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Transcript
Amino Acids and Proteins Proteins are macromolecules (polymers) They are made up of monomers which are known as amino acids Amino Acids structure of amino acids The simplest amino acids has R = H as its side chain. Glycine There are 20 different amino acids involved in protein synthesis Each amino acid has a different side chain; a. If it is oxygen or nitrogen polarity, hydrophilic b. If it is hydrogen and carbon hydrophobic 1. 2. 3. Peptide Bonds All proteins contain NITROGEN and some contain SULPHUR because amino acids do. This is significant to how proteins bond. Proteins contain peptide bonds These join amino acids together Many amino acids joined by peptide bonds form a macromolecule which is a polypeptide. If 100+ amino aids present = protein. Condensation hydrolysis Protein Structure Primary Structure Secondary Structure Tertiary Structure Quaternary Structure Sequence of amino acids Sequence determined by genetic code in genes (DNA) Chain of amino acids that coil helix or pleated sheet Hydrogen bonds hold in structure on place (configuration) Secondary structure coils/ folds into complex 3D shape (v. precise) Held together by bonds between side chains Proteins of greater than one polypeptide have quaternary structures either GLOBULAR or FIBROUS If primary structure is wrong the tertiary structure is wrong and hence the protein will not function correctly Protein shape determines its function 4 Types of bonds hold protein structures together 1. HYDROGEN BONDS Occur between polar groups. (any 2 polar amino acids) Broken by pH and high temperature 2. DISULPHIDE BRDGES Occur between cysteine molecules (type of amino acid) S=S ; covalent bond; very strong Broken by reducing agents 3. IONIC BONDS Occur between ionized amines and carboxylic acid groups Electrons from one atom leave its outer shell and enter the outer shell of another atom. Gainer reduced -ve ion Loser oxidised +ve ion Form weak attractions between bonds (weaker than covalent bonds) 4. HYDROPHOBIC INTERACTIONS Helps some proteins as water hating ‘hydrophobic’ groups point inwards, therefore hold structure together Occurs between non-polar side chains Protein shape related to function Globular Fibrous Globular – e.g. Haemoglobin 4 polypeptide chains with disulphide bridges nearly spherical at the centre of each polypeptide Fe containing haem group. This is a non-protein prosthetic group which combines with protein conjugated protein present in red blood cells, carries oxygen from lungs to respiring cells as oxyhaemoglobin Globular – e.g. Enzymes enzymes are a type of a protein- each enzyme has a specific shape, with an active site that locks onto the substrate molecule. amino acids with hydrophilic side chains towards the outside hydrophobic inwardly facing therefore, water molecules can surround the molecule hence it is soluble. Globular – e.g. Hormones (Insulin) is a hormone that reduces blood glucose levels. Globular = good for transport Disulphide bonds hold the molecule in shape It’s a small molecule – so it’s easily transported and absorbed by cells Fibrous – e.g. Collagen/Keratin/Elastin long strands insoluble chains are interlinked by strong covalent bonds polypeptides laid down in sheets collagen/Elastin SKIN Keratin nails and hair Collagen/elastin skin Actin/myosin muscle Biuret Test Detects presence of proteins Amine groups in side chains of some amino acids of a protein are at the site of ionized peptide bonds react with copper ions to form a complex with a violet colour Biuret reagent 2 chemicals used in succession 1. dilute alkali (KOH, NaOH) 2. dilute Cu2SO4(aq) violet purple = +ve test