chapter four: energy, chemical reactions & cellular respiration

What are the two classes of energy?

Potential and kinetic energy

What is potential energy vs kinetic energy?

potential energy is stored energy due to position or structure (chemical bonds)

kinetic energy– energy of motion (moving muscles)

What is chemical energy?

stored in chemical bonds (glucose, ATP, fats); released when bonds break.

What are the forms of kinetic energy?

heat, radiant energy, electricity energy, mechanical energy & sound energy

What does each form of kinetic energy do?

1. Heat: random molecular motion (waste product of energy conversion).

2. Radiant energy: energy in electromagnetic waves (vision).

3. Electrical energy: movement of charged particles (nerve impulses)

4. Mechanical energy: movement of objects (muscle contraction).

5. Sound energy: compression of molecules (hearing)

What are the three important molecules in the body that function primary in chemical energy?

1. Glucose (short-term, readily available fuel)

2. Triglycerides (long-term energy storage)

3. Adenosine triphosphate (ATP, immediate usable energy)

What is the first law of thermodynamics?

Energy cannot be created or destroyed, only transformed.

What is the second law of thermodynamics?

Every energy conversion increases disorder (entropy); energy conversions are inefficient.

Why is energy conservation always less than 100%?

Because some energy is always lost as heat, increasing entropy 

What occurs in a chemical reaction?

Chemical bonds are broken and/or formed, rearranging atoms to make new substances.

What is a reactant vs a product?

1. Reactants – starting substances

2. Products – substances formed at the end

What is a decomposition chemical reaction?

known as a catabolic reaction, large molecules broken into smaller ones (AB → A + B). Example: hydrolysis of sucrose.

What is a synthesis chemical reaction?

known as an anabolic reaction, it is a small molecules joined to form larger ones (A + B → AB). Example: protein synthesis.

What is an exchange?

atoms switched between molecules (AB + C → AC + B). Example: bicarbonate buffer system.

What is ATP cycling?

ATP cycling–  continuously broken down to ADP + Pi (releasing energy), then re-formed from ADP + Pi during cellular respiration.

Irreversible vs reversible chemical reaction

1. Irreversible: proceed in one direction to completion (e.g., glucose → CO₂ + H₂O).

2. Reversible reactions: can go forward or backward depending on conditions (e.g., CO₂ + H₂O ⇌ H₂CO₃).

What is chemical reaction rate?

Speed at which reactants are converted to products

What is activation energy?

Minimum energy required to start a chemical reaction 

What is the general function of enzymes?

Biological catalysts that speed up reactions by lowering activation energy.

What are cofactors are their roles?

Nonprotein helpers (metal ions or organic molecules) required for enzyme activity.

What’s the effects of temperature and pH on enzymes structure and reaction rates?

1. Too high temp → denaturation (loss of shape).

2. Too low/high pH → disrupts bonds, lowers activity.

3. Each enzyme has an optimal temp and pH

What is the competitor inhibitor and how does it control enzyme action?

competes with substrate for active site.

What is the noncompetitor inhibitor and how does it control enzyme action?

binds elsewhere on enzyme, changes shape.

What is the role of negative feedback in enzyme regulation?

End product of a metabolic pathway inhibits an enzyme earlier in the pathway (prevents overproduction).

List the four stages of cellular respiration involving glucose and where each stage occurs within a cell.

1. Glycolysis – cytosol 

2. Intermediate stage (Pyruvate oxidation) – mitochondrial matrix

3. Citric acid cycle (Krebs cycle) – mitochondrial matrix.

4. Electron transport system (ETS) – inner mitochondrial membrane 

Summarize the metabolic pathway of glycolysis, including(a) where it occurs in a cell, (b) if it requires oxygen, (c) the initial substrate and final product, and (d) the molecules formed during energy transfer.

1. Glycolysis:

   1. Location: cytosol.

   2. Oxygen: not required (anaerobic).

   3. Initial substrate: glucose.

   4. Final product: 2 pyruvate.

   5. Energy transfer: 2 ATP (net), 2 NADH.

Explain the enzymatic reaction of the intermediate stage, including (a) where it occurs in a cell, (b) if it requires oxygen, (c) the initial substrate and final product, and (d) the molecules formed during energy transfer.

1. Intermediate stage

   1. Location: mitochondrial matrix.

   2. Oxygen: required.

   3. Initial substrate: pyruvate.

   4. Final product: acetyl-CoA + CO₂.

   5. Energy transfer: 1 NADH per pyruvate (2 per glucose).

Summarize the metabolic pathway of the citric acid cycle, including (a) where it occurs in a cell, (b) if it requires oxygen, (c) the initial substrate and final product, and (d) the molecules formed during energy transfer.

1. Citric Acid Cycle

   1. Location: mitochondrial matrix.

   2. Oxygen: required.

   3. Initial substrate: acetyl-CoA.

   4. Final products: 2 CO₂, oxaloacetate (regenerated).

   5. Energy transfer (per acetyl-CoA): 1 ATP, 3 NADH, 1 FADH₂ (doubled per glucose).

Review the importance of NADH and FADH2 in energy transfer and the actions that take place in the electron transport system.

1. Carry high-energy electrons from earlier stages to ETS, where their energy is converted into ATP.

2. Electron transport system 

   1. Location: inner mitochondrial membrane.

   2. Requires oxygen (final electron acceptor → H₂O).

   3. NADH and FADH₂ donate electrons → pump protons → proton gradient drives ATP synthase.

   4. Produces ~34 ATP per glucose.