In which of the following is the first molecule becoming reduced to the second molecule? a. pyruvate → acetylCoA b. pyruvate → lactate c. glucose → pyruvate d. NADH + H+ →NAD+ + 2H

Verified step by step guidance

1. Understand the concept of reduction in a chemical reaction, which involves the gain of electrons or a decrease in oxidation state by a molecule.
2. Identify the molecule in each pair that is gaining electrons or hydrogen atoms, or losing oxygen atoms, as these are indicators of reduction.
3. Examine option (a) pyruvate → acetylCoA to determine if pyruvate gains electrons or hydrogen, or loses oxygen in the conversion to acetylCoA.
4. Examine option (b) pyruvate → lactate to check if pyruvate is gaining electrons or hydrogen atoms in the conversion to lactate.
5. Examine option (d) NADH + H+ → NAD+ + 2H to see if NADH is losing electrons or hydrogen atoms in the conversion to NAD+.

Key Concepts

Reduction and Oxidation Reactions

Reduction and oxidation (redox) reactions are chemical processes where electrons are transferred between molecules. Reduction refers to the gain of electrons or hydrogen, while oxidation involves the loss of electrons or hydrogen. Understanding these concepts is crucial for identifying which molecules are being reduced or oxidized in metabolic pathways.

Metabolic Pathways

Metabolic pathways are sequences of chemical reactions occurring within a cell, where specific substrates are converted into products through enzymatic activity. Each step in a pathway can involve reduction or oxidation, and recognizing these pathways helps in understanding how energy and matter are transformed in biological systems.

Role of NADH and NAD+

NADH and NAD+ are key coenzymes in cellular metabolism, particularly in redox reactions. NAD+ acts as an electron acceptor, becoming reduced to NADH, while NADH can be oxidized back to NAD+. This cycling between NAD+ and NADH is vital for energy production in processes like cellular respiration and fermentation.