Biological molecules

• Most carbohydrates are polymers (polymers are large, complex molecules composed of long chains of monomers joined together)
• Monomers are small, basic molecular units. Examples of monomers include monosaccharides, amino acids and nucleotides
• All carbohydrates contain the elements C, H and O
• The monomers that they're made from are monosaccharides e.g. Glucose, fructose and galactose
• A condensation reaction is when two molecules are joined together with the formation of a new chemical bond and a water molecule is released when the bond is formed
• Monosaccharides are joined together by condensation reactions
• A glycosicic bond is formed between the two monosaccharides as a water molecule is released
• A disaccharide is formed when two molecules join together.
• Maltose is formed from two alpha glucose molecules
• Sucrose is a disaccharide formed from a condensation reaction between a glucose molecule and a fructose molecule.
• Lactose is a disaccharide formed from a glucose molecule and a galactose molecule
• Polymers can be broken down into monomers by hydrolysis
• A hydrolysis reaction breaks the chemical bond between monomers using a water molecule.
• The process of breaking down polysaccharides to form monosaccharides is called hydrolysis.
• Benedict's test for reducing sugars. Add Benedict's reagent to a sample and heat it in a water bath that's been brought to boil. If the test is positive it will form a coloured precipitate from blue to brick red.
• Benedict's test for non-reducing sugars. Get a new sample and add dilute hydrochloric acid and heat in a water bath. Then neutralise it with sodium hydrogencarbonate. Then carry out benedict's test.
• Polysaccharides are formed when mire than two monosaccharides are joined together by condensation reaction.
• plants store excess glucose as starch (when a plant needs more glucose for energy, it breaks down starch to release the glucose)
• Starch is a mixture of two polysaccharides of alpha glucose - amylose and amylopectin
• Amylose is a long unbranched chain of alpha glucose. The angles of the glycosicic bonds give it a coiled structure. This makes it compact, so it's really good for storage because you can fit more in to a small space
• Amylopectin is a long, branched chain of alpha glucose. Its side branches allow the enzymes that break down the molecule to get at the glyosidic bonds easily. This means that the glucose can be released quickly
• Starch is insoluble in water and doesn't affect water potential, so it doesn't cause water to enter the cell by osmosis, which would make them swell. This makes them good for storage.
• Iodine test for starch. Add iodine dissolved in potassium iodide solution to the test sample. If positive it will turn to blue-black.
• Animals store excess glucose as glycogen(another polysaccharide of alpha glucose). It's structure is very similar to amylopectin, except that it has loads more side branches. Loads of branches means that stored glucose can be released quickly,which is important for energy release in animals. It is also a very compact molecule, so it's good for storage.
• Cellulose is made of long, unbranched chains of beta glucose. When beta glucose molecules bond, they form straight cellulose chains. The cellulose is linked together by hydrogen bonds to form strong fibres called microfibrils. The strong fibres mean cellulose provides structural support for cells
• Triglycerides have one molecule of glycerol with three fatty acids attached to it. Fatty acid molecules have long 'tails' made of hydrocarbons. The tails are hydrophobic(they repel water molecules). These tails make lipids insoluble in water. All fatty acids have the same basic structure but the hydrocarbon tail varies.
• Triglycerides are formed by condensation reactions. Creating a ester bond.
• Saturated fatty acids don't have any double bonds between their carbon atoms. The fatty acid is saturated with hydrogen. Unsaturated fatty acids have at least one double bond between carbon atoms, which cause the chain to kink.
• Phospholipids are found in the cell membrane. Phospholipids are similar to triglycerides except one of the fatty acid chains is replaced by a phosphate group. The phosphate group is hydrophilic(attracts water). This is important in the cell membrane.
• Triglycerides


  Mainly used as energy storage molecules
• Triglycerides


  • The hydrocarbon tails of the fatty acids contain a lot of chemical energy
  • Lipids contain about twice as much energy per gram as Carbohydrates
  • They're insoluble, so they don't affect the water potential of the cell and cause water to enter the cells by osmosis
  • The triglycerides clump together as insoluble droplets in cells because the fatty acid tails are hydrophobic-the tails face inwards, shielding themselves from water with their glycerol heads
• Phospholipids make up the bilayer of cell membranes, cell membranes control what enters and leaves a cell.

  • Their heads are hydrophilic and their tails are hydrophobic, so they form a double layer with their heads facing out towards the water on either side.
  • The centre of the bilayer is hydrophobic, so water-soluble substances can't easily pass through it, the membrane acts as a barrier to those substances.
• The monomers of proteins are amino acids. A depeptide is formed when two amino acids join together. A polypeptide is formed when more then two amino acids join together. Proteins are made of one or more polyleptides.
• Amino acids have the same general structure:

  • Carboxyl group (COOH)
  • amine group (NH2)
  • R group
• Amino acids are linked together by condensation reactions to form polypeptides. A molecule of water is released during the reaction. The bonds formed between amino acids are called peptide bonds. The reverse reaction happens during digestion.
• • Primary structure - the sequence of amino acids in the polypeptide chain
  • Secondary structure - hydrogen bonds form between the amino acids in the chain. This makes it coil into an alpha helix or fold into a beta pleated sheet
  • Tertiary structure - coiled and folded further. More bonds form including:hydrogen bonds, ionic bonds and disulfide bridges. Forms a 3d structure.
  • Quaternary structure - several polypeptide chains held together by bonds. Could include a prosthetic group. Final 3d structure
• Protein functions:

  • Enzymes - they're usually roughly spherical in shape due to the tight folding of the peptide chains. They're soluble and often have roles in metabolism.
  • Antibodies - are involved in immune response. They're made up of two light polypeptide chains and two heavy polypeptide chains bonded together. Antibodies have variable regions.
  • Transport proteins
  • structural proteins
• Biuret test for proteins.

  • The test solution needs to be alkaline so add sodium hydroxide solution
  • The add copper sulfate solution
  • If positive solution turns purple. If negative it will remain blue.
• • Enzymes catalyse metabolic reactions - both at a cellular level and for the organism as a whole
  • Enzymes can affect structures in a organism as well as functions
  • Enzyme action can be intracellular(within cells) or extracellular(outside cells)
  • Enzymes are proteins
  • Enzymes have an active site, which has a specific shape. The active site is the part if the enzyme where to substrate molecules bind to.
  • Enzymes are highly specific due to their tertiary structure.