NAD Acts As A Hydrogen Carrier in Cell Respiration
- NAD (nicotinamide adenine dinucleotide) is a key molecule in cellular respiration.
- It transfers electrons and hydrogen atoms between reactions, allowing cells to capture and use energy efficiently.
What is Oxidation and Reduction?
- Before diving into NAD’s role, let’s clarify two essential concepts: oxidation and reduction.
- Oxidation: The loss of electrons (or hydrogen atoms) from a molecule.
- Reduction: The gain of electrons (or hydrogen atoms) by a molecule.
OIL RIG, Oxidation Is Loss, Reduction Is Gain.
Note- These reactions always occur together, forming redox reactions.
- NAD⁺ acts as an electron sink, capturing high-energy electrons during metabolic reactions.
NAD in Cell Respiration
- NAD is a molecule that can carry electrons and hydrogen atoms from one molecule to another.
- This is important in processes like cell respiration, where energy stored in glucose is released step by step.
- In the first part of cell respiration, glycolysis and the Krebs cycle, NAD helps remove hydrogen from substrates (like glucose or fatty acids).
- When NAD removes hydrogen, it becomes reduced (NAD+ becomes NADH), and the substrate it took the hydrogen from is oxidized.
- NAD+ is a coenzyme, meaning it helps enzymes but is not consumed in the process.
- Once it becomes NADH, it can later release its electrons to help produce ATP.
- NAD+ does not provide energy directly.
- It carries energy in the form of electrons and hydrogen.
1. Glycolysis
- Occurs in the cytoplasm.
- Glucose is split into two molecules of pyruvate.
- NAD⁺ is reduced to NADH as it accepts hydrogen atoms from glucose intermediates.
In glycolysis, the oxidation of triose phosphate produces NADH, which is later used to generate ATP.
2. The Link Reaction and Krebs Cycle
- Takes place in the mitochondrial matrix.
- Pyruvate is converted to acetyl-CoA, then enters the Krebs cycle.
- NAD⁺ is reduced to NADH multiple times, capturing high-energy electrons.
3. The Electron Transport Chain (ETC)
- Located in the inner mitochondrial membrane.
- NADH donates electrons to the ETC, returning to its oxidized form, NAD⁺.
- The energy from these electrons is used to pump protons, creating a gradient that drives ATP synthesis.
- Don’t confuse NAD⁺ with NADH.
- NAD⁺is the empty carrier, while NADHis the loaded carrier, ready to deliver electrons.
- Imagine NAD+ as a taxi that picks up passengers (electrons and hydrogen ions) and takes them to a molecular train station (the electron transport chain) where the energy from the passengers is used to generate power for the cell.
- NAD+ is the empty taxi.
- When it picks up the passengers (electrons and hydrogen), it becomes NADH (the full taxi).
- The NADH then drives to the electron transport chain, drops off the passengers, and the cell can use the energy from those passengers (electrons) to produce ATP.
- How does the concept of oxidation and reduction in biology connect to other fields, such as chemistry or physics?
- Can you think of other systems where energy transfer is critical?
