Reaction Kinetics

Question 1

Endothermic process

Answer 1

Energy is absorbed to break bonds.
ΔH>0 
More energy than reactant.
ΔH: Change in enthalpy (heat)(energy).
E break - E form
Usually non-spontaneous

Question 2

Exothermic process

Answer 2

Energy is released when new bonds form.
ΔH<0
Less energy than reactant.
ΔH: Change in enthalpy (heat)(energy).
E break - E form
Usually spontaneous

Question 3

Transition state

Answer 3

• Molecules are stable so they must be deformed to be broken.
• They need energy to change the structure (Activation energy Ea).
• The transition state of a reaction is always at a higher energy level than the reactants or products → Ea always has a positive value.

Question 4

Exergonic reaction (spontaneous)

Answer 4

ΔG<0
ΔG: change in free energy
No outside interventions at standard conditions.
Processes will only happen spontaneously, without added energy, if it increases the entropy of the universe as a whole.
Entropy: measure of disorder ΔS
Non-spontaneous in the other direction

Question 5

Endergonic reaction (non-spontaneous)

Answer 5

ΔG>0
ΔG change in free energy
Spontaneous in the other direction.

Question 6

Gibbs free energy

Answer 6

Measure of the amount of useful energy in a system.
ΔG = ΔH - TΔS
ΔH: Change in enthalpy (heat)(energy)
ΔS: Change in entropy
T: Temperature in kelvin

Question 7

Catalysis

Answer 7

Process that reduces the Ea → increases the reaction rate (faster reaction)

Question 8

Catalyst

Answer 8

Substance that speeds up a reaction (by lowering the activation energy) without being consumed.

Question 9

Enzymes

Answer 9

Catalyst for biochemical reactions. Enzymes are usually PROTEINS.

Question 10

Substrates

Answer 10

The molecules upon which enzymes may act, they are the reactants of the reaction.

Question 11

Active site

Answer 11

The portion of the enzyme that bind the

substrate and catalyze the reaction.

Question 12

Induced fit

Answer 12

An enzyme changes shape slightly when it binds its substrate, resulting in an even tighter fit.
All enzymes return to original state after reaction.

Question 13

Enzyme regulation

Answer 13

1. Regulatory molecules
2. Cofactors and coenzymes
3. Compartmentalization
4. Feedback inhibition

Question 14

Regulatory molecules

Answer 14

1. An allosteric inhibitor binds the enzyme at a site different than the active site: the allosteric site.
   Activators: increase enzyme’s activity. Inhibitors: decrease enzyme’s activity.
2. Non-competitive inhibitors
   Binds to any other site than active site. Substrate can bind but reaction is blocked.
3. Competitive inhibitors
   Binds at the active site, thus preventing the substrate to bind to the enzyme.

Question 15

Cofactors and Coenzymes

Answer 15

Non-protein molecules that make the enzyme capable of catalysis.
Coenzyme: Organic compounds (vitamin)
Cofactor: Inorganic compound (ions)

Question 16

Compartmenalization

Answer 16

Storing enzymes in a specific compartments of the cell.

Question 17

Feedback inhibition

Answer 17

The end product of a metabolic pathway inhibits the key enzyme, preventing more of the end product from being produced.

Question 18

Isoenzymes

Answer 18

Enzymes that catalyze the same reaction but display different kinetic parameters.

• Hexokinase
• Glucokinase

Question 19

Hexokinase

Answer 19

• Has a low Km → high affinity for glucose → efficient catalysis even at low glucose concentrations.
• Small Vmax → it’s saturated at normal blood concentration of sugar and won’t respond to increased glycaemia.

Question 20

Glucokinase

Answer 20

• Has a much higher Km → functions only
  when glucose concentration is elevated.
• High Vmax allows the liver to effectively remove glucose from the blood.