Lecture 30 – Lecture 31 Cellular Respiration Ozgur Unal NIS - BIOLOGY Lecture 30 – Lecture 31 Cellular Respiration Ozgur Unal

Cellular Respiration How do most autotrophs produce food? Can anyone predict how heterotrophs obtain energy?

C6H12O6 + 6O2 ---------------> 6CO2 + 6H2O + energy Cellular Respiration What is respiration? Cellular respiration is the catabolic pathway in which organic molecules are broken down to release energy for use by the cell. In cellular respiration, O2 is used to break down organic molecules, resulting in the production of CO2 and water. C6H12O6 + 6O2 ---------------> 6CO2 + 6H2O + energy Opposite of photosynthesis!

Cellular Respiration Cellular respiration occurs in two main parts: Glycolysis and Aerobic respiration. Glycolysis is an anaerobic process. Anaerobic processes do not require oxygen. Aerobic respiration is an aerobic process and it includes Krebs cycle and electron transport. Aerobic processes require oxygen.

Glycolysis Glucose is broken down in the cytoplasm through the process of glycolysis. Two molecules of ATP and two molecules of NADH are produced for each molecule of glucose. Follow Figure 8.12 as you read the text.

Krebs Cycle Most of the energy from the glucose is still contained in the pyruvate. Pyruvate is transported to mitochondria where it is broken down into CO2 by a process called Krebs Cycle, aka TCA cycle or Citric acid cycle. Follow the steps of the Krebs cycle in Figure 8.13.

Electron Transport In aerobic respiration, electron transport is the final step in the breakdown of glucose. Most of the ATP is produced in this process. Follow Figure 8.14 for the details of the electron transport. In eukaryotic cells 1 glucose yields 36 ATP. In prokaryotic cells 1 glucose yields 38 ATP. This difference is due to the fact that prokaryotes do not spend energy to transport pyruvate to a mitochondrion because they do not have mitochondria.

Cellular Respiration If you drink a soft drink containing 33 grams of sugar (sucrose) why don’t you gain the weight of the sugar? The body will store only a fraction of the 33 grams, while breaking down the rest. The sugar will be broken down to ultimately form CO2 by aerobic respiration. The H atoms found in the sucrose molecules will unite with O gas to produce H2O. Most of the water produced will be eliminated by breathing and urination. However, some sugar wil be retained in the cell. If the sugar is not needed for cellular respiration, it will be converted to glycogen or lipids for storage.

Anaerobic Respiration Some cells can function for a short time when O2 levels are low. Some prokaryotes are anaerobic organisms: They grow and reproduce without O2. These cells continue to produce ATP through glycolysis. However, when NAD+ supply finishes, glycolysis cannot continue. In order to regenerate the supply of NAD+, cells do anaerobic respiration, also called fermentation. There are two main types of fermentation: Lactic Acid Fermentation and Alcohol Fermentation.

Lactic Acid Fermentation In lactic acid fermentation, cells convert pyruvate produced in glycolysis into lactic acid. This process produces NAD+. Skeletal muscle cells produce lactic acid when the body cannot supply enough O2. When lactic acid builds up in the muscle, muscles become fatigued and might feel sore. Other examples: Production of some food such as cheese and yoghurt.

Alcohol Fermentation In alcohol fermentation, pyruvate is converted into ethyl alcohol and CO2. Similar to lactic acid fermentation, this process produces NAD+. Example: Production of wine.

Photosynthesis and Cellular Respiration