16 - CARBOHYDRATES

Question 1

polyhydroxy aldehydes or polyhydroxy ketones or substances that yield such compounds on hydrolysis

Answer 1

Carbohydrates

Question 2

What are the three major classes of carbohydrates?

Answer 2

Monosaccharides
Oligosaccharides
Polysaccharides

Question 3

simple sugars and consists of a single polyhydroxy aldehyde or polyhydroxy ketone unit

Answer 3

Monosaccharides

Question 4

are classified based on the carbonyl grp.

Answer 4

Monosaccharides

Question 5

consist of short chains of monosaccharide units, or residues, or substances joined by glycosidic bonds

• most abundant are the disaccharides, with two monosaccharide units

Answer 5

Oligosaccharides

Question 6

sugar polymers containing more than 20 or so monosaccharide units, and some have hundreds or thousands of units

Answer 6

Polysaccharides

Question 7

What are the two classifications of monosaccharides?

Answer 7

Aldose and ketose

Question 8

a monosaccharide containing an aldehyde grp.

Answer 8

Aldose

Question 9

a monosaccharide containing a ketone grp.

Answer 9

Ketose

Question 10

naturally occurring monosaccharides contain 3-7/8 carbon atoms per molecule

Question 11

Triose - monosaccharide w/ 3 carbon atoms
Tetrose - monosaccharide w/ 4 carbon atoms
Pentose - monosaccharide w/ 5 carbon atoms
Hexose - monosaccharide w/ 6 carbon atoms

Question 12

are the simplest carbohydrate monosaccharides

Answer 12

Triose

Question 13

Aldotetrose - aldoses w/ 4 carbon atoms
Aldopentose - aldoses w/ 5 carbon atoms
Ketopentose - ketoses w/ 5 carbon atoms
Ketoheptose - ketoses w/ 7 carbon atoms

Question 14

are a common way to represent the stereochemistry of monosaccharides; help visualize the 3D arrangement of atoms in a 2D plane

Answer 14

Fischer projections

Question 15

developed the Fischer projections

Answer 15

H. Emil Fischer

Question 16

use horizontal and vertical lines to indicate the 3D structure of a molecule

horizontal = project forward
vertical = project backward
intersecting lines = carbon

Answer 16

Fischer projections

Question 17

Monosaccharides can be classified as D- or L- forms based on the configuration of the chiral carbon farthest from the carbonyl grp.; forms are mirror images of each other

Question 18

the chiral center that is the most distant or farthest from the carbonyl carbon

Answer 18

Penultimate carbon

Question 19

a monosaccharide that, when written as a Fischer projection, has the -OH on its penultimate carbon on the RIGHT

Answer 19

D-monosaccharide

Question 20

a monosaccharide that, when written as a Fischer projection, has the -OH on its penultimate carbon on the LEFT

Answer 20

L-monosaccharide

Question 21

Natural monosaccharides are in the D- form while, synthetically produced monosaccharides are usually in the L-form

Question 22

D sugars are more abundant in nature; present in all plants and animals.

Animals = use it as a source of energy

L- glucose is not abundant in nature.

Question 23

stereoisomers that are mirror images

ex. D-erythrose and L-erythrose

Answer 23

Enantiomers

Question 24

stereoisomers that are not mirror images

ex. D-erythrose and D-threose

Answer 24

Diastereomers

Question 25

dextrorotatory (+)
levorotatory (-)

labels for monosaccharides refer to the direction in which they rotate plane-polarized light

Question 26

monosaccharides rotate the plane of polarized light clockwise

Answer 26

Dextrorotatory (+)

Question 27

monosaccharides rotate the plane of polarized light counterclockwise

Answer 27

Levorotatory (-)

Question 28

D- does not always mean dextrorotatory (+), and L- does not always mean levorotatory (-)

ex.
D-glucose is D-(+)-glucose (dextrorotatory)

D-fructose is D-(-)-fructose (levorotatory)

Question 29

Monosaccharides can be classified by the

(a) number of carbon atoms in the molecule (e.g. pentose vs. hexose)
(b) functional group (aldoses vs. ketoses)
(c) configuration (D- and L- configuration)
(d) optical activity ((+) vs. (-) isomers)
(e) ring structure (furanoses vs. pyranoses)
(f) stereochemistry at an anomeric carbon (alpha vs. beta isomers)

Question 30

What happens if a sugar forms a cyclic molecule?

Answer 30

• cyclization of sugars takes place to make a cyclic hemiacetal
• cyclization can also result in hemiketal formation
• in both cases, the carbonyl carbon becomes the new chiral center called the anomeric carbon