protein

Cards (18)

  • Enzymes-Proteins that catalyse chemical reactions. 
    Antibodies-Proteins that fight pathogens as part of the immune response.
    Transport proteins-Proteins that transport ions and molecules across the cell membrane. ​
    Structural proteins-Strong proteins found in hair, nails and connective tissue. 
  • Proteins all contain the elements carbon, nitrogenoxygen , hydrogen
    Amino acids are the monomers that make up proteins​
    Within living organisms there are 20 amino acids used as protein building blocks. ​
  • A protein is an organic compound made up of made up of polypeptide chains, which are amino acids joined together with peptide bonds
  • Each amino acid has the same fundamental structure, which consists of a central carbon atom, also known as the alpha (α) carbon, bonded to an amino group (NH2), a carboxyl group (COOH), and to a hydrogen atom
    • The carboxyl group (COOH) is acidic and  the amine group (NH2) is basic.​
    • The R group is the variable part of the molecule, which determines the identity/properties of the amino acids.​
    • In animals such as humans there are 20 different amino acids , each with a different R group.
  • lable the groups
    A) amino group
    B) R group
    C) carboxyl group
    • To break the peptide bonds in a protein, a hydrolysis reaction is needed similar to that involved in breaking up carbohydrates.​
    •  Enzymes known as proteases are needed to break up the protein.​
    • The primary structure of proteins is the order and sequence of amino acids in a polypeptide chain​
    • Proteins are coded by DNA, so it is an organisms genes that determine the sequence of amino acids.​
    • This primary structure determines all other structures, so it’s hugely important
    • Our primary structure can fold to form two secondary structures:​
    • -Alpha helix/helices​
    • -Beta pleated sheets​
    • Both structures are the result of weak hydrogen bonds formed between amino acids
  • what is this
    A) alpha helix
  • what is this
    A) beta pleated sheet
    • The secondary structure of proteins is further folded into our 3Dimensional tertiary structure with the help of three types of bonds:​
    • Hydrogen bonds – numerous and weak​
    • Ionic bonds – stronger than hydrogen, easily broken by changes in pH​
    • Disulfide bridges/bonds – strong covalent bonds between 2 sulphur groups and not easily broken​
    • These are formed between R groups, so they depend on the specific amino acids in the primary structure
  • Some proteins become functional after the tertiary structure, while others need an additional step – where more than one polypeptide chains join together
    • Polypeptide chains are held together in these quaternary structures by the same type of forces responsible for the formation of tertiary structures
    • As we’ve just seen, different proteins have different functions.​
    •  Proteins can be split into two broad groups:​
    • Globular – carry out metabolic functions (eg. haemoglobinenzymes)​
    • Fibrous – carry out structural functions (eg. collagen, keratin)​
    • What determines whether a protein is globular or fibrous?​
    • Their primary structure/polypeptide sequence and therefore the DNA that codes for this protein​
  • Fibrous Proteins
    ¨ Little or no tertiary structure.
    ¨ Long parallel polypeptide chains.
    ¨ Cross linkages at intervals forming long fibres or sheets.
    ¨ Usually insoluble.
    ¨ Many have structural roles.
    ¨ E.g. keratin in hair and the outer layer of skin, collagen (a connective tissue).
  • Globular Proteins
    ¨ Have complex tertiary and sometimes quaternary structures.
    ¨ Folded into spherical (globular) shapes.
    ¨ Usually soluble as hydrophobic side chains in centre of structure.
    ¨ Roles in metabolic reactions.
    ¨ E.g. enzymes, haemoglobin in blood.
  • Haemoglobin
    An example of a globular protein
    ¨ Reddish-purple oxygen carrying pigment found in red blood cells.
    ¨ Made up of 4 polypeptide chains.
    ¨ 2 identical a-chains and 2 identical b-chains.
    ¨ Each polypeptide chain contains a haem group.
    ¨ Haem group has an iron ion (Fe2+) at its centre.
    ¨ The iron combines with oxygen at high oxygen concentrations and releases oxygen at low oxygen concentrations.
    ¨ One haemoglobin molecule can carry 4 oxygen molecules.
  • Collagen
    An example of a fibrous protein
    ¨ Found in skin, tendons, cartilage, bones, teeth, walls of blood vessels.
    ¨ Structural protein in most animals.
    ¨ Collagen molecule made of 3 polypeptide chains, each in the shape of a helix (not as tightly wound as an a-helix).
    ¨ Each chain contains 1000 amino acids - every third amino acid is glycine (the smallest amino acid).
    ¨ 3 helical chains wind around each other to form a three-stranded 'rope'.
    ¨ 3 strands held together by H bonds.
    ¨ Very strong - one quarter the tensile strength of mild steel