carbohydrates:

• these include sugars, starch, glycogen, and cellulose and they only contain carbon, oxygen, and hydrogen

structure of glucose:

• has the molecular formula of C6H12O6

• the carbon atoms are numbered from 1 on the far right, to 6 at the top

The isotopes of glucose:

1. Alpha glucose, where both the OH groups are ‘below the ring’

   

Beta glucose, where one OH is below and the other is above ‘the ring’

Testing for glucose:

• using Benedict’s solution which is actually copper (II) sulphate which has a blue colour

• When a reducing sugar is heated with Benedict’s, the COOH group in the molecule reduces the Cu2+ ion to Cu+ ions which formed a brick red precipitate of copper (I) oxide.

• There is a range of results from blue → green → yellow → brown → red

disaccharides:

Are made of two monosaccharides jointed together by glycosidic bonds that form from condensation reactions and produce water (hydrolysis uses water to break these bonds in the opposite reaction)

• the glycosidic linkage occurs between C-1 and C-4 of the alpha glucose molecule

polysaccharides:

Are polymers made up of many monosaccharides linked together by glycosidic bonds formed during condensation reactions.

Polysaccharides are macromolecules as they’re giant molecules.

starch:

• is a mixture of 2 polysaccharides, both of which are polymers of alpha glucose

  1. Amylose - unbranched chain of alpha glucose

  2. Amylopectin - highly branched chains of alpha glucose

• The molecule is highly coiled due to the 1-4 glycosidic bonds in amylose and highly branched due to the 1-6 and 1-4 glycosidic bonds in amylopectin

• Starch is a major store of energy in plants and therefore has to be compact.

• It’s useful as it is compact and insoluble so it doesn’t have an osmotic effect

• Starch is fast at being hydrolysed in order to produce energy which is used in respiration to form energy due to the highly branched nature of it

glycogen:

• is a polymer of alpha glucose

• It is very similar to amylopectin, but is larger and has more branches

• Glycogen is found in the liver cells and the muscle cells and is a energy store in humans and animals

• Glycogen is very quickly hydrolysed due to the branching that forms because of the 1-6 and 1-4 glycosidic bonds between 2 molecules of alpha glucose

• Glycogen is branched after every 10 glucose residues where as amylopectin is branched every 30 glucose residues (residues = when monomers are linked together in a polymer)

cellulose:

• is a polymer of beta glucose

• Cellulose is a very straight and unbranched molecule

• This is because every other beta glucose molecule is inverted which allows the 1-4 glycosidic bonds to form in a straight way that produces long straight chains

• The chains naturally become packed into fibres which are held together by hydrogen bonds - these strong fibres that are arranged in different directions are what make plant cell walls strong and able to withstand the hydrostatic pressure