Energy from Biological Molecules (College Board AP® Biology): Study Guide

Glycolysis

• Glycolysis is the first stage of cellular respiration; it takes place in the cytosol of cells

• During glycolysis glucose is:

  • phosphorylated

  • split into two 3-carbon molecules

• The products of glycolysis include:

  • 2 pyruvate molecules

  • a net gain of two molecules of ATP

    • ATP is synthesized from ADP + inorganic phosphate (Pi)

    • This is described as a 'net gain' because some ATP is also used during glycolysis

  • two molecules of NADH

    • NADH is synthesized from NAD⁺

Oxidation of pyruvate

• Pyruvate from glycolysis is transported from the cytosol into the mitochondria, where oxidation occurs

  • Movement of pyruvate across the double membrane of the mitochondria occurs by active transport

• Pyruvate is oxidized and acetyl coenzyme A (acetyl CoA) is formed; during this process:

  • NAD⁺ is converted to NADH

  • Carbon dioxide is released

Krebs cycle

• The Krebs cycle involves a series of enzyme-controlled reactions in the matrix of the mitochondria

• Acetyl CoA, from the oxidation of pyruvate, enters the cyclic pathway, resulting in:

  • synthesis of ATP from ADP and inorganic phosphate

  • transfer of electrons to coenzymes NAD and FAD, producing NADH and FADH₂

  • release of carbon dioxide from organic intermediates

• The products of the Krebs cycle are then used as follows:

  • carbon dioxide is released as a waste product

  • NADH and FADH₂ are transferred to the electron transport chain in the mitochondrial membrane