2 Flashcards
(14 cards)
carbohydrates
- 80% used by organs and 20% goes to liver to be metabolised and stored
- comes from plants (initially from the sun)
monosaccharides
- ketone: 8 stereoisomers (3 chiral atoms)
- aldehyde: 16 stereoisomers (4 chiral atoms)
CnH(2n)On
Visually differentiate ketone and aldehyde group
most hexoses of living organisms are D isomers
epimers
two sugars that differ only in the configuration around one carbon atom
I.e. A pair of stereoisomers
carbohydrate derivatives
sorbitol:
- found naturally in stone fruit and added in chewing gum
- cannot be digested by bacteria, low calorie
gluconic acid:
- found in fruit, honey, etc
- used as a food additive to regulate acidity
- used in medicine to avoid necrosis of deep tissues and treat malaria
Dissacharides
- sucrose: 2 monomers of glucose joined by a alpha 1-2 glycosidic bond.
- main form of sugar transported in plants
- contains more energy per molecule than monosaccharides
polysaccharides
homopolysaccharides: formed from at least 6 identical monosaccharides.
- well defined chemical structure
e. g. glycogen, starch, cellulose
heteropolysaccharides: contain two or more diff. monosacc units
- pectin, lignin, glycoproteins and glycolipids
glycogen
-main energy reserve in humans and animals
- is stored in liver and muscle tissue as an ‘instant’ source of energy.
-formed when excess glucose is eaten
- branching occurs every 8-12 glucose units
alpha (1-4 glycosidic bonds)
starch
contains two molecules:
- linear amylose (~25%) and branched amylopectin (~75%)
- plants store starch in specialised organelles called amyloplasts
amylose
- linear polymer of glucose, with few bonds which cause it to be hydrolysed more slowly
amylopectin
- highly branched polymer of glucose,
- insoluble in water
- lined a(1-4 glyco) bonds
- branching occurs every a(1-6) bonds.
- when energy is need for cell work the plant hydrolyses starch releasing the glucose subunits
- humans and other animals that eat plant foods use amylase to break down amylopectin
cellulose
-no taste
- cannot be digested by plants/ animals but can be by bacteria, fungi
-component of dietary fibre
beta(1-4) glyco bond
carbs in food
Bread–glucose polysaccharides (starch)
Honey-glucose monosaccharaides (glucose, fructose)
Coffee–sucrose disaccharide
Milk–galactose & glucose disaccharide (lactose)
Sugar–glucose & fructose disaccharides (sucrose)
Lactose intolerance
hydrolysed by lactase but mammals are unlikely to encounter lactose after they are weaned, thus levels and activity of lactase are low.
- lactose moves thru digestive tract to colon- bacteria ferments the lactose and large amounts of co2, h2 and acids are produced
- lactose intolerance- lacking of lactase
glycolysis
