Introduction to enzymes

Question 1

What are the characteristics of enzymes (7)

Answer 1

Enzymes are:
– Globular proteins that catalyse reactions of ‘substrates’
– Required for almost all biochemical reactions within cells

• Enzymes have:
  – An active site that binds the substrate, prior to the reaction
  – High efficiency
  – High chemical and stereo-specificity
  – pH optima
  – Temperature optima

Question 2

What is the mechanism of action of enzymes (4)

Answer 2

E + S → ES → EP → E + P

1. start with enzyme and substrate
2. enzyme and substrate bind to form enzyme-substrate complex through bonding, but NOT covalent bonding
3. A chemical reaction takes place where the substrate turns into a product and an enzyme-product complex is formed
4. dissociation occurs when the enzyme loses affinity for the product, so the enzyme-product complex breaks apart, splitting into separate enzymes and products.

Question 3

What are the classifications of enzymes according to the type of reactions they catalyse. (6)

Answer 3

1. Oxidoreductases → Oxidation or reduction
2. Transferases → Transfer of a small group (e.g. CH3) from one molecule to another
3. Hydrolases → Hydrolysis e.g. aminoacylase
4. Lyases → Split molecules, by any mechanism except for hydrolysis
5. Isomerases → Isomerisation
6. Ligases → Join two molecules

Question 4

Define the term cofactor

Answer 4

These are non-proteins that many enzymes require in order to work and allow organisms to regulate enzymatic action. (e.g. Zinc ion at the active site of aminoacylase)

Question 5

Define the term coenzyme.

Answer 5

Small organic cofactors molecules called coenzymes that help enzymes catalyse reactions.

(e.g. Adenosine triphosphate (ATP), Thiamine (Vitamin B1), Ascorbic acid (Vitamin C))

Question 6

What are the forces that enzymes use bind substrates to the active site. (4)

Answer 6

• The forces that bind the enzyme and substrate together are always NOT covalent
• Hydrogen bonds - Between polarised hydrogen atoms and the lone pair of an electronegative element (e.g. O, N, S).
• Electrostatic interactions - Between positive and negative charges with full (+/-) or partial (𝛿+/ 𝛿-). (e.g. Zn2+ | | | | | Od-)
• Hydrophobic bonds - occur between non-polar regions (e.g. hydrocarbons).