Topic 10 - Cellular Respiration

Question 1

Cellular respiration

Answer 1

The process by which organisms transform food energy into ATP in the presence of oxygen

Question 2

What is the chemical equation for cellular respiration?

Answer 2

C6H12O6 + 6O2 → 6CO2 + 6H2O + Energy (38 ATP and heat)

Question 3

What are the four main steps of cellular respiration? Describe them briefly.

Answer 3

1. Glycolysis
   - Process of breaking glucose into 3-carbon molecules (pyruvate) with the production of ATP and NADH
2. Pyruvate oxidation
   - The decarboxylation and oxidation of pyruvate to produce acetyl-CoA (in preparation for the Krebs cycle under aerobic conditions)
3. Krebs cycle
   - Series of enzyme-catalyzed reactions of central importance in all living cells for extraction of energy from carbohydrates
   - Acetyl group from acetyl-CoA is attached to oxaloacetate to form citrate
   - Citrate is oxidized, producing NADH, FADH2, CO2, and ATP
   - Oxaloacetate reenters the cycle
4. Oxidative phosphorylation
   - ETC: series of electron carriers embedded in the inner mitochondrial membrane (cristae) that shuttles electrons from NADH and FADH2 to molecular oxygen; in the process, protons are pumped from the mitochondrial matrix to the intermembrane space, and oxygen is reduced to form water
   - Chemiosmosis: process in which ATP is produced in cellular metabolism by the involvement of a proton gradient across a membrane (electrochemical gradient); the potential energy of the H+ gradient is used to generate ATP by ATP synthase

Question 4

Name where each step of cellular respiration takes place in the cell.

Answer 4

1. Glycolysis - cytoplasm
2. Pyruvate oxidation - mitochondria
3. Krebs cycle - mitochondrial matrix
4. Oxidative phosphorylation - cristae/inner membrane of mitochondria

Question 5

What are the net products of glycolysis (per glucose)?

Answer 5

2 ATP
2 NADH
2 pyruvate

Question 6

What are the net products of pyruvate oxidation (per glucose)?

Answer 6

2 CO2
2 NADH
2 acetyl-CoA

Question 7

What are the net products of the Krebs cycle (per glucose)?

Answer 7

2 ATP
4 CO2
6 NADH
2 FADH2
Oxalacetate to start cycle over

Question 8

What are the net products of oxidative phosphorylation (ETC and chemiosmosis)? Why?

Answer 8

34 ATP
- NADH and FADH2 bring their electrons to ETC
- 1 NADH = 3 ATP
- 1 FADH2 = 2 ATP
- As a result for ETC, 10 NADH x 3 = 30 ATP, plus 2 FADH2 x 2 = 4, therefore 34 ATP are produced.

Question 9

What is the TOTAL amount of ATP produced by cellular respiration?

Answer 9

38

Question 10

Substrate-level phosphorylation

Answer 10

Production of ATP from ADP using energy from a chemical reaction and a phosphate group from a reactant

Question 11

Oxidative phosporylation

Answer 11

Production of ATP using the process of chemiosmosis in the presence of oxygen

Question 12

ATP synthase

Answer 12

Membrane-embedded protein complex that adds a phosphate to ADP with energy from protons diffusing through it

Question 13

How is energy transferred in the ETC/chemiosmosis?

Answer 13

Electron transport is a series of redox reactions; as the electrons are transferred, the electron energy is used to pump H+ across the membrane from the matrix to the inter-membrane space. From there, H+ moves back to the matrix through chemiosmosis.

Question 14

What is the role of NAD+ and NADH in cellular respiration?

Answer 14

• Electron accepters/carriers used to transfer energy (electrons) during cellular respiration
• NAD+ accepts electrons from other molecules and becomes reduced; this reaction forms NADH, which can then be used as a reducing agent to donate electrons
• NADH is the source of electrons in the ETC

Question 15

What is the source of electrons in the ETC (in cellular respiration)?

Answer 15

NADH

Question 16

What is the final acceptor of electrons in the ETC (in cellular respiration)?

Answer 16

O2

Question 17

How is water formed from the ETC?

Answer 17

O2 binds with H+ in the matrix, forming water.

Question 18

How is a concentration gradient used to generate ATP?

Answer 18

Protons flow down their concentration gradient into the matrix through the membrane protein ATP synthase, causing it to spin and catalyze conversion of ADP to ATP

Question 19

What happens if no oxygen is present?

Answer 19

Anaerobic respiration - if oxygen is not present, other molecules become the final electron acceptor depending on the organism
- In animals and bacteria, it is pyruvate (when pyruvate is reduced it becomes lactic acid)
- In yeast, acetyl aldehyde is reduced and becomes ethanol

Question 20

What are the reactants of cellular respiration?

Answer 20

Glucose (C6H12O2) and oxygen (O2)

Question 21

What are the products of cellular respiration?

Answer 21

Water (H2O), carbon dioxide (CO2), and energy (ATP and heat)

Question 22

Why is cellular respiration important?

Answer 22

It converts food (organic molecules) into usable energy for cells.