Respiration A2 Flashcards
What coenzymes are involved in Glycolysis?
NAD, FAD and Coenzyme a
What do NAD and FAD do?
they carry hydrogen ions take from the reactant, allowing the reactant to be reduced
what are the two stages of glycolysis?
Phosphorylation and oxidation
What are the start and end products of the phosphorylation stage of glycolysis?
Glucose——-two pyruvate molecules
How does phosphorylation turn Glucose to triose phosphate?
Clue- hexose bisphosphate
The initial glucose molecule is bonded to two phosphate molecule to create a more unstable six carbon molecule called hexose bisphosphate. (These two phosphate molecules are taken from hydrolysis of two ATP. This hexose bisphosphate is then split into two (as if straight down the middle) into two triose phosphate molecules (each has 3 carbons).
Why do we change glucose to hexose bisphosphate in phosphorylation?
As hexose bisphosphate is more reactive than glucose, so can be split into the triose phosphate molecules more easily.
What are the input and output products in the oxidation phase of glucose?
Input- 2 triose phosphate
output- 2 pyruvate molecules
How are coenzymes involved in the oxidation phase of glycolysis?
the two triose phosphate molecules are dehydrogenated (oxidised) and the electrons/H+ ions are taken on by 2 NAD enzymes, leaving two reduced NAD and two triose phosphate molecules.
What happens in the oxidation phase of glycolysis?
First, the TP molecules are dehydrogenated
then, two of the phosphate groups from the TP molecules are then combined with ADP to each create two ATP molecules (one phosphate from each TP molecule is used to create two ATP) therefore creating 4 ATP molecules. The TP that the phosphate was removed from has now become Pyruvate, so we are finally left with two pyruvate molecules (which each have 3 carbons).
What are the end products of glycolysis?
2 pyruvate molecules, 2 reduced NAD and 2 net ATP. (we subtract the two ATP used in the phosphorylation phase from the 4 produced in the oxidation phase).
Where does The Link Reaction occur?
What does this mean in terms of transport of the products from glycolysis?
It takes place in the mitochondrial matrix
It means that the products from Glycolysis- the two pyruvate- have to be transported from the cytoplasm, across the mitochondrial membrane and into the matrix via active transport.
What is the aim of the link reaction?
To convert one 3-carbon pyruvate molecule into one 2-carbon acetate, which will then be used in the krebs cycle.
How can 3-carbon pyruvate become 2-carbon acetate in the Link reaction?
The pyruvate must lose one carboxyl group and on hydrogen atom
What do you call it when a compound loses a hydrogen atom/ion?
dehydrogenation
What do you call it when a compound loses a carbon atom/ion?
decarboxylation
How are coenzymes used in the link reaction?
Remember the ending?
When the pyruvate is dehydrogenated to form acetate, the hydrogen is taken up by an NAD molecule (the NAD becomes reduced).
After the acetate is formed, it combines with coenzyme a temporarily, in order to stabilise it, therefore becoming Acetyl CoA.
What happens to the carboxyl group removed from Pyruvate in the link reaction?
How does this relate to the original respiration equation
(Oxygen + Glucose →→→ CO2 and Water)
The carboxyl is combined with two oxygen to make CO2.
This is one of the waste products produced in respiration. The waste product of water is produced in oxidative phosphorylation.
What is the equation for the link reaction?
Pyruvate + NAD + Coenzyme A →→→ Acetyl CoA + Reduced NAD + Carbon Dioxide
What are the desired products of the Krebs Cycle?
Reduced NAD, reduced FAD and ATP.
These are needed for oxidative phosphorylation (Oxaloacetate is also produced in order to restart the cycle)
What are the waste products of the Krebs Cycle?
Carbon Dioxide
What enzyme is used in the Krebs cycle to aid the change of a 4 carbon compound to Oxaloacetate?
Isomerase
Where does oxidative phosphorylation take place?
In the christae of the mitochondria
what reactant and product are used/produced in oxidative phosphorylation?
Oxygen- reactant
Water- product
what products from EACH of the previous stages of respiration are used in oxidative phosphorylation?
Glycolysis- 2 reduced NAD
Link Reaction- 2 reduced NAD
Krebs Cycle- 6 reduced NAD and two reduced FAD
What are the two stages of oxidative phosphorylation?
the electron train and chemiosmosis
What are the three carrier proteins/enzymes in the electron transport chain (in correct order)?
NADH hydrogenase, cytochrome and cytochrome oxidase
How does a lack of oxygen affect the electron chain in oxidative phosphorylation?
If oxygen is not present, it can not act as the final electron acceptor and take the electrons from the chain after it reaches cytochrome oxidase, meaning the chain is not able to repeat the process. It also can not take up the two excess hydrogen atoms that would have been used to convert the oxygen into water.
How does a lack of oxygen affect the protein gradient in oxidative phosphorylation?
Lack of oxygen means that the oxygen is not there to take up extra hydrogen ions. Also, the electron transport chain is not functioning due to the lack of oxygen as well (therefore meaning less hydrogen atoms are being pumped into the intermembrane space). These both result in an excess of hydrogen ions in the matrix, so there is no concentration gradient down the inner membrane.
How does a lack of oxygen affect the synthesis of ATP in oxidative phosphorylation?
As there is no protein/electrochemical gradient, the H+ ions don’t move through the ATP synthase channels, so the ATP does not have the energy to be synthesized.
A lack of Oxygen in aerobic respiration leads to a buildup of H+ ions in the matrix.
How can this affect NAD and the Krebs cycle.
If there is no oxygen to take up the excess H+ ions in the electron chain, they build up in the matrix. This can block the NADH from the start of the chain (that originally gives up the electrons and hydrogen atoms) from reaching the electron carrier proteins and being dehydrogenated- aka giving up H+. This would usually leave oxidised NAD (after dehydrogenation). This oxidised NAD is required by the krebs cycle in order to continue, so if this oxidation does not occur, the krebs cycle will be ineffective.
How does the inhibition of the krebs cycle by a lack of oxygen affect the link reaction?
If the krebs cycle is not functioning, it can not use up the Acetyl coA made as a product of the links reaction. There is then a build up of Acetyl CoA, so the links reaction would stop occurring.
(Briefly) analyse how a lack of oxygen can affect each of these stages of respiration:
Links Reaction-
Krebs Cycle
Links Reaction- build up of Acetyl CoA (not being used in Krebs Cycle) results in the reaction ceasing.
Krebs Cycle– Lack of oxidised NAD (due to inefficiencies in oxidative phosphorylation) means the dehydrogenation reactions in the cycle- and th cycle itself- can not take place.
Oxidative Phosphorylation- Oxygen is not there to be the final electron acceptor, so the electron transport chain can not repeat, so H+ ions build up in the matrix (stopping oxidation of NADH and synthesis of ATP)
How must glycolysis be modified in anaerobic respiration/
It must be combined with an alternative pathway for re-oxidising the NADH.
What is the word equation (ish) for glycolysis.
Glucose + 2 phosphates (taken from 2 ATP that are hydrolysed to ADP) →→→ Hexose Phosphate →→→ then split into →→→ 2 Triose Phosphate molecules →→→ gives 2 H+ ions to 2 NAD (releases two NADH) →→→ Also gives 2 phosphate molecules that each synthesize 2 ATP (4 ATP in total) →→→ Leaves 2 pyruvate molecules
What pathway do mammals use to re-oxidise NADH in anaerobic respiration?
The Lactate fermentation Pathway
What happens in The Lactate fermentation Pathway?
NADH gives it’s hydrogen atom to a pyruvate produced in glycolysis, creating lactate and re-oxidised NAD.
What enzyme catalyses The Lactate fermentation Pathway?
Lactate Dehydrogenase
What happens to the lactate after anaerobic respiration and why?
Lactate is acidic (also known as lactic acid) so it can lower the pH of the cytoplasm and affect enzyme production. Therefore, it is transported to the liver, where it is converted back to pyruvate once there is more oxygen available.
What pathway do fungi and plants use to re-oxidise NADH in anaerobic respiration?
First they decarboxylate pyruvate to ethanal. This ethanal then takes on a Hydrogen ion from and NADH molecule, leaving the reduced ethanal and a re-oxidised NAD.
What enzyme catalyses the changing of pyruvate to ethanal in anaerobic respiration in plants?
Pyruvate dehydrogenase
What occurs in anaerobic respiration in mammals?
Glycolysis and the Lactate fermentation Pathway
What occurs in anaerobic respiration in plants and animals?
Glycolysis, decarboxylation of Pyruvate and the dehydrogenation of Ethanal/ re-oxidation of NADH.
What are the 4 stages of respiration (in order)?
Glycolysis
Link Reaction
Krebs Cycle
Oxidative Phosphorylation
Briefly summarise what happens in glycolysis
The 6 carbon glucose molecule is split into two 3 carbon pyruvate molecules. (though it first becomes hexose bisphosphate and then becomes triose phosphate)
Briefly summarise what happens in the link reaction
The 3 carbon pyruvate experience a series of reactions which eventually lead to the formation of acetylcoenzyme A, a 2-carbon molecule.
Briefly summarise what happens in the Krebs Cycle?
Acetylcoenzyme A is used in a cycle of reactions in order to yield ATP and a large quantity of reduced NAD and FAD, which are essential products for Oxidative Phosphorylation.
Briefly summarise what happens in Oxidative Phosphorylation?
Electrons and H+ ions from the NAD and FAD produced in the krebs cycle use the ATP synthesis channels in the christae to produce a large amount of ATP (water is produced as a by-product)
How is energy released by ATP different to energy released by glucose?
It yields a smaller, more manageable amount of energy
Why is ATP often used as a go-to source of energy?
Only one bond needs to be broken to release its energy. In hydrolysis, ATP —— ADP + Phosphate and energy.
Name two reasons ATP is often used in metabolic reactions?
ATP releases a phosphate group when hydrolysed. This phosphate group can be added on to other elements to either increase their reactivity or lower their activation energy
It can easily be reformed/regenerated.
What is the equation for the link reaction?
Pyruvate + NAD + Coenzyme A ———- Acetylcoenzyme A + Reduced NAD + CO2
How is the pyruvate released in glycolysis prepared for the Krebs cycle?
First, the three-carbon pyruvate is oxidised to form acetate by losing a carbon dioxide and two hydrogen. These hydrogen are taken up by NAD to produce reduced NAD. This leaves the two carbon acetate. It must then bind with coenzyme A to produce acetylcoenzyme A.
Why is aerobic respiration better at producing ATP?
because glycolysis only produces 2 ATP molecules, and anaerobic respiration gets its ATP from glycolysis. However, aerobic respiration has the chemiosmosis stage that produces around 34 net ATP.
What is another name for anaerobic respiration in plants and microorganisms?
Alcohol fermentation pathway
Describe the process of alcohol fermentation
2 pyruvate molecules hydrogen from reduced NAD (causing it to be reoxidised to normal NAD). The pyruvate then loses a carbon to form carbon dioxide and ethanol.
What is another name for anaerobic respiration in animals?
Lactic Acid Fermentation Pathway
Describe the process of lactic acid fermentation
2 Pyruvate molecules take hydrogen ions from reduces (re-oxidising it into normal NAD), causing it to become 2 lactate molecules
What two biological molecules can be used as substrates for aerobic respiration?
Lipids and proteins
How can lipids be used as substrates in aerobic respiration?
In the absence of glucose, lipids can be hydrolysed into glycerol and fatty acids. Glycerol can be phosphorylated and converted to triose phosphate, which is then used in glycolysis
How can proteins be used as substrates in aerobic respiration?
Proteins can be broken down into amino acids, which can then be broken down into their different chemical groups (i.e. amino group, carboxyl group) which can then be used in the krebs cycle or glycolysis.
How can fatty acids be used as substrates in aerobic respiration?
They can be broken down into two-carbon fragments which are then converted to acetyl coenzyme A, which is then used in the krebs cycle.
