Topic 8 - Carbohydrates

Question 1

Describe the structure and chemical reactivity of alcohol functional group

Answer 1

Is an -OH group attached to a saturated C atom. -due to -OH group, can H bond -are polar -

Question 2

Describe the structure and chemical reactivity of the aldehyde & ketone functional groups

Answer 2

carbonyl functional group is a carbon double bonded to an oxygen
-can undergo oxidation reactions

-can undergo keto-enol tautomerism. This refers to the equilibrium between the two possible tautomers. The interconversion of the two forms involves the movement of a proton and the shifting of bonding electrons. This equilibrium affords the compounds more reactivity

Question 3

Describe the structure and function of ether functional group

Answer 3

• inability to form H bonds w/ each other
• slightly polar
• subject to reacting w/ strong acids due to two lone pairs of electrons on O atom

Question 4

Describe the structure and chemical reactivity of the anhydride functional group

Answer 4

Question 5

List the major functions of Carbohydrates

Answer 5

Energy storage e.g. starch (plants) glycogen (animals)

Structural e.g. cellulose, chitin

Extenders of protein function e.g. when combined w/ proteins, CHD increase H2O binding capacity

**Informational molecules **e.g. bar codes on proteins, secind messengers in signal transduction

Question 6

Define Carbohydrates and give their formula

Answer 6

A CHD is a compound w/ 3 or more C atoms which as an aldehyde or keto functional group & two or more hydroxyl groups

C_n(H₂O)_n

• Produced from CO₂ and H₂O during photosynthesis in plants
• Can be covalently linked w/ proteins to form glycoproteins & proteoglycans

Question 7

What is a mono/di/trisaccharide?

Answer 7

Mono: A simple CHD; consists of only one sugar unit. Cannot be hydrolysed to smaller CHD molecule

Di: complex CHD; 2 sugar units

Tri: complex CHD; 3 sugar units

Question 8

What is a oligosaccharide?

Answer 8

A complex CHD

consists or two or more sugar units

Question 9

What is a polysaccharide?

Answer 9

consists of many sugar units (more than 20); it is a CHD polymer (complex)

Question 10

(monosaccharides)

How many carbons does a….
triose have?

tetrose?

pentose?

hexose?

Answer 10

triose =3

tetrose =4

pentose =5

hexose =6

Question 11

What two groups can monosaccharides be divided into?

Answer 11

aldehydes and ketones

• name beginning w/ “aldo” =terminal carbonyl group is aldehyde
• name beginning w/ “keto” =NON-terminal carbonyl group is ketone

Question 12

(monosaccharides)

Trioses are either aldo trioses or ketotrioses and so on up to aldohexoses and ketohexoses

Answer 12

Question 13

What are stereoisomers?

Answer 13

are different compounds that have the same structure, but differ only in the arrangement of the atoms in 3D space.

Question 14

All monosaccharides, except dihydroxyacetone, contain at least 1 chiral C and therefore occur as stereoisomers.
T or F?

Answer 14

True

Question 15

Molecules w/ one chiral C have 1 type of stereoisomer. Name and describe this stereoisomer.

Answer 15

Enantiomers (pair)

-is one of two stereoisomers that are mirror images of each other that are “non-superposable”

Question 16

How do we know if a monosaccharide is a D series or L series

Answer 16

• A monosaccharide is a member of the D-series, if the hydroxyl group on the chiral carbon farthest from carbon 1 is on the right.
• A monosaccharide is a member of the L-series, if the hydroxyl group on the chiral carbon farthest from carbon 1 is on the left.

Question 17

What are diastereomers?

Answer 17

Any pair of stereoisomers that are NOT enantiomers (not mirror images) and differ in 1 or more chiral centres

Question 18

What are epimers?

Answer 18

Non mirror image isomers that differ only in the configuration around one chiral atom

**not epimers if they differ by more than one chiral atom

Question 19

Stereoisomer nomenclatural summary

Answer 19

Question 20

What is the formula used to determine the number of isomers of aldo and keto sugar families?

Answer 20

2ⁿ
where n is the number of chiral centres

e.g. Aldotetroses (with 4C) have two chiral centres.
Thus 2² equals 4 stereoisomers.

Question 21

What kind of pentose is Ribose?

Answer 21

aldo-pentose

Question 22

What kind of hexose is glucose?

Answer 22

aldo-hexose

Question 23

What kind of hexose is fructose?

Answer 23

keto-hexose of glucose

Question 24

Please read over practice (clicker) Q’s in lecture
:)

Answer 24

do it!!!!!!!!!

Question 25

Monosaccharides with a 5+ C atoms occur predominantly as what? How is this formed?

Answer 25

cyclic structures -formed by aldehyde or ketone groups reacts w/ a hydroxyl group along the chain, forming a covalent bond

Question 26

Describe how to ID alpha and beta forms of simple CHD's

Answer 26

The middle step where the OH migrates down =\>this can cause rotation, so the molecule either becomes stuck as **alpha (OH below ring) beta (OH above ring)**

Question 27

What is an anomer?

Answer 27

Compounds that differ in configuration only aroun the C atom that may yield a carbonyl group (ketone or aldehyde) on rearrangement.

Question 28

Number of cyclic stereoisomers | (see answer)

Answer 28

* Therefore, from the 16 (2⁴) aldohexose stereoisomers, there are an additional 32 cyclic isomers * i.e. 16 pairs of anomers * Plus 16 LINEAR isomers * = 48 total aldohexose isomers

Question 29

What are conformers? How do they differ from configurational isomers? (enantiomers, diastereomers, anomers)

Answer 29

Molecules w/ the same stereochemical configuration, but differ in 3D conformation -differ from configurational as they can interconvert w/out breaking & reforming bonds

Question 30

What is mutarotation?

Answer 30

alpha and beta anomers interconvert in solution

Question 31

Monosaccharides are reducing agents. -read description in answer

Answer 31

•Because of rapid interconversion between 99% ring form and 1% linear form, 100% of glucose molecules in solution can be rapidly oxidised in the reactive (aldehyde) linear form

Question 32

For info on Disaccharides (glycosidic bonds) see lecture.

Question 33

What do dissacharides consist of? How is the bond formed?

Answer 33

two monosaccharides joinded covalently by an O-glycosidic bond. a glycosidic bond can form b/w the hemiacetal group of one monosaccharide and the alcohol group of another

Question 34

What does Maltose consist of?

Answer 34

Two D-glucose units joined by a **_alpha 1-4 glycosidic bond._** -wavy lines indicate it can Beta OG group can freely interconvert with alpha-D-glucose via mutarotation

Question 35

What does Lactose consist of?

Answer 35

Composed of D-galactose and D-glucose -Beta-lactose, contains a **beta1-4 glycosidic bond**

Question 36

What does Sucrose consist of?

Answer 36

Disaccharide of glucose & fructose NON REDUCING SUGAR **glycosidic bond forms b/w C1 of glucose and C2 of fructose** -bond involves the anomeric C of both monosaccharides =locked configuration, no mutarotation (interconversion) or reducing end (will not oxidise)

Question 37

Are there alpha or beta isomers of sucrose? explain.

Answer 37

No. All the anomeric carbons are involved in bond formation

Question 38

What is a homopolysaccharide? Name the 3 most important ones and give a brief description of their role

Answer 38

Contain only one single type of monosaccharide - starch (energy store in plants) - glycogen (energy store in animals) - cellulose (structural role in plants)

Question 39

What is a heteropolysaccharide?

Answer 39

Contain two or more different monosaccharides

Question 40

Which two kinds of homopolysaccharides does starch contain?

Answer 40

Amylose (water soluble, simpler structure) Amylopection (water insoluble, complex structure)

Question 41

Describe Amylose

Answer 41

- linear polymer of D-glucose residues - glucose monomers are linked by an alpha1-4 glycosidic bond - vary in length, form coiled helical structures

Question 42

Describe Amylopectin

Answer 42

branched polysaccharide, consisting of glucose residues joined by: **-alpha1-4 linkages** **-alpha1-6 linkages** Branches occur every 24-30 residues

Question 43

Describe Glycogen

Answer 43

Glucose homopolysaccharide **-a1-4linkage** **-a1-6 linkages** Is similar to amylopectin, but more highly branched. Branches occur every 8-12 glucose residues

Question 44

Describe Cellulose

Answer 44

structural homopolysaccharide water insoluble similar to amylose, though **cellulose is unbranched & linear** **BETA1-4 linkages** (amylose alpha) parallel cellulose chains linked together by H bonding

Question 45

SUMMARY OF STRUCTURES AND BOND LINKAGES | (amylose, amylopectin, glycogen, cellulose)

Answer 45