Energy Transfers in and Between Organisms: Aerobic Respiration - Krebs Cycle

Question 1

What is the Krebs cycle?

Answer 1

• Series of oxidation-reduction reactions, which take place in the mitochondrial matrix
• Produces reduced coenzymes and ATP, by substrate-level phosphorylation
• Carbon dioxide is lost

Question 2

Where does the Krebs cycle occur?

Answer 2

• In the mitochondrial matrix

Question 3

How often does the Krebs cycle occur for each pyruvate and glucose molecule?

Answer 3

• Takes place once for every pyruvate molecule
• 2 pyruvates are produced for every glucose molecule that enters glycolysis
• Krebs cycle occurs twice for every glucose molecule

Question 4

What are the main stages of the Krebs cycle?

Answer 4

• Formation of citrate (6C)
• Formation of a 5C compound
• Regeneration of oxaloacetate (4C)

Question 5

What happens during the formation of citrate (6-carbon compound)?

Answer 5

• Acetyl CoA (2C) from link reaction joins with a 4C compound (oxaloacetate) to form a 6C compound (citrate)
• This releases CoA which goes back to the link reaction

Question 6

What happens during the formation of a 5C compound?

Answer 6

• The 6C citrate compound is decarboxylated, where carbon dioxide is removed
• Dehydrogenation also occurs
• This releases hydrogen which is used to produce reduced NAD (NADH) from NAD

Question 7

What happens during the regeneration of 4C compound oxaloacetate?

Answer 7

• 5C compound is decarboxylated and dehydrogenated
• NADH is produced
• A phosphate group is directly transferred from ATP, an intermediate compound, to another ADP - forming ATP (substrate-level phosphorylation)
• 4C compound is converted to another 4C compound
• This releases reduced FAD (FADH2)
• 4C compound is converted to the 4C compound that started the cycle, oxaloacetate
• Another NADH is produced

Question 8

What does dehydrogenation mean?

Answer 8

• The removal of hydrogen from a molecule

Question 9

What is substrate-level phosphorylation?

Answer 9

• This is when a phosphate group is directly transferred from one molecule to another

Question 10

Outline all the steps in the Krebs cycle

Answer 10

• Formation of citrate (6C)

• Acetyl CoA (2C) from link reaction joins with a 4C compound (oxaloacetate) to form a 6C compound (citrate)
• This releases CoA which goes back to the link reaction

• Formation of a 5C compound

• The 6C citrate compound is decarboxylated, where carbon dioxide is removed
• Dehydrogenation also occurs
• This releases hydrogen which is used to produce reduced NAD (NADH) from NAD

• Regeneration of oxaloacetate (4C)

• 5C compound is decarboxylated and dehydrogenated
• NADH is produced
• A phosphate group is directly transferred from ATP, an intermediate compound, to another ADP - forming ATP (substrate-level phosphorylation)
• 4C compound is converted to another 4C compound
• This releases reduced FAD (FADH2)
• 4C compound is converted to the 4C compound that started the cycle, oxaloacetate
• Another NADH is produced

Question 11

What are the products of one turn of the Krebs cycle?

Answer 11

• 1 coA
• Oxaloacetate
• 2 carbon dioxides
• 1 ATP
• 3 reduced NADs (NADHs)
• 1 reduced FAD (FADH2)

Question 12

What is the 1 CoA produced from the Krebs cycle used for?

Answer 12

• Reused in the next link reaction

Question 13

What is the oxaloacetate produced from the Krebs cycle used for?

Answer 13

• Regenerated for use in the next Krebs cycle

Question 14

What are the 2 carbon dioxides produced in the Krebs cycle used for?

Answer 14

• Released as a waste product

Question 15

What is the 1 ATP produced from the Krebs cycle used for?

Answer 15

• Used for energy

Question 16

What are the 3 reduced NADs produced from the Krebs cycle used for?

Answer 16

• Used in oxidative phosphorylation

Question 17

What is the 1 reduced FAD produced from the Krebs cycle used for?

Answer 17

• Used in oxidative phosphorylation