Cellular RespirationAP Biology

ATP—Adenosine triphosphate• The energy currency

of the cell. ATP powers almost every energy requiring process in cells

http://student.ccbcmd.edu/biotutorials/energy/adpan.html

Cellular respiration relies on electron acceptors & electron carriers

NAD+ is an electron acceptor

NAD+ + e- NADH

NADH is an electron carrier

FAD+ is an electron acceptorFAD+ + e- FADH2 FADH2 is an electron carrier

Key Questions in Cellular Respiration

• What is the purpose of glucose?• When does oxygen get consumed?• When does CO2 get produced?• What are the most important end

products?

Cellular Respiration—Four Stages Master Chart

Stage

Stage Name

Location Reactants Used

Products

1 Glycolysis

2 Pyruvate Oxidation

3 Krebs Cycle

4 Electron Transport

Stage 1—Glycolysis

Glycolysis

Glyco—

Lysis—

Step 1. Two ATP molecules each provide a phosphate to form a new 6-carbon compound. Two ATP molecules are used.

Step 1

Step 2. The six carbon compound is split into two three carbon molecules of PGAL.

Step 1

Step 2

Step 3. The two PGAL molecules are oxidized (lose an electron) and receive a phosphate group. The electrons are added to NAD+ to form NADH

Step 1

Step 2

Step 3

Step 4. The phosphate groups added are removed and each added to ADP to form ATP. The result is the formation of two, three carbon molecules called pyruvic acid.

Step 1

Step 2

Step 3

Step 4

Major Outcomes of Glycolysis

• Splits glucose into two molecules of pyruvate

• Yields a net of 2 ATP molecules• Produces 2 NADH molecules

Cellular Respiration—Aerobic RespirationStage 2: Oxidation of Pyruvate

Steps of Pyruvate Oxidation

1.Pyruvic acid enters the mitochondrial matrix & reacts with coenzyme A to form acetyl CoA.

2. CO2 is released

3. NAD+ is reduced to NADH

Stage 3: The Krebs Cycle

Step 1. Acetyl CoA (2 C) combines with OAA (4 C) to form citric acid (6 C).

Stage 3: The Krebs Cycle

Step 2. Citric Acid releases a CO2 molecule to form a five-carbon molecule. A hydrogen atom is transferred to NAD+ forming NADH.

Stage 3: The Krebs Cycle

Step 3. The five carbon molecule releases a CO2 to form a four carbon compound. NAD+ is reduced again to NADH & ATP is formed.

Stage 3: The Krebs Cycle

Step 4. The four carbon compound releases another hydrogen to reduce FAD to FADH.

Stage 3: The Krebs Cycle

Step 5. The four carbon compound releases another hydrogen to reduce NAD+ to NADH. This regenerates OAA.

Major Outcomes of the Kreb’s Cycle

• Two pyruvic acid molecules convert to two acetyl CoA molecules

• The acetyl CoA breaks down• 6 molecules of CO2 are released (waste)• 2 ATP molecules are produced (energy)• 8 NADH are formed (fuels ATP synthesis)• 2 FADH2 are formed (fuels ATP synthesis)• Oxaloacetic Acid is reformed, regenerating the

cycle

Electron Transport in the Mitochondria

The electron transport chain lines the inner membrane of the mitochondria

Electron Transport in the Mitochondria

Step 1. NADH & FADH2 release hydrogen atoms and regenerate NAD+ and FAD.HH+ + e-

Electron Transport in the Mitochondria

Step 2. High energy electrons move through the electron transport chain. The energy they lose, pumps the protons (H+) to the other side of the membrane.

Electron Transport in the Mitochondria

Step 3. The high concentration of protons move through ATP synthase & form ATP.

Electron Transport in the Mitochondria

Step 4. The protons and electrons that reenter the matrix are accepted by oxygen to form H2O.

Major Outcomes of Electron Transport Chain

• From one molecule of glucose, each of the eight NADH generates 3 ATP molecules—24 ATP molecules are produced

• Each of the two FADH2 generates 2 ATP molecules—4 ATP molecules are produced

• Electrons and hydrogen from the two cytoplasmic NADH (produced in glycolysis) are transferred into the mitochondria & yield 6 ATP

• Oxygen accepts electrons and protons to form water as a byproduct