C-9-3

Cellular Respiration

Cellular Respiration: Chemical Pathways

Cellular Respiration – the process that releases ENERGY by breaking down GLUCOSE in the presence of OXYGEN.

3 main stages

GLYCOLYSIS (in the cytoplasm)

KREBS CYCLE (in mitochondria)

ELECTRON TRANSPORT CHAIN (in the inner membrane of the mitochondria)

Each of the three stages captures some of the chemical energy available in FOOD molecules and uses it to produce ATP.

ATP – HIGH ENERGY molecule that the cell can us for an energy source

ADP – LOW ENERGY molecule

Cellular Respiration

Oxygen + glucose ---> carbon dioxide + water + energy

1st stage:

GLYCOLYSIS - “to break apart glucose”

Glycolysis

Takes place in the CYTOPLASM of the animal cell

One molecule of GLUCOSE (6 C’s) is broke in half to make 2 PYRUVIC ACID molecules (3 C’s each)

2 ATP molecules are used up in the beginning of glycolysis in order to break apart the glucose molecule

When glycolysis is complete 4 ATP molecules are produced (net gain of 2 ATP molecules)

Glycolysis

NAD+- an electron carrier involved in glycolysis

NADH - reduced form of NAD+ (NAD+ turns into NADH when it receives electrons)

Glycolysis

4 high energy ELECTRONS are removed during glycolysis and passed to NAD+

When electrons get passed to NAD+ it changes to NADH

NADH holds electrons until they can be transferred to other molecules (THEN it goes to the electron transport chain)

FERMENTATION - releases energy from food molecules by producing ATP in the absence of oxygen

Because fermentation does NOT require oxygen it is said to be ANAEROBIC

Alcoholic Fermentation

Pyruvic acid + NADH --->alcohol + carbon dioxide + NAD+

Produces ALCOHOLIC FERMENTATION and CARBON DIOXIDE

Yeast – causes bread dough to rise; when yeast runs out of oxygen it begins to ferment giving off bubbles of CARBON DIOXIDE that forms the holes you see in a slice of bread (the alcohol evaporates when its baked)

Beer and wine and other alcoholic beverages use this process

Lactic Acid Fermentation

Pyruvic acid + NADH ---> lactic acid + NAD+

Produces LACTIC ACID

Lactic acid is produced in your MUSCLES during rapid EXERCISES when the body cannot supply enough oxygen to the tissues

Without enough oxygen, the body can’t produce the ATP that is required so lactic acid fermentation allows NAD+ to be produced so glycolysis continues

*Your muscles can get SORE quickly because of the build-up of lactic acid in the muscle cells

*This process is also used by unicellular organisms to produce foods such as cheese, yogurt, sour cream, pickles, and sauerkraut.