The Link Reaction and the Kreb’s Cycle Flashcards
What has to happen to the pyruvate molecules produced in glycolysis for them to enter the Krebs cycle?
They must be oxidised
In eukaryotic cells where do the Krebs cycle and the link reaction take place?
Inside the mitochondria
(The link reaction) How do the pyruvate molecules produced in glycolysis get into the matrix of the mitochondria?
They are actively transported in
(The link reaction) What happens to the the pyruvate molecules once they are actively transported into the matrix of the mitochondria?
The pyruvate is oxidised to acetate
(The link reaction) How is pyruvate oxidised to acetate?
The pyruvate loses a carbon dioxide molecule and two hydrogens
(The link reaction) What happens to the hydrogens removed from pyruvate?
They re accepted by NAD to form reduced NAD
(The link reaction) Which enzymes remove carbon dioxide?
Decarboxylases
(The link reaction) Which enzymes remove hydrogen?
Dehydrogenases
(The link reaction) How many carbons does acetate have?
2
(The link reaction) What happens to the acetate?
It combines with coenzyme A to form acetyl coenzyme A
How can the link reaction be summarized in an equation?
Pyruvate + NAD + CoA => acetyl CoA + reduced NAD + CO2
What reactions does the Krebs cycle involve?
Oxidation-reduction
Where does the Krebs cycle take place?
The matrix of the mitochondria
(Krebs cycle) What happens to (2-carbon) acetyl coenzyme A?
It combines with a 4-carbon molecule to form a 6-carbon molecule
(Krebs cycle) What happens to the 6-carbon molecule formed?
It loses a carbon dioxide molecule and a hydrogen to give a 4-carbon molecule and a single molecule of ATP
(Krebs cycle) How is the single molecule of ATP formed?
Substrate-level phosphorylation
(Krebs cycle) What happens to the 4-carbon molecule at the end of the Krebs cycle?
It can combine with a new molecule of acetylcoenzyme A to begin the cycle again
For each molecule of pyruvate what do the link reaction and the Krebs cycle produce?
- reduced coenzymes
- one molecule of ATP
- three molecules of carbon dioxide
What reduced coenzymes are produced as a result of the Krebs cycle and the link reaction?
NAD and FAD
Why are reduced NAD and FAD an important product of the Krebs cycle and link reaction?
They have the potential to provide energy to produce ATP molecules by oxidative phosphorylation
How many pyruvate molecules are produced in glycolysis?
2
Per glucose molecule (entered into glycolysis) what are the overall products?
2 ATP and 6 molecules of carbon dioxide
What are coenzymes?
Molecules that some enzymes require in order to function
What are the important coenzymes in respiration?
NAD and FAD
Why is NAD important in respiration?
It works with dehydrogenase enzymes which catalyse the removal of hydrogen atoms from substrates and transfer them to other molecules involved in oxidative phosphorylation
What is the significance of the Krebs cycle?
- it breaks down macromolecules into smaller ones
- it produces hydrogen atoms which are carried by NAD to the electron transfer chain
- it regenerates the 4 carbon molecule that combines with acetylcoenzyme A
- it is a source of intermediate compounds
Give an example of the Krebs cycle breaking down macromolecules?
Pyruvate is broken down into carbon dioxide
Why is it important that the Krebs cycle produces hydrogen atoms?
The hydrogen atoms are carried by NAD to the electron transfer chain and provide energy for oxidative phosphorylation. Leading to the production of ATP which provides metabolic energy for the cell
Why is it important that the Krebs cycle regenerates the 4 carbon molecule that combines with acetyl coenzyme A?
It would otherwise accumulate
Why is it important that the Krebs cycle is a source of intermediate compounds?
The intermediate compounds are used in the manufacture of other important substances such as fatty acids, amino acids and chlorophyll
How many carbons does pyruvate have?
3
Name the 2-carbon molecule that pyruvate in converted to during the link reaction
Acetate
In which part of the cell does the Krebs cycle take place?
The matrix of the mitochondria
Is ATP produced in the Krebs cycle?
Yes
Is ATP needed in the Krebs cycle?
No
Is NAD reduced in the Krebs cycle?
Yes
Is NADP oxidised in the Krebs cycle?
No
Is carbon dioxide produced in the Krebs cycle?
Yes
Is carbon dioxide needed in the Krebs cycle?
No
