Download Cellular Respiration

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+ 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:
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
 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
2 ATP
4 ADP
4 ATP
2 ADP
2NAD+
2
2 Pyruvic
acid
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 2carbon molecule, forming
acetyl-CoA.
The Krebs Cycle
4. Acetyl-CoA 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 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
Carrier molecules
produced are used to
generate ATP via the
Electron Transport
Chain
Electron Transport Chain = 3rd step in cellular
respiration, aerobic process, uses the highenergy electron carriers from the Krebs Cycle to
convert ADP into ATP.
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

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.