Biological Molecules

Question 1

What is an aldose?

Answer 1

Sugars with an aldehyde group

Question 2

What is a ketose?

Answer 2

Sugars with a ketone group

Question 3

What is a pyranose?

Answer 3

sugars in a 6 membered ring structure = hexagon shaped. For example, glucopyranose = glucose in a 6 membered ring.

Question 4

What is furanose?

Answer 4

sugars in a 5 membered ring structure = pentagon shaped. For example, fructofuranose = fructose in a 5 membered ring.

Question 5

In order to be classified as a carbohydrate, a molecule must have what:

Answer 5

1. at least a 3 carbon backbone.
2. an aldehyde or ketone group.
3. at least 2 hydroxyl groups.

Question 6

What are the structures for the smallest carbohydrates?

Question 7

The three common monosaccharides are:

Question 8

What is the difference between deoxyribose and ribose?

Question 9

What determines an absolute configuration of a sugar?

Answer 9

The chiral carbon furthest from the carbonyl group determines the absolute configuration L or D of the sugar.

Question 10

What are epimers?

Answer 10

different configuration in just one chiral carbon.

Question 11

What are anomers?

Answer 11

different configuration in the chiral, anomeric carbon when the molecule is in the cyclic form.

Question 12

To assign the cyclic form of a carbohydrate as the α- or β- form:

Answer 12

• In the α- form, the exocyclic O group at the anomeric center is on the opposite face to the -CH2OH group, and
• In the β- form, the exocyclic O group at the anomeric center is on the same face as the -CH2OH group.

Question 13

Hydrolysis of a glycoside linkage

Answer 13

glycoside + H₂O + catalyst → hydrolysis.

Catalysts include: Amylase for starch and glycosylase for nucleotide.

Question 14

Hemiacetal formation from monosaccharide

Answer 14

-OH attacks carbonyl group = produces ring form.

Question 15

Acetal formation from monosaccharide

Answer 15

another -OH attack on the same carbonyl group = produces polysaccharides if the -OH is from another monosaccharide.

Question 16

Mutatorotation

Answer 16

equilibrium between the α and β anomers.

Question 17

Strong oxidation of monosaccharides.

Answer 17

• Strong oxidation turns aldehyde and terminal hydroxyls to carboxylic acids, and other hydroxyls to ketones.
• The strongest kind of oxidation turns everything to CO2, and this occurs in cellular respiration.

Question 18

Mild oxidation of monosaccharides

Answer 18

• Mild oxidation is more selective.
• Tollens agent (the test for aldoses, silver reagent) selectively oxidizes the aldehyde to carboxylic acid.
• Nitric acid oxidizes both the aldehyde and the terminal hydroxyl to carboxylic acids, but leaves the other hydroxyls alone.

Question 19

Reduction of monosaccharides

Answer 19

Reduction turns monosaccharides into polyalcohols.

Question 20

For proteins, are L and D analogous to R and S?

Answer 20

No. L is not always S, and D is not always R.

Question 21

When can you interconvert between L/D and R/S?

Answer 21

• If the priority of NH2 > COOH > R, then L=S and D=R. For example, L-Alanine = S-Alanine.
• If the priority of NH2 > R > COOH, then L=R, and D=S. For example, L-Cysteine = R-Cysteine.

Question 22

When do amino acids exist in a cationic form, anionic form, and a zwitterion?

Answer 22

• At low pH, amino acids exist in the cationic form.
• At high pH, amino acids exist in the anionic form.
• At pH = pI, amino acids exist in the zwitterion form, which is overall neutral.

Question 23

Acidic amino acids: how to tell if so?

Answer 23

If the R group contains carboxylic acid, then it’s an acidic amino acid. There are two acidic amino acids: aspartic acid and glutamic acid.

Question 24

Basic amino acids: how to tell if so?

Answer 24

If the R group contains an amine group, then it’s a basic amino acid. There are three basic amino acids: lysine, arginine, and histidine.

Question 25

When is an amino acid hydrophilic?

Answer 25

Hydrophilic: If the R group contains acids, bases, amines or alcohols.

Question 26

How is a peptide bond formed?

Answer 26

The peptide bond is formed by the amine group attacking the carbonyl carbon.

Question 27

Hydrolysis of a peptide bond

Answer 27

The peptide bond is very difficult to hydrolyze. It requires a strong base, or a biological enzyme.

Question 28

What are three steroids?

Answer 28

Cholesterol, Testosterone, Estrogen

Question 29

Where are steroids made from?

Answer 29

Steroids are made from the cyclization of squalene, which is a terpene.

Question 30

What are terpenes and how are they synthesized?

Answer 30

Terpenes are made from the polymerization of isoprene.

Terpenes contain double bonds, which gives the molecule the ability to undergo cyclization.

Question 31

What is a squalene?

Answer 31

Squalene, the precursor of steroids, is a terpene that consists of 6 isoprene subunits. A complex self-cyclization reaction converts squalene to make steroids.

Question 32

How are triacyl glycerols made?

Answer 32

Glycerol + 3 Fatty acids → Triacyl Glycerol.

The reverse of triacyl glycerol synthesis is saponification.

Question 33

Witting Reaction