CHAPTER 8.1Overview of Energy-Releasing Pathways

AP BiologyFall 2010

HETEROTROPHS AND AUTOTROPHS

Heterotrophs: get energy by eating plants and one another

Autotrophs: get energy from the sun

ATP is the prime energy carrier for all cells, both autotrophic and heterotrophic

MAIN TYPES OF ENERGY-RELEASING PATHWAYS

Anaerobic: reactions that do not use free oxygen

Anaerobic respiration and fermentation can release small quantities of energy without the use of oxygen First energy-releasing metabolic pathways Skeletal muscles use fermentation

MAIN TYPES OF ENERGY-RELEASING PATHWAYS

Aerobic: reactions that use free oxygen

Aerobic respiration is the main energy-releasing pathway leading to ATP formation in eukaryotes Occurs in mitochondria

MAIN TYPES OF ENERGY-RELEASING PATHWAYS

Every cell begins its energy-releasing pathways with glycolysis, which occurs in the cytoplasm and produces two molecules of pyruvate

Fermentation produces a net yield of two ATPs

Aerobic respiration yields 36 ATPs

OVERVIEW OF AEROBIC RESPIRATION Aerobic respiration gets the most ATP

for each glucose molecule “The most bang for your buck”

The aerobic route is summarized: C6H12O6 + O2 CO2 + H2O

OVERVIEW OF AEROBIC RESPIRATION Three series of reactions are required for

aerobic respiration1. Glycolysis: the breakdown of glucose to

pyruvate; small amounts of ATP are generated

2. Krebs cycle: degrades pyruvate to carbon dioxide and water, ATP is produced, and NAD and FAD accept H+ ions and electrons to be carried to the electron transfer chain

OVERVIEW OF AEROBIC RESPIRATION

3. Electron transfer phosphorylation: processes the H+ ions and electrons to generate high yields of ATP; oxygen is the final electron acceptor

OVERVIEW OF AEROBIC RESPIRATION Coenzymes:

NAD+ (nicotinamide adenine dinucleotide) FAD (flavin adenine dinucleotide)

Both accept electrons and hydrogen derived from intermediates that form during glucose breakdown

When two coenzymes are carrying electrons and hydrogen, in reduced form NADH and FADH2

REVIEW

1. What are NAD+ and FAD?2. What is the formula for aerobic

respiration?3. What are the three stages of aerobic

respiration?4. How much energy does fermentation

and anaerobic respiration produce? Do they use oxygen?

ANSWERS

1. They are coenzymes that both accept electrons and hydrogen derived from intermediates that form during glucose breakdown.

2. The formula for aerobic respiration is: C6H12O6 + O2 CO2 + H2O

3. The three stages of aerobic respiration are: Glycolysis, Krebs cycle, electron transfer phosphorlation.

4. Fermentation and anaerobic respiration produces small amounts of energy and does not require oxygen.