Link reaction and Krebs Cycle Flashcards
Where does the krebs cycle take place?
Involves a series of oxidation reduction reactions that take place in the matrix of mitochondria
What happens during the krebs cycle
•The 2-carbon acetyl-coenzyme A from the link reaction combines with a 4 carbon molecule to produce a 6 carbon molecule
•coenzyme A is recycled
•In a series of reactions this 6 carbon molecule loses carbon dioxide and hydrogen to give a 5c molecule and then a 4 carbon molecule and a single molecule of ATP produced as a result of substrate- level phosphorylation (creation of ATP without ATP synthase)
NAD is reduced
•The 4 carbon molecule can now combine with a new molecule of acetylocoenyme A to begin the cycle again
•(lipids and proteins can also be repaired aerobically and are broken down into acetyl CoA to enter cycle)
For each molecule of pyruvate, the link reaction and the krebs cycle therefore produce…
•reduced enzymes such as NAD and FAD. These have the potential to provide energy to produce ATP molecules by oxidative phosphorylation
1x FADH 1x NADH
• one molecule of ATP
• 2 molecules of CO2
(As two produced for each glucose molecule the yield from a single glucose molecule is double the above)
What is a coenzyme + examples
Not enzymes. Molecules that some enzymes require in order to function. Carry hydrogen atoms from one molecule to another.
NAD- throughout respiration
FAD- important in krebs cycle
NADP- important in photosynthesis
What does NAD do?
It works with dehydrogenase enzymes that catalyse the removal of hydrogen atoms from substrates and transfer them to other molecules involved in oxidative phosphorylation
Four reasons the krebs cycle plays an important role in the cells of organisms
- breaks down macromolecules into smaller ones (pyruvate to CO2)
- produces hydrogen atoms that are carried by NAD to the electron transfer chain and provide energy for oxidative phosphorylation. Leads to theproduction of ATP (metabolic energy)
- regenerates the 4 carbon molecule that combines with acetycoenzyme A which would otherwise accumulate
- a source of intermediate compounds used by cells in the manufacture of other important substances such as fatty acids
what is dehydrogenation?
the loss of a hydrogen atom/ion
what is decarboxylation?
a loss of carbon atom
what must happen to pyruvate molecules before entering the krebs cycle?
they must be oxidised in the link reaction
What happens during the link reaction
• pyruvate is dehydrogenated and decarboxylated to form acetate (loses a CO2 molecule and two hydrogens)
-NADH is formed
• the 2C acetate combined with coenzyme A to produce a compound called acetyl coenzyme A
What are the products of the link reaction per reaction and per glucose
• per reaction: 1x CO2 1x NADH
• per glucose: 2 x CO2 2x NADH
where does the link reaction occur
the matrix of mitochondria
