Ch. 8 Exam

Question 1

Define energy.

Answer 1

The capacity to cause change or perform work

Question 2

Explain the two types of energy.

Answer 2

• Kinetic energy: energy of motion
  
  • Movement
    -Heat: kinetic energy of molecular motion
  • In cells, molecules are broken to obtain kinetic energy
• Potential energy: energy of position or configuration
  
  • In cells, potential energy is often stored in chemicals

Question 3

Where do molecules store potential energy?

Answer 3

In chemicals

Question 4

Explain the first law of thermodynamics.

Answer 4

Laws of thermodynamics govern energy conversions
- Matter and energy cannot be created or destroyed, and energy conversions increase entropy (disorder
- Molecules (fats and carbohydrates) store potential energy i their bonds (because electrons have potential energy

Question 5

Explain the second law of thermodynamics.

Answer 5

• In cells, some reactions release energy whereas others take up energy.
• Free energy (deltaG) of a reaction is the amount of energy available to do work
• Exothermic reaction: releases heat energy
  
  • Products have less potential energy than reactants
• Endothermic reaction: Heat energy is taken up
  
  • Products have higher potential energy than reactants

Question 6

During any energy conversion, some energy is “lost” as heat. Explain this phenomenon.

Question 7

Define free energy.

Answer 7

• Free energy (deltaG) of a reaction is the amount of energy available to do work

Question 8

Compare and contrast exothermic and endothermic reactions.

Answer 8

• Exothermic reaction: releases heat energy
  
  • Products have less potential energy than reactants
• Endothermic reaction: Heat energy is taken up
  
  • Products have higher potential energy than reactants

Question 9

When the concentration of reactants is high, ____ (more/less) collisions should occur, and reactions should proceed more _______ (quickly/slowly).

Answer 9

• more
• quickly

Question 10

Explain how energetic coupling works.

Answer 10

• Occurs between exergonic and endergonic reactions
• This allows chemical energy released from one reaction to drive another reaction

Question 11

What transfers in a reduction—oxidation (redox) reaction?

Answer 11

• Chemical reactions that involve electron transfer
• Protons (H+) usually accompany an electron during its transfer
• Oxidation and reduction events are always coupled
  -If one atom loses an electron, another has to gain it
  
  • Electron donors are always paired with electron acceptors

Question 12

(Not a question, just information!) Oxidation and reduction events are coupled. If one atom loses an electron, another had to gain it. Thus, electron donors are always paired up with electron acceptors to keep the exchange equal.

Question 13

Define and explain reduction.

Answer 13

• When an atom or molecule gains an electron
  
  • “adds Hs)
  • Occurs when molecules are assimilated
  • Increases potential energy

Question 14

Define and explain oxidation.

Answer 14

• When an atom or molecule loses an electron
  
  • “remove Hs)
  • Occurs when molecules are being broken up
  • Loses potential energy

Question 15

During a redox reaction, electrons can be used for two different purposes. List those purposes.

Answer 15

• Be transferred completely from one atom to another
• Be used to form different covalent bonds

Question 16

What is reduced to form NADH? What is NADH’s function?

Answer 16

• Nicotinamide adenine dinucleotide (NAD+)
• NADH is a high energy electron carrier that has the ability to acquire, then donate electrons to other molecules

Question 17

List three aspects of ATP (adenosine triphosphate).

Answer 17

• Has high potential energy and is used for most cellular activities
• Works by phosphorylating target molecules (transferring a PO4 3-)
• Have high potential energy because negative charges in its 3 phosphate groups repel each other

Question 18

How does ATP work on target molecules?

Answer 18

Phosphorylating

Question 19

Why do the electrons in ATP have high potential energy?

Answer 19

Negative charges in its 3 phosphate groups repel each other

Question 20

What is ATP hydrolysis important for?

Answer 20

For transport contraction and energy for enzymes to catalyze chemical reactions

Question 21

Define enzyme. Why are they important?

Answer 21

• Protein catalysts that facilitate specific chemical reactions within a cell
• Important because they speed up chemical reactions that are required for life

Question 22

Define and explain anabolism. Is anabolism endergonic or exergonic?

Answer 22

• Refers to chemical reactions that build smaller molecules into larger molecules
  
  • Dehydration reactions
  • Endergonic
    
    • They require an input of energy
    • The larger product molecules are more ordered and therefore have more potential energy than the smaller reactant molecules

Question 23

Define and explain catabolism. Is catabolism endergonic or exergonic?

Answer 23

• Refers to chemical reactions that break down larger molecules into smaller molecules
  -Hydrolysis
• exergonic
  
  • They release energy
  • The smaller products molecules are less ordered and therefor have less potential energy than the larger reactant molecules
• Although catabolic reactions are exergonic, they do not occur spontaneously

Question 24

Where do substrates bind in an enzyme?

Answer 24

Active site

Question 25

Define the conformational change that enzymes undergo when the substrate are bound to the enzyme.

Answer 25

Induced fit

Question 26

Define activation energy (Ea).

Answer 26

• The energy required by reactant molecules to get the reaction started (activated).
  
  • Energy is required to weaken the chemical bonds of the reactants

Question 27

How do enzymes catalyze chemical reactions? Meaning: how do they speed reactions along?

Answer 27

• By lowering the amount of activation energy required
  
  • Enzymes make it easier to break the reactants’ chemical bonds

Question 28

List and explain the three steps of enzyme catalysis.

Answer 28

1. Initiation: Substrates are precisely oriented as they bind to the active site
2. Transition state facilitation: Interactions between the substrate and active site of enzyme (lowering Ea)
3. Termination: Reaction products have a lower affinity to active site and, therefore released

Question 29

Are enzymes used only once before degradation, or multiple times?

Question 30

How are enzymes named? Give an example.

Answer 30

• Enzymes are named for the substrate (reactant) molecules on which they act
  
  • Enzymes generally have an ase suffix
• The enzyme sucrase catalyzes the hydrolysis of sucrose into glucose and fructose

Question 31

There are three factors that affect the rate of enzyme activity. Explain the first: substrate concentration, and how it affects the rate of enzyme activity.

Answer 31

• Enzyme activity increases as substrate concentration increases
• At very high substrate concentrations, all of the enzyme’s active sites are occupied by substrate
  
  • Enzymes activity cannot increase any further

Question 32

The second factor affecting the rate of enzyme activity is temperature. Explain how temperature affects the rate of enzyme activity.

Answer 32

• Enzyme activity increases as temperature increases
• At extremely high temperatures, enzyme activity decreases as the enzyme becomes denatured

Question 33

The third and final factor affecting the rate of enzyme activity is pH. Explain how pH affects the rate of enzyme activity.

Answer 33

• Each enzyme has an optimal pH at which activity is maximized
• A much lower or higher pH can cause enzyme to denature because they operate at an optimal pH

Question 34

List and describe the three molecules/atoms that assist enzymes.

Answer 34

• Coenzymes: non-protein organic molecules that aid enzyme function
  
  • Vitamins
• Cofactors: Inorganic ions that aid enzyme function
  
  • Minerals
• Functional groups: sometimes a function group must be added or removed for enzyme function
  
  • Phosphorylation

Question 35

Define and explain competitive inhibitors. Specifically: where do they bind to an enzyme?

Answer 35

• Molecules that have a shape similar to the enzymes substrate
  
  • They bind to the active site and block the binding of the substrate
  • No chemical reaction occurs

Question 36

Define and explain noncompetitive inhibitors. Specifically: where do they bind to an enzyme?

Answer 36

• They bind to a site other than the active site called the allosteric site
  
  • Binding at the allosteric site alters configuration of the enzymes, ultimately interfering with the ability of the substrate to interact with the active site of the enzyme
  • The enzyme and substrate shapes no longer match
  • No chemical reaction occurs

Question 37

Define and explain allosteric activation. Specifically: where do they bind to an enzyme?

Answer 37

• Some molecules called inducers interact with the allosteric site of an enzyme changing its configuration
• Rather than deactivating the enzyme, they activate it

Question 38

When does feedback inhibition occur? When are pathways shut down?

Answer 38

• Occurs when an anthem in a pathway is inhibited
• By the final product of that pathway
• Pathway can shut down when
  
  • Products are no longer needed by the cell