Proteins

Protein

Polymer made up of the monomer: amino acids

Formula of amino acids

• NH2

• R group

• COOH

Why are amino acids buffers?

They minimise changes in pH

Name of reaction and the bond that forms a dipeptide

• Condensation reaction

• Peptide bond

Primary structure of a protein

The order of amino acids in a polypeptide, joined together by peptide bonds

Secondary structure of a protein

The shape it forms because of H bonds forming between the amino group of one monomer & the carboxyl group of another monomer

2 types of secondary structure & an example of each

• α helices e.g keratin

• β pleated sheets e.g silk

Tertiary structure of a protein

Further folded in secondary structure due to bonds between R groups

Example of a tertiary structure protein

Enzymes

Bond types in tertiary structure proteins, in order from weakest to strongest

• Hydrophobic interactions - non polar R groups

• Hydrogen bonds - polar R groups

• Ionic interactions - charged R groups

• Disulphide linkages - R groups containing S

Quaternary structure of a protein

• 2 or more types of polypeptides joined together by disulphide linkages

• Associated with non-protein groups as not many proteins reach this stage

Example of a molecule with a quaternary structure

Haemoglobin

Qualities of fibrous proteins

• Long narrow fibres α helices or β-pleated sheets

• Insoluble

• Structural function

• Repetitive amino acid sequence

• Stable molecule as it’s linked by H bonds

• Examples: collagen, keratin, silk

Qualities of globular proteins

• Spherical 3D shape & compact

• Soluble to water

• Metabolic functions - involved in chemical reactions

• Irregular (not repetitive amino acid sequence)

• Low durability

• Examples: enzymes, haemoglobin, antibodies

Test for proteins

• Add Biuret’s solution to sample being tested

• If solution changes form blue to purple, protein is present

• If solution remains blue, protein is not present

Roles of organelles in protein trafficking

• Nucleus - transcription (produces mRNA)

• RER - translation at ribosomes

• Golgi body - modifies and packages proteins into vesicles

• Cell membrane - if protein is needed outside cell, it passes through cell membrane

• Mitochondria - steps 1-4 require ATP (made at mitochondria)