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
