Module 5: Respiration Flashcards
What is aerobic respiration?
Splitting of the respiratory substrate, to release carbon dioxide as a waste product and reuniting of hydrogen with atmospheric oxygen with the release of a large
amount of energy whereas anaerobic respiration occurs in the absence of oxygen.
Respiration is a multi-step process with each step controlled and catalysed by a specific
intracellular enzyme.
What is glycolysis? What does this process result in?
First stage of both aerobic and anaerobic respiration and occurs in cytoplasm.
Molecule of glucose is phosphorylated to produce 2
molecules of pyruvate (3C), 2 molecules of reduced NAD, and a net production of 2 molecules of ATP.
Describe the steps of glycolysis.
- Phosphorylation - glucose (6C) is phosphorylated by 2 ATP (converted to 2ADP) to form fructose bisphosphate (6C).
- Lysis - fructose bisphosphate (6C) splits into 2 molecules of triose phosphate (3C).
- Oxidation - hydrogen is removed from each molecule of triose phosphate and transferred to coenzyme NAD to form 2 reduced NAD.
4H + 2NAD → 2NADH + 2H+ - Dephosphorylation: phosphates are transferred from the intermediate substrate molecules to form 4 ATP through substrate-linked phosphorylation
4Pi + 4ADP → 4ATP. - 2 Triose phosphate → 2 Pyruvate
What is the purpose of pyruvate being formed in glycolysis?
Pyruvate contains lots of energy that can be used to generate more ATP.
Where does the link reaction take place?
Mitochondrial matrix.
Describe what happens in the Link reaction.
What are the products of the Link reaction?
- When oxygen is available, pyruvate will enter mitochondrial matrix. Pyruvate moves across double membrane of mitochondria by active transport. It requires a transport protein and some ATP.
- Pyruvate is oxidised by enzymes to produce acetate and CO2 (as pyruvate is decarboxylated), requiring the reduction of NAD to NADH.
- Acetate binds with coenzyme A to form acetyl CoA.
The products are:
=> Acetyl coA
=> CO2
=> Reduced NAD (NADH)
What is the role of coenzyme A?
In the Link reaction, it binds to the acetyl group to form acetyl coA. Then it delivers the acetyl group to the Krebs cycle.
Where does the Kreb’s cycle take place?
Mitochondrial matrix.
Describe what happens in the Kreb’s cycle.
- 2C acetyl coA enters the circular pathway from the link reaction. Acetyl coA formed from fatty acids (after the breakdown of lipids) and amino acids enter directly into Krebs through other metabolic pathways.
- 4C oxaloacetate accepts the 2C fragment from acetyl coA to for 6C citrate. Citrate then converted back to oxaloacetate through oxidation-reduction reactions.
Acetyl to the Krebs cycle where glucose is oxidised and carbon
dioxide, ATP, reduced NAD and reduced FAD are produced. Each glucose molecule causes the cycle to turn twice so per glucose we produce 4CO2, 4NADH, 2FADH and 2ATP molecules in the Krebs cycle. The ATP molecules produced by the Kreb’s cycle are done so by substrate level phosphorylation.
Describe how oxaloacetate is regenerated in the Krebs cycle.
Through redox reactions:
=> Decarboxylation of citrate
=> Releasing 2CO2 as waste gas
=> Dehydrogenation of citrate
=> Releasing H atoms that reduce coenzymes NAD and FAD
What happens in oxidative phosphorylation?
Oxidative phosphorylation is the process in which ATP is synthesised in the electron
transport chain in mitochondria. This process generates the majority of ATP in aerobic respiration and it occurs as following:
* Reduced coenzymes (NADH and FADH) carry hydrogen ions and electrons to
the electron transport chain which occurs on the inner mitochondrial membrane
* Electrons are carried from one electron carrier to another in a series of redox
reactions: the electron carrier which passes the electron on is oxidised whereas
the electron carrier which receives it is reduced
The energy provided by the electrons to the electron carriers is used to
moveHydrogen ions across the inner membrane into the intermembrane space –
as a result of that the concentration of the hydrogen ions in the intermembrane
space is high
The inner membrane is impermeable to H+
* Hydrogen ions diffuse into the mitochondrial matrix down the electrochemical
gradient through the ATPase enzyme.
* ATP is produced on stalked particle using ATP synthase
* Hydrogen atoms are produced from hydrogen ions and electrons. The hydrogen atoms are then combined with O2 to produce water
* Oxygen acts as the final electron acceptor
What is substrate level phosphorylation?
A phosphate is transferred from one intermediate to ADP, forming 1 ATP.
There is a theoretical yield of 38 ATP molecules per glucose molecule but in real life this is
rarely achieved due to the inner mitochondrial membrane being ‘leaky’ to H+ therefore not
all H+ move through the ATPase. The pyruvate made during glycolysis in cytoplasm needs
moving into the matrix by active transport and so this uses ATP.
Respiratory substrates include carbohydrates, lipids and proteins which release varying
amounts of energy, depending on the number of hydrogens in the structure which are
oxidised to water. For instance, the number of hydrogens is greater in fatty acids than
carbohydrates.
The respiratory quotient (RQ) can be measured to determine which respiratory substrate is
being used and to determine if the organism is undergoing anaerobic respiration.
RQ = carbon dioxide produced / oxygen consumed
Different respiratory substrates have different RQ values e.g. carbohydrates have a value of
1.0, lipids – 0.8 and proteins 0.9.
What is anaerobic respiration?
This occurs when the concentration of oxgen is low. ATP production still needs to happen
but this can’t be done by oxidative phosphorylation due to the lack of oxygen to act as the
final electron acceptor.
In order for some ATP to be produced anaerobic respiration allows glycolysis to continue.
(Glycolysis has a net production of 2 ATP per glucose molecule).
In mammals pyruvate is converted to lactate. Pyruvate acts as the hydrogen acceptor to
enable NADH to be reoxidised to NAD which can then be used to continue the reactions
in glycolysis.
Lactate can then be converted back to pyruvate in the liver cells when the oxygen levels
rise again.
Yeast and plants use alcoholic fermentation to enable glycolysis to continue. In this
process Pyruvate is decarboxylated to EthanAl which in turn is reduced to ethanOl
reoxidising NAD in the process. So ethanAl is the hydrogen acceptor. The first step in this
process produces CO2 and therefore this is an irreversible reaction.
What is oxidative phosphorylation? Where does it occur?
Last stage of aerobic respiration that takes place in the inner mitochondrial membrane. I results in the production of many ATP molecules and water from O2.
What is the current model for oxidative phosphorylation?
Chemiosmotic theory. energy from electrons passed through a chain of proteins in the membrane (the electron transport chain) is used to pump protons (hydrogen ions) up their concentration gradient into the intermembrane space
The hydrogens are then allowed to flow by facilitated diffusion through a channel in ATP synthase into the matrix
The energy of the hydrogens flowing down their concentration gradient is harnessed (a bit like water flowing through a hydroelectric dam) resulting in the phosphorylation of ADP into ATP by ATP synthase
