Theme 1

Question 1

What is energy? What are the two main types of energy?

Answer 1

The capacity to do work. Kinetic and Potential energy.

Question 2

Differentiate between an isolated, open and closed system, and provide and example of each.

Answer 2

Isolated: does not exchange matter or energy with surroundings, eg Thermos
Closed: exchanges energy but not matter, eg. Earth
Open: exchanges both matter and energy, eg. ocean

Question 3

From a thermodynamics perspective, why do we eat food?

Answer 3

To maintain low entropy

Question 4

Define entropy.

Answer 4

measure of the randomness or disorder of the universe

Question 5

Explain why living organisms do not defy the second law of thermodynamics.

Answer 5

The entropy of the system can decrease as long as the entropy of the universe as a whole increases. Living organisms give off heat and by-products of metabolism (such as CO2) that increase entropy of the surroundings.

Question 6

What is a spontaneous reaction?

Answer 6

A reaction that will occur (without continuous input of energy).

Question 7

What two factors determine if a reaction will be spontaneous?

Answer 7

1. products have less potential energy than reactants (HproductsSreactants)

Question 8

What is free energy? What equation determines change in free energy (G)?

Answer 8

portion of system’s energy available to do work;

∆G=∆H - T∆S

Question 9

Explain whether a reaction will be spontaneous in term of ∆G.

Answer 9

• ∆G is negative, reaction is exergonic, spontaneous.

- ∆G is positive, reaction is endergonic, not spontaneous.

Question 10

What happens if a cell reaches a point of chemical equilibrium (∆G=0)?

Answer 10

It is dead.

Question 11

What is the sum of all chemical reactions taking place within and organism called?

Answer 11

Metabolism.

Question 12

What is the difference between anabolic and catabolic metabolic pathways?

Answer 12

Anabolic: consume energy to build complex molecules
Catabolic: releases energy through breakdown of complex molecules

Question 13

Why does the hydrolysis of ATP release free energy?

Answer 13

1. ADP and Pi carry -ve charge; repulsion between these ionic products favours hydrolysis.
2. release of terminal phosphate allows for greater hydration, which is an energetically favoured state.
3. Orthophosphate (Pi) group can exist in many resonance forms, which are not all available when it is bonded. (=> release of Pi increases disorder of system)

Question 14

Is ATP hydrolyzed in energy coupling?

Answer 14

NO.
Hydrolysis is prevented because the site on the enzyme where ATP and substrate react is inaccessible to water. Phosphate group is transferred to the reactant molecule, making it more unstable and reactive. Hence the energy is NOT simply lost as heat.

Question 15

The initial energy investment required to start a reaction is called the _____ and molecules that gain this necessary energy are said to occupy the _______ state.

Answer 15

Activation energy; transition

Question 16

What is the function of an enzyme within a reaction?

Answer 16

Lowers activation energy

Question 17

Do enzymes alter ∆G?

Answer 17

No.

Question 18

Which hypothesis for enzyme activity states that before substrate binding, the enzyme changes conformation?

Answer 18

Induced-fit hypothesis

Question 19

Enzymes often require cofactors; organic cofactors are termed _______.

Answer 19

Coenzymes

Question 20

Are enzyme active sites complementary to the substrate or the transition state? Why?

Answer 20

They are complementary to the transition state; if they were complementary to the substrate, they may stabilize the substrate and increase EA