Lecture 4

Question 1

Where are most lipids found in the cell and what is their function?

Answer 1

Membranes. Function as selective barriers

Question 2

What fatty acid characteristics are used to predict fluidity/rigidity of a membrane?

Answer 2

Chain length and double bonds

Question 3

Define saturated and unsaturated.

Answer 3

Unsaturated = contains 1 or more dbl. bonds

Question 4

Discuss how cis and trans double bond configurations affect fatty acid structure and properties.

Answer 4

Cis- puts a kink in the chain; chains don’t pack as well; more fluid (oils)

Trans- straight chain; pack tightly to make stiff membranes (solid at room temp)

Question 5

What components are most lipids in cells composed of? List the molecules and bonds involved.

Answer 5

Fatty acids covalently bonded to glycerol

Question 6

What is triacylglycerol composed of and used for?

Answer 6

3 fatty acid tails bonded to glycerol; used in energy storage

Question 7

Draw a 16 carbon unsaturated fatty acid and label the parts.

Answer 7

me

Question 8

Draw a phospholipid and label the parts

Answer 8

me

Question 9

What are the chemical properties of these molecules that make them amphipathic?

Answer 9

Hydrophilic head, hydrophobic tail

Question 10

How are a saturated fatty acid and a phospholipid different?

Answer 10

Fatty acid- carboxylic acid head group (hydrophilic) and hydrocarbon tail (hydrophobic)

Phospholipid- polar head group (phosphate+polar group) attached to 2 hydrocarbon tails through through glycerol.

Question 11

What is meant by membrane fluidity?

Answer 11

The ease with which the lipid molecules move within the plane of the bilayer

Question 12

Why is membrane fluidity important?

Answer 12

Important for membrane function and must be maintained within certain limits

Question 13

What are three determinants of a membrane’s fluid properties (in an animal cell)?

Answer 13

Fatty acid tail/chain length, saturation, cholesterol

Question 14

. Define transition temperature.

Answer 14

The temperature at which liquid state changes to gel state and vice versa

Question 15

Discuss the role of cholesterol concerning animal cell membrane properties

Answer 15

Broadens the transition temperature range

Question 16

A lipid bilayer in its gel state is (below/at/above) its transition T?

Answer 16

Below

Question 17

What are the components of a plasma membrane?

Answer 17

Phospholipids, proteins, lipoproteins, glycoproteins, glycolipids

Question 18

Compare the lateral mobility of lipids and proteins in a biological membrane.

Answer 18

Lipids are greater

Question 19

T or F: The only types of lipids in cell membranes are phospholipids.

Answer 19

False. Major component, but other membrane lipid molecules are sterols and glycolipids

Question 20

Name two properties of molecules that pass through the lipid bilayer by simple diffusion

Answer 20

Nonpolar, small polar uncharged

Question 21

What characteristics would prevent a molecule from being able to diffuse through a membrane?

Answer 21

Charge, highly polar

Question 22

On a recent fishing trip to the Caribbean you came across a fish not known to you or any of your colleagues that had washed up on shore. Thrilled by the opportunity to have discovered a new species of fish you decided to look a little further into its membrane makeup

Answer 22

Your results are as follows: Average length of fatty acid tail: 14
Low saturated fatty acid content

Question 23

Do these results support the idea that this fish is native to the Caribbean?

Answer 23

No, these characteristics imply that the fish is likely from cold water

Question 24

Micelles (pictured right) are spheres of phospholipids that form spontaneously in aqueous solution. With what you know about the properties of phospholipids, explain why lipid micelles form spontaneously in water?

Answer 24

To sequester hydrophobic molecules from water, less interference with water H-
bonds, achieve energy minimum

Question 25

Are the following hydrophilic, hydrophobic, or amphipathic? Monosaccharides, Amino acids, Fatty acids, Phospholipids

Answer 25

a) Monosaccharides - hydrophilic
b) Amino acids – hydrophilic, other properties depend on R group
c) Fatty acids - amphipathic
d) Phospholipids - amphipathic

Question 26

All amino acids are hydrophilic, but the R group can be either hydrophilic or hydrophobic

Answer 26

All amino acids are hydrophilic, but the R group can be either hydrophilic or hydrophobic

Question 27

Examine the four groups of amino acids and the chemical characteristics of their “R” groups that distinguish them. (You do not need to memorize each amino acid, but you are expected to understand their properties.)

Answer 27

1. Acidic, negatively charged; carboxyl groups- hydrophilic R groups
2. Basic, positively charged; amino groups-hydrophilic R groups
3. Polar, uncharged; hydroxyl, amide groups-hydrophilic R groups
4. Nonpolar; methyl, phenyl- hydrophobic R groups

Question 28

Draw an amino acid backbone. Use “R” as the side chain and specify the amino (N terminus) and acid (C terminus) portions

Answer 28

m e

Question 29

Show a polymerization reaction of 2 amino acids to a dipeptide. Again, label the amino and carboxyl ends, as well as the peptide (amide) bond that is formed.

Answer 29

m e