Chapter 7

Cellular Respiration

Section 7-1: Glycolysis and Fermentation

Harvesting Chemical Energy:All organisms require the energy

stored in carbohydrates.

Section 7-1: Glycolysis and Fermentation

Harvesting Chemical Energy:Cellular respiration: the process of

breaking down carbohydrates into ATP (energy).

Cellular respiration begins with a biochemical pathway called glycolysis.

Section 7-1: Glycolysis and Fermentation

Glycolysis:Glycolysis: the beginning steps of

cellular respiration.Spends 2 ATP and releases 4 ATP.

After glycolysis, cellular respiration can follow either of two biochemical pathways:Fermentation (anaerobic respiration).Aerobic respiration.

Section 7-1: Glycolysis and Fermentation

Aerobic vs. Anaerobic Respiration:Aerobic respiration: the process of

converting carbohydrates into ATP in the presence of oxygen.Lots of ATP.

Anaerobic respiration: the process of converting carbohydrates into ATP in the absence of oxygen.Small amounts of ATP.

Section 7-1: Glycolysis and Fermentation

Glycolysis:Glucose: a simple sugar.Glycolysis: a process in which

glucose is changed to pyruvic acid and ATP.

Glycolysis requires the input of two molecules of ATP.

Steps of Glycolysis

1. Two phosphate groups supplied by two molecules of ATP are attached to the glucose. This forms a new six-carbon molecule.

2. The new six-carbon molecule then splits into two three-carbon molecules called PGAL.

Steps of Glycolysis

Steps of Glycolysis

3. Each molecule of PGAL gains another phosphate group changing the substance into another three-carbon molecule.

Steps of Glycolysis

4. The phosphate groups added in steps 1 and 3 are removed, which leaves you with 2 molecules of pyruvic acid. Each of the four phosphate groups that was removed is attached to its own ADP molecule, forming ATP. Thus, resulting in four molecules of ATP being formed.

Steps of Glycolysis

Section 7-1: Glycolysis and Fermentation

Outcome of Glycolysis: 4 molecules of ATP. Net yield of 2 molecules of ATP

(input of 2 ATP). Formation of 2 molecules of pyruvic

acid. Well, what happens to the pyruvic

acid?

Section 7-1: Glycolysis and Fermentation

Fermentation:If no oxygen is present, then the

pathway is called fermentation.As a result of fermentation, either

lactic acid or ethyl alcohol is produced.

Section 7-1: Glycolysis and Fermentation

Lactic Acid Fermentation:No more ATP molecules are formed

as a result of lactic acid fermentation.Process of converting pyruvic acid to

lactic acid.The resulting energy output of

glycolysis and lactic acid fermentation is 2 ATP.

Section 7-1: Glycolysis and Fermentation

Steps of Glycolysis

Section 7-1: Glycolysis and FermentationLactic Acid Fermentation:

Production of yogurt and cheese.Lactic acid fermentation also takes place in

your muscle cells during physical activities.The reason that your muscles feel sore.Muscle cells use up all of the local oxygen

and thus need to switch to lactic acid fermentation.

This causes muscle cells to become unable to continually contract.

Section 7-1: Glycolysis and Fermentation

Alcoholic Fermentation:Used in some plant cells and other

unicellular organisms, such as yeast.The result of alcoholic fermentation is

that pyruvic acid is converted to ethyl alcohol and CO2.

Steps of Glycolysis

Section 7-1: Glycolysis and Fermentation

Alcoholic Fermentation:The basis for the beer and wine

industry:Yeast is added to a mixture to produce

ethyl alcohol.Also used in the baking industry:

Yeast is added to a mixture, which causes CO2 to be produced.

The CO2 makes the bread “rise”.

Section 7-2: Aerobic Respiration

Overview of Aerobic Respiration:There are two major steps in aerobic

respiration:The Krebs Cycle.The Electron Transport Chain.

Section 7-2: Aerobic Respiration

Overview of Aerobic Respiration:In prokaryotes, aerobic respiration

takes place in the cytoplasm of the cell.

In eukaryotes, these biochemical pathways occur inside the mitochondria.

Section 7-2: Aerobic Respiration

Overview of Aerobic Respiration:When pyruvic acid (from glycolysis)

enters the cell’s mitochondria, it reacts with an enzyme called coenzyme A to form acetyl CoA.What does an enzyme do?

Section 7-2: Aerobic Respiration

The Krebs Cycle:Krebs cycle: a biochemical pathway

that breaks down acetyl CoA to produce CO2, and 2 more ATP.

Note the word “cycle”.There are 5 steps to the Krebs cycle,

which all occur in the mitochondria.

The Krebs Cycle

1. A 2-carbon molecule of acetyl CoA combines with a 4-carbon molecule called oxaloacetic acid to form a 6-carbon molecule called citric acid.

2. Citric acid releases CO2 and a hydrogen atom to form a 5-carbon molecule.

The Krebs Cycle

3. The 5-carbon molecule also releases CO2 and a hydrogen atom to form a 4-carbon molecule. In this step, ATP is formed from ADP.

4. The 4-carbon molecule releases another hydrogen to form a new 4-carbon molecule.

The Krebs Cycle

5. The new 4-carbon molecule loses another hydrogen molecule.

The Krebs Cycle

Section 7-2: Aerobic Respiration

The Krebs Cycle:For every molecule of glucose, there

is 2 ATP and 4 CO2 molecules formed during the Krebs cycle.

Two turns of the Krebs Cycle for every glucose molecule.

How many molecules of ATP are formed after glycolysis and the Krebs cycle?4 ATP.

Section 7-2: Aerobic Respiration

The Electron Transport Chain:Electron Transport Chain: the

second stage of aerobic respiration.In eukaryotic cells:

Occurs in the folds of the inner membranes of the mitochondria.

In prokaryotic cells:Occurs in the cell membrane.

Section 7-2: Aerobic Respiration

The Electron Transport Chain:The result of the electron transport

chain is 34 ATP.

Section 7-2: Aerobic Respiration

Summarizing Cellular Respiration:The overall chemical equation for

aerobic respiration is:C6H12O6 + 6O2 → 6CO2 + 6H2O +

energy

Section 7-2: Aerobic Respiration

Summarizing Cellular Respiration:The final result of aerobic respiration is

38 ATP (2 from glycolysis, 2 from the Krebs cycle, and 34 from the electron transport chain) vs. 2 ATP for anaerobic respiration.