Cellular Respiration I

Topics Review

Q: In the following metabolic pathway, the reactant A will be converted to E or G. Letters indicate the substrates and products, and numbers for each step indicate the enzymes. The intermediate, C, is substrate to be converted to D and F with equal efficiency by enzymes 3 and 5. If end product G inhibits enzyme 5, what would you expect as the amount of G increases in cell?

A: an increase in the production of E

Lecture Question

Q: How is carbon dioxide produced during the process of respiration?

A: it is produced from Pyruvate Oxidation and the Citric Acid Cycle

Core Concepts

1. Cellular Respiration is a series of catabolic reactions that convert energy in fuel molecules into ATP

2. Glycolysis is the partial oxidation of glucose and results in the production of pyruvate, as well as ATP and reduced electron carriers

3. Pyruvate Oxidation: pyruvate is oxidized to acetyl-CoA, connecting glycolysis to the citric acid cycle

4. The Citric Acid Cycle results in the complete oxidation of fuel molecules and the generation of ATP and reduced electron carriers

5. The Electron Transport Chain transfers electrons from electron carriers to oxygen, using the energy released to pump protons and synthesize ATP by oxidation phosphorylation

Cellular Respiration

• involves a serious of reactions

• a process meant to breakdown carbohydrates, lipids, and proteins

• it’s purpose is to convert energy in fuel molecules into ATP

• allows cells to work

• made up of a serious of catabolic process

• has four stages;

  1. Glycolysis → occurs in the cytoplasm and glucose is partially broken down, producing ATP and electron carriers

  2. Pyruvate Oxidation → occurs in the mitochondria matrix and takes the priorly produce pyruvate and converts it to Acetyl CoA

  3. Citric Acid Cycle → occurs in the mitochondria and takes the produced Acetyl CoA to then produce ATP and electron carriers

  4. Oxidative Phosphorylation → occurs in the mitochondria and takes the priorly produced electron carriers which will release their electrons causing the process to produce large amounts of ATP

Generating ATP

• ATP can come from multiple sources

• small amount of ATP is synthesized in Substrate-Level Phosphorylation → an enzyme/substrate complex is used in a hydrolysis reaction that drives the synthesis of ATP in this process

Oxidation-Reduction Reactions

• Oxidation is the loss of electrons → the reducing agent

• Reduction is the gain of electrons → the oxidative agent

• Glucose Breakdown Reaction;

  • Glucose will be oxidized = Carbon Dioxide

  • Oxygen will be reduced = Water

Electron Carriers

• NAD⁺ the oxidized form is FAD

• NADH the oxidized form is FADH₂

Glycolysis

• this process is anabolic

• can be divided into 3 phases

• begins with a 6-carbon glucose

• the end product is Pyruvate x6

Phase I

• the phosphorylation of glucose traps the molecule inside the cell and de-stabilizes it for phase 2

• starts with a 6-carbon glucose and produces fructose, 1-6 biphosphate

• 2x ATP are consumed in this phase of the process

Phase II

• starts with fructose, 1-6 biphosphate and ends with glyceraldehyde 3-phosphate x2

• during the process the fructose is cleaved into two different molecules

Phase III

• starts with glyceraldehyde 3-phosphate x2 and produces pyruvate x2

• produces NADH x2 and H⁺ x2

• produces ATP x4

Conclusion

• Gross ATP: 4

• Net ATP: 2

• 2 NADH

Mitochondria

• contains an inner membrane

• possess an outer membrane

• the space between the inner and outer membranes is the intermembrane space

Acetyl-CoA Synthesis

• the pyruvate is transported into the mitochondrial matrix from the cytosol and converted to Acetyl-CoA within the mitochondria

• pyruvate is oxidized to form carbon dioxide leaving an acetyl group to then produce Acetyl-CoA

Conclusion

• 1 NADH

• 2 Acetyl-CoA → contains carbon x2

• consumes 1 Coenzyme A

Citric Acid Cycle

• fuel molecules are completely oxidized in this process, which takes place in the mitochondrial matrix as well

• Acetyl-CoA is completely oxidized

Conclusion

• occurs 2x

• Gross ATP:

• Net ATP: 2

• 6 NADH and H⁺

• 2 FADH₂

• 4 CO₂

• consumes 1 H₂O

Oxidative Phosphorylation

• occurs in the mitochondrial inner membrane

• takes the produce electron carriers from the previous cycle and has four complexes

• electrons enter through complex I or complex II depending on whether they are NADH or FADH₂

  • NADH enters through complex I

  • FADH₂ enters through complex II

• electrons must be transported between the four complexes;

  • complexes I and II harvest electrons from NADH and FADH₂

  • coenzyme Q is reduced to CoQH₂ and transfers electrons from complexes I and II to complex III

  • cytochrome c moves to complex IV where oxygen is reduced to form water

  • the transport of electrons in complexes I, III and IV is coupled with the transport of protons across the inner membrane, from the mitochondrial matrix to intermembrane space

  • ATP synthase uses the electrochemical proton gradient to drive the synthesis of ATP

• the proton gradient has two components; a chemical gradient that results from the different concentration of hydrogen ions; and an electrical gradient resulted from the difference in charge between the two side of the membrane

ATP Synthase

1. the F₀ subunit forms a channel that rotates as protons pass through it

2. the F₁ subunit then uses this rotational energy to catalyze the synthesis of ATP

3. ATP synthase is a molecular machine that is composed of two subunits, F₀ and F₁

• the rotation of the F₀ subunit leads to rotation of the F₁ subunit in the mitochondrial matrix

• the rotation of the F₁ subunit causes conformational changes that allow it to catalyze the synthesis of ATP