ENERGY AND METABOLISM (LECTURE 2)

Question 1

Define metabolism. (2)

Answer 1

It is the sum of all chemical reactions within an organism. These chemical reactions are organized into metabolic pathways.

Question 2

Define metabolic pathways. (2)

Answer 2

A metabolic pathway is a chain of reactions. Enzymes catalyze every step in the metabolic pathway.

Question 3

What are catabolic reactions? (2)

Answer 3

Catabolic reactions breakdown complex molecules into simpler compounds. These reactions release energy.

Question 4

What are anabolic reactions? (2)

Answer 4

Anabolic reactions build complex molecules from simpler ones. These reactions consume energy.

Question 5

What is the most significant example of a catabolic reaction?

Answer 5

Cellular respiration is a catabolic reaction.

Question 6

What is the most significant example of an anabolic reaction?

Answer 6

Photosynthesis is an anabolic reaction.

Question 7

What is energy coupling?

Answer 7

It is when a catabolic reaction is used to drive an anabolic reaction.

Question 8

What is the first law of thermodynamics?

Answer 8

Energy is neither created nor destroyed (but it can be transformed).

Question 9

What is the second law of thermodynamics?

Answer 9

Every energy transformation makes the universe more disordered (increases entropy), due to the inevitable loss of usable energy as heat.

Question 10

What is Gibbs free energy (G)?

Answer 10

The portion of a system’s energy that is available for work.

Question 11

What is the formula for Gibbs free energy (G)?

Answer 11

G = H - TS, where H is enthalpy (the total energy of the system; energy in chemical bonds), T is the temperature and S is the entropy (disorder in a system).

Question 12

What are the formulas for the change in free energy (ΔG)? (2)

Answer 12

ΔG = G(products) - G(reactants)
ΔG = ΔH - TΔS

Question 13

What can the change in Gibbs free energy (ΔG) tell us about a reaction?

Answer 13

ΔG tells you whether a reaction is spontaneous or not.

Question 14

(-)ΔG implies what? (4)

Answer 14

That the reaction is spontaneous and that energy is released. These reactions proceed alone and are exergonic (net release of energy).

Question 15

(+)ΔG implies what? (3)

Answer 15

That the reaction is non-spontaneous. These require energy to proceed and are endergonic (net input of energy).

Question 16

The change in free energy (ΔG) of photosynthesis is (+), meaning what? (3)

Answer 16

This means that photosynthesis is non-spontaneous, endergonic and the products have more free energy.

Question 17

The change in free energy (ΔG) of cellular respiration is (-), meaning what? (3)

Answer 17

This means that cellular respiration is spontaneous, exergonic and the products have less free energy.

Question 18

If a reaction is exergonic, what can we say about the reverse reaction?

Answer 18

The reverse reaction must be endergonic.

Question 19

What can we say about a reaction when ΔG = 0? (3)

Answer 19

If ΔG = 0, that reaction is at equilibrium (forward and reverse reactions occur at the same rate) and the system cannot do any work.

Question 20

Can a cell survive if it is at equilibrium (ΔG = 0)?

Answer 20

A cell at equilibrium cannot be alive.

Question 21

What is metabolic disequilibrium? How does this apply to cells?

Answer 21

This is when products are displaced to be used as reactants for other metabolic pathways - cells are open systems; things are constantly added and removed.

Question 22

Describe energy coupling using the terms: spontaneous, non-spontaneous, exergonic and endergonic.

Answer 22

Cells power endergonic (non-spontaneous) reactions using the energy released by exergonic (spontaneous) reactions.

Question 23

Work in your body is ____, meaning it ____ energy.

Answer 23

Work in your body is endergonic, meaning it requires energy.

Question 24

What are the 3 types of work that occur in the body? Provide an example for each.

Answer 24

Chemical (protein synthesis), mechanical (muscle contraction) and intracellular transport (active transport across the cell membrane).

Question 25

What is ATP? (full name)

Answer 25

Adenosine triphosphate.

Question 26

Describe the significance of the hydrolysis of ATP.

Answer 26

The hydrolysis of ATP (ATP --> ADP + Pi) is a highly exergonic reaction (the products are much more stable than the reactant). In our cells, ATP hydrolysis is coupled to the body's endergonic processes.

Question 27

What does Pi stand for and what is its chemical formula?

Answer 27

Pi stands for inorganic phosphate, H3PO4.

Question 28

If the hydrolysis of ATP occurred in a test tube, what would happen?

Answer 28

The test tube would get hot.

Question 29

What is the ATP cycle? (2)

Answer 29

ATP is renewable. Its synthesis requires energy, its hydrolysis yields energy.

Question 30

If cellular respiration releases 686 kcal/mol (-ΔG) and ATP synthesis required 7.3 kcal/mol (+ΔG), then how many ATP molecules could we create per 1 glucose molecule? How many would actually be formed?

Answer 30

There is enough energy to form 94 ATP molecules, but only enough free energy to form 38 ATP molecules (60% of the energy released is lost as heat).

Question 31

How is ATP hydrolysis coupled to chemical (synthesis) work? (not conceptually, on a molecular level)

Answer 31

ATP transfers a phosphate group to a reactant to "activate it".

Question 32

When is the phosphate group inorganic?

Answer 32

The phosphate group is considered inorganic (Pi) when alone. If it is attached to an ATP molecule or other, it is simply a phosphate group (denoted P).

Question 33

How is ATP synthesis coupled to transport work (active transport)?

Answer 33

The transfer of a phosphate group onto a carrier protein causes a change in the conformation of the protein, allowing it to move a molecule across the membrane.