Carbohydrates Flashcards
Carb sugars are..? Give examples of each.
Monosaccharides (ribose, glucose) & oligosaccharides (sucrose, lactose, maltose)
Carbohydrates can be classified as..?
Soluble (non-fibrous), insoluble (fibrous); sugars or non-sugars
Carb non-sugars..? Give examples.
Polysaccharides (starch, cellulose, glycogen) & complex carbohydrates (hemicellulose)
Give example of non-fibrous CHO
Lactose (disaccharide) & starch (polysaccharide)
Fibrous CHO properties & example?
Structural component of plants.
Animal’s enzymatic enzymes can not digest.
eg. cellulose
What are enantiomers (optical isomers)? Give examples
Mirror images.
Same chemical structure & molecular order.
Rotate plane-polarised light in opposite direction
eg. L & D-glucose
D-glucose & D-fructose form which molecule? What bond is used?
Sucrose via alpha glycosidic bond
Properties of starch?
CHO storage in plants
High in seeds & fruit
Made up of amylose & amylopectin
Properties of cellulose?
Most abundant CHO Structural rigidity in plants Comprises B-D-glucose units Often bound with lignin & hemicellulose Hydrogen bonds between hydroxyl groups
Similarity & difference between cellulose & starch?
Both glucose based, but different digestibility
Monosaccharide derivatives?
Amino sugars (hydroxyl group replaced by amino group) Deoxy sugars (hydroxyl group replaced by hydrogen) Glycosides
Properties of glycosides?
Hydrogen on C1 hydroxyl group replaced by alcohol/phenol
Cyanogenetic glycosides liberate HCN (toxic) on hydrolysis
Plants have enzymes to enable hydrolysis (linamarin in linseed)
Properties of heteroglycans?
Pectic substances found in primary cell walls & intercellular regions
Joint lubrication (hyaluronic acid) & cartilage (chondroitin)
Gel-like properties, saps
Hemicelluloses
Properties of hemicelluloses?
Polysaccharide Alkali cell wall Composed of hexoses & pentoses (joined by beta glycosidic bonds) [ ] increase with plant age > grasses than legumes
Properties of lignin?
Not a CHO
Mechanical strength of plants
Decreases digestibility by encrusting plant fibres (can not access beta-glycosidic bond)
2 phases of monogastric digestion of non-fibrous CHO’s?
Luminal & membraneous
Describe luminal phase of monogastric digestion (non-fibrous CHO)
Dietary polysaccharides such as starch & glycogen broken down in GI lumen by salivary & pancreatic AMYLASE into maltose & sucrose.
Describe membraneous phase of monogastric digestion (non-fibrous CHO)
Maltose, sucrose & lactose -> monosaccharides by brush border enzymes -> glucose & galactose absorbed apical membrane by Na+ cotransport. Fructose by facilitated diffusion
Describe monogastric fibre digestion
Possible by microbial enzyme digestion in LI
Which animal is efficient at fibre digestion?
Horse
Which animal is not efficient at fibre digestion?
Pig
Describe ruminant digestion of non-fibrous CHO
Microbial enzymes access first
Fermentation -> VFA’s -> absorbed across rumen wall for energy use
Describe ruminant digestion of fibrous CHO
CHO attacked by hydrolytic enzymes
Mono- & short polysaccharides -> rumen -> rapidly absorbed by microbes -> energy -> end products (VFA’s, CO2, CH4)
Effects of high roughage diet?
Increase acetate
Effects of high water soluble CHO?
Increase proprionate
Increase acetate:proprionate ratio?
Decrease efficiency of methane use & microbial protein prod.
Why is methane important?
Prod. oxidised cofactors -> acetate & butyrate
Acetic acid -> methane prod.
Importance of VFA’s?
End products of anaerobic microbial metabolism
Accumulation of VFA’s -> ?
Decreases pH
Host animal maintain fermentation conditions by ..?
Buffering (increasing salivation)
removing VFA’s via absorption
