Biological molecules

proteins
1. structural levels
  1. primary structure
    1. this is the sequence of amino acids in the polypeptide chain
  2. secondary structure
    1. the polypeptide chain doesnt remain flat so hydrogen bonds form between the amino acids in the chain which makes it automatically coil into an alpha helix or fold into a beta pleated sheet
  3. tertiarty structure
    1. the coiled or folded chain of amino acids is often coiled and folded further. more bonds form between different parts of the polypeptide chain
  4. quarternary structure
    1. some proteins are made of several different polypeptide chains held together by bonds, the quarternary structure is the way these polypeptides are assembled together
2. protein facts
  1. amino acids are linked together by peptide bonds to form dipeptides and polypeptides. A molecule of water is released during the reaction. The opposite of this reaction is a hydrolyisis reaction which uses a water molecule to break the peptide bond.
  2. all amino acids have the same general structure - a carboxyl group (-COOH) and an amino group (-NH2) attached to a carbon atom. The difference between different amino acids is the variable group they contain
3. protein shape and function
  1. collagen
    1. fibrous protein that forms supportive tissues in animals, its made up of three polypeptide chains that are tightly coiled into a tripple helix. The chains are interlinked by strong covalent bonds.
  2. haemoglobin
    1. globular protein with iron containing heam group that binds to oxygen. The structure is curled up so that the hydrophilic side chains are on the outside and the hydrophobic chains face inwards. this makes heamoglobin soluble
lipids
1. cholesteol
  1. strengthens cell membranes by interacting with the phosphlipid bilayer
  2. small size and flattened shape allows the cholesterol to fit between the phospholipid molecules in the membrane
  3. binds to hydrophobic tails of phospholipids causing them to pack more closely together which helps the memprane to be less fluid and more rigid
  4. has hydrocarbon ring structure which it attached to a hydrocarbon tail. The ring has a polar hydroxyl group attached to it which makes the cholesterol soluble
2. phospholipids
  1. they make up the bilayer of cell membranes
  2. they are very similar to triglycerides except one of the fatty acid molecules is replaced with a ionised phosphate group
  3. the ionised phosphate group attracts water but the rest of the molecule (the fatty acis tails) are hydrophobic.
3. triglycerides
  1. used mainly as energy storage because they have long hydocarbon chains of fatty acids which contains loads of energy which is released when they are broken down
  2. its made up of one glycerol molecule with three fatty acids attached to it. The fatty acid molecules have long, hydrophobic, hydrocarbon tails which make these lipids insoluble
  3. All of the fatty acids consist of the same basic structure but the hydrocarbon tails vary, this is ofter represented by an R group
carbohydrates
1. polysaccharides
  1. starch
    1. cells get energy from glucose, plants store excess glucose as starch.
    2. starch is a mixture of two polysacharides of alpha-glucose, amylose and amylopectin
      1. amylose
        long unbranched chain of alpha glucose. The angles of the glycosidic bonds give it a coiled structure, like a cylinder. This makes it compact and good for starage as you can fit more into a small space
      2. amylopectin
        long, branched chain of alpha glucose. its side branches allow the enzymes that break down the molecule to get to the glycosidic bonds eaisly so gucose can be released quickly.
    3. starch is insoluble in water, so it doesnt cause water to enter the cells by osmosis this makes it good for storage
  2. glycogen
    1. animals store excess glucose as glycogen - another polysaccharide of alpha glucose.
    2. the structure is very similar to amylopectin except there are lots more side branches. loads of branches means that stored glucose can be released quickly
  3. cellulose
    1. made up of lots of unbranched chains of beta glucose. the bonds between the sugars are straight so the cellulose chains are straight. The cellulose chains are linked by hydrogen bonds to form strong fibres called microfibrils, the strong fibres mean cellulose provides structural support for cells (e.g. in plant cell walls)

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Biological molecules

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