3B_Carbonhydrates

Carbonhydrates Carbohydrate characteristics > Trioses – C3H6O3 e.g. glyceraldehyde > Pentoses – C5H10O5 e.g. deoxyribose > Hexoses – C6H12O6 e.g. glucose, fructose
 * Contain the elements C, H, O: CnH2nOn
 * They are either made from single monosaccharide monomers or from several monosaccharides joined together
 * Monosaccharides are:

Carbohydrates are classified as:
 * 1) Monosaccharides eg glucose, fructose, galactose
 * 2) Disaccharides eg sucrose, maltose, lactose
 * 3) Polysaccharides eg cellulose, glycogen, starch
 * 4) Other polysaccharides and polysaccharide derivatives eg pectins, chitin and mucopolysaccharides

Monosaccharides Glucose Glucose can exist in two forms, the α form and the β form. The two forms of glucose have the same properties. The only difference between them is the position of one of the OH groups. This has a great effect on the property of molecules made when glucose molecules link together.

Disaccharides Other disaccharides
 * Disaccharides – made by combining 2 monosaccharides together
 * This is a __condensation reaction__ producing a __glycosidic bond__ (broken by __hydrolysis__ )
 * Disaccharides made from hexoses have the formula C12H22O11
 * Examples – sucrose (glucose + fructose), maltose (glucose + glucose)

Disaccharides Examples Maltose-Formed from 2 glucose molecules, formed in germinating seeds from the breakdown of starch, providing energy Sucrose -Formed from 1 glucose and 1 fructose molecule and is the form in which carbohydrates are transported in the phloem in plants Lactose -Formed from 1 glucose and 1 galactose molecule, it is an energy source found in the milk of nearly all mammals

Polysaccharides - made from condensing many similar monosaccahrides - Polymerization

Reactions Hydrolosis - end product is always glucose *Glycosidic bond Starch & Glycogen
 * Their molecules have many side branches where glucose molecules can be removed from their tips (by enzymes)
 * Their insolubility stops them interfering with osmosis
 * Their compactness provides an efficient way to store lots of glucose for future cellular respiration

Glycogen granules in skeletal muscles || || Glycogen granules in skeletal muscles || Starch grains in potato cells ||
 * [[image:webkit-fake-url://A1C077A6-F107-405B-B3F2-3DD1C2764706/pastedGraphic_8.pdf caption="pastedGraphic_8.pdf"]]

Starch
 * Found in two forms, which are both made up of α glucose
 * [[image:webkit-fake-url://A1C077A6-F107-405B-B3F2-3DD1C2764706/pastedGraphic_10.pdf caption="pastedGraphic_10.pdf"]] One form is amylose which consists of un-branched chains of α glucose,this coils into a helical compact structure
 * [[image:webkit-fake-url://A1C077A6-F107-405B-B3F2-3DD1C2764706/pastedGraphic_11.pdf caption="pastedGraphic_11.pdf"]] The other form is amylopectin which consists of branched chains of α glucose, this forms a branched compact brush.
 * Starch is the main storage carbohydrate in plants.
 * Hydrolysis reaction:- A chemical process whereby a compound is cleaved into two or more simpler compounds along with the uptake of water

Glycogen - A polymer of α glucose monomers. - It is the main storage carbohydrate in mammals found in liver and muscle cells. - It is more branched in structure than amylopectin. - The more branched the molecule, the quicker it can be made and broken.

“Animal Starch” - storage form of carbohydrate in animals and fungi. Formed from condensation of many glucose molecules Cellulose > a very small number of > animals can secrete cellulase > enzymes. - Is a polymer of β glucose monomers. - It is an important component of plant cell walls. - It does not spiral as with α glucose - β glucose consists of chains that are straight and long, they lie parallel to each other bound together by hydrogen bonds. General uses of monosaccharides and disaccharieds Building blocks for larger molecules (e.g. DNA, cellulose, starch, glycogen) Source of respiratory energy (glucose) Transport compound (sucrose in plant phloem) Infant milk (lactose) Attraction – flower nectuary, fruit (fructose) Honey – Bees food storage
 * Made from long, straight chains of glucose
 * Chains cross-linked by H-bonds which holds them tightly together (excludes water)
 * Chemically very inert and insoluble – few ‘tips’ on molecule make it difficult to digest
 * Many molecules form strong fibrils
 * Only some bacteria, fungi and

General uses of polysaccharides Polysaccharides are many monosaccharides linked by glycosidic bonds Examples – starch, glycogen, cellulose Energy Storage - starch (plant) and glycogen (animal) Structural - Cellulose cell wall (plant) and Chitin (insects/crab/shrimp)

Function of Starch
 * 1) Form supporting structures E.g. cellulose cell wall.
 * 2) Source of energy - glucose is the raw material needed for cellular respiration yielding ATP, the energy molecule.
 * 3) Converted into other organic compounds E.g. amino acids
 * 4) For formation of nucleic acids
 * 5) Synthesis of lubricants, e.g. mucus
 * 6) Produce nectar in some flowers.

Fibre
 * Indigestible e.g. cellulose
 * Provides bulk to intestinal contents
 * Aids in peristalsis - rhythmic wave like contractions along the gut
 * Prevents constipation
 * Sources : fresh fruits, vegetables, bran, cereals, wholemeal bread

Food test Benedict’s reagent – tests for a reducing sugar (e.g. glucose) Blue colour turns brick red when heated Non-reducing sugars (e.g. sucrose) need to be hydrolysed before testing Hydrolysis needs HCl acid or an enzyme (and, of course, water) HCl needs neutralising before test!