Glycolysis
***Takes place in the cytosol of the cell Step 1) Two phosphate groups are attached to glucose, forming a new six­carbon compound. The phosphate groups are supplied by two molecules of ATP, which are converted into two molecules of ADP in the process. Step 2) The six­carbon compound formed in Step 1 is split into two three­carbon molecules of PGAL (glyceraldehyde phosphate). Step 3) The The two PGAL molecules are oxidized, and each receives a phosphate group. The product of this step is two molecules of a new three­carbon compound. The oxidation of PGAL is accompanied by the reduction of two molecules of NAD+ to
NADH. NAD+ (nicotinamide adenine dinuecleotide), is similar to NADP+. Step 4) The phosphate groups added in Step 1 and Step 3 are removed from the three­carbon compounds formed in Step 3. This reaction produces two molecules of pruvic acid. Each phosphate group is combined with a molecule of ADP to make a molecule of ATP. Because a total of four phosphate groups were added in Step 1 and
Step 3, four molecules of ATP are produced. ***Notice that two ATP molecules were used in Step 1, but four were produced in Step
4. Therefore, glycolysis has a net yield of two ATP molecules for every molecule of glucose that is converted into pyruvic acid. Aerobic Respiration
**Two major stages­ Krebs cycle and the electron transport chain ● In the Krebs cycle, the oxidation of glucose that began with glycolysis is completed. ● As glucose is oxidized, NAD+ is reduced to NADH
● In the electron transport chain, NADH is used to make most of the ATP produced during aerobic respiration

Pyruvic acid reaction
**To begin the biochemical pathways that make up aerobic respiration, pyruvic acid, formed from glycolysis, combines with coenzyme A to form acetyl CoA. This reaction occurs in the mitochondrial matrix­ pyruvic acid diffuses across the double membrane of a mitochondrion. CO2, NADH, and H+ are also produced.

Krebs Cycle
** Occur in the mitochondrial matrix Step 1) A two­carbon molecule of acetyl CoA combines with a four­carbon compound, oxaloacetic acid, to produce a six­carbon compound, citric acid. This reaction regenerates

coenzyme A.
Step 2) Citric acid releases a CO2 molecule and a hydrogen atom to form a five­carbon compound. By losing a hydrogen atom with its electron, citric acid is oxidized. The hydrogen atom is transferred to NAD+, reducing it to NADH. Step 3) The five­carbon compound formed in Step 2 also releases a CO2 molecule and a hydrogen atom, forming a four­carbon compound. Again, NAD+ is reduced to NADH.
In this step a molecule of ATP is also synthesized from ADP. Step 4) The four­carbon compound formed in Step 3 releases a hydrogen atom to form another four­carbon compound. This time, the hydrogen atom is used to reduce FAD to
FADH2. FAD, (flavin adenine dinucleotide) is a molecule very similar to NAD+. Like
NAD+ FAD accepts electrons during redox reactions Step 5) The four­carbon compound fromed in Step 4 releases a hydrogen atom to regenerate oxaloacetic acid, which keeps the Krebs cycle operating. The hydrogen atom reduces NAD+ to NADH. *** Recall that in glycolysis one glucose molecule produces two pyruvic acid molecyles which can then