carbohydrates Flashcards

1
Q

what are carbohydrates made up of

A

Organic compounds of C, H, & O in the ratio C6H12O6

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2
Q

whats the basic unit of carbs

A

Basic unit is the sugar molecule or monosaccharide.

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3
Q

how are carbs derived

A

Derived from photosynthesis: synthesis of CHO from CO2 & H2O in plants in sunlight, with release of O2.

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4
Q

what are the 2 general sources where carbs come from. and name the carbs found from these sources

A

Plants - starch (storage CHO of plants)
- non-starch polysaccharides

Animals - glycogen (storage CHO of liver &
(skeletal) muscle)
- lactose (milk & dairy products)
- ribose (nucleic acids)

Foods providing CHO are the cheapest source of dietary energy and can provide between 40-80% TEI.

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5
Q

what are the roles of carbs

A

Sources of metabolic fuels (sometimes the only function in some cells) & energy stores.

Structural components of cell walls in plants & the exoskeleton of arthropods.

Parts of RNA and DNA structure, in which ribose & deoxyribose respectively are linked to purine & pyrimidine bases.

Integral features of many proteins & lipids (creating glycoproteins & glycolipids), especially in cell membranes - essential for cell-cell recognition & molecular targeting.

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6
Q

explain the ‘historical perspective’ of carbs

A

Main emphasis of CHO as an energy source. (theres not actually a large store of carbs in body)

Thought to be digested in small bowel, and the products absorbed, oxidised in muscle & other tissues and excreted as CO2 & H2O.

“Fibre” thought to pass through gut and be excreted.
- Glucose, galactose , and fructose must be broken down into monosaccharides to be absorbed and in the small intestine. Anything not digested or absorbed in passed to large bowel and so is excreted as waste

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7
Q

explain the digestion and absorption of carbs

A

Rate & extent to which CHO is digested & absorbed from the small intestine differs.

Some CHO reach large intestine where they are fermented and affect large bowel function.

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8
Q

what are the 3 categories that crabs can be classified into, depending upon monosaccharide bonding)

A

simple sugars (1-2 mono saccharides) - small
oligosaccharides (3-9) - longer in length
polysaccharides (>9) - large chains

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9
Q

what can simple sugars be classified into

A

monosaccharides
disaccharides
sugar alcohols

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10
Q

what can oligosaccharides be classified into

A

malto-oligosaccharides (alpha-glucans)
non alpha-glucans

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11
Q

what can polysaccharides be classified into

A

starch (alpha-glucans)
non starch polysaccharides (NSP)

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12
Q

explain monosaccharides structure

A

Consist of 3-7 C atoms, generally in a ring form.

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13
Q

what are monosaccharide sources

A

Glucose – honey, sugar, confectionery, fruit.
Fructose – honey, fruit & some veg. (mainly fruit)
Galactose – not usually found free in nature. (associated with dairy products)

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14
Q

what are examples of 6 carbon monosaccharides (hexose sugars)

A

glucose - predominant one , its in table sugar
fructose
galactose

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15
Q

what are examples of 5 carbon monosaccharides (pentose sugars)

A

ribose
ribulose

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16
Q

explain the physiology of monosaccharides

A

Absorbed from the small intestine.

Glucose & sucrose give rapid glycaemic responses.
The greater the digestion of food, the longer sugar absorption, giving a slower glycaemic response which is good. Free sugar gives a large glycaemic response which is bad

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17
Q

what does the ringed form in pentose sugars participate in

A

metabolic reactions

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18
Q

explain disaccharides structure

A

Polymer of 2 monosaccharides
Formed by condensation between 2 monosaccharides to form a glycoside bond

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19
Q

what are disaccharides sources

A

Sucrose: cane sugar, fruit, berries, veg
Lactose: milk
Maltose: sprouted wheat, barley
Trehalose: fungi, bread, honey

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20
Q

what 4 groups can disaccharides be split into

A

sucrose - glu+fru
lactose - glu+gal
maltose - glu + glu
trehalose - glu + glu

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21
Q

explain the physiology of disaccharides

A

Absorbed
Lactose is fermented in many populations

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22
Q

what does lactase do to glucose

A

Lactase is specific enzyme that only breaks down glucose

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23
Q

what enzyme do all new born mammalian species have

A

lactase

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24
Q

describe the breakdown of lactose by enzyme lactase

A

lactose —-lactase—> glucose + galactose

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25
Q

when does lactase activity rapidly decline

A

after weaning

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26
Q

when do people generally lose ability to produce lactase

A

adulthood

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27
Q

explain lactase intolerance

A

Large amounts of milk lead to unabsorbed lactose which can result in rapid gas production, abdominal pain & diarrhoea.

Occasionally seen in adults of European descent.

Unusual for European people to actually be lactose intolerant

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28
Q

what are sugar alcohols (polyols)

A

Alcohols of glucose and other sugars.

Found naturally in some fruits and made commercially.

they’re artificial sweeteners. Useful as sweeteners as Poorly absorbed and partly fermented.

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29
Q

what are examples of sugar alcohols

A

Sorbitol - sucrose replacement for people with diabetes.

Xylitol - has anti-cariogenic action.

lactitol

mannitol

erythritol

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30
Q

explain physiology of sugar alcohols

A

Poorly absorbed and partly fermented.

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31
Q

what 2 groups can monosaccharides and disaccharides be classified into, and explain them

A

intrinsic sugars - Naturally incorporated into the cell structure of foods

e.g. eating an apple hole, extrinsic sugars – having a juiced apple. As cellular structure destroyed so sugar is free

extrinsic sugars - Not incorporated into the cell structure of foods

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32
Q

what 2 groups can extrinsic factors be classified into and explain

A

lactose in milk
- Not a cause of dental caries
- Milk is the only significant source

non-milk extrinsic sugars (NMES)
- Major cause of dental caries
- Advice to cut intake

NMES – eg free sugar
NMES has sugar added or sugar free in product apart from in milk
If add sugar to dairy products like yoghurt its then NMES , but is the sugar is non added and is natural in the dairy then is lactose sugar in the dairy product so doesn’t cause dental carries

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33
Q

what are oligosaccharides

A

Short-chain carbohydrates.

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34
Q

what 2 groups do oligosaccharides fall into

A

Fall into 2 groups: maltodextrins and oligosaccharides that are not α-glucans.

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35
Q

what can malto-oligosaccharides (α-glucans) be classified into

A

maltodextrins

36
Q

what can other oligosaccharides (non α-glucans) be classified into

A

inulin
polydextrose
galacto-oligosaccharides
fructo-oligosaccharides
stachyose
raffinose

37
Q

describe malto-oligosaccharides

A

Mostly derived from starch.

Include maltotriose, αlpha-limit dextrins

38
Q

explain sources of malto-oligosaccharides

A

Widely used in the food industry as sweeteners and fat substitutes.

39
Q

explain the physiology of malto-oligosaccharides

A

Digested and absorbed.

40
Q

explain the structure of the raffinose oligosaccharide

A

3 monosaccharides: galactose + glucose + fructose

41
Q

explain the structure of the stachyose oligosaccharide

A

4 units: galactose + galactose + glucose + fructose

42
Q

what are the sources of the oligosaccharides Raffinose & verbascose

A

peas, beans & lentils

43
Q

what are the sources of the oligosaccharides Inulin & fructo-oligosaccharides

A

artichokes wheat, rye, onion

44
Q

describe the physiology of the other oligosaccharides (raffinose and stachyose)

A

Chemical bonds not susceptible to pancreatic or brush-border enzyme breakdown.

Fermented - some may selectively stimulate growth of bifido-bacteria in large bowel. – so promote large bowel health.

Prebiotics: foods containing oligosaccharides.
they support growth of commensal bacteria.

Probiotics: live micro-organisms added to food e.g. yoghurt.

45
Q

describe carb fermentation

A

Some sugars, some starch & all NSP escape digestion & absorption in the Small Intestine and become available as substrates for fermentation by the colonic microflora

46
Q

what are products of fermentation

A

CO2
H
CH4
SCFAs - mainly acetate, proprionate & butyrate

47
Q

explain what happens to the gasses from carb fermentation

A

absorbed & excreted through lungs or passed as flatus.

48
Q

explain what happened to the SCFAs from carb fermentation

A

absorbed by Large Intestine mucosa & may be used as E sources by various tissues.

SCFAs = short chain fatty acids
Fermentation products in particular SCFAs have benefits not just to bowel health but also cardiovascular and metabolic heath

49
Q

describe polysaccharides structure

A

Polymers of many 100s of monosaccharide units.
Most important are starch & glycogen (both polymers of glucose).

Other polysaccharides made of other monosaccharides or of glucose units linked differently from linkages in starch & glycogen. These can have mkore structural roles and form a large pprtion of fibre in diet.

Starch and glycogen are energy storing

Glycogen is a highly branching polymer, so isn’t just 1 straight chain

50
Q

what 2 groups can polysaccharides be subdivided into

A

non-starch polysaccharides (NSP)

starch (α-glucans)

51
Q

describe the structure of starch

A

Long chain glucose molecules arranged in straight or branched chains.

80-90% of all polysaccharide eaten.

Examples:
Amylose (straight)
Amylopectin (branched – 16 bond every 30th glucose)
Modified starches – have branches

52
Q

provide sources of starch - grains, legumes, and tubers

A

Grains: wheat, rice, corn, oats, millet, barley
Legumes: peas, beans, lentils
Tubers: potatoes, yams, cassava (starch levels are highest in tubers)

53
Q

explain the structure of starch

A

Arranged in granules of different shapes.

Soluble in water when heated – gelatinisation

During cooling – retrogradation (this forms modified starch)

Liquid may be expressed – syneresis = when starch takes on liquid form

54
Q

what in starch is constantly changing due to its structures

A

texture and appearance

55
Q

explain the physiology of starch

A

Rapidly digestible starch (Very ripe bananas have more digestible starch than under ripe bananas )

Slowly digestible starch – associated with wholegrain cereals

Resistant starch, i.e. resistant to pancreatic enzymes
- Starch physically trapped e.g. whole grains, seeds
- Resistant granules e.g. raw banana
- Retrograded e.g. potato salad
- Chemically modified to resist digestion

Very ripe bananas have more digestible starch than under ripe bananas

56
Q

why might manufacturers modify starch

A

to give a more branched molecule and change its properties

57
Q

what properties can modified starch act as in products made by manufacturers

A

Thickening agent
Stabilizer
Emulsifier

58
Q

what starches are used in manufacture starch modification

A

Arrowroot
Cornstarch
Potato starch
Sago
Tapioca

59
Q

what is glycogen

A

The storage form of carbohydrate in animals found in muscle and liver.

60
Q

in muscle glycogen provides an extra source of what

A

a source of extra glucose for strenuous activity.

61
Q

how is there little to no carbs in meat

A

because Tissue enzymes break glycogen down once animal slaughtered

62
Q

how many grams of glycogen are in human body

A

Only 200-500g of glycogen in human body unless carbohydrate loading by athletes.

63
Q

why do athletes need more glycogen

A

More glycogen in athletes muscles the longer they can contract for

64
Q

what stores glycogen

A

Liver stores glycogen to maintain blood glucose levels in the face of a fast

Livers glucose store is not a large store

65
Q

what are non starch polysaccharides (NSPs)

A

Polysaccharides that cannot be digested by normal enzymes of the human gut.

Non alpha-glucans

NOT to be used interchangeably with fibre

it is fermented

66
Q

what are examples of NSPs

A

cellulose, hemicelluloses, inulin, chitin, pectin, gums and mucilages

Chitin is carb that forms hard exoskeleton in shell fish.
Small shrimps that you don’t de shell, provide you with chitin in diet

67
Q

what source of food type does most fibre come from

A

plant sources

68
Q

what is the structure of cellulose

A

Straight chain of glucose residues connected in a beta 1-4 linkage

69
Q

what structure in plants is cellulose found in

A

cell wall

70
Q

if the Bond of oxygen is below plain of chairs what type of linkage is it

A

alpha linkage

71
Q

if the bond is sitting above the plain of the chairs what type of linkage is it

A

beta linkage

72
Q

name the other types of NSP

A

hemicellulose
inulin
chittin
pectin

73
Q

describe hemicelluloses
what they include and what theyre composed of

A

Include xylan, glucuronoxylan, arabinoxylan, glucomannan, and xyloglucan.

Composed of various monosaccharides (e.g. xylose, mannose, galactose, rhamnose and arabinose) with many branching side chains

Hemicellulose Have glucose backbone with branching side chains that vary depending on what monosaccharides they contain

74
Q

what are hemicelluloses found in

A

Found in outer bran layer of many cereal grains, legumes, veg & nuts.

If food has hard outer coating then the outer coating will be composed of hemicellulose. However often this outer coating is peeled off for ex in veg

75
Q

what is inulin, in terms of structure

A

Collection of fructose polymers of different lengths

76
Q

what is inulin found in

A

Found in wheat, onion, garlic, bananas & asparagus

77
Q

explain the structure of chittin

A

Long chain polymer of Nitrogen-acetylglucosamine

78
Q

what sources is chittin found in

A

In exoskeletons (e.g. crabs & lobsters) and cell walls of most fungi.

Chitin isn’t found in static shell fish like muscles and oysters

Chitins also found in prawns

Some insects also contain chitin

79
Q

describe pectin’s structure

A

Main component is units of galacturonic acid

80
Q

what are sources of pectin

A

fruits

81
Q

what is the property of pectin

A

its gel forming

82
Q

what is the function of gums and mucilages

A

Thick gel-forming fibres that hold plant cells together

83
Q

what are examples of gums

A

seaweeds (carrageenan)

trees (gum Arabic) – tree sap

bacterial fermentation (xanthan gum)

84
Q

what is an example of mucilages and explain their function

A

psyllium or ispaghula – of the Plantago ovata plant

this helps with constipation as is a fibre

85
Q

what are the consequences of low NSP diets

A

Small volumes of bowel contents which move slowly & allow harmful residues to persist.
Linked with:
Haemorrhoids
Diverticular disease - forms pouches in wall
Colon cancer-

Colon cancer- to bowel wall with toxic material