Enzymes One

Question 1

Name the six different classifications of reaction:

Answer 1

• Oxidoreductase- catalyse redox
• Transferase- transfer functional group
• Hydrolase- cause hydrolysis reactions
• Lyase- C-N, C-C, C-O bonds break
• Isomerase- re-arrange functional group
• Ligase- join 2 together

Question 2

Explain the differences between simple enzymes and holoenzymes:

Answer 2

• Simple enzymes- composed only of protein
• Holoenzymes- protein + other organic/inorganic molecule (advantage is these gives another level of control to the system)
• Apoenzyme = protein component
• Cofactor- Inorganic molecules bind temporarily to enzyme for activation (eg. Mn or Zn)
• Co-enzyme- same but organic (co-enzyme A or NAD)

Question 3

Define the term prosthetic group:

Answer 3

• Not part of polypeptide chain but permanently bound
• Metal ions or various parts of metal ions/organic compounds
• E.g. haemoglobin

Question 4

Define the term allosteric site:

Answer 4

• Interacting subunits act to change shape + function to moderate catalytic activity
• Regulatory site usually situated elsewhere
• Characterised by larger size

Question 5

Define the term Isoenzyme

Answer 5

• Differ in aa composition but can act on the same substrate
• Differ substrate turnover/ability to be regulated
• Certain step or development specific
• Fine metabolic tuning (e.g. lactate dehydrogenase- LDH)
• Different levels can indicate injury in different areas

Question 6

Describe the two main models of enzyme substrate interactions

Answer 6

o Lock and key model- fits perfectly and then catalysis occurs
o Induced fit model- doesn’t fit perfectly
• Binding of substrate leads to conformational change in active site
• Substrate strain leads to contorted bonds angles and activates the substrate
• Brings catalytic sites close to substrate bonds to be altered

Question 7

Describe the 4 main mechanisms of how this occurs:

Answer 7

1. Bond strain
2. Orientating substances
3. Acid/Base proton/donor catalysis
4. Covalent catalysis

Question 8

Explain how toxins affect functioning of enzymes:

Answer 8

o Organophosphates
• Bind reactive serines leading to a inactive complex
• Affect serine proteases
o Heavy Metals (Ag, Hg, Pb, Cu)
• Binds to sulphur (cysteine covalent intermediate)
• Renders the enzyme inactive

Question 9

Explain with examples of how enzymes are used in the diagnosis of disease:

Answer 9

o Aspartate transaminase (AST)
• Found in liver, heart and skeletal muscle
• after MI levels rise 6-8 hrs then peak at 24 and are then normal again @ 5 days)
o Alanine Transaminase (ALT)
• Functions in delivery skeletal muscle carbon and nitrogen
• In acute inflammatory conditions of the liver, ALT is higher than AST
o Creatinine Kinase (CK)
• Highest activity in heart and muscle
• CK-MB >6% = AMI
• CK-MB is greater than 6% then a heart attack is likely
o Always difficult to make diagnosis based purely on clinical signs, necessary to look at a wide variety of different levels