Introduction To Carbohydrates

Question 1

Carbohydrate functions

Answer 1

Energy storage, structure components

Question 2

Enantiomers

Answer 2

Mirror images that are NOT superimposable (C1 3-D structure)

• rotates polarized light in opposite and equal directions

Question 3

Most common version of glucose

Answer 3

D form (Dextrose)

Question 4

Why cant L-glucose be broken down?

Answer 4

Humans don’t possess enzymes specific to L-glucose

Question 5

Dextrorotary

Answer 5

Right angled polarized light

• originated via D-glucose (52.7)

Question 6

Levorotatory

Answer 6

Light rotation of polarized light

• originated via L-glucose (-52.7)

Question 7

Racemases

Answer 7

Interconvert D and L isomers

Question 8

Structural Isomers

Answer 8

Same molecular formula.

Same structure bonding is different at one chiral carbon

Question 9

Epimers (stereoisomers)

Answer 9

Same molecular formula

Differ in positioning of the hydroxyl group at 1 chiral carbon.

Question 10

Epimerases

Answer 10

Interconvert epimer pairs

Question 11

How to structurally tell the difference between L & D forms

Answer 11

L = hydroxyl group on the chiral carbon closest to the end is on the LEFT

D = hydroxyl group on the chiral carbon closest to the end is on the RIGHT

Question 12

Formation of hemiacetal

Answer 12

OH group on C5 bonds with O & C on C1 to form a cyclic structure

Question 13

Structural difference between alpha and beta cyclic structures of carbohydrates

Answer 13

alpha = C1 hydroxyl group points DOWN

Beta = C12 hydroxyl group points UP

• beta is more stable than alpha*

Question 14

Mutarotation

Answer 14

Spontaneous inter conversion between beta and alpha forms

• CANNOT happen if the anomeric carbon is bounded to another molecule other than hydroxyl group

Question 15

Anomers

Answer 15

Alpha and beta versions of the same carbohydrate

Question 16

Anomeric carbon

Answer 16

C1 in a cyclic version of a carbohydrate (now chiral)

Question 17

Glycosidic linkages

Answer 17

Enzymatic condensation reaction between the 1 OH group of one glucose with an OH group of another glucose

Question 18

Amylose

Answer 18

Linear polymer of D-glucose via a(1,4) glycosidic bonds

Question 19

Amylopectin & glycogen

Answer 19

Branched polymers of D-Glucose via a(1,4) or a(1,6) glycosidic linkages

• branches every 24-30 residues (amylopectin)
• branches every 8-12 residues (glycogen)

Question 20

Cellulose

Answer 20

Linear polymer of D-glucose via b(1,4) glycosidic bonds

• Humans CANNOT break this down due to lack of enzymes for b(1,4) between 2 glucose molecules.
• used by humans as a dietary fiber insoluble.

Question 21

Lactose

Answer 21

(A or b)Glucopyranose and (b) galactopyranose disaccharide

Bonded via b(1,4) linkage

Question 22

Most stable form of fructose furanose

Answer 22

Beta

Question 23

Sucrose

Answer 23

(A)D-glucopyranose and (b)D-fructofuranose

formed via a,b(1,2) bond

Question 24

Pyran

Answer 24

5 carbon ring with 1 oxygen molecule

Question 25

Furan

Answer 25

4 carbon ring with 1 oxygen

Question 26

Maltose

Answer 26

(A)glucopyranose and (a/b)glucopyranose Bonded via a(1,4) in maltose Bonded via a(1,6) in isomaltose