Cell types
• Different membranes of the same cell

Question 2

What are the biochemical components of membranes?

Answer 2

• proteins
• lipids
• carbohydrates

Question 3

What biochemical component of membranes are normally most abundant in terms of:
1. Number
2. Mass

Answer 3

1. Lipids
2. Proteins

Question 4

In terms of bicohemical components of a membrane, would the proportion of proteins by mass be higher in the inner or outer mitochondrial membrane? Why?

Answer 4

The inner membrane.
The location of ATP synthesis.

Question 5

What are the three major types of membrane lipid?

Answer 5

• phospholipids
• glycolipids
• cholesterol (or other sterol)

Question 6

What is the difference between the hydrophilic head group of a phospholipid and that of a glycolipid?

Answer 6

A phospholipid has a negatively charged phosphate group (-PO4) attached to a polar group.

Glycolipids have heads composed of a sugar residue (glucose or galactose), or multiple in a branching chain

Question 7

Of the three major types of membrane lipid, which can contain glycerol and what is the name of these glycerol-containing lipids?

Answer 7

Phospholipids and glycolipids may contain glycerol

Glycerolipids (glycerophospholipids and glyceroglycolipids)

Question 8

What are sphingolipids?

Answer 8

Lipids containg sphingosine

Question 9

What is the most common type of glycolipid found in animal cell membranes?

Answer 9

Sphingoglycolipid

Question 10

What are glycolipids and phospholipids that contain sphingosine called?

Answer 10

Sphingophospholipids and sphingoglycolipids

Question 11

How many hydrocarbon chains do phospholipids and glycolipids contain?

Answer 11

2

Question 12

In glycolipids and phospholipids, what are the origins of the 2 hydrocarbon chains?

Answer 12

Sphingolipids - One from sphingosine, one fatty acid
Glycolipids - Two fatty acids

Question 13

What are fatty acids?

Answer 13

Long hydrocarbon chains containing an acidic carboxyl (-COOH) group at one end.

Question 14

What does the acidic carboxyl group (-COOH) located at the end of a fatty acid react with and bond to in the formation of glycolipids and phospholipids?

Answer 14

The acidic carboxyl group (-COOH) of the fatty acid reacts with the hydroxyl group (-OH) belonging to a glycerol or sphingosine, forming an ester linkage in the lipid molecule.

Question 15

What are fatty acids that are incorporated into fatty lipid moecules called?

Answer 15

Fatty acyl chains.

Question 16

How long are fatty acyl chains usually, and what is the number of carbons almost always?

Answer 16

• 14 to 24 carbons
• Almost always even

Question 17

What is the difference between a saturated and unsaturated fatty acyl chain?

Answer 17

• Saturated (With hydrogen) : contains one or more double bonds between carbons.
• Unsaturated: Contains no double bonds between carbons.

Question 18

In animal and plant cells, are saturated or unsaturated fatty acids more abundant in membranes?

Answer 18

Over half of membrane fatty acids are unsaturated

Question 19

What properties of fatty acys affect physical properties of the membrane?

Answer 19

• the level of saturation
• Length of fatty acyl component of membrane lipids

Question 20

What are steroids characterised by?

Answer 20

Four ring structure
- Short hydrocarbon at one end of the four-ring structure
- Weakly polar hydroxyl group (-OH) at the other end

Question 21

What are sterols a type of?

Answer 21

Steroid

Question 22

What type of membrane lipid is very important and significant in animal cell membranes but not so much in intracellular membranes?

Answer 22

Cholesterol

Question 23

Animals have cholesterols in membranes. What do plants have?

Answer 23

Phytosterols (related molecules)

Question 24

Animals have cholesterol in membranes. What do prokaryotes have?

Answer 24

Hopanoids (sterol-like molecules)

Question 25

What does the relative solubility of membrane lipids in different solvents depend on?

Answer 25

The relative sizes of their hydrophobic and hydrophilic portions, and the polarity of the latter (Charged groups are more polar than the weakly polar hydroxyl groups found in cholesterol.)

Question 26

What properties of a solvent would cause non-polar hydrophobic molecules to readily dissolve?

Answer 26

- Non polar, hydrophobic

Question 27

What properties of a solvent would cause polar hydrophillic molecules to readily dissolve?

Answer 27

Polar, hydrophilic

Question 28

Why do membrane lipids most readily dossilve in non polar, or weakly polar organic solvents?

Answer 28

Because membrane lipids have relatively large hydrophobic components.