How Cells Harvest Chemical Energy

Introduction to Cell Metabolism

Glycolysis

Aerobic Cell Respiration

Anaerobic Cell Respiration

O2 CO2BREATHING

Lungs

CO2 O2Bloodstream

Muscle cells carrying out

CELLULAR RESPIRATION

Sugar + O2 ATP + CO2 + H2O

Breathing and Cell Respiration are related

Glucose Oxygen gas Carbon dioxide

Water Energy

Cellular Respiration uses oxygen and glucose to produce Carbon dioxide, water, and ATP.

Burning glucose in an experiment

Energy released from glucose

(as heat and light)

100%

Energy released from glucose

banked in ATP

“Burning” glucosein cellular respiration

About 40%

Gasoline energy converted to movement

Burning gasolinein an auto engine

25%

How efficient is cell respiration?

Loss of hydrogen atoms

Glucose

Gain of hydrogen atoms

Energy

Reduction and Oxidation

OILRIG

Oxidation is losing electrons

Reduction is gaining electrons

Glucose gives off energy as is is oxidized

Reduction and Oxidation

OILRIG Gain or loss of electrons is often in the form of hydrogen. The hydrogen is then passed to a coenzyme such as NAD+

Reduction and Oxidation

What are some common co-enzymes? NAD+ and FAD

NAD+ + 2 H NADH + H+

FAD + 2 H FADH2

Remember that H = 2 electrons and 2H+

Reduction and Oxidation

These co-enzymes are very important for cell respiration because they transfer high-energy electrons to electron transport systems (ETS).

Reduction and Oxidation

As the electrons move from carrier to carrier, energy is released in small quantities.

Electron transport system (ETS)

Generation of ATP

There are two ways to generate ATP

Chemiosmosis

Substrate-Level Phosphorylation

Generation of ATP

Chemiosmosis

Cells use the energy released by “falling” electrons in the ETS to pump H+ ions across a membrane

Uses the enzyme ATP synthase.

Generation of ATP

Chemiosmosis

ATP can also be made by transferring phosphate groups from organic molecules to ADP

Figure 6.7B

substrate

product

Enzyme

Adenosine

Adenosine

Generation of ATP

Substrate Level Phosphorylation

ATP can also be made by transferring phosphate groups from organic molecules to ADP

Figure 6.7B

substrate

product

Enzyme

Adenosine

Adenosine

Generation of ATP

Substrate Level Phosphorylation

General Outline

Glucose

Pyruvic Acid

Glycolysis

OxygenAerobic

No OxygenAnaerobic

Transition Reaction

Krebs Cycle

ETS

36 ATP

Fermentation

Glycolysis

Where? The cytosol

What? Breaks down glucose to pyruvic acid

Glycolysis

Steps – A fuelmolecule is energized,using ATP.

1 3

1

GlucoseStep

2

3

4

Glucose-6-phosphate

Fructose-6-phosphate

Glyceraldehyde-3-phosphate (G3P)

Step A six-carbonintermediate splits into two three-carbon intermediates.

4

Step A redoxreaction generatesNADH.

55

1,3-Diphosphoglyceric acid(2 molecules)

6

Steps – ATPand pyruvic acidare produced.

6 9 3-Phosphoglyceric acid(2 molecules)7

2-Phosphoglyceric acid(2 molecules)8

2-Phosphoglyceric acid(2 molecules)

9

(2 moleculesper glucose molecule)

Pyruvic acid

Fructose-1,6-diphosphate

Energy In: 2 ATP

Energy Out: 4 ATP

NET 2 ATP

General Outline

Glucose

Pyruvic Acid

Glycolysis

OxygenAerobic

No OxygenAnaerobic

Transition Reaction

Krebs Cycle

ETS

36 ATP

Fermentation

General Outline of Aerobic Respiration

Glycolysis

Krebs Cycle

Electron Transport System

Transition Reaction

Transition Reaction

Each pyruvic acid molecule is broken down to form CO2 and a two-carbon acetyl group, which enters the Krebs cycle

Acetyl CoAPyruvic Acid

General Outline of Aerobic Respiration

Glycolysis

Krebs Cycle

Electron Transport System

Transition Reaction

Krebs Cycle

Where? In the Mitochondria

What? Uses Acetyl Co-A to generate ATP, NADH, FADH2, and CO2.

Krebs Cycle

Krebs Cycle

General Outline of Aerobic Respiration

Glycolysis

Krebs Cycle

Electron Transport System

Electron Transport System

Figure 6.12

Intermembranespace

Innermitochondrialmembrane

Mitochondrialmatrix

Proteincomplex

Electroncarrier

Electronflow

ELECTRON TRANSPORT CHAIN ATP

SYNTHASE

Electron Transport System

Electron Transport System

For each glucose molecule that enters cellular respiration, chemiosmosis produces up to 38 ATP molecules

Overview of Aerobic Respiration

General Outline

Glucose

Pyruvic Acid

Glycolysis

OxygenAerobic

No OxygenAnaerobic

Transition Reaction

Krebs Cycle

ETS

36 ATP

Fermentation

Fermentation

Requires NADH generated by glycolysis.

Where do you suppose these reactions take place?

Yeast produce carbon dioxide and ethanol

Muscle cells produce lactic acid

Only a few ATP are produced per glucose

Fermentation