Lecture 8: Glycolysis, Pyruvate--> Acetyl-CoA, TCA, ETC

Carbohydrate catabolism

Process of cells taking in glucose (carb) and turning it into energy

2 forms of carbohydrate catabolism

Respiration and fermentation

What do both forms of carbohydrate catabolism start with?

Glycolysis

Glycolysis location

Cell cytosol.

Glycolysis (overview)

Breaks down 1 glucose into two molecules of pyruvate

Glycolysis net gain

2 ATP and 2 NADH per glucose molecule.

In glycolysis, 1 glucose (6-C sugar) breaks into…

2, 3-C sugars (pyruvate)

Glycolysis input

1 Glucose, 2 ATP, 2 NAD+, 2P

Where does ATP get input in glycolysis?

When glucose crosses the membrane it gets phosphorylized requiring an input of 2 ATP

Glycolysis output

2 pyruvate, 4 ATP, and 2 NADH.

Post-glycolysis requirement

Aerobic respiration or fermentation to replenish NAD+.

Next step after glycolysis

Conversion of pyruvate to acetyl-CoA.

Output of pyruvate to Acetyl-CoA

2 NADH (per 2 pyruvate)

What is NOT made when going from 2 pyruvate to 2 Acetyl-CoA?

ATP

Each pyruvic acid --> 1 acetyl CoA yields…

1 NADH

How many NADH are output per glucose molecule?

2 NADH (2 pyruvate-->2 acetyl CoA= 2 NADH)

Why do we need to convert pyruvate to acetyl-CoA?

Pyruvate cannot go through the TCA cycle

How many cycles of TCA are done per 1 glucose?

2 cycles (2 acetyl-CoA are generated from 2 pyruvate)

Where does the TCA occur?

Cytosol

How many ATP are generated from 1 cycle of TCA?

1 ATP

How many ATP are generated through TCA per glucose molecule?

2 ATP (since 2 acetyl-CoA requires 2 cycles of TCA)

Output of one cycle of TCA

1 ATP, 3 NADH, 1 FADH2

Why are there 2 cycles of TCA/ why do we multiply the outputs by 2?

There are 2 acetyl-CoA that enter the cycle requiring 2 cycles

Outputs of TCA cycle/glucose molecule

6 NADH, 2 FADH2, 2 ATP

Electron transport chain goal

Make ATP

Electron Transport Chain location

Occurs on membranes (bacterial cytoplasmic membrane) because molecules passing through the membrane need to be close to each other

Respiration

Electrons are passed to inorganic molecules

Respiration final electron acceptors (aerobic and anaerobic)

Aerobic respiration uses O2; anaerobic uses Nitrogen or Sulfur compounds.

What does respiration create?

A proton motive force and ATP

How do electrons get passed to generate energy to move protons out of the cell?

Electrons get passed from molecule (transport protein) to molecule which generates energy to pump protons out of the cell

What does pumping protons out of the cell create?

An electrochemical (proton) gradient

Chemiosmosis/oxidative phosphorylation

Utilizes electron transport chain and ATP synthase to generate ATP.

Oxidative phosphorylation (making ATP)

Once there is a proton gradient, protons go into the cell which spins ATP synthase to phosphorylate ADP (ADP +P) into ATP

ETC energy yield/cash in of NADH and FADH2

1 NADH yields 3 ATP; 1 FADH2 yields 2 ATP.

Why does NADH create more ATP than FADH2?

NADH enters more transport proteins in the membrane allowing more transfer of electrons creating more energy, while FADH2 enters later, generating less ATP

How many NADH do you get from the TCA cycle (per molecule of glucose/2 cycles)?

6 NADH per 1 glucose molecule (3NADH / 1 TCA cycle)

How many FADH2 do you get from the TCA cycle (per molecule of glucose/2 cycles)?

2 FADH2 per 1 glucose molecule. (1 FADH2 /TCA cycle)

ETC Energy gain/output

34 ATP (30 from 10 NADH and 4 from 2 FADH2)

Alternative energy sources

Proteins, fats, and sugars can all be sources of energy.

NET ATP gain of entire glycolysis of one glucose (respiration)

38 ATP (2 glycolysis, 0 pyruvate-->acetyl-CoA, 2 TCA, 34 ETC)

Net NADH from repiration

10 NADH (2 glycolysis, 2 pyruvate-->acetyl-CoA, 6 TCA cycle)

Net FADH2 from respiration

2 FADHs from TCA cycle