Cellular Respiration Cellular respiration process in which mitochondria

Cellular Respiration

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+ CO 2 The equation for cellular respiration is: 6 O 2 + C 6 H 12 O 6 → 6 CO 2 + 6 H 2 O + Energy oxygen + glucose → carbon dioxide + water + energy Process changes organic chemical energy (glucose) into inorganic chemical energy ATP

Overview of Cellular Respiration 3 Stages: 1. Glycolysis – anaerobic process; does not require oxygen - cytoplasm 2. Citric Acid (Krebs) Cycle – aerobic; does require oxygen – mitochondria 3. Electron Transport Chain – aerobic; does require oxygen - mitochondria

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. 2 ATP 4 ADP 2 NAD+ 2 4 ATP 2 Pyruvic acid To the electron transport chain

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 O 2 is scarce Ex. ) released during vigorous exercise; “feel the burn” 2. Alcoholic fermentation – used to produce CO 2 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/O 2 start the 2 nd stage of cellular respiration Pyruvic acid is broken down into CO 2 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 CO 2, & electrons are removed, changing NAD+ to NADH. 3. Coenzyme A joins the 2 carbon molecule, forming acetyl-Co. A.

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

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 CO 2 are released and electrons join NAD+ and FAD, forming NADH and FADH 2.

The Krebs Cycle Result: 1 molecule of ATP is produced

Energy totals from 1 molecule of pyruvic acid is : 4 NADH q 1 FADH 2 q 1 ATP q Carrier molecules produced are used to generate ATP via the Electron Transport Chain = 3 rd step in cellular respiration, aerobic process, uses the highenergy electron carriers from the Krebs Cycle to convert ADP into ATP.

Electron Transport Chain n High-energy electrons from NADH and FADH 2 are passed along the electron transport chain from one carrier protein to the next.

The Totals n n 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 n 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.