General properties of proteins


Amino acids

  • The monomers from which proteins are made 
  • Amino group -NH2
  • Acid group -COOH
  • 20 different R groups 
  • Joined by condensation reactions, forming peptide bonds 
  • 2 amino acids in a dipeptide
  • 3 amino acids in a tripeptide
  • Many amino acids in a polypeptide
  • Protein is made from one or more polypeptides
  • An infinite variety of proteins 
1 of 5

Protein structure

Primary structure

  • Sequence of amino acids (e.g. valine, serine, proline, valine)
  • Insulin is a small protein consisting of 51 amino acids (many proteins have hundreds)

Secondary structure

  • Shape formed when part of the chain of amino acids becomes folded and coiled 
  • The two most common structures are an a-helix (spiral shape) and a B-sheet (pleated like a folded sheet of paper)

Tertiary structure 

  • Overall shape of the amino acid chain (i.e. the whole polypeptide)
  • When in water, a wide variety of forces combine to twist, fold and bend the polypeptide into its most stable shape

Quaternary structure

  • Occurs when the protein has more than one polypeptide chain
2 of 5

General properties of proteins

  • Examples: enzymes, antibodies and hormones
  • Functions include: holding your body together, allowing movement, digestions and absorption of food, controlling body chemistry, fighting off disease
  • Proteins are large, complex molecules
  • Always contain the elements: carbon, hydrogen, oxygen and nitrogen 
3 of 5

Protein function

Globular proteins (rounded in shape, tend to have a chemical function)

  • Enzymes
  • Membrane proteins that control the movement of ions and other substances in and out of the cell
  • Hormones such as insulin 
  • Haemoglobin
  • Antibodies to help fight disease

Fibrous proteins (long, thin molecules that generally have a structural function)

  • Collagen - gives strength to tissues such as bone, tendon and ligaments
  • Keratin - gives strength to skin, hair and nails 
  • Actin and myosin - make muscles contract

Shape of globular proteins is maintaines by relatively weak forces such as hydrogen bonds and ionic bonds. Fibrous proteins rely more on strong disulfide bridges.

4 of 5

Testing for proteins

Biuret Test

  • Biochemical test used for detecting the presence of peptide bonds
  • First, disolve the test substance in water, then add the biuret reagent (mixture of copper sulfate and sodium hydroxide)
  • Change in colour from blue to lilac/purple indicates the presence of protein 
5 of 5


No comments have yet been made

Similar Biology resources:

See all Biology resources »See all Biological molecules, organic chemistry and biochemistry resources »