Cell Respiration

The process by which cells turn food molecules into

cell energy

The Complete breakdown of foods occurs in aerobic respiration

The general reaction of aerobic respiration is:

glucose + O2 CO2 + H2O + ATP + heat

• This reaction occurs in steps:– Glycolysis– Transition reaction– Krebs Cycle– Electron Transport Chain

Glycolysis

• Occurs in the cytoplasm• Splits a 6-carbon sugar into 2

x 3-C pyruvates• Reaction sequence:

Sugar (6C) 2 Pyruvates (3C)• Produces:

– 2 ATP molecules

– 2 NADH2

Transition reaction

• Processes pyruvate so that it can enter mitochondrion

• The reaction sequence:

2 pyruvate (3C) 2 acetyl (2C)• Produces:

– 2 NADH2

• 2 acetyl groups easily enter the mitochondrion of the cell

Transition between cytoplasm and mitochondrion

Krebs Cycle

• Occurs in the cytoplasm of the mitochondria (stroma)

• Cyclical series of reactions which breaks down acetyls releasing CO2

• Produces:– 2 ATP’s– 6 NADH2

– 2 FADH2

Up to this point, the entire molecule of glucose has been broken down to form 6 CO2’s

Yet, only 4 ATP’s have been formed during:

•Glycolysis

•Transition &

•Krebs CyclePotential energy of NADH2 and FADH2 can be released in Electron Transport Chain

Electron Transport Chain – harvests potential energy of NAD and FAD coenzymes

Occurs along inner membrane (cristae) of mitochondrion

Overall Energy Harvest of Aerobic Cell Respiration

Much more ATP than the 4 molecules

received through Gly, Trans, and

Krebs!!

We metabolize more than sugars!!

Can cells produce ATP without oxygen being present?

• Oxygen removes e-’s from the Electron Transport Chain to help make ATP

• If oxygen is not present, NADH2 must be oxidized to NAD+ to allow cells to make ATP

Animal cells engage in fermentation

• Fermentation allows NAD+ to be recycled

• Fermentation produces 2 ATP’s per molecule of glucose broken down

• Glucose is not completely broken down

Plant and fungal cellsengage in fermentation

• This process also allows NAD+ to be recycled

• Produces 2 ATP’s per molecule of glucose broken down

• Glucose is not completely broken down

Fermentations producemany foods and drinks!

• Dairy fermentations– Cheeses– Yogurts– Sour cream

• Fermented foods– Breads – Tofu and tempeh– Pickles, sauerkraut

• Fermented beverages– Wines, beers, ales