Enzymes

Question 2

Enzymes definition

Answer 2

Biological catalysts that are able to speed up biochemical reaction by lowering activation energy without being themselves changed at end of reaction

Question 3

What is metabolism

Answer 3

Catabolism (breakdown of molecule eg hydrolysis) + anabolism (synthesis of molecule, eg condensation)

Question 4

Activation energy definition

Answer 4

Minimum amount of energy required to start a chemical reaction

Question 5

Catalyst

Answer 5

Substance that increases rate of chemical reaction but remains unchanged itself at the end of reaction

Question 6

Energy profile diagram ad explanation of enzyme catalyzed chemical reaction

Answer 6

1. Uphill portion: activation energy - represents initial investment of energy required t start reaction
2. Peak of energy profile: transition state - where bonds can be broken / formed
3. Downhill portion: conversion to product - molecules settle into their new bonding arrangement to form product

Question 7

Describe effect of an enzyme

Answer 7

1. Activation energy is lowered
2. More reactant molecules can surmount the energy barrier to reach transition state to be converted into product molecules

NOTE: total energy difference / free energy change or Gibbs free energy btw reactant molecules and product molecules remains the same

Question 8

Enzyme properties

Answer 8

1. effective in small amounts: they remain chemically unaltered at the end of the reaction and can be reused.
2. extremely efficient.
3. high degree of specificity: Most enzymes are specific to one type of substrate molecule. Other enzymes are specific to a group of similar substrates.
4. Enzymes can be denatured by heat, act most efficiently at an optimum temperature.
5. Enzymes are affected by pH and they act most efficiently at their optimum pH.
6. Enzymes activity can be regulated by activators and inhibitors.

Question 9

What is the structure of an enzyme?

Answer 9

1. Globular protein with specific 3D conformation (which can be denatured when bonds holding them in specific 3D conformation are disrupted)
2. 4 categories of amino acid residues:
   - catalytic amino acid residues -> The R groups of these amino acids are directly involved in the
   catalytic activity (making/breaking chemical bonds once substrate is bound)
   - Binding amino acid residues -> The R groups of these amino acids hold the substrate(s) in
   position via NON- COVALENT BONDS while catalysis takes place
   - Structural amino acid residues -> involved in maintaining the specific 3D conformation of the active site, as well as the enzyme as a
   whole
   - Non essential amino acid residues -> no specific functions, and can be removed or
   replaced without the loss of the enzyme’s catalytic function.

Question 10

What are cofactors and what are types of cofactors

Answer 10

Cofactors: additional non -protein component that is associated with enzymes via covalent bonds or weak interactions, that allow enzyme to function

3 types of cofactors:
1. Inorganic metal ions
• Mostly small divalent ions eg. Ca2+
• May either be component of active site or affect enzyme activity through allosteric
regulation. Allosteric enzymes have multiple subunits and through conformational
changes, bind activators of inhibitors at sites other than the active site.
• They usually bind reversibly to the enzyme and act by altering the enzyme’s active and/or
allosteric sites to facilitate the catalytic reaction carried out by the enzyme.
• e.g. salivary amylase activity is increased in the presence of chloride ions.
2. Coenzymes
• Loosely associates with the enzyme during the reaction. Coenzymes act as transient
carriers of specific functional groups, hydrogen or electrons. Most coenzymes are derived
from vitamins.
• e.g. Nicotinamide adenine dinucleotide (NAD) is an important coenzyme in respiration (KIV:
Cellular Respiration).
3. Prosthetic group
• Prosthetic groups are tightly bound to the enzyme on a permanent basis.
• Eg. the prosthetic group of enzyme catalase is an iron-containing haem group.

Question 11

How are enzyme substrate complexes formed

Answer 11

1. Enzyme and substrate collides in correct orientation, substrate is bound to enzyme at active site. This is an effective collision
2. Enzyme substrate complex is formed
3. Substrate is held in the active site by non-covalent bonds (eg. hydrogen and
   ionic bonds) between the R groups of the binding amino acids and the substrate molecule
4. R groups of the catalytic amino acid residues at the active site catalyse the conversion of the substrate to product
5. The alteration in chemical conformation results in the product molecule being released from the active site as it is no longer complementary to the active site structure.
6. enzyme active site is free for the binding of another substrate molecule

Question 12

How does enzyme Lower activation energy

Answer 12

1. Enzyme orientates substrates in close proximity, in correct orientation, to undergo chemical reactions
2. Enzyme strains critical bonds in substrate, allowing hem to attain unstable transition state
3. Enzyme provides microenvironment that favours reaction