12.2 - Link Reaction And krebs Cycle Flashcards
What do pyruvate molecules produced during glycolysis possess
Potential energy that can be released in the Krebs cycle.
What must happen to pyruvate molecules before they enter the Krebs cycle?
They must be oxidised in a process called the link reaction.
Where do the link reaction and Krebs cycle occur in eukaryotic cells?
Exclusively inside the mitochondria.
How are pyruvate molecules transported into the mitochondria?
They are actively transported from the cytoplasm into the matrix of mitochondria.
What happens to pyruvate during the link reaction?
Pyruvate is oxidised to acetate, losing a carbon dioxide molecule and two hydrogens.
What happens to the hydrogens removed from pyruvate during oxidation?
They are accepted by NAD, forming reduced NAD, which is later used to produce ATP.
What compound is formed when acetate combines with coenzyme A?
Acetylcoenzyme A (acetyl CoA).
What is the overall equation for the link reaction?
Pyruvate + NAD + CoA → acetyl CoA + reduced NAD + CO2.
Who was the Krebs cycle named after?
The British biochemist Hans Krebs, who worked out its sequence.
What types of reactions occur during the Krebs cycle, and where do they take place?
- The Krebs cycle involves a series of oxidation-reduction reactions, where molecules are oxidised and reduced to transfer energy.
- These reactions occur in the matrix of the mitochondria
Describe the steps in the Krebs cycle
- The 2-carbon acetylcoenzyme A from the link reaction combines with a 4-carbon molecule (oxaloacetate) to produce a 6-carbon molecule (citrate)
- In a series of reactions this 6-carbon molecule loses carbon dioxide and hydrogen to give a 4-carbon molecule and a single molecule of ATP produced as a result of substrate-level phosphorylation
- The 4-carbon molecule can now combine with a new molecule of acetylcoenzyme A to begin the cycle again
What are the key products of the Krebs cycle and link reaction for each pyruvate molecule
For each pyruvate molecule, the link reaction and Krebs cycle produce:
- 3 molecules of reduced NAD (NADH),
- 1 molecule of reduced FAD (FADH₂),
- 1 molecule of ATP,
- 3 molecules of carbon dioxide (CO₂).
What is the total yield from one molecule of glucose after the Krebs cycle and link reaction?
Since two pyruvate molecules are generated from one glucose molecule, the total yield per glucose is:
- 6 NADH molecules,
- 2 FADH₂ molecules,
- 2 ATP molecules,
- 6 molecules of CO₂.
What are coenzymes, and how do they differ from enzymes?
- Coenzymes are not enzymes but are molecules that assist enzymes in their function.
- They are essential for the activity of some enzymes but do not have catalytic properties themselves.
What role do coenzymes play in biological processes like photosynthesis and respiration?
Coenzymes carry hydrogen atoms from one molecule to another, playing a crucial role in energy transfer during photosynthesis and respiration.
What are some key examples of coenzymes and where are they important?
- NAD: Important throughout respiration.
- FAD: Plays a role in the Krebs cycle.
- NADP: Crucial in photosynthesis.
Which coenzyme is the most important in respiration, and what does it do?
- NAD is the most important coenzyme in respiration.
- It works with dehydrogenase enzymes to remove hydrogen atoms from substrates and transfer them to molecules involved in oxidative phosphorylation.
How does NAD function with dehydrogenase enzymes in respiration?
NAD works with dehydrogenase enzymes to catalyse the removal of hydrogen atoms from substrates, transferring these atoms to molecules that are part of the oxidative phosphorylation process, contributing to ATP production.
The Krebs cycle performs an important role in the cells of organisms for four reasons, what are they?
1) It breaks down macromolecules into smaller ones - pyruvate is broken down into carbon dioxide.
2) It produces hydrogen atoms that are carried by NAD to the electron transter chain and provide energy for oxidative phosphorylation. This leads to the production of ATP that provides metabolic energy for the cell.
3) It regenerates the 4-carbon molecule that combines with acetylcoenzyme A, which would otherwise accumulate.
4) It is a source of intermediate compounds used by cells in the manufacture of other important substances such as fatty acids, amino acids and chlorophyll.
State how many carbon molecules there are in a single molecule of pyruvate
3
Name the 2-carbon molecule that pyruvate is converted to during the link reaction
acetylcoenzyme A
State precisely which part of the cell the Krebs cycle takes place
Matrix of mitochondria
