Lesson 2: Energy and Enzymes

Question 1

What is a chemical reaction?

Answer 1

Occurs when atoms have enough energy to combine or change bonding partners

Question 2

What is metabolism?

Answer 2

The SUM TOTAL of all chemical reactions

Question 3

How do metabolic reactions involve energy changes?

Answer 3

1) An input of energy is needed to build things (like macromolecules) -> think condensation
2) Energy is generated when things (like macromolecules) are broken down -> think hydrolysis

Question 4

What is energy?

Answer 4

The capacity to do work, or the capacity for change

Question 5

What are the two types of metabolism?

Answer 5

Anabolic and catabolic reactions

Question 6

What is an anabolic reaction?

Answer 6

Complex molecules are MADE from simple molecules; energy is required (ex: condensation reactions)

Question 7

What is a catabolic reaction?

Answer 7

Complex molecules are BROKEN DOWN to simple ones; energy is released (ex: hydrolysis reactions)

Question 8

How are catabolic and anabolic reactions linked?

Answer 8

Catabolic pathways produce subunits and releases energy that can be used for anabolic pathways

Question 9

What is free energy (G)?

Answer 9

The usable energy for work

Question 10

What is an exergonic reaction?

Answer 10

Reactions that release free energy (- delta G). They are spontaneous

ex: catabolism (hydrolysis reactions)

Question 11

What is an endergonic reaction?

Answer 11

Reactions that consume free energy (+ delta G). They are non-spontaneous

ex: anabolism (condensation reactions)

Question 12

What are more characteristics of an exergonic reaction?

Answer 12

• High energy state to a low energy state (energetically favorable)
  - The free energy of the reactants is HIGHER than the
  free energy of the products (- delta G)

Question 13

What are more characteristics of an endergonic reaction?

Answer 13

Low energy state to a high energy state (energetically unfavorable)
- The free energy of the reactants is LOWER than the
free energy of the products (+ delta G)

The activation energy for an endergonic reaction is MUCH LARGER than for an exergonic reaction. Therefore, this reaction must be coupled to an exergonic reaction to overcome the energy barrier

Question 14

What is the activation energy?

Answer 14

The amount of energy required to start the reaction (activation energy must be added for the molecule to reach the TRANSITION STATE)
- higher activation energy -> slower the reaction
- lower activation energy -> faster the reaction

Question 15

What is the transition state?

Answer 15

As the reaction goes from reactants to products, the molecules must be contorted into an unstable higher energy state (which is the the TRANSITION STATE)

Question 16

What are enzymes?

Answer 16

Enzymes are primarily proteins and they are highly specific.

They serve as catalysts that lower the activation energy (energy barrier) for reactions, specifically exergonic reactions. Therefore, they increase the rate of chemical reactions.

Question 17

What determines the specificity of an enzyme?

Answer 17

The 3-D shape and composition of the enzyme determines the specificity (noncovalent interactions allow the enzyme to bind its substrate/reactant)

Question 18

How do enzymes reduce the activation energy?

Answer 18

By providing the framework in which reactions can take place. They stabilize the structure of the transition state.

Note: Enzymes can increase reaction rates by 1 million to 10^17 times

Question 19

What is another function of an enzyme?

Answer 19

Many enzymes participate directly in the catalytic process. Enzymes can form or break chemical bonds.

ex: amylase, sucrase, lactase, or maltase can break down carbohydrates

Question 20

What are the steps for how enzymes work?

Answer 20

1) Substrate binds to enzyme
2) Substrate is converted to products
3) Products are released
4) Active site is available for another substrate
- Enzyme is left completely unchanged (enzyme can be used over and over)

Question 21

Can enzymes overcome the activation energy for an endergonic reaction?

Answer 21

No, the activation energy is too large and MUST be coupled with an exergonic reaction.

Note: enzymes can still stabilize the transition state and break/form bonds in endergonic reactions.

Question 22

What is reaction coupling?

Answer 22

The activation energy for an endergonic reaction is too large and cannot occur UNLESS it is coupled to an exergonic reaction. This results in a NEGATIVE net free-energy change for the pair of reactions.

Question 23

Describe the steps of reaction coupling.

Answer 23

1) If you want to form a polymer, the reaction must be coupled with an exergonic reaction or it will not occur.

2) ATP hydrolysis (ATP –> ADP + P) is an example of an exergonic reaction that will power the energetically unfavorable condensation reaction.

3) ACTIVATION STEP: ATP can transfer a phosphate group to the reactants to produce a high-energy intermediate. The reaction will now become energetically favorable since we are going from a high energy to low energy state.

4) CONDENSATION STEP: This high energy intermediate reacts with the other reactant to form the product.

Question 24

What is ATP?

Answer 24

ATP is a nucleotide and stands for adenosine triphosphate

• An active cell must produce millions of molecules of ATP per second
• An ATP is typically consumed within a second of its formation
• Each ATP molecule undergoes about 10,000 cycles of synthesis and hydrolysis every day!

Question 25

How is ATP an activated carrier?

Answer 25

ATP transfers and captures free energy through ATP hydrolysis and condensation

Question 26

What are two characteristics of ATP that account for the free energy released?

Answer 26

1) Phosphate groups have negative charges and repel each other – the energy needed to get them close enough to bond is stored in the P~O bond.
- Therefore, when you remove a phosphate group. All
this energy needed to keep them close together will be
released.

2) The free energy of the P~O bond is much higher than the energy of the O~H bond that forms after hydrolysis.
- After you remove a phosphate group, it becomes a P-O-
H bond which is more energetically favorable, therefore
energy is released.

Question 27

How is ATP hydrolysis reversible?

Answer 27

Cells often use the energy released from ATP hydrolysis to fuel the regeneration of ATP from ADP + P