Glycolysis and Krebs Cycle Flashcards
Cellular Respiration
The major catabolic pathway to produce energy from food (in eukaryotes).
Metabolism: Catabolic pathways
- Breakdown of complex organic molecules to generate energy
- Cellular respiration: “burning” of food to produce energy (use O2).
Metabolism: Anabolic pathways
Use of energy and small organic molecules to make (large) macromolecules
Energy Release from molecules
Cellular respiration:
2H from food via NADH and 1/2 O2
- Electron transport chain: stepwise oxidation yields a controlled release of energy that can be used by cells.
- controlled release of energy for synthesis of ATP
Reduction/Oxidation Reactions
Oxidation: A loss of electrons (the oxidized molecule loses electrons and is the “reducing agent:)
Reduction: A gain of electrons (the Reduced molecules Receives electrons and is the “oxidizing agent”).
- Redox reactions do not always involve the total loss of electrons. They can change the degree of electron sharing
Burning of sugar Redox
Electrons moved from carbon to oxygen, thus oxygen was reduced and carbon was oxidized. Exergonic reaction (-686 kcal/mol) so this energy is used to make ATP.
NAD+
NAD+ is an intermediate energy transport. During respiration, most energy is transferred to ATP through a coenzyme NAD+
Location of Cellular respiration
Glycolysis: cytosol, substrate level phosphorylation
Krebs: Matrix of mitochondrion, substrate level phosphorylation
Electron Transport Chain: Cristae of mitochondrion, oxidative phosphorylation
Glycolysis
Glycolysis = splitting of sugar (one 6 carbon ring is split into two 3-carbon molecules of pyruvate)
- DOES NOT REQUIRE OXYGEN
- Occurs in the cytosol
- Includes 10 steps:
- > 5 require energy (activation)
- > 5 produce energy (exergonic reactions)
- Products: ATP for use, NADH and pyruvate to go to the mitochondrion.
- ATP is made by substrate level phosphorylation
- 2 Net ATP (4 created, 2 used)
- 2 pyruvate (for Krebs), 2 water, 2 NADH (later make ATP), 2 H+
Substrate level phosphorylation
(last stage of glycolysis)
In substrate level phosphorylation, an enzyme transfers phosphate groups from an organic substrate (and not inorganic phosphate) to ADP.
- Pyruvate kinase enzyme.
- PEP (substrate) + ADP enter enzyme and PEP loses phosphate to make ATP and PEP becomes pyruvate.
Pyruvate to Krebs
Pyruvate is converted to acetyl CoA before entering Krebs cycle
- 2 pyruvate molecules are translocated from the cytosol into the mitochondrion, then
- Reactants: 2 pyruvate + 2 NAD+ + 2 coenzyme A
- Products: 2 Acetyl CoA + 2 CO2 + 2 NADH
- Products sent to Krebs cycle
Conversion of Pyruvate to Acetyl CoA
- Pyruvate is transported to into the mitochondrial matrix
- The carboxyl group is removed in the form of CO2, which diffuses out of the cell
- The rest of pyruvate is further oxidized and NAD+ is reduced to NADH
- The oxidized acetyl group of pyruvate is attached to CoA, forming acetyl CoA.
- Produces 2 NADH (Glycolysis also makes its own 2 NADH)
Mitochondria
- Have a double membrane
- Are the sites for cellular respiration
- They have their own genome and are thought to have evolved from prokaryotic symbionts
- Cellular respiration enzymes are in the matrix and in the inner membrane.
The Krebs Cycle
- 8 steps (do not require oxygen)
- Input: Acetyl CoA from glycolysis, NAD+, ADP, FAD+
- Output: 2 ATP, 6 NADH, 2 FADH2, 2 CO2
- All other intermediates are recycled within the Krebs cycle.
Cellular Respiration: Energy Yields
- Glycolysis: 2 ATP by substrate level phosphorylation
- Pyruvate to Acetyl CoA: 0-2 ATP depending on transport of NADH in cytosol
- Krebs cycle: 2 ATP by substrate level phosphorylation
- Electron Transport Chain: 34 ATP by oxidative phosphorylation
- NADH yields 3 ATP
- FADH2 yields 2 ATP
- Typical total ATP yield is 32 ATP.
