5.7.7 The Role Coenzymes Flashcards
What is the role of Coenzyme A?
A coenzyme is a molecule that helps an enzyme carry out its function but is not used in the reaction itself
Coenzyme A consists of a nucleoside (ribose and adenine) and a vitamin
In the link reaction, CoA binds to the remainder of the pyruvate molecule (acetyl group 2C) to form acetyl CoA
It then supplies the acetyl group to the Krebs cycle where it is used to continue aerobic respiration
This is the stage that brings part of the carbohydrate (or lipid/amino acid) into the further stages of respiration and links the initial stage of respiration in the cytoplasm to the later stages in the mitochondria
What is the role of NAD and FAD?
Coenzymes NAD and FAD play a critical role in aerobic respiration as hydrogen carriers
When hydrogen atoms become available at different points during respiration NAD and FAD accept these hydrogen atoms
A hydrogen atom consists of a hydrogen ion and an electron
When the coenzymes gain a hydrogen they are ‘reduced’
OIL RIG: Oxidation Is Loss, Reduction Is Gain
They transfer the hydrogen atoms (hydrogen ions and electrons) from the different stages of respiration to the electron transport chain on the inner mitochondrial membrane, the site where hydrogens are removed from the coenzymes
When the hydrogen atoms are removed the coenzymes are ‘oxidised’
Hydrogen ions and electrons are important in the electron transport chain at the end of respiration as they play a role in the synthesis of ATP
Electrons from reduced NAD (NADH) and reduced FAD (FADH2) are given to the electron transport chain
Hydrogen ions from reduced NAD (NADH) and reduced FAD (FADH2) are released when the electrons are lost
The electron transport chain drives the movement of these hydrogen ions (protons) across the inner mitochondrial membrane into the intermembrane space, creating a proton gradient (there are more hydrogen ions in the intermembrane space)
Movement of hydrogen ions down the proton gradient, back into the mitochondrial matrix, gives the energy required for ATP synthesis
What is the role of sources of reduced NAD and FAD?
A certain amount of reduced NAD and FAD is produced during the aerobic respiration of a single glucose molecule
Reduced NAD:
2 x 1 = 2 from Glycolysis
2 x 1 = 2 from the Link Reaction
2 x 3 = 6 from the Krebs cycle
Reduced FAD:
2 x 1 = 2 from the Krebs cycle
