Chapter 8: Lipids and Membranes

Question 1

What are the criteria to classify a compound as a lipid?

Answer 1

• They lack a common functional group
• Water-insoluble bio-compounds
• Some contain polar neutral or
  polar charged groups; but:
• the bulk of their structure is
  hydrocarbon-like

Question 2

What are the properties of fatty acids?

Answer 2

The simplest lipids are fatty acids, which are long-chain carboxylic acids (at physiological pH, they are ionized to the carboxylate form).

Question 3

Classification of fatty acids based on absence or presence of double bonds?

Answer 3

• Saturated fatty acids can be “saturated” with hydrogen.
• Unsaturated fatty acids contain one or more double bonds, such as oleate and linoleate.
• F.A. can be monounsaturated or polyunsaturated
• Double bonds are usually in the cis conformation

Question 4

How to identify omega fatty acids

Answer 4

Question 5

What are other names for Triacylglycerols?

Answer 5

The fats and oils found in animals and plants are triacylglycerols (sometimes called triglycerides)

Question 6

What are the components of Triacylglycerols?

Answer 6

triacylglycerols (sometimes called triglycerides) have acyl groups (the ROCOO groups) of three fatty acids are esterified to the three hydroxyl groups of glycerol (right)

Question 7

Identify the ester linkages on Triacylglycerols

Answer 7

Free fatty acids are relatively scarce in biological systems. Instead, they are usually esterified, for example, to glycerol.

Question 8

How to distinguish fats and oils?

Answer 8

Fats and oils are called triglycerides (or triacylglycerols) because they are esters composed of three fatty acid units joined to glycerol, a trihydroxy alcohol:
1. Fats
- animals
- solids at RT
- 2/3 or 3/3 saturated
- high MP and BP

2. Oils
   - plants
   - liquid at RT
   - 2/3 or 3/3 unsaturated
   - BP lower

Question 9

How to identify Glycerophospholipids

Answer 9

Glycerophospholipids have polar or charged head groups. Glycerophospholipids are amphipathic.

Question 10

What are the individual components of Glycerophospholipids?

Answer 10

Glycerophospholipids are not completely hydrophobic:
They are amphipathic, with hydrophobic tails attached to polar or charged head groups. Their structure is ideal for forming bilayers.

Question 11

What linkages reside in Glycerophospholipids?

Answer 11

Among the major lipids of biological membranes are the glycerophospholipids, which contain a glycerol backbone with fatty acyl groups esterified at positions 1 and 2 and a phosphate derivative, called a head group, esterified at position 3. The bonds that link the various components of a glycerophospholipid can be hydrolyzed by phospholipases to release the acyl chains or portions of the head group

Question 12

What is the specificity of phospholipases?

Answer 12

Phospholipases cleave glycerophospholipids at specific sites

Question 13

How to identify sphingolipids

Answer 13

In sphingolipids the backbone is sphingosine
- Some sphingolipids have
monosaccharides as head groups.
- Some sphingolipids have
oligosaccharides as head groups.

Question 14

What are the individual components of Sphingolipids?

Answer 14

The sphingomyelins, with phosphocholine or phosphoethanolamine head groups, are sterically similar to their glycerophospholipid counterparts. The major difference is that sphingomyelins are not built on a glycerol backbone. Instead, their basic component is sphingosine, a derivative of serine and the fatty acid palmitate.

Question 15

What linkages reside in Sphingolipids?

Answer 15

In a sphingolipid, a second fatty acyl group is attached via an amide bond to the serine nitrogen

Question 16

How to distinguish cerebrosides and gangliosides

Answer 16

Some sphingolipids include head groups consisting of one or more carbohydrate groups. These glycolipids are known as cerebrosides and gangliosides.
1. A cerebroside has a monosaccharide as a head group rather than a phosphate derivative.
2. A ganglioside includes an oligosaccharide head group.

Question 17

What is the structure of cholesterol (steroid)?

Answer 17

Cholesterol is an important component of membranes and is also a metabolic precursor of steroid hormones such as estrogen and testosterone. Cholesterol is one of many types of terpenoids, or isoprenoids, lipids that are constructed from 5-carbon units with the same carbon skeleton as isoprene.

Question 18

What are the properties of cholesterol?

Answer 18

1. The most common steroid
2. The precursor to all other steroids
3. Found in all animal cells
4. Cholesterol is also an important component of membrane lipids
5. It is stored in the membrane and reduces its fluidity

Question 19

What components make up a wax?

Answer 19

• Esters made of a fatty acid and a very long alcohol

Question 20

What is the function of a wax?

Answer 20

Waxes
* Esters made of fatty acid and a very long alcohol
* Function as waterproofing agents. Ex. beeswax is an ester of palmitate
and a 30-C alcohol

Question 21

What is the structure of a lipid bilayer?

Answer 21

Is an array of amphipathic molecules whose tails associate with each other, out of contact with water, and whose head groups interact with water

Question 22

What are the properties of a lipid bilayer?

Answer 22

An array of amphipathic molecules, with polar heads and non-polar tails forming the bilayer that acts as a barrier to diffusion

Question 23

Name the types of membrane proteins

Answer 23

Integral membrane protein
Peripheral membrane protein
Lipid linked protein

Question 24

Name the properties of membrane proteins

Answer 24

(1) Cell membranes are thin enclosures that form closed boundaries.
(2) Cell membranes are made up of lipids, proteins and carbohydrates.
(3) Cell membranes consist of a phospholipid bilayer.
(4) Cell membranes are held together by non-covalent interactions
(5) Membranes are fluid-like structures.
(6) Proteins diversify the functionality of cell membranes.
(7) Membranes have polarity.
(8) Membranes are asymmetrical structures.

Question 25

What are the components of the fluid mosaic model?

Answer 25

extracellular space, protein, carbohydrate

Question 26

Examples of saturated fatty acids

Answer 26

Palmitate and Stearate