CH 9 Cellular Respiration

Energy

• Arrives as sunlight

• Photosynthesis

Photosynthesis

• plants capture sunlight

  • organic molecules and generates O₂

• Carbs used in cellular respiration

  • Cells use energy stored in organic molecules

    • to regenerate ATP

  • Energy eventually leaves as heat

The breakdown of organic molecules is

exergonic

Aerobic respiration

• Consumes organic molecules and O₂ and yields ATP

  • Typically glucose

Aerobic respiration

• consumes organic molecules and O₂ and yields ATP

  • Typically glucose

Fermentation

Partial degradation of sugars that occurs without O₂

Anaerobic respiration

• similar to aerobic respiration

  • but uses compounds other than O₂ as the final electron acceptor 

Cellular respiration

Includes both aerobic and anaerobic respiration but is often used to refer to aerobic respiration

• 3 of 4 macromolecule classes may be used as fuel

  • carbohydrates, fats, and proteins

Redox reactions 

• Oxidation-reduction reactions

  • chemical reactions that transfer electrons between reactants are called

Oxidation

A substance loses electrons

Reduction

A substance gains electrons

Glucose and other organic molecules

Broken down in a series of steps

NAD⁺ (nicotinamide adenine dinucleotide)

• electron carrier

• electrons from organic compounds transferred

• functions as an oxidizing agenda during cellular respiration

NADH is the

• reduced form of NAD⁺

  • represents stored energy that is used to synthesize ATP

NADH delivers

electrons to the electron transport chain (ETC)

ETC passes electrons in a series of steps

• instead of one explosive reaction

  • slow controlled energy release

O₂ receives electrons from the ETC

• After an energy-yielding tumble down the chain

• final electron acceptor

• The energy yielded is used to regenerate ATP

cellular respiration has three stages:

1. Glycolysis

2. Citric acid cycle

3. Oxidative phosphorylation

1. Glycolysis

• Literally “sugar breaking”

• breaks down glucose into two molecules of pyruvate 

2. Citric acid cycle

• completes the breakdown of glucose

• also called krebs cycle

3. Oxidative phosphorylation

• accounts for most of the ATP synthesis

• Includes electron transport chain

OXidative phosphorylation

• accounts for almost 90% of the ATP generated by cellular respiration

  • 32 of 36-38 total

Substrate-level phosphorylation

ATP formed in glycolysis and the citric acid cycle

Glycolysis

• breaks down glucose into two molecules of pyruvate

• occurs in the cytoplasm

• two major phases:

  • energy investment phase

  • energy payoff phase

If O₂ is present

• pyruvate enters the mitochondrion

  • two per original glucose

acetyl CoA formed when

• pyruvate added to coenzyme A

  • as it crosses the mitochondrial membranes

  • yields first CO₂ wastes

  • Reduces a NAD+ to NADH

• enters the citric acid cycle

Citric acid cycle

• also called the Krebs cycle

• occurs in the mitochondrial matrix

• oxidizes organic fuel derived from pyruvate

  • generates 1 ATP, 3 NADH, and 1 FADH₂ per cycle

    • and 2 CO₂