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biomolecular science > carbs part 1 > Flashcards

carbs part 1 Flashcards

1
Q

whats the carb general formula

A

Cm(H2O)n

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2
Q

what are carbs and what groups do they contain

A

hydrates of carbon though some contain other elements such as nitrogen

Synthesis by plants from CO2 & H2O + energy

they contain the carbonyl (C=O) and hydroxyl (OH) groups. which hydrogen bonds occur between

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3
Q

discuss alcohol solubility

A

Alcohols tend to be very soluble in water due to hydrogen bonding between water molecules and the polar OH groups.

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4
Q

name the 3 major carb groups

A

monosaccharide, oligosaccharide, and polysaccharide

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5
Q

monosaccharides NO. units and ex

A

they have 1 unit

e.g. ribose, glucose, fructose,

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6
Q

oligosaccharides unit NO. and ex

A

they have 2 or more units that don’t have to be same they can be different from each other

e.g. sucrose, maltose, lactose

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7
Q

polysaccharides NO. units and ex

A

they have many units (100 - 1000)
as poly means many

e.g. cellulose, starch, glycogen

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8
Q

what are the most common monosaccharides

A

pentoses (5 carbons) and the hexoses ( 6 carbons).

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9
Q

naming monosaccharides

A

Common names are used, ending in ‘ose’

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10
Q

what are monosaccharides classified as and how

A

Classified as aldoses or ketoses, depending on whether they contain an aldehyde or a ketone group.

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11
Q

what do stereoisomers have

A

multiple chiral carbons

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12
Q

in what shape are sugars found in nature

A

in a ring

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13
Q

in an aldose sugar what is attached to the first and last carbon

A

the first carbon is at top of chain and has an aldehyde group attached

the last carbon has the primary alcohol group attached (hydroxyl group)

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14
Q

how many chiral carbons does a hexose aldose sugar have

A

4
Therefore there are 2 to the power of 4 =16 stereoisomers , ie. 8 pairs of mirror images.
so 8 sugars

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15
Q

what does a chiral carbon have that a non chiral carbon doesn’t have

A

4 diff groups attached to the carbon

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16
Q

are ketoses rare or common in nature

A

rare.
fructose is the most interesting and common one

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17
Q

how many chiral carbons does a hexose ketose sugar have

A

3 chiral carbons …. Therefore there are 23=8 stereoisomers , ie. 4 pairs of mirror images.

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18
Q

what is D/L nomenclature is based on for

A

orientation of the hydroxyl group on the greatest number chiral Carbon, ex c6 on the aldose or ketose
as chiral carbons are numbered after the c=o group

D for right hand side
L foe left hand side

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19
Q

what are enantiomer optical isomers

A

non-superimposable mirror images of one another eg. D and L glucose

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20
Q

what are Diastereoisomer optical isomers

A

if not mirror images but their chiral carbons are connected to the exactly the same substrates but connected at differing configurations

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21
Q

what are epimer optical isomers

A

two diastereoisomers that differ only at one stereocenter eg. D-Arabinose and D-Ribose

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22
Q

what do cyclic forms result from

A

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

sugars in nature exist by large as a ring structure, as there most stable. But aren’t a ring structure in solution.

Its reversible reaction as ring opens and closes continuously but at very high speed
But theres always a time when we have a number of closed molecules at one time as they have to be in closed form in nature

Theyre intramolecular as it happens within the molecule

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23
Q

what forms when alcohol reacts with aldehydes and ketones

A

“hemi acetyls” or “hemi ketals”

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24
Q

what are pyranose form of a monosaccharide and furanose form

A

The pyranose form of a monosaccharide has a six-membered ring, while the furanose form has a five-membered ring.

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25
Q

what is the chair type structure

A

sugars exist in solution in the most thermodynamically favourable arrangement. For most 6-membered rings this is the chair-type structure.

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26
Q

what is Mutarotation (interconversion)

A

When sugars such as glucose are in the ring form, carbon 1 is chiral and is called the anomeric carbon.

The new stereoisomers, termed anomers, are designated a and b.

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27
Q

what is an alpha anomer

A

OH group at C-1 is on the opposite side of the ring from the CH2OH group…. shown here below the plane of the ring.

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28
Q

what does glucose crystallised from ethanoic acid give

A

pure beta form
[beta]D +19 degrees

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29
Q

what does glucose crystalised from methanol give

A

pure alpha form
[alpha]D +113 degrees

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30
Q

the alpha and beta anomers differ in the degree of rotation of what

A

plane-polarized light

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31
Q

what happens during recrystallisation and whats it used for

A

you take a compound eg glucose and you crystallise it in a lil bit of warm solvent, eg, ethanol, methanol, etc. and you leave it until the crystals form

Crystallisation is used to purify compounds

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32
Q

what can the change in the Mutarotation of glucose be monitored by

A

a polarimeter

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33
Q

what happens in mutarotation of glucose when the pure alpha and beta forms of glucose are dissolved in water

A

the rotation gradually changes until it reaches an equilibrium value of + 52 degrees

due to the slow conversion of pure anomers into a 37a:63b equilibrium mixture. . in This the example, the beta form is dominant for glucose

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34
Q

what happens in a polarimeter during glucose mutarotation

A

the light shines through the sample, this analyses what comes out and then you detect the results

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35
Q

whats the Most stable form of Glucose in solution

A

C1 conformation and the b anomer is preferred for D-glucose in solution and therefore this form predominates. this keeps all the hydroxyl groups apart from each other

36
Q

what is oxidation reaction

A

the addition of oxygen

37
Q

what are weak oxidising agents and what do they do

A

Tollens, Fehlings and Benedicts solutions oxidise the carbonyl group end of the monosaccharide.

38
Q

what are tests for reducing sugars and explain the test

A

With Fehling’s solutions, glucose reduces the copper Cu2+ ion (blue) to the Cu+ (red) ion.

We get oxidation of the aldehyde to a carboxylic acid and the sugars are called reducing sugars.

This is used as a test for reducing sugar
Fehling’s is copper sulphate in sodium hydroxide
The oxidising agent is reduced to copper oxide, from blue to orange. So Fehling’s solution is reduced to copper oxide
So we go from aldose sugar to an acid sugar
So glucose is a reducing sugar cos of what happened to Fehling’s solution

39
Q

what do sugars need in order to be reducing

A

a free aldehyde group.

this isn’t present when in ring form

40
Q

how is glucose able to react with Fehling’s, Benedict’s and Tollen’s reagents.

A

because even though Glucose is mainly in the cyclic form in solution, the equilibrium to the open chain form is established quickly enough to allow it to react with the Fehling’s, Benedict’s and Tollen’s reagents.

41
Q

how can A ketose undergo oxidation reactions even though it does not possess an aldehyde group

A

because in alkaline solution the ketose form is in equilibrium with the aldose form through an enediol intermediate.

So if put fructose in water with Fehling’s reagent then fructose will reducing sugar, even tho there’s no aldehyde, because of the intermediate

42
Q

what does a strong oxidising agent do and give an ex of a strong oxidising agent

A

Such as dilute nitric acid, can oxidise both ends of a monosaccharide at the same time - so is why its called strong. (carbonyl group + terminal primary OH group) to produce a dicarboxylic acid.
Eg. glucaric acid

43
Q

what groups are most easily oxidised by a strong oxidising agent

A

Aldehyde groups most easily oxidised, followed by the primary alcohol group

44
Q

what can enzyme systems do

A

oxidise the primary alcohol end of an aldose such as glucose, without oxidising the aldehyde group to give a uronic acid.

enzymes are selective so that’s why there good

45
Q

what are uronic acids

A

Often components of polysaccharides. Glucuronic acid is, for example, a component of hyaluronic acid, the main component of vitreous humour of the eye.

46
Q

what happens during reduction

A

The carbonyl group (CHO) can be reduced to an hydroxyl group (OH), using hydrogen as the reducing agent to produce a polyhydroxy alcohol (sugar alcohol).

47
Q

what are examples of reduction made sugars

A

glucitol - occurs naturally in some fruits and berries and is sold commercially as the bulk sweetener “Sorbitol”.

sweetener in “tooth friendly” gum.

moisturising agent in food and cosmetics

48
Q

what are deoxy sugars

A

one of the OH groups is completely reduced to H

49
Q

how are phosphate esters formed

A

The hydroxyl group of a monosaccharide can react with inorganic oxyacids such as phosphoric acid to form inorganic esters.

acid + alcohol -> ester + water

50
Q

what are the important roles of phosphate esters

A

carbohydrate metabolism and is a component of DNA and RNA.

51
Q

how are glycosides formed

A

Cyclic forms of monosaccharides react with alcohols or with amines to form glycosides.

52
Q

how do glycosides bond

A

through the anomeric carbon

53
Q

how are cyclic molecules that reacat with another alcohol such as disaccharides bound

A

by glycosidic linkage

54
Q

how are foxgloves toxic glycosides

A

Foxgloves (Digitalis purpurea) provide the important heart stimulant, digitalin.

They become harmful when the glycon portion is stripped off during digestion.

55
Q

amino sugars of what are common in nature

A

glucose, mannose and galactose

56
Q

how does the amino sugars structure differ from other sugars

A

Hydroxyl group on carbon-2 is replaced with an amino group (NH2) (enzymic reaction). this occurs under enzymes in nature

57
Q

what is good about amino sugars being present in the biological marker on red blood cells

A

it allows us to distinguish blood types

58
Q

explain the glycosidic linkage/bond in oligosaccharides

A

The cyclic form of one monosaccharide can react with an alcohol group from another to form a disaccharide.

The mono units are linked by glycosidic bond, which is covalent so strong bond

59
Q

how big are oligosaccharide chains

A

big , usually 25 onwards

60
Q

whats the diff between hydrolysis and condensation reactions

A

Hydrolysis is splitting apart a molecule usually in water
condensation is the opposite and water is produced

61
Q

what are the Properties of glycosidic bonds

A

Stable under normal conditions

Hydrolysed by acid + heat or specific enzymes

62
Q

explain the occurrence of free oligosaccharides

A

Free oligosaccharides other than disaccharides, are rarely found in biological systems and are usually associated with proteins or lipids.

63
Q

disaccharides examples

A

Sucrose: Main food sweetener. Digestible by humans.

Lactose: 5-8% in milk. Digestible by many humans.

Cellobiose: From cellulose hydrolysis. Does not occur naturally. Not digestible by humans.

Maltose: From starch hydrolysis, used in food fermentations. Digestible by humans. Common ingredient in baby food.

64
Q

what does lactose structure consist of and hows it bonded

A

Lactose consists of β-D-galactose and D-glucose molecules bonded through a β1-4 glycosidic linkage.

The C1 on the glucose unit is not involved in bonding

65
Q

what do reducing sugars do

A

open the ring

66
Q

how can the disaccharides of lactose, cellobiose and maltose, possess a free aldehyde group

A

The glucose unit, shown on the right, in lactose, cellobiose and maltose can exist in the open chain form in solution

They are therefore reducing and can exist in both alpha and beta anomeric forms in solution.

67
Q

explain the glycosidic bond structure of sucrose

A

The glycosidic bond in sucrose is an a, b (1-2) linkage and involves the anomeric carbons of both its constituent sugar residues.

its made up of 2 anomeric carbons, not alcohol

68
Q

what does the locked closed ring of glucose and fructose cause for the disaccharide

A

disaccharide does not possess a free aldehyde group in solution and sucrose is non reducing.

69
Q

enzymes are specific so hydrolyse the linkage in which 3 structures, and dont hydrolyse the linkage in which 1 structure

A

Human enzymes can hydrolyse the linkage in sucrose, lactose and maltose but not the b 1-4 linkage in cellobiose (a derivative of cellulose).

70
Q

sucrose can be hydrolysed by acids or invertase to produce what

A

glucose and fructose, this is invert sugar

71
Q

what can invert sugar be used for

A

Crystallisation control
Texture softening
Moistness
Increased viscosity
Reduced freezing point

72
Q

what are the general properties of polysaccharides

A

Contain many, often tens of thousands of monosaccharide units joined by glycosidic linkages. so very long

Each addition carried out by a specific enzyme.

Linear or branched.

May be homogeneous (contain similar sugar units in chain), or heterogeneous. (heterogeneous contain diff sugar units in their chain)

Commonly food reserves and structural components of cells.

Often insoluble and difficult to purify.

73
Q

how do we name polysaccharides

A

Originally named according to their source, properties or function.

Now named on the basis of their monosaccharide units:
- homopolysaccharides - replace “ose” of sugar with “an” eg. glucan.

  • heteropolysaccharides - use structural unit of main chain, prefixed with names of other units. eg. galactomannan
74
Q

what are examples of common glucans

A

Starch - stored polysaccharides in plants

Glycogen - stores polysaccharides in animals such as humans

cellulose - in structure in plants

75
Q

why store glucose as a polysaccharide

A

Osmotic pressure is proportional to the number of solute molecules … So 1000 glc molecules has a 1000 x higher osmotic pressure than 1 molecule of glucose polymer with 1000 units.

carb sugars are stored as polysaccharides

76
Q

what is the glucan - starch

A

Is the main food reserve in plants eg. Cereals, potatoes, rice etc. (present as granules)

77
Q

whats the structure of amylose

A

Linear with all the glucose units linked via a(1-4) linkages [200-2000 glc units long].

its soluble in cold water

78
Q

what chape does amylose form

A

helix

79
Q

what colour does amylose form with iodine

A

blue complex

80
Q

what is the structure of amylopectin

A

Branched, having a small no. of a(1-6) linkages at various points along an a(1-4) chain [up to 100,000 units].

Branching is similar to the veins of a leaf, starting with a single strand which branches out every 20-25 units.

81
Q

what percentage do most starches (maize, potato, rice) contain of amylose

A

20 - 30%

some cereals contain only 0 - 5% (waxy mutants).

82
Q

what is glycogen

A

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

83
Q

explain the structure of glycogen

A

Similar to amylopectin in structure but more highly branched, with shorter branches (average of 12 glucose units). Around 60,000 glucose units .

84
Q

how is glycogen built up and broken down

A

by enzymic reactions

85
Q

where is cellulose found

A

Structural component of plants cell walls.

86
Q

what is the structure of cellulose

A

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

87
Q

whats the importance of linearity in cellulose in plants

A

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

biomolecular science (6 decks)

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