Cellular Respiration

Chapter 5Section 3

Cellular Energy

• All of the energy you use comes from the food you eat

• Before you can use that energy, the food is broken down and the energy is stored as ATP.

• The transfer of the energy in organic compounds (particularly glucose) to ATP is called RESPIRATION.

• Aerobic vs. anaerobic

The Stages of Respiration

Balanced chemical Equation for Cellular Respiration (aerobic)

Stages of Respiration

1. Glucose is broken down to pyruvateduring glycolysis

Glycolysis

• Glycolysis-the first stage of cellular respiration in which glucose is broken down in the cytoplasm.

• Glycolysis is an enzyme-assisted anaerobic process that breaks down 1 six-carbon sugar(glucose) into 2 three carbon pyruvate molecules

• Net Yield vs. Net Gain?

2

Stages of Respiration

1. Glucose is broken down to pyruvateduring glycolysis

2. Krebs Cycle

The Krebs Cycle• Named for Hans Krebs, who

first described the cycle in 1937.

• When O₂ is present, the pyruvate produced by glycolysis enters the mitochondrion and is converted to a 2-carbon compound Acetyl CoA.

• Also called the Citric Acid Cycle

Krebs CycleNet Gain for the Krebs Cycle is 2 ATP’s.

Remember that Glycolysis produces 2 pyruvate molecules, thus providing 2 rounds of the Krebs Cycle.

Electron Transport Chain

• In eukaryotic organisms, the ETC is located in the inner membranes of the mitochondria.

• Hydrogen ions accumulate in the outer compartment producing a concentration gradient across the inner membrane.

• H+ ions diffuse back into the inner compartment through a carrier protein that adds a phosphate group to ADP→ATP.

Electron Transport Chain

Stages of Respiration

Respiration in the Absence of O₂

• Fermentation-The recycling of NAD+ (nicotinamide adenine dinucleotide phosphate-oxidase ion) using an organic hydrogen acceptor.

• Two Important types:– 1. Lactic Acid Fermentation– 2. Alcoholic Fermentation

Lactic Acid Fermentation

• Three Carbon Pyruvate molecule (glycolysis product) is converted to 3-carbon lactate.

• Lactate is the ion of an organic acid called lactic acid.

• Allows glycolysis to continue in the absence of O₂• During vigorous exercise, pyruvate in muscles is

converted to lactate when muscles must operate without enough O₂, causing soreness.

• Blood removes most lactate

Lactic Acid Fermentation

Alcoholic Fermentation

• Used by some bacteria, fungi and prokaryotes.• Occurs in a two-step process:– The three carbon pyruvate is broken down into a , a

two-carbon compound, releasing carbon dioxide.– Electrons are transferred from a molecule of NADH

to the two-carbon compound, producing ethyl alcohol.

– As in lactic acid fermentation, the NAD+ is recycled and glycolysis continues.

Alcoholic Fermentation

In the Presence of O₂…

Without the Presence of O₂

Alcohol Fermentation

Lactic Acid Fermentation