AP BIOLOGY

CELL RESPIRATION

GLYCOLYSIS

Question [CLICK ON ANY CHOICE TO KNOW THE RIGHT ANSWER]
What process happens after glycolysis but before the citric acid cycle?
A
coenzyme A is broken off of pyruvate
B
a carbon atom is added to pyruvate to make a four carbon compound
C
glucose is split and produces two molecules of pyruvate
D
pyruvate is oxidized
Explanation: 

Detailed explanation-1: -In the presence of oxygen, the next stage after glycolysis is oxidative phosphorylation, which feeds pyruvate to the Krebs Cycle and feeds the hydrogen released from glycolysis to the electron transport chain to produce more ATP (up to 38 molecules of ATP are produced in this process).

Detailed explanation-2: -Pyruvate oxidation steps Pyruvate is produced by glycolysis in the cytoplasm, but pyruvate oxidation takes place in the mitochondrial matrix (in eukaryotes). So, before the chemical reactions can begin, pyruvate must enter the mitochondrion, crossing its inner membrane and arriving at the matrix.

Detailed explanation-3: -Summary. In the presence of oxygen, pyruvate is transformed into an acetyl group attached to a carrier molecule of coenzyme A. The resulting acetyl CoA can enter several pathways, but most often, the acetyl group is delivered to the citric acid cycle for further catabolism.

Detailed explanation-4: -Breakdown of Pyruvate In order for pyruvate, the product of glycolysis, to enter the next pathway, it must undergo several changes to become acetyl Coenzyme A (acetyl CoA). Acetyl CoA is a molecule that is further converted to oxaloacetate, which enters the citric acid cycle (Krebs cycle).

Detailed explanation-5: -Glycolysis is the process by which glucose is broken down within the cytoplasm of a cell to form pyruvate. Under aerobic conditions, pyruvate can diffuse into mitochondria, where it enters the citric acid cycle and generates reducing equivalents in the form of NADH and FADH2.

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