Biology Unit 1 Carbohydrates and lipids

• Carbon forms covalent bonds
• Covalent bonds are formed when a pair of electrons are shared between 2 atoms
• Monomers are small units from which large molecules are made
• Polymers are molecules made from a large number of monomers joined together in a chain
• the process which monomers join to form polymers is polymerisation
• Macromolecules are formed during condensation reactions, forming covalent bonds and resulting in polymers or macromolecules
• Examples of condensation reactions include polysaccharides and polypeptides
• Macromolecules often need to be broken down into monomers, this happens in digestion. The reaction allowing this is a hydrolysis reaction
• In the hydrolysis of macromolecules, covalent bonds are broken when water is added
• Examples of hydrolysis reactions include peptide bonds in polypeptides to produce amino acids as well as glycosidic bonds in poly or disaccharides to produce monosaccharides
• The monomers of carbohydrates are monosaccharides
• Monosaccharides join together via a condensation reaction, the new chemical bond that forms is known as a glycosidic bond
• The isomers of glucose are alpha glucose and beta glucose
• Starch and glycogen are formed from alpha glucose
• Cellulose is formed from beta glucose
• Glucose has a stable structure due to its covalent bonds making it strong and hard to break
• A source of chemical energy is given when covalent bonds are broken
• Glucose is soluble in water because of its polar nature
• Glucose is easily transportable due to its water solubility
• Carbohydrates function as essential energy storage molecules and as structural molecules
• Starch and glycogen are effective storage polysaccharides because they are compact and insoluble
• Cellulose is a structural polysaccharide because its strong and durable, insoluble and slightly elastic and is chemically inert, meaning few organisms posses enzymes that can hydrolyse it
• Starch is the storage polysaccharide of plants as granules in the chloroplast
• Amylose is unbranched (1,4 glycosidic bonds), and , more compact making it more resistant to digestion
• Amylopectin is branched (1,4 and 1,6 glycosidic bonds)
• Glycogen is the storage polysaccharide in animals and fungi and the monomer is alpha glucose
• Glycogen is more branched than amylopectin, providing more free ends where glucose molecules can be hydrolysed
• Cellulose is found in the cell walls of plants
• In beta glucose the hydroxyl group sits above the carbon ring whereas in alpha glucose it sits below the ring
• The alternating pattern of the monomers in cellulose allows hydrogen bonding to occur between strands of beta-glucose monomers, adding strength to the polymer
• Carbohydrates and polypeptides can combine, via covalent bonds, to make structures called glycoproteins
• Glycoproteins are classed as proteins
• Glycolipids act as receptor molecules in cell recognition, receptors, endocytosis and cell adhesion and stabilisation
• Endocytosis is engulfing of substances into the cell
• Cell adhesion is the process by which cells interact and attach to neighbouring cells through specialised molecules on the outer layer of the cell surface membrane
• Lipid macromolecules contain carbon, hydrogen and oxygen
• The structure of lipids affects their solubility
• Lipids contain hydrocarbon molecules which contain many non-polar covalent bonds
• The non-polar nature of lipid molecules means that lipids are insoluble in water or other polar solvents
• In living organisms, lipid solubility can be improved by combining lipid molecules with other molecules for example, glycolipids and lipoproteins