Cellular Respiration Ch. 9

Energy for Life - ATP All cells require energy (ATP) to carry out life functions they do so through Cellular Respiration. To make the maximum amount of energy (ATP) oxygen is needed (aerobic conditions). In the absence of oxygen (anaerobic conditions) organisms can still make energy (ATP) but they make very low amounts. This energy for life comes from the breakdown of glucose.

Part 1 - Glycolysis 1st part of the process of cellular respiration is anaerobic - does not require oxygen! One molecule of glucose is broken in half, producing two molecules of pyruvic acid (3-carbon compound) Takes place in cytoplasm (cytosol) 2 molecules of ATP are used up 4 molecules of ATP are produced = a net gain of 2 ATP molecules

Part 2 - Aerobic Cellular Respiration Only happens if oxygen is present! Process that releases energy by breaking down glucose and other food molecules in the presence of oxygen. 6O2 + C6H12O6  6CO2 + H2O +ENERGY Requires: oxygen and glucose Gives off: carbon dioxide, water, and energy

Glycolysis Steps – Part 1 Two molecules of ATP provide energy to split glucose Glucose splits, releasing enough energy to form 4 ATP Hydrogen is released and picked up by an NAD+ NADH

Glycolysis Electron Carrier - NAD+ Like NADP+ in photosynthesis, each NAD+ accepts a pair of high energy electrons NADH holds the electrons until they can be transferred to other molecules.

Fermentation When oxygen is not present Releases energy from food molecules by producing ATP in the absence of oxygen (anaerobic) Cells convert NADH to NAD+ by passing electrons back to pyruvic acid

Alcoholic Fermentation: Used by yeast and a few other microorganisms Pyruvic acid + NADH  alcohol + CO2 + NAD+ Waste: ethyl alcohol and carbon dioxide Causes: bread to rise When yeast runs out of oxygen, it begins to give off bubbles of carbon dioxide that form the air spaces you see in a slice of bread.

Lactic Acid Fermentation: Pyruvic acid that accumulates as a result of Glycolysis can be converted to lactic acid Pyruvic acid + NADH  lactic acid + NAD+ Lactic acid is produced in your muscles during rapid exercise when the body cannot supply enough oxygen to the tissues

Your cells rapidly begin to produce ATP by lactic acid fermentation The buildup of lactic acid causes a painful, burning sensation. This is why muscles may feel sore after only a few seconds of intense activity

Aerobic Stage – Part 2 Occurs after Glycolysis if oxygen is present. The chemical bonds of pyruvic acid are broken down in a series of reactions Occurs in the mitochondria Requires oxygen (aerobic) Divided into The Krebs Cycle and The Electron Transport Chain.

Krebs Cycle The first part of the Krebs Cycle is called the Citric Acid Cycle. Pyruvate is converted to Acetyl CoA which is converted to Citric Acid. Citric Acid is broken down (two carbons are removed) releasing CO2, NAD+ and FAD which pick up electrons and become NADH and FADH2.

Krebs Cycle (cont.) Each turn of the cycle yields 4 molecules of NADH, two molecules of ATP, and one molecule FADH2. The NADH formed during the citric-acid cycle feeds the next step - the electron transport system.

Electron Transport Chain NADH releases electrons and hydrogen atoms NAD+ The electrons contained in the hydrogen atoms pass through a series of steps Each time an electron moves from one acceptor to another, energy is released.

At the end of the chain, the electron still exists, but it has less energy than at the beginning of the electron transport chain This energy is used to form ATP from ADP + P

Energy Total: Source Number ATP Produced Glycolysis 2 ATP Transport of NADH into Matrix. -2 ATP Krebs Cycle Electron Transport 34 ATP NET TOTAL 36 ATP