BIOCHEM Biochemical Energy Production (copy)

Stage 1

Digestion begins in the mouth, continues in the stomach, and is completed in the small intestine.

Stage 1

The end products of digestion - glucose and other monosaccharides from carbohydrates, amino acids from proteins, and fatty acids and glycerol from fats and oils are small enough to pass across intestinal membranes and into the blood, where they transported to the body’s cells

Stage 2

Acetyl group formation, involves numerous reactions, some of which occur in the cytosol of cells and some in cellular mitochondria.

Stage 2

the small molecules from digestions are further oxidized during this stage. primary products include two-carbon acetyl units (which become attached to coenzyme A to give acetyl CoA) and the reduced coenzyme NADH

Stage 3

The citric acid cyle, occurs inside mitochondria. here acetyl groups are oxidized to produced CO2 and energy.

Stage 3

some of the energy released by these reactions is lost as heat, and some is carried by the reduced coenzymes NADh and FADH2 to the 4th stage. The CO2 that we exhale as part of the breathing process comes primarily from this stage.

Stage 4

The electron transport chain and oxidative phosphorylation, also occurs inside mitochondria.

Stage 4

NADH and FADH2 supply the “fuel“ (hydrogen ions and electrons) needs for the productions of ATP molecules, the primary energy carriers in metabolic pathways. Molecular O2 inhaled via breathing, is converted to H2O in this stage.

Stage 3 & 4

same for all types of foods (carbohydrates, fats, proteins). These reactions constitute the common metabolic pathway.

common metabolic pathway

the sum total of the biochemical reactions of the citric acid cycle, the electron transport chain, and oxidative phosphorylation.

Citric Acid Cycle

the series of biochemical reactions in which the acetyl portion of acetyl CoA is oxidized to carbon dioxide and the reduced coenzymes FADH2 and NADH are produced

1 Condensation

Acetyl CoA C2

2 Isomerization

Citrate C6

3 Oxidation and decarboxylation

Isocitrate C6

4 Oxidation and decarboxylation

α-keto-glutarate C5

5 Phosphorylation

succinyl CoA C4

6 Oxidation

Succinate C4

7 Hydration

fumarate C4

8 Oxidation

Malate C4

Acetyl CoA C2 and Oxaloacetate C4

Starting point of Citric Acid Cycle

Step 1

formation of Citrate. Acetyl CoA, which carries the two-carbon degradation product of carbohydrates, fats, and proteins, enters the cycle by combining with four carbon keto dicarboxylate species oxaloacetate.

Step 1

This results in the transfer of the acetyl group from coenzyme A to oxaloacetate, producing the C6 citrate species and free coenzyme A.

Step 2

Formation of Isocitrate. Citrate is converted to its less symmetrical isomer isocitrate in an isomerization process that involves a dehydration followed by a hydration, both catalyzed by the enzyme aconitase.

Step 2

The net result of these reactions is that the -OH group from citrate is moved to a different carbon atom

Step 3

Oxidation of Isocitrate and formation of CO2. this step involves oxidation-reduction (the first of four redox reactions in the citric acid cycle) and decarboxylation. This step yields the first molecules of CO2 and NADH in the cycle

Step 4

oxidation of α-ketoglutarate and formation of CO2. This second redox reaction of the cycle involves one molecule each of NAD+, CoA-SH, and α-ketoglutarate.

Step 5

Thioester bond cleavage in succinyl CoA and phosphorylation of GDP. Two molecules react with succinyl CoA - A molecule of GDP and a free phosphate group (Pi)

Step 5

The energy released is used to combine GDP and Pi to form GTP. Succinyl CoA has been converted to succinate.

Step 6

Oxidation of succinate. This is the third redox reaction of the cycle. the enzyme involved is succinate dehydrogenase, and the oxidizing agent is FAD rather than NAD+.

Step 7

Hydration of fumarate. the enzyme fumarase catalyzed the addition of water to double bond of fumarate. the enzyme is stereospecific, so only the L isomer of the product malate is produced.

Step 9

Oxidation of L-Malate to regenerate oxaloacetate. im the fourth oxidation-reduction of the cycle, a molecule of NAD= reacts with malate, picking up two hydrogen atoms with their associated energy to form NADH + H+.