carbohydrates Flashcards
what are carbohydrates made up of
Organic compounds of C, H, & O in the ratio C6H12O6
whats the basic unit of carbs
Basic unit is the sugar molecule or monosaccharide.
how are carbs derived
Derived from photosynthesis: synthesis of CHO from CO2 & H2O in plants in sunlight, with release of O2.
what are the 2 general sources where carbs come from. and name the carbs found from these sources
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.
what are the roles of carbs
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.
explain the ‘historical perspective’ of carbs
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
explain the digestion and absorption of carbs
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.
what are the 3 categories that crabs can be classified into, depending upon monosaccharide bonding)
simple sugars (1-2 mono saccharides) - small
oligosaccharides (3-9) - longer in length
polysaccharides (>9) - large chains
what can simple sugars be classified into
monosaccharides
disaccharides
sugar alcohols
what can oligosaccharides be classified into
malto-oligosaccharides (alpha-glucans)
non alpha-glucans
what can polysaccharides be classified into
starch (alpha-glucans)
non starch polysaccharides (NSP)
explain monosaccharides structure
Consist of 3-7 C atoms, generally in a ring form.
what are monosaccharide sources
Glucose – honey, sugar, confectionery, fruit.
Fructose – honey, fruit & some veg. (mainly fruit)
Galactose – not usually found free in nature. (associated with dairy products)
what are examples of 6 carbon monosaccharides (hexose sugars)
glucose - predominant one , its in table sugar
fructose
galactose
what are examples of 5 carbon monosaccharides (pentose sugars)
ribose
ribulose
explain the physiology of monosaccharides
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
what does the ringed form in pentose sugars participate in
metabolic reactions
explain disaccharides structure
Polymer of 2 monosaccharides
Formed by condensation between 2 monosaccharides to form a glycoside bond
what are disaccharides sources
Sucrose: cane sugar, fruit, berries, veg
Lactose: milk
Maltose: sprouted wheat, barley
Trehalose: fungi, bread, honey
what 4 groups can disaccharides be split into
sucrose - glu+fru
lactose - glu+gal
maltose - glu + glu
trehalose - glu + glu
explain the physiology of disaccharides
Absorbed
Lactose is fermented in many populations
what does lactase do to glucose
Lactase is specific enzyme that only breaks down glucose
what enzyme do all new born mammalian species have
lactase
describe the breakdown of lactose by enzyme lactase
lactose —-lactase—> glucose + galactose
when does lactase activity rapidly decline
after weaning
when do people generally lose ability to produce lactase
adulthood
explain lactase intolerance
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
what are sugar alcohols (polyols)
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.
what are examples of sugar alcohols
Sorbitol - sucrose replacement for people with diabetes.
Xylitol - has anti-cariogenic action.
lactitol
mannitol
erythritol
explain physiology of sugar alcohols
Poorly absorbed and partly fermented.
what 2 groups can monosaccharides and disaccharides be classified into, and explain them
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
what 2 groups can extrinsic factors be classified into and explain
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
what are oligosaccharides
Short-chain carbohydrates.
what 2 groups do oligosaccharides fall into
Fall into 2 groups: maltodextrins and oligosaccharides that are not α-glucans.