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PL1003 > Topic 1 Biomolecules - Carbohydrates > Flashcards

Topic 1 Biomolecules - Carbohydrates Flashcards

1
Q

What are carbohydrates composed of?

A

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

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2
Q

What are carbohydrates general formula?

A

Cm(H2O)n

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3
Q

What are carbohydrates chemistry made up of?

A

Carbonyl and hydroxyl groups

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4
Q

What is the only functional group present in all carbohydrates?

A

Hydroxyl

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5
Q

What are carbohydrates classified into?

A

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

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6
Q

What are monosaccharides?

A

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’)

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7
Q

What are aldoses?

A

Sugars with aldehyde groups

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8
Q

What are ketoses?

A

Sugars with ketone groups

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9
Q

According to Fischers projection which carbon is C1?

A

the most oxidised carbon. AKA the C=O end

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10
Q

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?

A

D

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11
Q

According to Fischer projection which orientation does D represent?

A

Right (D form occurs in nature)

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12
Q

According to Fischer projection which orientation does L represent?

A

Left

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13
Q

What are enantiomers?

A

Non-superimposable mirror images

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14
Q

According to fischer projection are D and L enantiomers?

A

Yes

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15
Q

How do cyclic forms, form?

A

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)

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16
Q

How are hemiacetals or hemiketals formed?

A

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

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17
Q

Which conformation is favoured in chair-type structure?

A

C1

18
Q

In mutarotation what are the stereoisomers, termed anomers designated?

A

Alpha and beta

19
Q

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

A

No, they are on opposite sides

20
Q

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

A

yes

21
Q

What is the most stable form of glucose in solution?

A

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

22
Q

How are glycosidic bonds formed?

A

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

23
Q

What things occur in cells as glycosides?

A

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

24
Q

What are some toxic glycosides?

A

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

25
Q

What do cyclic monosaccharides form?

A

Can form isomers called anomers

26
Q

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

A

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

27
Q

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

A

A disaccharide (enzyme catalysed condensation reaction)

28
Q

What are some properties of glycosidic bonds?

A

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

29
Q

What are some examples of disaccharides?

A

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

30
Q

What does Lactose consist of?

A

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)

31
Q

What is maltose and how is it formed?

A

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

32
Q

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

A

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.

33
Q

Why is sucrose unique?

A

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.

34
Q

What is enzyme hydrolysis?

A

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

35
Q

What are some general properties of polysaccharides?

A

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

36
Q

What are some common Glucans?

A

Starch, glycogen and cellulose

37
Q

Describe Amylose

A

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

38
Q

Describe amylopectin

A

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

39
Q

What are properties of starch?

A

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

40
Q

What are some properties of glycogen?

A

Polyglucan

Energy reserve polysaccharide, abundant in the liver and in muscle cells

built up and broken down by enzymic reactions

41
Q

what are some properties of cellulose?

A

polyglucan

structural component of plant cell walls

Composed of linear chains of 2000-3000 glucose units, joined by β(1 → 4) linkages.

42
Q

What does linearity allow cellulose in plants to do?

A

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

PL1003 (8 decks)

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