Lecture 13

Question 1

Carbohydrate abundance?

Answer 1

Carbohydrates are the most abundant biomolecule in
nature. This is mainly due to cellulose in plants as it is a main component of plant cells.

Question 2

Variety of carbohydrate functions?

Answer 2

They have a wide variety of cellular functions: energy, structure, communication, and precursors for other biomolecules.
- They are versatile and have many cellular roles

Question 3

Carbohydrates and solar energy?

Answer 3

They are a direct link between solar energy and chemical bond energy.

Question 4

What is the composition of a carbohydrate?

Answer 4

In terms of composition, a carbohydrate can be thought of as a
hydrate of carbon (C with H2O).

Question 5

How else are carbohydrates called?

Answer 5

A carbohydrate can also be referred to as a saccharide (another name for carbohydrate, derived from the Greek word for sugar).

Question 6

What are monosaccharides?

Answer 6

Monosaccharides are aldehyde or ketone derivatives of straight chain polyhydroxyalcohols containing a minimum of 3 C atoms.
- multiple monosaccharides can be assembled to form polysaccharides

Question 7

How many kinds of monosaccharides are there and how are they distinguished?

Answer 7

There are many different monosaccharides.
- They can be distinguished from one another according to their carbonyl functional group.

Question 8

The three types of carbohydrates?

Answer 8

• Alcohol carbohydrates have a hydroxyl group. Sugars are polyhydroxyl ester alcohols with more than one hydroxyl group.
• Aldehyde carbohydrates have a carbonyl group and are aldoses
• Ketone carbohydrates have a carbonyl group and are ketoses

Question 9

How are monosaccharides distinguished?

Answer 9

Monosaccharides can also be distinguished from one another
according to the number of carbons (C) they contain.
The simplest contain 3 C:
- glyceraldehyde (3-C aldose) an aldotriose
- dihydroxyacetone (3-C ketose) a ketotriose

Question 10

Names of monosacchariedes with different carbon numbers (3-9)?

Answer 10

The names of carbohydrates with different C numbers are given here.

3 = triose = glyceraldehyde
4 = tetrose = erythrose
5 = pentose = ribose
6 = hexose = glucose, mannose, galactose
7 = heptose = mannoheptulose
9 = nonose = neuraminic acid (sialic acid)

Question 11

What are the two different forms of monosaccharides and what is more common?

Answer 11

Monosaccharides can occur in D and L form, they tend to be in D form (opposite of what amino acids are like).

Question 12

What does D form indicate?

Answer 12

According to standard convention, the D form of a monosaccharide has its asymmetric carbon most distant from the carbonyl group (in linear form) in the same configuration as does D-glyceraldehyde (OH on the
right). The L form has this centre in the opposite configuration.

• D forms are far more common. If not specified, it is reasonable to assume D.

Question 13

Monosaccharides as stereoisomers?

Answer 13

Monosaccharides exist as stereoisomers. There are many different kinds of isomers, stereoisomers are optical isomers.

Question 14

Enantiomers?

Answer 14

Exact mirror image stereoisomers are enantiomers. This is like your hands.

Question 15

Diasteromers?

Answer 15

Other stereoisomers are diastereomers that are differently
rotated at one or more specific bonds.

Question 16

Epimer?

Answer 16

diastereomers that differ at a single bond.

Question 17

Enantiomers and D/L forms?

Answer 17

Enantiomers are stereoisomers that are exact mirror images of one another.
* Enantiomers are noted as D and L according to the convention for sugars, but that is not enough to make them enantiomers.
* Because they are identical,
enantiomers are D and L forms of the same sugar (hence, same name).

Question 18

Example of D and L forms of enantiomers?

Answer 18

D-Ribose and L-Ribose are two aldopentoses and are enantiomers

Question 19

Diastereomers and D/L forms?

Answer 19

Diastereomers are stereoisomers that are not exact mirror images of one another.
* They are noted as D and L according to the convention for sugars, but that alone is not how they are determined to be diastereomers.
* Diastereomers are stereoisomers that are not enantiomers

Question 20

Example of D and L form of diastereomers?

Answer 20

D-Arabinose and L-Ribose are two aldopentoses and are diastereomers. They are not mirror images.

Question 21

How are epimers arranged?

Answer 21

Epimers are stereoisomers that differ in arrangement at a single chiral carbon (e.g. D-glucose and D-
galactose).

Question 22

Epimer example?

Answer 22

D-Glucose and D-Galactose are two aldohexoses and their arrangement at C4 differs. There are no other differences.

Question 23

How does cyclization occur?

Answer 23

Let’s look at glucose. The linear form becomes cyclic when the OH at C5 attacks C1. This forms a covalent bond between the groups, creating a cyclic molecule
- This results in an intramolecular hemiacetal or hemiketal

Question 24

Hemiacetal?

Answer 24

Alcohol and aldehyde

Question 25

Hemiketal?

Answer 25

Alcohol and ketone

Question 26

What kinds of rings can be formed?

Answer 26

Monosaccharides commonly form 5-member rings (4 C and 1 O) or 6- member rings (5 C and 1 O).

Question 27

5 member rings are called?

Answer 27

5 member rings (4 C and 1 O) are called furan structures, which make furanose monosaccharides

Question 28

6 member rings are called?

Answer 28

6 member rings (5C and 1O) are called pyran structures, which make pyranose monosacchacharides OSE dictates that it is a carbohydrare

Question 29

Mechanism behind how cyclic monosaccharides form?

Answer 29

The OH on C5 attacks C1, forming s covalent bond. The bond formed is shown here as a long line. The bonds is not abnormally long as depicted in the diagram. The Fischer diagram is a flat representation of a molecule that is curled back into the page such that the ends are close together. * Note that a new chiral centre is formed at C1

Question 30

beta and alpha notation?

Answer 30

Beta = OH on left Alpha = OH on right

Question 31

Haworth structures?

Answer 31

Haworth projections (also referred to as Haworth structures) more accurately depict bond angle and length in ring structures than the original Fischer structures. ▪ In the D-sugar form, when the anomer hydroxyl is up it gives a β-anomeric form (left in Fischer projection) while down gives the α-anomeric form (right).

Question 32

OH down vs up in Haworth structures?

Answer 32

OH down = right in Fischer OH up = left in Fischer

Question 33

How do we convert Fischer to Haworth?

Answer 33

To transfer from the linear form to the cyclic form, the right side needs to go down. Any OH on the left will face up and OH on the right will be pointing down. One of them will become part of the hemiacetal bond.

Question 34

What are the different conformations of the pyranose ring?

Answer 34

The pyranose ring is not planar (flat). It can adopt a “boat” or a “chair” position. Stability of the two forms depends upon the positions of substituents on the rings. Boat = unstable, steric crowding Chair = less steric crowding

Question 35

Can ketoses and 5-member rings be Haworth structures as well?

Answer 35

Ketoses and 5-member rings are depicted in Haworth projections in the same way as we saw for aldoses and 6-member rings.

Question 36

Forms around the asymmetric carbonyl c?

Answer 36

With cyclization, the carbonyl C becomes asymmetric and there are two anomers - α and β.

Question 37

alpha anomer?

Answer 37

In the α form, the OH at C1 is on the opposite side of the sugar from the C6 (CH2OH). - For D sugars, remember that in the α anomer, H is up at C1. - To remember, you can say “AAHA!” (meaning α-anomer-H-up). (It is the opposite for L sugars.)

Question 38

beta anomer?

Answer 38

In the β form, the OH is on the same side of the sugar as the C6 (CH2OH). - In other words, for D sugars, OH is up and H is down. (Again, it is the opposite for L sugars.)

Question 39

How are the different forms of monosaccharides interconverted?

Answer 39

The α- and β-forms of monosaccharides are readily interconverted in aqueous environments.

Question 40

What is mutarotation?

Answer 40

This spontaneous process, mutarotation, produces an equilibrium mixture of α- and β- forms in both furanose and pyranose ring structures. * Open chain form can participate in redox reactions. * There are some that prefer to form and others that don't like to form at all.

Question 41

What are reducing sugars?

Answer 41

Reducing sugars that can reduce compounds such as Benedict’s reagent are called reducing sugars. A reaction with Benedict's Reagent involves copper ions and hydroxyl groups. Glucose reduces the copper.

Question 42

What is required to have a reducing sugar?

Answer 42

This requires an open chain with the aldehyde, so all aldoses are reducing sugars and ketoses such as fructose are reducing sugars as well due to isomerization.

Question 43

Common monosaccharides - Glucose?

Answer 43

Glucose (D-glucose) is found in large quantities throughout the natural world. * The primary fuel for living cells * 6 member ring

Question 44

Common monosaccharides - Fructose?

Answer 44

Fructose (D-fructose) is often referred to as fruit sugar, because of its abundance in fruit. * On a per-gram basis, it is twice as sweet as sucrose; therefore, it is often used as a sweetening agent in processed food * 5 member ring

Question 45

Common monosaccharides - Galactose?

Answer 45

Galactose is necessary to synthesize a variety of important biomolecules, including lactose, glycolipids, phospholipids, proetoglycan, and glycoproteins. * 6 member ring

Question 46

What are some interesting monosaccharide derivatives?

Answer 46

Ribose in RNA is B-D-Ribose Deoxyribose is a derivative in DNA and is B-D-2-Deoxyribose

Question 47

Amino sugars as derivatives?

Answer 47

In amino sugars, a hydroxyl group (usually on carbon 2) is replaced with an amine group * D-glucosamine, and D- galactosamine, N-acetyl- D-glucosamine, and N- acetylneuraminic acid (sialic acid) are examples of amino sugars. * They are common and they are often attached to proteins or lipids.