Cellular Respiration and Enzymes

Adenosine triphosphate (ATP) is the direct chemical energy source used by myosin heads to bind, pull, and release actin filaments during muscle contraction. While glucose and food are ultimate sources of energy, they must first be converted into ATP.

The mitochondria is known as the powerhouse of the cell because its primary function is to perform cellular respiration, which produces adenosine triphosphate (ATP). Therefore, the statement that it does not produce ATP is false.

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

Oxalic acid is an organic acid with a high oxygen content relative to carbon, resulting in a high Respiratory Quotient (RQ) of 4.0.

Malic acid is an organic acid that, when oxidized, yields an Respiratory Quotient (RQ) of 1.33.

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.

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.

Peter Mitchell proposed the chemiosmotic hypothesis in 1961, which explains how ATP synthesis is coupled to electron transport via a proton gradient.

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.

Hexokinase requires a divalent metal ion, typically Mg+2, to coordinate the phosphate groups of ATP and facilitate the transfer to glucose.