Getting energy to make ATP

Cellular RespirationThe process by which mitochondria break

down food molecules to produce ATP is called cellular respiration.

There are 3 stages of cellular respiration.

1. Glycolysis (anaerobic)

2. The citric acid cycle

3. The electron transport chain. (aerobic)

Glycolysis

Energy used and made in glycolysis

Takes 2 ATP to start glycolysis

Only 4 ATP are produced

4-2= 2 ATP gained (not very effective)

Glycolysis uses an electron carrier called NAD+.

NAD+ forms NADH which it accepts 2 electrons.

Glycolysis

Glycolysis is a series of chemical reactions in the cytoplasm of a cell that breaks down glucose into 2 molecules of pyruvic acid.

Glucose 2 pyruvic acid

Glucose is a 6 carbon molecule.

Pyruvic acid is a 3 carbon molecule.

Glycolysis

• Before citric acid cycle and electron transport chain stages begin, pyruvic acid undergoes a series of reactions in which it gives off a molecule of CO2 and bines with a molecule called coenzyme A to form acetyl-CoA.

The citric acid cycle

• Occurs in the mitochondria

Citric acid cycle also called Krebs cycle

For every turn of the cycle, 1 ATP molecule of ATP and 2 molecules of carbon dioxide are produced.

NAD+ and FAD+ (electron carriers) form NADH and FADH2 (carry electrons to electron transport chain)

Electron Transport chain

• Occurs in the inner membrane of the mitochondrion.

• Energized electrons are carried by NADH and FADH2 to the top of the chain.

• The electrons are passed from protein to protein within the membrane, slowly releasing their energy in steps. Some of that energy is used directly to form ATP.

Electron Transport Chain

• The final electron acceptor at the bottom of the chain is oxygen, which reacts with four hydrogen ions (4H+) and four electrons to form two molecules of (H2O). This is why oxygen is so important to our bodies.

• Without oxygen, the proteins in the electron transport chain cannot pass along the electrons.

Electron Transport Chain

• If a protein cannot pass along an electron to oxygen, it cannot accept another electron. Very quickly, the entire chain becomes blocked and ATP production stops.

• Overall, the electron transport chain add 32 ATP molecules.

• Aerobic process of ATP is very effective.

Other ways to make ATP

FermentationFermentation occurs after glycolysis.

Is a process of making ATP when there is no oxygen present. (Anaerobic process)

Ex. Happens during heavy exercise, when your cells are without oxygen for a short period of time.

Fermentation

• There are two major types of fermentation

1. Lactic acid fermentation

2. Alcoholic fermentation

Lactic acid fermentation

• Lactic acid fermentation is one of the processes that supplies energy when oxygen is scarce.

• Two molecules of pyruvic acid produced in glycolysis use NADH to form two molecules of lactic acid. This releases NAD+ to be used in glycolysis, allowing 2 ATP molecules to be formed for each glucose molecule.

Lactic acid fermentation

• The soreness feeling you get after you workout is due to the build up of lactic acid in the muscles cells.

• The lactic acid is transferred from muscle cells, where it is produced during strenuous exercise, to the liver that converts it back to pyruvic acid.

Alcoholic fermentation

• Is used by yeast cells and some bacteria to produce CO2 and ethyl alcohol.

Ex. When making bread, yeast cell produce CO2 that forms bubbles in the dough.