Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.6-1

Energy and Organisms

Organisms are classified based on the kind of energy they use.– Autotrophs

Use the energy from sunlight to make organic molecules (sugar)

Use the energy in the organic molecules to make ATP– Heterotrophs

Obtain organic molecules by eating the autotrophs Use the energy in the organic molecules to make ATP

Autotrophs use photosynthesis.– To use the energy from light to make organic molecules

All organisms use cellular respiration.– To harvest the energy from organic molecules and use it

to make ATP

Chapter 6

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.6-2

Energy Transformation

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.6-3

Aerobic Respiration: An Overview

A series of enzyme controlled reactions– Oxygen is used to oxidize glucose.– Glucose is oxidized to form carbon dioxide.– Oxygen is reduced to form water.

During the oxidation of glucose– The C-H and O-H bonds will be broken.– The electrons will be transferred to electron carriers,

NAD, and FAD. Glycolysis and Kreb’s cycle

– The electrons will be passed through an electron transport chain.

The energy from the electrons will be used to pump protons.

The energy from the diffusion of protons will be used to make ATP.

6-4

Aerobic Cellular Respiration: Overview

Glycolysis occurs in the cytoplasm of all cells.

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.6-5

Glycolysis

The breakdown of glucose into pyruvic acid

Two ATP molecules are used to energize glucose.

As glucose is metabolized, enough energy is released to

– Make 4 ATP molecules 4 ATP made - 2 ATP

used = net production of 2 ATP

– Reduce 2 NAD+ to make 2 NADH

Occurs in the cytoplasm

Anaerobic

6-6

Kreb’s Cycle

Also known as the citric acid cycle or the tricarboxylic acid (TCA) cycle

The breakdown of pyruvic acid

– Released as carbon dioxide Enough energy is released

as one pyruvic acid molecule is metabolized to

– Make 1 ATP– Reduce 4 NAD+ to form 4

NADH– Reduce 1 FAD to form 1

FADH2.

Occurs in the mitochondrial matrix

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.6-7

Electron-Transport System

NADH and FADH2 release the electrons they received during glycolysis and the Kreb’s cycle to the electron transport chain (ETC).

The proteins of the ETC transfer the electrons and use the energy released to pump protons.– Protons are pumped from the matrix to the

intermembrane space.– Creates a concentration gradient

6-8

Electron-Transport System

Oxygen is the final electron acceptor at the end of the ETC.

– Oxygen accepts the electrons, combines with protons, and becomes water.

The accumulated protons diffuse back into the matrix through ATP synthase.

The energy released from the diffusion fuels the formation of ATP.

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.6-9

The Details of the Electron Transport System

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.6-10

Total Yields for Aerobic Cellular Respiration per Glucose Molecule

Glycolysis– 2 ATP– 2 NADH (converted to 2 FADH2)

Kreb’s cycle– 2 ATP– 8 NADH– 2 FADH2

Electron transport chain– Each NADH fuels the formation of 3 ATP.

8 NADH x 3 ATP = 24 ATP– Each FADH2 fuels the formation of 2 ATP.

4 FADH2 x 2 ATP = 8 ATP Total ATP = 2 + 2 + 24 + 8 = 36 ATP made from the

metabolism of one glucose molecule.

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.6-11

Anaerobic Cellular Respiration

Some organisms do not have the enzymes for Kreb’s cycle or the electron transport system.

Some organisms can metabolize glucose in the absence of oxygen.

Metabolizing glucose in the absence of oxygen is called anaerobic respiration.

– Involves the incomplete oxidation of glucose– Fermentation is an anaerobic pathway that uses an organic

molecule as the final electron acceptor.

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.6-12

Anaerobic Cellular Respiration

Anaerobic respiration usually starts with glycolysis.– Glucose is metabolized into pyruvic acid.– 2 ATP are made.

The fermentation reactions oxidize NADH to regenerate the NAD+ that is needed in glycolysis.– In the process, pyruvic acid is reduced to either

lactic acid or ethanol or another organic molecule.

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.6-13

Alcoholic Fermentation

Starts with glycolysis– Glucose is metabolized to pyruvic

acid.– A net of 2 ATP is made.

During alcoholic fermentation– Pyruvic acid is reduced to form

ethanol.– Carbon dioxide is released.

Yeasts do this– Leavened bread– Sparkling wine

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.6-14

Lactic Acid Fermentation

Starts with glycolysis– Glucose is metabolized to pyruvic acid.– A net of 2 ATP is made.

During lactic acid fermentation– Pyruvic acid is reduced to form lactic acid.– No carbon dioxide is released.

Muscle cells have the enzymes to do this, but brain cells do not.

– Muscle cells can survive brief periods of oxygen deprivation, but brain cells cannot.

– Lactic acid “burns” in muscles.

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.6-15

The Bottom Line

Carbohydrates, fats, and proteins can all be used for energy.– Glycolysis and the Kreb’s cycle allow these types of

molecules to be interchanged.– If more calories are consumed than used– The excess food will be stored as fat

Homeotherms – have a high metabolic rate and use this energy to maintain their body temperature.

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.6-16

What’s next?

Review your notes– Review this presentation if you feel you have

missed something or need clarification

Review the animations located in the learning module to help you understand these processes.

Finally, use your book and notes to answer your HW questions; then submit them before the end of the day on Wednesday (6/22).