Carbohydrates

Question 1

What is a chiral carbon?

Answer 1

Carbon with 4 different groups attached to it

Question 2

Which of the ff amino acids DOES NOT have a chiral carbon?

(a) valine (b) tryptophan (c) glycine (d) phenylalanine

Answer 2

(c) glycine

* Glycine is the ONLY non-chiral amino acid. (It has 2 H’s attached to its alpha-carbon)

Question 3

What is mutarotation?

Answer 3

Conversion between alpha- and beta-anomers

RECALL: alpha-anomer is the form with -OH below and beta-anomer is the form with -OH above the plan of the molecule

Question 4

What is the form of carbohydrates naturally occurring in nature?

Answer 4

D-carbohydrates such as D-glucose, D-mannose, etc

Question 5

What is the most stable conformational isomer for a 6-C sugar?

(a) boat (b) chair (c) envelope

Answer 5

(b) chair

The chair conformation does not have any steric strain, and has the most stable angles (60 degrees) in its structure.

Question 6

What the reactive groups in carbohydrates? (also forms a basis of classification)

Answer 6

Aldehydes and ketones

Carbohydrates can be classified as either aldoses or ketoses.

Question 7

Which among the following is an aldose-ketose pair?

(a) glucose-fructose (b) glucose-mannose (c) fructose-ribulose

Answer 7

(a) glucose-fructose

(b) glucose and mannose are both ALDOSES and (c) fructose and ribulose are both KETOSES

Question 8

Carbohydrates can also be classified according to the number of carbons.

If ribose has 5 carbons, how will you name it?

Answer 8

Pentose

Question 9

Which among the ff are monosaccharides? How would you classify those which are NOT monosaccharides in the choices?

Fructose, maltose, glucose, galactose, lactose

Answer 9

Glucose, galactose and fructose are MONOSACCHARIDES.

Maltose and lactose are DISACCHARIDES.

Question 10

What monosaccharides make up maltose?

Answer 10

Glucose-glucose

Question 11

What monosaccharides make up lactose?

Answer 11

Galactose-glucose

Question 12

What monosaccharides make up sucrose?

Answer 12

Glucose-fructose

Question 13

What bond joins 2 monosaccharides?

Answer 13

Glycosidic bond

Question 14

What is a polysaccharide?

Answer 14

A polymer of monosaccharides

Question 15

Examples of polysaccharides

Answer 15

Glycogen, cellulose, starch

Question 16

Differentiate heteropolysaccharides and homopolysaccharides. Give 1 example each.

Answer 16

Heteropolysaccharides: made up of more than 1 type of monosaccharide

ex. peptidoglycan (found in bacterial cell walls)

Homopolysaccharide: made up of 1 type of monosaccharide only

ex. glycogen, starch

Question 17

Difference between starch and cellulose?

Answer 17

Starch forms alpha (1-4) bonds. Cellulose forms beta (1-6) bonds.

Question 18

Starch has 2 kinds of glycosidic bonds, alpha (1-4) and alpha (1-6). Which forms linear chains, and which gives rise to branches?

Answer 18

Alpha (1-4): for linear chains

Alpha (1-6): forms branches

Question 19

What are reducing sugars?

Answer 19

Sugars with a free anomeric carbon (meaning that the aldehyde group is free and not involved in a glycosidic bond to form a cyclic structure).

Question 20

A solution, when added with a solution of Cu2+ ions, formed a precipitate with Cu+ as one of its components. Did the solution contain a reducing sugar?

Answer 20

YES

Cu2+ was reduced to Cu+, therefore the solution contained reducing sugars.

Question 21

What are optical isomers?

Answer 21

Isomers that can either rotate plane-polarized light to the right (dextrorotatory, small letter d) or the left (levorotatory, small letter l).

Question 22

What are stereoisomers?

Answer 22

Isomers wherein the hydroxyl group attached to the penultimate carbon (or the last chiral carbon, C5 if the sugar is a hexose) is either on the right (D) or the left (L).

Question 23

What are enantiomers?

Answer 23

Isomers which are mirror images of each other.

Question 24

What are epimers?

Answer 24

Isomers whose structures differ only in their configuration around 1 carbon atom

Question 25

Glucose forms many epimers, which are called C-(number) epimers of glucose. In the choices below, match the correct carbon number with the epimer. C-2 and C-4 mannose and galactose

Answer 25

C2: mannose C4: galactose This means that glucose would have exactly the SAME structure with mannose and galactose except at carbon # 2 (for mannose) and carbon # 4 (for galactose).

Question 26

One monosaccharide derivative is phosphate esters, such as glucose-6-phosphate. Why is there a need for phosphorylation?

Answer 26

Attaching a phosphate group makes the molecule CHARGED. Once it is charged, the molecule would not be as easily diffusible through the LIPID bilayer, thus trapping the molecule inside and committing it to specific pathways.

Question 27

Another monosaccharide deriviative is acids. Which carbons are oxidized to become acids?

Answer 27

C1 and C6

Question 28

If only C1 is oxidized, what is the acid derivative called?

Answer 28

Aldonic acid ex. gluconic acid

Question 29

If only C6 is oxidized, what is the acid derivative called?

Answer 29

Alduronic acid ex. glucoronic acid

Question 30

If BOTH C1 and C6 are oxidized, what is the acid derivative called?

Answer 30

Aldaric acid ex. glucaric acid

Question 31

If carbonyl groups in a monosaccharide are reduced, what is the derivative called?

Answer 31

Alditols ex. mannitol

Question 32

How are amino sugars derived? Example of an amino sugar?

Answer 32

The -OH group is replaced with an amino (-NH2) group at C2. An acetyl group may also be added to give rise to N-acetyl-sugars. ex. N-acetyl-neuraminic acid (sialic acid)

Question 33

Glycosides are also monosaccharide derivatives. Examples of glycosides?

Answer 33

Ouabain, amygdalin

Question 34

What are proteoglycans?

Answer 34

Glycosaminoglycans + protein Proteoglycans form a "bottlebrush" look. Sulfate and acetyl groups from glycosaminoglycans have negative charges that repel each other and make the strands look "stiff." Used as a lubricant by the body (because its negative groups attract water)

Question 35

Examples of glycosaminoglycans?

Answer 35

Heparan sulfate, chondroitin sulfate, heparin

Question 36

What is the most prevalent glycosaminoglycan?

Answer 36

Chondroitin sulfate

Question 37

What are glycoproteins?

Answer 37

In glycoproteins, there is a protein core with carbohydrate groups attached to it.

Question 38

In glycoproteins, carbohydrates link to proteins either through O-glycosidic bonds or N-glycosidic bonds. Through which amino acids do they form these links?

Answer 38

O-glycosidic bonds: serine and threonine | N-glycosidic bonds: asparagine

Question 39

Carbohydrates serve as informational molecules, T/F?

Answer 39

T. For interaction with one another and with other cell types (attachment, migration).

Question 40

Carbohydrates play a role in cell recognition, T/F?

Answer 40

T. Found in self, non-self recognition process by immune cells of the body, apoptosis, cell differentiation, recognition of the egg by the sperm.

Question 41

Deficiency in galactokinase?

Answer 41

Galactosemia (accumulates in the blood)/galactosuria (accumulates in the urine)

Question 42

Deficiency in fructokinase?

Answer 42

Fructosuria

Question 43

What enzyme is deficient in lactose intolerance?

Answer 43

Lactase