Chapter 9: Cellular Respiration

9.1: Catabolic pathways yield energy by oxidizing

organic fuels• Living cells require transfusions of energy

from outside sources to perform tasks• Energy flows into ecosystem as sunlight and

leaves as heat• Chemical elements essential to life are

recycled• Cellular respiration breaks down fuel to

generate ATP, and the waste products become the reactants for Photosynthesis

Catabolic Pathways and Production of ATP

Organic compounds store energy in their arrangement of atoms

- enzymes help break down products to simpler waste products with less energy One catabolic process,

fermentation is a partial degradation of sugars that occurs without the use of oxygen

Catabolic Pathways and Production of ATP

Cellular Respiration- oxygen is consumed as a reactant with organic fuel

- 2 of 3 processes take place in mitochondria- similar to combustion of gasoline- CHO’s, proteins, and fats can

combust and consume fuel

The Principles of Redox

Redox Reactions or Oxidation-reduction reactions deal with the transfer of one or more electrons from one reactant to another.• Oxidation-the loss of electrons from one

substance• Reduction- the addition of electrons to

another substance• Reducing Agent-the electron donor• Oxidizing agent- electron acceptor

Stepwise Energy Harvest via NAD+

Reactions do not occur all at once, but it steps to properly harness energy

- gas tank explosion doesn’t drive car Glucose broken in a series of catalyzed

steps by an enzyme NAD+ - a oxidizing agent or coenzyme

that will strip electrons along with a proton (hydrogen)

NADH is reduced form that is potential energy and can make ATP

Stages of Cellular Respiration

Glycolysis-breaks glucose into two molecules of a compound pyruvate

- cytosol of cell- does not require oxygen- catabolic

Stages of Cellular Respiration

Citric Acid Cycle- Completes the breakdown of glucose by oxidizing a derivative of pyruvate to carbon dioxide

- mitochondrial matrix- redox reaction transfers

electrons and forms NADH- Also referred to as the Krebs

cycle

Stages of Cellular Respiration

Oxidative phosphorylation: electron transport and chemiosmosis

- inner membrane of mitochondria-accounts for 90% of ATP

generated by respiration

Substrate-Level Phosphorylation ATP synthesis that occurs when an

enzyme transfers a phosphate group from the substrate to ADP

- generates a smaller amount of ATP

- substrate is generated from catabolism of glucose

9.2: Glycolysis harvests chemical energy by oxidizing

glucose to pyruvate

Glycolysis Glycolysis- (splitting of sugar) breaks

a six-carbon sugar into two three-carbon sugars

3 carbon sugars are oxidized and remaining atoms form 2 molecules of pyruvate

10 steps in the reaction

Phases of Glycolysis Energy investment phase – 2 ATP are

spent in the initial break down of glucose to its first 5 intermediates

Energy Payoff phase – ATP is produced by substrate-level phosphorylation and NAD+ is reduced to NADH by electrons released from oxidation of food

- produces 4 ATP molecules Net production is 2 ATP molecules

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