Cellular Respiration

Nutrients + oxygen water+ ATP+ CO2 Cellular respiration – process in which mitochondria break down food molecules to produce ATP in plants & animals; occurs in the presence of oxygen Nutrients + oxygen water+ ATP+ CO2 The equation for cellular respiration is: 6O2 + C6H12O6 → 6CO2 + 6H2O + Energy oxygen + glucose → carbon dioxide + water + energy Process changes organic chemical energy (glucose) into inorganic chemical energy ATP

Overview of Cellular Respiration 3 Stages: Glycolysis – anaerobic process; does not require oxygen - cytoplasm Citric Acid (Krebs) Cycle – aerobic; does require oxygen – mitochondria Electron Transport Chain – aerobic; does require oxygen - mitochondria

Glycolysis Glycolysis – breaks down glucose into two molecules of pyruvic acid (colorless acid) This reaction uses enzymes and takes place in the cytoplasm of the cell (anaerobic reaction) Produces: 2 Pyruvic acid molecules (used in Step 2 of cellular respiration) 2 ATP molecules (energy cell can use) 2 NADH molecules (electron carrier)

At the beginning of glycolysis, the cell uses up 2 molecules of ATP to start the reaction. 4 ADP 2 ATP 4 ATP 2 ADP 2 ATP 2NAD+ 2 Pyruvic acid 2 To the electron transport chain

Fermentation Fermentation releases energy from food molecules by producing ATP in the absence of oxygen; anaerobic process During fermentation, cells convert NADH to NAD+ by passing high- energy electrons back to pyruvic acid. This action converts NADH back into NAD+, and allows glycolysis to continue producing a steady supply of ATP.

2 Types of Fermentation 1. Lactic acid fermentation – process that supplies energy when O2 is scarce Ex.) released during vigorous exercise; “feel the burn” 2. Alcoholic fermentation – used to produce CO2 and ethyl alcohol Ex.) Yeast Cells

The Krebs Cycle Named after Hans Krebs – British biochemist; won Nobel Prize in 1953 for discovery of this cycle Aerobic process Pyruvic acid produced from glycolysis along w/O2 start the 2nd stage of cellular respiration Pyruvic acid is broken down into CO2 in a series of endergonic reactions

2 Parts of the Krebs Cycle Part A Step 1: Cycle begins when pyruvic acid enters the mitochondrion

The Krebs Cycle 2. Carbon molecule is removed, forming CO2, & electrons are removed, changing NAD+ to NADH. 3. Coenzyme A joins the 2-carbon molecule, forming acetyl-CoA.

The Krebs Cycle Citric acid 4. Acetyl-CoA then adds the 2-carbon acetyl group to a 4-carbon compound, forming citric acid. Citric acid

The Krebs Cycle Part B Step 1: Citric acid is broken down into a 5-carbon compound, then into a 4-carbon compound.

The Krebs Cycle Step 2: Two more molecules of CO2 are released and electrons join NAD+ and FAD, forming NADH and FADH2.

The Krebs Cycle Result: 1 molecule of ATP is produced

Energy totals from 1 molecule of pyruvic acid is : 4 NADH 1 FADH2 1 ATP Electron Transport Chain = 3rd step in cellular respiration, aerobic process, uses the high-energy electron carriers from the Krebs Cycle to convert ADP into ATP. Carrier molecules produced are used to generate ATP via the Electron Transport Chain

Electron Transport Chain High-energy electrons from NADH and FADH2 are passed along the electron transport chain from one carrier protein to the next.

The Totals Glycolysis produces just 2 ATP molecules per molecule of glucose. The complete breakdown of glucose through cellular respiration, including glycolysis, results in the production of 36 molecules of ATP.

The Totals: Overview

Comparing Photosynthesis and Cellular Respiration The energy flows in photosynthesis and cellular respiration take place in opposite directions.

On a global level, photosynthesis and cellular respiration are also opposites. Photosynthesis removes carbon dioxide from the atmosphere and cellular respiration puts it back. Photosynthesis releases oxygen into the atmosphere and cellular respiration uses that oxygen to release energy from food.