Chapter 8 Section 3: Cellular Respiration Ms. Diana and Ms. Su’ad

Overview of Cellular Respiration Organisms get energy in a process called cellular respiration. The function of cellular respiration is to harvest electrons from carbon compounds, such as glucose, and use that energy to make ATP.

Overview of Cellular Respiration Cellular respiration occurs in two main parts: glycolysis and aerobic respiration. Glycolysis - an anaerobic process, which means it does not require oxygen. Aerobic respiration – includes the Krebs Cycle and electron transport. It is an aerobic process, which means it requires oxygen.

Glycolysis Glycolysis – the process of breaking down glucose in the cytoplasm. For every molecule of glucose that is broken down, 2 molecules of ATP and 2 molecules of NADH are formed. So, at the end of the glycolysis process, 2 molecules of pyruvate are formed and 4 molecules of ATP are formed.

Steps of Glycolysis First, two phosphate groups, coming from two molecules of ATP are joined to glucose. ATP energy is required to start the reactions that will produce energy for the cell. The 6-carbon glucose molecule is broken down into two 3-carbon compounds (G3P). Next, two phosphates are added and electrons and hydrogen ions (H+) combine with two NAD+ molecules to form two NADH molecules. Last, the two 3-carbon compounds are converted into two molecules of pyruvate. At the same time, 4 molecules of ATP are produced.

A Closer Look at Glycolysis

KREBS Cycle Most of the energy from the glucose is still contained in the pyruvate. In the presence of oxygen, pyruvate is transported into the mitochondrial matrix, where it is eventually converted to carbon dioxide. Krebs Cycle – the series of reactions in which pyruvate is broken down into carbon dioxide. (also called the citric acid cycle)

Steps of the Krebs Cycle Before the cycle starts, pyruvate first reacts with coenzyme A (CoA) to form a 2-carbon intermediate called acetyl CoA. Acetyl CoA then moves to the mitochondrial matrix. Then, Acetyl CoA combines with a 4-carbon compound to form citric acid. Next, citric acid is broken down releasing 2 molecules of carbon dioxide and generating 1 ATP, 3 NADH, and 1 FADH2. Finally, acetyl CoA and citric acid are generated and the cycle continues.

A Closer Look at the Krebs Cycle

Simple Steps: Krebs Cycle 1. Pyruvate is broken down. 2. Coenzyme A reacts with pyruvate. 3. Citric acid is formed. 4. Citric acid is broken down. 5. 5-carbon molecule broken down. 6. 4-carbon molecule is rearranged. **Up to 38 ATP molecules are made from the breakdown of 1 glucose molecule.

Krebs Cycle

Electron Transport Electron transport is the final step in the breakdown of glucose. It’s also the point where most of the ATP is produced. NADH and FADH2 from the Krebs cycle are used to convert ADP to ATP. Electron transport and chemiosmosis is aerobic repiration are similar to the process of photosynthesis. Overall, electron transport produces 32-38 ATP.

Electron Transport

Prokaryotic Cellular Respiration Some prokaryotes undergo aerobic respiration. They do not have mitochondria, so they use the cellular membrane as the location of electron transport.

Anaerobic Respiration When oxygen is not available, cells cannot follow glycolysis with the aerobic respiration (Krebs cycle and electron transport). The anaerobic pathway that follows glycolysis is fermentation. Fermentation – occurs in the cytoplasm of the cell, and produces NAD+ and a small amount of ATP. There are 2 main types of fermentation: lactic acid fermentation and alcohol fermentation.

Lactic Acid Fermentation Enzymes convert pyruvate made during glycolysis into lactic acid. Skeletal muscles produce lactic acid when the body cannot supply enough oxygen, especially during times of extreme exercise.

Alcohol Fermentation Occurs in yeast and bacteria. Converts the pyruvate into ethyl alcohol and carbon dioxide.

Comparing Photosynthesis and Cellular Respiration

Photosynthesis and Cellular Respiration

Questions