- organic molecules of carbon, hydrogen, oxygen and nitrogen
- may contain sulfur if cysteine or methionine is present
- Each protein molecule is made up of smaller units called amino acids
- Amino acids are made up of:
- an amino group ()
- an acid group ()
- O-H bond is polar, causing the shared electron to be closer to O
- allows ion to escape easily
- a side chain ()
- Two amino acid molecules are combined by condensation reaction to form a dipeptide and broken down via hydrolysis into its constituent amino acids
- Peptide bonds link up with many amino acids to form a polypeptide via condensation reaction (Remember polysaccharides?)
- One or more polypeptide chains fold to become a 3D molecule, called a protein
Levels of Organisation §
- Primary level: the sequence of amino acids in the polypeptide chain
- Secondary level: local folding of polypeptide chain causes formation of helices and sheets
- Tertiary level: Further folding of polypeptide chain to form 3D shape
- Quaternary level: association of more than one polypeptide to form final functional protein
Function §
- used in the synthesis of new protoplasm for growth & repair of worn-out cells
- Can function as:
- Enzymes (biological catalysts)
- Hormones (chemical messengers in the blood)
- Transport proteins (e.g. Haemoglobin)
- Structural proteins (e.g. Collagen (in bones, skin, tendons), keratin (in hair, nails))
- Antibodies (specialised proteins that fight bacteria and viruses)