Biological Molecules

Question 1

What is the general molecular formula for carbohydrates?

Answer 1

Cn(H2O)m
​

Question 2

What are the three main functions of carbohydrates?

Answer 2

*Energy storage (e.g., glucose)
*Recognition and interaction (e.g., blood types)
*Structural components (e.g., cell walls)

Question 3

What is the difference between an aldose and a ketose?

Answer 3

Aldose: A sugar with an aldehyde group (e.g., glucose).
Ketose: A sugar with a ketone group (e.g., fructose)

Question 4

What are monosaccharides?

Answer 4

Simple sugars that cannot be hydrolyzed into smaller units. Examples include glucose and fructose.

Question 5

What are the three criteria for classifying monosaccharides?

Answer 5

*Functional group: Aldose or ketose
*Stereochemistry: D or L configuration
*Number of carbons: Trioses (3C), Tetroses (4C), Pentoses (5C), Hexoses (6C), etc.

Question 6

What is an epimer?

Answer 6

Sugars that differ only by the stereochemistry at a single carbon (e.g., glucose and mannose at C2).

Question 7

What is a hemiacetal and how does it form?

Answer 7

*A hemiacetal is a functional group that contains both an –OH and –OR group.
*It forms when an aldehyde or ketone reacts with an alcohol.

Question 8

What is an anomeric carbon?

Answer 8

The carbon that was part of the carbonyl group in the open-chain form and is now linked to two oxygens in the cyclic form

Question 9

What are the two types of anomers?

Answer 9

α-anomer: The OH group on the anomeric carbon points down.
β-anomer: The OH group on the anomeric carbon points up

Question 10

What is mutarotation?

Answer 10

The interconversion between α- and β-anomers in solution

Question 11

What are the three common disaccharides and their glycosidic linkages?

Answer 11

*Maltose: α-1,4’ glycosidic bond
*Lactose: β-1,4’ glycosidic bond
*Sucrose: α-1, β-2’ glycosidic bond

Question 12

What is the difference between oligosaccharides and polysaccharides?

Answer 12

Oligosaccharides: 3–10 monosaccharide units (e.g., raffinose).
Polysaccharides: Hundreds or thousands of monosaccharide units (e.g., starch, cellulose).

Question 13

What are the two main types of polysaccharides and examples?

Answer 13

*Storage polysaccharides: Starch (plants), Glycogen (animals).
*Structural polysaccharides: Cellulose (plants), Chitin (exoskeletons)

Question 14

Why can’t humans digest cellulose?

Answer 14

Humans lack the β-glucosidase enzyme needed to break β-1,4’ glycosidic bonds in cellulose.

Question 15

What is the significance of glucosamine?

Answer 15

A derivative of glucose with an amino group at C2, commonly used in joint health supplements

Question 16

How do oxidation and reduction affect sugars?

Answer 16

Oxidation converts aldehydes to carboxylic acids (e.g., glucose → glucuronic acid).
Reduction converts aldehydes or ketones to sugar alcohols (e.g., glucose → sorbitol)

Question 17

What is a glycosidic bond?

Answer 17

A covalent bond between the anomeric carbon of a sugar and an alcohol or another sugar.

Question 18

What are the different ways of representing sugars?

Answer 18

*Fischer projection: Linear structure, used to show D/L configuration.
*Haworth projection: Cyclic form, shows α/β-anomers.
*Chair conformation: More accurate 3D representation of the cyclic form.

Question 19

What are the three main types of carbohydrates?

Answer 19

*Monosaccharides (single sugar units)
*Oligosaccharides (3–10 sugar units)
*Polysaccharides (many sugar units)

Question 20

How are monosaccharides classified?

Answer 20

*By functional group: Aldoses (contain aldehyde) vs. Ketoses (contain ketone).
*By number of carbons: Trioses (3C), Tetroses (4C), Pentoses (5C), Hexoses (6C), etc.
*By stereochemistry: D-sugars (OH on right in Fischer projection) vs. L-sugars (OH on left).

Question 21

What are isomers, and what are the types found in monosaccharides?

Answer 21

Molecules with the same molecular formula but different structures.

Structural isomers: Different connectivity (e.g., glucose vs. fructose).
Stereoisomers: Same connectivity, different spatial arrangement (e.g., D- vs. L-glucose).
Epimers: Differ at one carbon only (e.g., glucose vs. mannose at C2).
Anomers: Differ at the anomeric carbon (α vs. β).

Question 22

What is a Fischer projection?

Answer 22

A 2D representation of sugars showing stereochemistry. The most oxidized carbon is placed at the top.

Question 23

What is a Haworth projection?

Answer 23

A cyclic representation of sugars, showing α- and β-anomers.

Question 24

How do you convert from Fischer to Haworth projection?

Answer 24

Groups on the right of the Fischer projection point down in the Haworth projection; groups on the left point up.

Question 25

What happens when monosaccharides form rings?

Answer 25

The carbonyl group reacts with an OH group to form a hemiacetal (aldoses) or hemiketal (ketoses), creating a ring structure

Question 26

Name three important disaccharides and their glycosidic bonds

Answer 26

Maltose: α-1,4’ glycosidic bond (glucose + glucose). Lactose: β-1,4’ glycosidic bond (galactose + glucose). Sucrose: α-1, β-2’ glycosidic bond (glucose + fructose).

Question 27

What are the key differences between starch, glycogen, and cellulose?

Answer 27

*Starch: α-1,4’ and α-1,6’ glycosidic bonds, used for energy storage in plants. *Glycogen: Highly branched α-1,4’ and α-1,6’ glycosidic bonds, energy storage in animals. *Cellulose: β-1,4’ glycosidic bonds, structural component in plants (not digestible by humans).

Question 28

What are the major chemical reactions of carbohydrates?

Answer 28

Oxidation: Aldehydes → carboxylic acids (e.g., glucose → glucuronic acid). Reduction: Aldehydes/ketones → sugar alcohols (e.g., glucose → sorbitol). Acylation: Hydroxyl groups → esters (e.g., glucose → acetate esters). Alkylation: Hydroxyl groups → ethers (e.g., methylation using CH₃I). Glycoside formation: Conversion of hemiacetal to acetal by reacting with alcohols

Question 29

What is glucose monitoring, and how does it work?

Answer 29

A method to measure blood glucose using electrodes that detect oxidation of glucose by glucose oxidase.

Question 30

What is glucosamine, and why is it important?

Answer 30

A glucose derivative with an amino group at C2, used in joint health supplements.

Question 31

What is N-acetylglucosamine (NAG), and what is its role?

Answer 31

A glucose derivative involved in bacterial cell wall structure, forming N-acetylmuramic acid (NAM).

Question 32

How do carbohydrates determine blood type?

Answer 32

Type A: Contains N-acetyl-D-galactosamine. Type B: Contains D-galactose. Type AB: Contains both A and B sequences. Type O: Lacks both modifications

Question 33

What does reduction of sugars lead to?

Answer 33

Reduction of sugars results in the corresponding polyalcohol called sugar alcohol or alditol. Those are widely used in industry, primarily as food additives and sugar substitutes (e.g. Sorbitol, mannitol – 60% as sweet as sucrose - table sugar).

Question 34

What does sorbitol do?

Answer 34

Sorbitol is also used in the manufacture of softgel capsules to store single doses of liquid medicines. As an over-the-counter drug, sorbitol is used as a laxative to treat constipation.

Question 35

What are some extra reactions of carbohydrates?

Answer 35

Acylation of OH -> ester formation Acetic anhydride and pyridine convert all the hydroxy groups of a sugar to acetate esters. Alkylation of OH -> formation of ethers Treatment with methyl iodide (CH3I) and silver oxide (Ag2O) converts the hydroxy groups to methyl ethers.