Biology AS proteins for all ( Based on WJEC)

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Proteins intro

protiens are madee up of many amino acids - there are 20 amino acids in total and each ones bond together form many different types of polypeptides and proteins

Key features 

  • structure - primary secondary tertiary and quaternary
  •  amnio acid bonding is peptide bond and are made by condensations reactions just as sugars are bonded
  • Amino acids - have an R group which is different in all amnio acids a carboxyl group and an amino group and finally a hydrogen all coming off a central carbon atom 
  • bonding within a protein occurs on three types 
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Structure of a protein

  • the primary structure of a protein is a chain of amino acids aka a polypeptide ( all proteins are poly peptides) this is the primary structure of a protein as it is a protein in its simplest form but a protein will be made up of many chains of these polypeptides 
  • the secondary structure of a protein is when it is coiled round ( this is called an alpha helix or when it is pleated ( called a beta pleated sheet which looks sort of like a zig zag )
  • the tertiary structure is when the protein is folded and this turns it into what is called a globular protein which is effctively a ball shape - this is what an enzyme is ( structually speaking)- this is a 3D shape
  • quaterary structure is when this ball joins to another ball through similar bonding as the tertiary bonding
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Amino acid bonding

  • they bond by condensation reactions between the carboxyl group( just like the functional group of carboxylic acids) of one amino acid and the amino group of another amino acid this reaction will release one molecule of water , to reverse this you can add water and this is called a hydrolysis reaction 
  • they bond to form peptide bonds which occur between a carbon atom and a nitrogen atom 
  • when two amino acids bond together this is called a dipeptide molecule
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bonding in a protein

these are all used in the tertiary and quarternary structure of a protein 

hydrogen bonds -weak -  the same as the ones formed in water are weak but in high numbers can form stability for the the protein as they form cross links with other chains of polypeptides

ionic bonds - fairly weak these form when atoms of different charges are attracted to one another this often happens between a metal and a non metal they do not share elctrons

sulpher bridges - Sulphur bonds- are very strong and hard to break some amino acids contain (SH groups ) which have reducing properties and can get rid of Hs and if 2 of these groups are near the oxidise to form S-S bonds .

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amino acids - what do they look like inside


this is what a protein looks like this is the basis of all of them please note that the hydrogen and the r group can be swapped around when they are drawn but the carboxyl group and the amino groups must be on the sides they are here it is the carbxyl groups and amino groups that form peptide bonds

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testing for proteins

this is called the biurette test 

  • you will need dilute sodium hydroxide and copper sulfate to form the reagent and your test solution
  • add these one by one but the sample to test first about 2cm of the sample, 5cm of sodium hydroxide
  • and add the copper sulfate drop by drop 
  • if the test is positive you will get a purple/ lilac colour if it is negative it will not change 
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there are 2 groups

  • proteins can be globular or fibrous
  • fibrous proteins like collagen have a stable structure are very strong  , insoluble and stay in long polypeptide strands and are used for structural functions
  • globular like haemoglobin are soluble in water , a ball shape and have an unstable they are used in metabolic functions

they can have prosthetic groups which are parts of a protein that are not parts of amino acids for example iron in haemoglobin , this means it is a conjuncted protein as opposed to  a simple protein

globular proteins are soluble as they fold all of the hydrophobic parts of the protein to the centre of the ball so you have the hydrophilic parts on the outside of the protein

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