A6. Aerobic Respiration - The Mitochondrial Reactions Flashcards
The link reaction
The link reaction converts the ___________produced in glycolysis to __________ ___________ _. ____________is _________________, so ____carbon atom is removed from ____________in the form of ________ _________. At the same time, ___________is ___________to form __________ and ____ is ___________to form ___________ ____. __________is then combined with ___________ _ (___) to form __________ ___________ _ (_________ ____). No ____is produced in this reaction.
The link reaction converts the pyruvate produced in glycolysis to acetyl coenzyme A. Pyruvate is decarboxylated, so one carbon atom is removed from pyruvate in the form of carbon dioxide. At the same time, pyruvate is oxidised to form acetate and NAD is reduced to form reduced NAD. Acetate is then combined with coenzyme A (COA) to form acetyl coenzyme A (acetyl CoA). No ATP is produced in this reaction.
How many times does the link reaction occur per glucose molecule?
____ pyruvate molecules are made for every glucose molecule that enters glycolysis. This means the link reaction and the third stage (the Krebs cycle) happen _______for every glucose molecule.
Two pyruvate molecules are made for every glucose molecule that enters glycolysis. This means the link reaction and the third stage (the Krebs cycle) happen twice for every glucose molecule.
The products of the link reaction
Here’s what happens to the products of two link reactions (i.e. for one glucose molecule)
The Krebs cycle
The Krebs cycle produces __________ ___________ and ___. It involves a series of ____________-__________reactions, which take place in the ________of the ______________. The cycle happens ____for every pyruvate molecule.
The Krebs cycle
The Krebs cycle produces reduced coenzymes and ATP. It involves a series of oxidation-reduction reactions, which take place in the matrix of the mitochondria. The cycle happens once for every pyruvate molecule.
Figure 1: One turn of the Krebs cycle.
The Krebs Cycle - 3 Steps - Formation, Formation, Regeneration
- Formation of a 6-carbon compound
Acetyl CoA from the link reaction combines with a four-carbon molecule (oxaloacetate) to form a six-carbon molecule (citrate). Coenzyme A goes back
to the link reaction to be used again. - Formation of a 5-carbon compound
The six-carbon citrate molecule is converted to a five-carbon molecule. Decarboxylation occurs, where carbon dioxide is removed. Dehydrogenation also occurs. The hydrogen is used to produce reduced NAD from NAD. - Regeneration of oxaloacetate
The five-carbon molecule is then converted to a four-carbon molecule. Decarboxylation and dehydrogenation occur, producing one molecule of reduced FAD and two of reduced NAD. ATP is produced by the direct transfer of a phosphate group from an intermediate compound to ADP. When a phosphate group is directly transferred from one molecule to another it’s called substrate-level phosphorylation. Citrate has now been converted into oxaloacetate.
Some products of the Krebs cycle are reused, some are released and others are used for the next stage of respiration-oxidative phosphorylation.
Tip: The table only shows the products of one turn of the Krebs cycle. The cycle turns twice for one glucose molecule, so one glucose molecule produces twice as much as what’s shown in the table.
Krebs Cycle in 3 Steps
1) Acetyl Coenzyme A combines with 4C compound to form 6C compound, and sends CoA back to the link reaction
2) 6C compound undergoes dehydrogenation and decarboxylation to form reduced NAD, CO2 and a 5C compound
3) 5C compound undergoes dehydrogenation and decarboxylation to form 2 reduced NAD, CO2, reduced FAD and substrate level phosphorylation occurs to produce ATP - 4C compound is regenerated
Oxidative phosphorylation
Oxidative phosphorylation is the process where the energy carried by ___________, from __________ __________(reduced NAD and reduced FAD), is used to make ___. (The whole point of the previous stages is to make reduced NAD and reduced FAD for the final stage.) Oxidative phosphorylation involves the _________ __________ ______and _________________
Oxidative phosphorylation is the process where the energy carried by electrons, from reduced coenzymes (reduced NAD and reduced FAD), is used to make ATP. (The whole point of the previous stages is to make reduced NAD and reduced FAD for the final stage.) Oxidative phosphorylation involves the electron transport chain and chemiosmosis
Tip: The regenerated coenzymes from the electron transport chain are reused in the _____ ______.
Tip: The regenerated coenzymes from the electron transport chain are reused in the Krebs cycle.
Oxidative phosphorylation
The numbers of the steps below correspond to the circled numbers in the diagram above. (7 steps)
- Hydrogen atoms are released from reduced NAD and reduced FAD as they’re oxidised to NAD and FAD. The hydrogen atoms split into protons (H) and electrons (e-).
- The electrons move down the electron transport chain (made up of electron carriers), losing energy at each carrier
- This energy is used by the electron carriers to pump protons from the mitochondrial matrix into the intermembrane space (the space between the inner and outer mitochondrial membranes).
- The concentration of protons is now higher in the intermembrane space than in the mitochondrial matrix-this forms an electrochemical gradient (a concentration gradient of ions).
- Protons then move down the electrochemical gradient, back across the inner mitochondrial membrane and into the mitochondrial matrix, via ATP synthase (which is embedded in the inner mitochondrial membrane). This movement drives the synthesis of ATP from ADP and inorganic phosphate (P).
- This process of ATP production driven by the movement of H’ ions across a membrane (due to electrons moving down an electron transport chain) is called chemiosmosis (which is described by the chemiosmotic theory).
- In the mitochondrial matrix, at the end of the transport chain, the protons, electrons and oxygen (from the blood) combine to form water. Oxygen is said to be the final electron acceptor.
Tip: The job of a carrier is to transfer electrons. When a carrier receives electrons it’s reduced and when it passes on electrons it becomes _________again.
Tip: The job of a carrier is to transfer electrons. When a carrier receives electrons it’s reduced and when it passes on electrons it becomes oxidised again.
Figure 2: As electrons move down the electron transport chain, they lose energy.
Aerobic respiration and ATP
As you know, oxidative phosphorylation makes ATP using energy from the reduced coenzymes-2.5 ATP are made from each reduced NAD and 1.5 ATP are made from each reduced FAD.
The table below shows that a cell can make 32 ATP from 1 molecule of glucose in aerobic respiration. (Remember, 1 molecule of glucose produces 2 pyruvate, so the link reaction and Krebs cycle happen twice.)
Tip: For each molecule of glucose, __molecules of ATP are produced by oxidative phosphorylation (i.e. that’s the ATP made from reduced ___and reduced ___).
Tip: For each molecule of glucose, 28 molecules of ATP are produced by oxidative phosphorylation (i.e. that’s the ATP made from reduced NAD and reduced FAD).
Aerobic respiration summary
Glycolysis, the link reaction and the Krebs cycle are basically a series of reactions which produce ATP, reduced NAD, reduced FAD and CO2. The reduced coenzymes (NAD and FAD) are then used in oxidative phosphorylation, to produce loads more ATP. The overall process is shown below:
