Enzymes
Definitions
Enzymes
- catalysts
- proteins that facilitate reaction mechanisms
- catalyse specific reactions
- increase rate of reaction
Active Site: regions of an enzyme that binds the substrate during the reaction
- Small relative to the total volume of the enzyme
- AA + cofactors are held in precise arrangement with respect to structure of the substrate
- Composition
→ AAs align the active site
→ AAs give specificity in substrate binding
- Site: occurs in clefts and crevices in the protein
→ excludes solvents that would otherwise reduce the catalytic activity of the enzyme
Substrate: reactant(s) in an enzyme-catalysed reaction
What do enzymes do?
1. Provide higher reaction rates:106~1012 times greater than uncatalysed
2. Milder reactions conditions needed: neutral pH, atmospheric pressure, close to ambient T
3. Greater specificity: in terms of substrates and products
4. Capacity for control: responds to concentration of substances
How do enzymes bind the substrates?
- Lock and key model: ligand binding site is rigid and complementary to the shape of the ligand
- Induced fit: flexible interaction between the ligand and active site induces a conformational change
- Transition state stabilisation
1. Lock and Key
- Active site structure: complementary to its substrate
- Active site shape: determined by the tertiary and quaternary structure of the protein
2. Induced Fit
- Certain enzymes can catalyse similar reactions
- Suggests that the active site interacts with the substrate and adapt to it to make a perfect fit (undergo conformational change)
- Eg) Hexokinase and glucose
How is substrate specificity produced?
- Geometric: The active site in complementary to the structure of the substrate
- Electronic: The AAs in the active site interact specifically with the substrate (charged AAs)
- Active site recognises specific functional groups on the substrate
- Lock & Key model / Induced Fit model
Stereospecificity
- Enzymes are highly specific in binding chiral substrates
- Enzymes are absolutely stereospecific → binds to 1 isomer/stereoisomer
- How?
1. locates chiral centre
2. orient molecules so that the lowest priority group (determined by molecular weight) faces away
3. Number 3 groups in increasing priority
4. Determine rotation of groups in decreasing priority
Enzymes Page 1
Definitions
Enzymes
- catalysts
- proteins that facilitate reaction mechanisms
- catalyse specific reactions
- increase rate of reaction
Active Site: regions of an enzyme that binds the substrate during the reaction
- Small relative to the total volume of the enzyme
- AA + cofactors are held in precise arrangement with respect to structure of the substrate
- Composition
→ AAs align the active site
→ AAs give specificity in substrate binding
- Site: occurs in clefts and crevices in the protein
→ excludes solvents that would otherwise reduce the catalytic activity of the enzyme
Substrate: reactant(s) in an enzyme-catalysed reaction
What do enzymes do?
1. Provide higher reaction rates:106~1012 times greater than uncatalysed
2. Milder reactions conditions needed: neutral pH, atmospheric pressure, close to ambient T
3. Greater specificity: in terms of substrates and products
4. Capacity for control: responds to concentration of substances
How do enzymes bind the substrates?
- Lock and key model: ligand binding site is rigid and complementary to the shape of the ligand
- Induced fit: flexible interaction between the ligand and active site induces a conformational change
- Transition state stabilisation
1. Lock and Key
- Active site structure: complementary to its substrate
- Active site shape: determined by the tertiary and quaternary structure of the protein
2. Induced Fit
- Certain enzymes can catalyse similar reactions
- Suggests that the active site interacts with the substrate and adapt to it to make a perfect fit (undergo conformational change)
- Eg) Hexokinase and glucose
How is substrate specificity produced?
- Geometric: The active site in complementary to the structure of the substrate
- Electronic: The AAs in the active site interact specifically with the substrate (charged AAs)
- Active site recognises specific functional groups on the substrate
- Lock & Key model / Induced Fit model
Stereospecificity
- Enzymes are highly specific in binding chiral substrates
- Enzymes are absolutely stereospecific → binds to 1 isomer/stereoisomer
- How?
1. locates chiral centre
2. orient molecules so that the lowest priority group (determined by molecular weight) faces away
3. Number 3 groups in increasing priority
4. Determine rotation of groups in decreasing priority
Enzymes Page 1
