Cellular Respiration and Enzymes

Enzymes are biological catalysts that increase the rate of chemical reactions in the body by lowering the activation energy required.

Glucose is a simple sugar (monosaccharide) with the chemical formula C6H12O6, which organisms use as a primary source of energy.

Iron (Fe) is a vital cofactor for several enzymes, including catalase and peroxidase, which are involved in the breakdown of hydrogen peroxide.

The pyruvate dehydrogenase complex, which converts pyruvate to acetyl-CoA, requires TPP, lipoic acid, FAD, NAD+, and coenzyme A as essential cofactors.

Palmitic acid (16 carbons) undergoes 7 cycles of beta-oxidation, producing 8 acetyl-CoA, 7 NADH, and 7 FADH2. Calculating the total ATP yield (including TCA cycle and electron transport chain) results in a net gain of 129 ATP.

In glycolysis, steps 1 (hexokinase), 3 (phosphofructokinase), and 10 (pyruvate kinase) are highly exergonic and thus irreversible under physiological conditions.

One turn of the Krebs cycle produces 3 NADH, 1 FADH2, and 1 GTP (or ATP). Converting these to ATP (3*2.5 + 1*1.5 + 1 = 10) gives 10 ATP, but older textbooks often cited 12 based on different P/O ratios (3*3 + 1*2 + 1 = 12). Given the options, 12 is the standard textbook answer.

Brown adipose tissue contains a high density of mitochondria with uncoupling protein 1 (UCP1), which allows the energy from the proton gradient to be released as heat rather than being used to synthesize ATP.

ATP synthase consists of two main components: F0 and F1. The F0 subunit is embedded in the membrane and contains the proton pore, while the F1 subunit is the catalytic head that synthesizes ATP.

In the electron transport system (ETS), the complexes are numbered I through IV, with ATP synthase being referred to as Complex V.

Glycolysis involves the breakdown of glucose. Fructose 1,6-bisphosphate is a key intermediate formed during the preparatory phase of glycolysis.

The conversion of Fructose 6-phosphate to Fructose 1,6-bisphosphate by PFK-1 is the rate-limiting and first committed step of glycolysis.

Phosphofructokinase-1 (PFK-1) is the primary enzyme responsible for the phosphorylation of Fructose 6-phosphate to Fructose 1,6-bisphosphate in glycolysis.