AP biology review - Krebs cycle

Question 1

What is the net reaction for glycolysis

Answer 1

Glucose + 2 NAD+ + 2 ADP + 2Pi -> 2 pyruvate + 1H2O + 2 NADH + 2 ATP

Question 2

what is pyruvate oxidation?

Answer 2

• when oxygen is available, the pyruvate produced in the cytosol is transported into the mitochondrial matrix

Question 3

What happens in the Krebs cycle?

Answer 3

• process occurs in five major steps. One of the three carbons in the pyruvate is cleaved off and released as carbon dioxide
• the remainder, called an acetyl group, becomes associated with a carrier molecule called coenzyme A (Co-A) to produce acetyl-CoA
• this reaction is coupled to the reduction of NAD+ to produce NADH
• for each glucose molecule that enter glycolysis, two pyruvate molecules undergoes oxidation, producing two molecules of acetyl-CoA and two NADH molecules
• pyruvate oxidation can be thought of as linking glycolysis to the Krebs cycle

Question 4

What is the Krebs cycle?

Answer 4

• The cyclic metabolic pathway that acquired acetyl-CoA and oxidizes it to carbon dioxide while regenerating the compound that icks uo more acetyl-CoA. It converts released energy to ATP, NADH, and FADH2

Question 5

The breakdown of the Krebs cycle

Answer 5

• Each molecule of acetyl-CoA carries two carbons from the molecule of glucose that originally entered glycolysis. These two carbons will be released later as carbon dioxide through the activity of the Krebs cycle. For each molecule of glucose that enters glycolysis, two molecules of acetyl-CoA enter the Krebs cycle
• The krebs cycle occurs twice for each molecule of glucose processed

Question 6

reactions 1-5 of the Krebs cycle

Answer 6

• acetyl-CoA “delivers” two carbons from glucose to the krebs cycle by reacting with oxaloacetate to produce a six-carbon molecule called citrate
• Once citrate is formed, it undergoes a series of reactions that break it down to a four-carbon molecule called succinate. Two of these reactions are oxidation reactions that result in the release of two carbons in the form of carbon dioxide molecules. Coupled to these oxidation reactions are two reduction reactions, each of which reduces a molecule of NAD+ to produce a molecule of NADH

Question 7

reaction 6

Answer 7

• In reaction 6 of the cycle, ATP is produced by substrate-level phosphorylation. This is a complex reaction in which a phosphate group replaces the CoA whale the substrate succinate, is bound to the enzyme
• The phosphate group is then added to a molecule of guanosine triphosphate (GTP). The terminal phosphate group from GTP is then transferred to ADP to produce ATP. Although most of the GTP is used to make ATP< a few reactions in the cell use GTP itself for energy

Question 8

reactions 7-9

Answer 8

• Oxidation reactions
• These reactions are coupled to the reduction of NAD+ to form NADH and the reduction of FFAD to form FADH2
• These electron carriers are used to produce ATP in the oxidative phosphorylation pathway
• The final product of the last three is oxaloacetate. This makes the pathway cyclical-oxaloacetate is regenerated and ready to react with more acetyl-CoA entering the Krebs cycle
• By the end of the Krebs cycle, all six carbon atoms of glucose have been oxidized to CO2 and released from the cell as waste
• Throughout the cycle, 2 co2 molecules are release while 3 NADH, 1 ATP, and 1 FADH2 are produced. Oxaloacetate is regenerated and free to bind to the next acetyl-CoA