Topic 1 Biomolecules - Carbohydrates

Question 1

What are carbohydrates composed of?

Answer 1

Carbohydrates are molecules composed almost exclusively of carbon, hydrogen and oxygen

Question 2

What are carbohydrates general formula?

Answer 2

Cm(H2O)n

Question 3

What are carbohydrates chemistry made up of?

Answer 3

Carbonyl and hydroxyl groups

Question 4

What is the only functional group present in all carbohydrates?

Answer 4

Hydroxyl

Question 5

What are carbohydrates classified into?

Answer 5

Classified into simple carbohydrates or monosaccharides (1 unit), oligosaccharides (2 or more units) and complex carbohydrates or polysaccharides (many units)

Question 6

What are monosaccharides?

Answer 6

They are carbohydrate monomers, the simplest carbohydrates and are classified by the number of carbons they contain.
most common monosaccharides are pentoses (5 carbons) or hexoses (6 carbons) (common names are used, ending in ‘ose’)

Question 7

What are aldoses?

Answer 7

Sugars with aldehyde groups

Question 8

What are ketoses?

Answer 8

Sugars with ketone groups

Question 9

According to Fischers projection which carbon is C1?

Answer 9

the most oxidised carbon. AKA the C=O end

Question 10

According to Fischer Projection, if the OH and NH2 on the highest numbered chiral carbon is on the right of the vertical carbon chain, then is the molecule designated D or L?

Answer 10

D

Question 11

According to Fischer projection which orientation does D represent?

Answer 11

Right (D form occurs in nature)

Question 12

According to Fischer projection which orientation does L represent?

Answer 12

Left

Question 13

What are enantiomers?

Answer 13

Non-superimposable mirror images

Question 14

According to fischer projection are D and L enantiomers?

Answer 14

Yes

Question 15

How do cyclic forms, form?

Answer 15

Cyclic forms result from the intramolecular reversible reaction of their C=O group with an OH group (usually the OH on the highest numbered chiral carbon)

Question 16

How are hemiacetals or hemiketals formed?

Answer 16

When alcohols react with aldehydes or ketones, and a cyclic formation results

Question 17

Which conformation is favoured in chair-type structure?

Answer 17

C1

Question 18

In mutarotation what are the stereoisomers, termed anomers designated?

Answer 18

Alpha and beta

Question 19

In an alpha-anomer is the OH group at the C-1 on the same side of the ring as the CH2OH group?

Answer 19

No, they are on opposite sides

Question 20

In a beta-anomer is the OH group at the C-1 on the same side of the ring as CH2OH group?

Answer 20

yes

Question 21

What is the most stable form of glucose in solution?

Answer 21

C1 conformation and the beta anomer is preferred for D-glucose in solution and therefore this form predominates, this conformation minimises steric hindrance between the large OH groups

Question 22

How are glycosidic bonds formed?

Answer 22

These bonds are formed by loss of water between two adjacent hydroxyl groups

Question 23

What things occur in cells as glycosides?

Answer 23

Many plant pigments, toxins, flavourings and steroids e.g. salicin butter rasting glycoside form willow bark, traditionally used to reduce fever, these molecules have glycone (sugar) and aglycone (non-sugar) portions

Question 24

What are some toxic glycosides?

Answer 24

Foxgloves provide the important heart stimulant, digitalin. they become harmful when the glycone portion is stripped off during digestion

Question 25

What do cyclic monosaccharides form?

Answer 25

Can form isomers called anomers

Question 26

What is the difference between amino sugars and a typical carbohydrate?

Answer 26

Hydroxyl group on carbon 2 is replaced with an amino group (NH2) (enzymic reaction)

Question 27

What is formed when the cyclic form of one monosaccharide reacts with an alcohol group?

Answer 27

A disaccharide (enzyme catalysed condensation reaction)

Question 28

What are some properties of glycosidic bonds?

Answer 28

Strong and stable under normal conditions, to break it requires hydrolyses with acid+heat or specific enzymes

Question 29

What are some examples of disaccharides?

Answer 29

Sucrose-main food sweetener, digestible by humans Lactose- 5-8% in milk, digestible by many humans cellobiose - form cellulose hydrolysis. does not occur naturally. not digestible by humans Maltose - from start hydrolysis, used in food fermentations, digestible by humans, common ingredient in baby food

Question 30

What does Lactose consist of?

Answer 30

Lactose consists of Beta-D-galactose and D-glucose molecules bonded through a Beta1-4 glycosidic linkage (This linkage indicates that C1 (anomeric carbon) of galactose is linked to C4 of the glucose. The OH at C1 which reacted was above the plane of the ring i.e. β)

Question 31

What is maltose and how is it formed?

Answer 31

Maltose is a disaccharide formed by the linkage of two monosaccharides with the elimination of water.

Question 32

How are lactose, cellobiose and maltose reducing and are able to exist in both alpha and beta anomeric forms in solution?

Answer 32

The glucose unit in lactose, cellobiose and maltose can exist in the open chain form in solution and therefore these disaccharides possess a free aldehyde group.

Question 33

Why is sucrose unique?

Answer 33

Sucrose is unique in that the anomeric carbons of both sugars are involved in forming the glycosidic bond. The rings of glucose and fructose are effectively locked closed and therefore the disaccharide does not possess a free aldehyde group in solution and sucrose is non reducing.

Question 34

What is enzyme hydrolysis?

Answer 34

Enzymatic hydrolysis is a process in which enzymes facilitate the cleavage of bonds in molecules with the addition of the elements of water and plays an important role in the human system for the digestion of food. ANSWER FROM GOOGLE

Question 35

What are some general properties of polysaccharides?

Answer 35

Contain many, often tens of thousands of monosaccharide units joined by glycosidic linkages. Each addition carried out by specific enzymes Linear or branched May be homogeneous or heterogeneous commonly food reserves and structural components of cells often insoluble and difficult to purify

Question 36

What are some common Glucans?

Answer 36

Starch, glycogen and cellulose

Question 37

Describe Amylose

Answer 37

Linear with all the glucose units linked via alpha(1-4) linkages (200-2000 glucose units long) Amylose tends to form a helix. the polysaccharide forms a blue complex with iodine

Question 38

Describe amylopectin

Answer 38

Branched, has a small number of alpha(1-6) linkages at various points along an alpha(1-4) chain (up to 100,000 units)

Question 39

What are properties of starch?

Answer 39

Is the main food reserve in plants e.g. cereals, potatoes, rice etc (present as granules) The proportion of amylase and amylopectin varies depending on plant source most starches (maize, potato, rice) contain 20-30% amylose

Question 40

What are some properties of glycogen?

Answer 40

Polyglucan Energy reserve polysaccharide, abundant in the liver and in muscle cells built up and broken down by enzymic reactions

Question 41

what are some properties of cellulose?

Answer 41

polyglucan structural component of plant cell walls Composed of linear chains of 2000-3000 glucose units, joined by β(1 → 4) linkages.

Question 42

What does linearity allow cellulose in plants to do?

Answer 42

Allows polymers to line up in fibres with a great deal of hydrogen bonding between adjacent chains (strong) and little interaction with water (insoluble)