Amino acids

  • Building block of a protein=amino acids
  • Amino acids are monomers that are joined in a sequence to form a protein
  • The sequence of the amino acids determines the protein+its function
  • Structure of an amino acid: amino group, carboxyl group, residual group
  • Each of the 20 different amino acids have a different residual group

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Forming peptide bonds

  • A protein is a polymer of amino acids 
  • Two amino acids are joined together by a condesation reaction to form a peptide bond
  • The bond can be broken by hydrolysis, which involves adding water.
  • When a larger chain of amino acids is formed=polypeptide

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Levels of protein structure: primary+secondary

  • Primary structure: seqeunce, type+number of amino acids in the chain. The structure+amino acids present determine the protein's function.
  • Secondary structure:
  • Chain takes a particular shape by folding or coiling as a result of the bonds formed between amino acids. Order of amino acids determines where bonds are formed=what shape occurs.
  • Two forms of secondary folding: alpha helix and the beta pleated sheet. Alpha helix=held in place by H bonds between amino acids from different parts of the chain. Beta pleated sheet=folds in a concertina like way, H bonds connect to adjacent pleated sheet.

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Levels of protein structure: tertiary- gobular+fib

  • Tertiary structure: 3D shape of protein molecule=further coiled or twisted into a more complex shape. Two types of tertiary structure: globular and fibrous
  • Globular: when protein folds to form 3D shape=important in metabolic processes=enzymes=have specific active site for subsrate to bind too
  • Fibrous: protein twists into a long thin structure, has important structural roles: keratin-hair, collagen in skin.

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Levels of protein structure: tertiary,types of bon

  • Globular and fibrous proteins have a no.of different type of bonds to stabilise the molecule:H bonds, Ionic bonds, hydrophobic interations and disuphide bonds.
  • H bond: attraction between slight + charge of a group and slight - charge of another
  • Ionic bond: attraction between + charged R group of an amino acid and - charged R group of another.
  • Hydrophobic interaction: association between hydrophobic R groups of amino acids (where H2O is excluded).
  • Disulphide bond: Covalent bond between sulfur atoms of two R groups.

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Levels of protein structure: quaternary

  • Some proteins=made of more than 1 polypeptide chain
  • Two or more chains are held together+function as a whole
  • Protein will not function unless all subunits are together
  •  Haemoglobin: quaternary structure+haem prothestic group (inorganic ion)
  • Conjugated protein: globular protein with a prosthetic group

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Comparison between Haemoglobin and Collagen

Feature                                      Haemoglobin                      Collagen

Type of protein stucture            globular                               fibrous

No.of polypeptides                          4                                         3

3D structure                            folded into ball                      twisted into long fibres

Helical structure                    right-handed alpha                  left-hand

Solubility in water                    soluble                                  insoluble

Types of amino acids              Most of the 20                       Just 3 amino acids

Prosthetic group                       haem                                    none

Role                                     transport of 02                         provides strength in many areas of the                                                                                                body: cartilage, bone, elasticity of skin

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