5.2.2 - Respiration Flashcards
What can respiration be said to be ?
The reverse of photosynthesis
Where is the energy trapped in glucose molecules ?
In the carbon hydrogen bonds
What is released when the C-H bonds break in glucose ?
Energy is released
What is the energy in glucose used for ?
- Energy is used for the synthesis of ATP by chemiosmosis
- ATP is constantly being used up and synthesised
What is the first stage of respiration ?
Glycolysis
Where does glycolysis occur ?
In the cytoplasm of the cell
What type of a process is glycolysis ?
- It is an anaerobic process
- It does not require oxygen
What happens in glycolysis (brief) ?
- Glucose is split into two pyruvate molecules
- ATP and reduced NAD are also produced
What are the 4 stages in glycolysis ?
- Phosphorylation 1
- Lysis
- Phosphorylation 2
- Dehydrogenation and formation of ATP
What happens in the first phosphorylation in glycolysis ?
- Two phosphates, released from two ATP molecules, are attached to glucose
- Forms hexose bisphophate
What happens in the lysis stage in glycolysis ?
The molecule is destabilised and splits into two TP molecules
What happens in the second phosphorylation in glycolysis ?
- Another phosphate group is added to each TP
- Forms two triose bisphosphate molecules
Where do the phosphates come from in the second phosphorylation stage ?
Come from free inorganic phosphate ions present in the cytoplasm
What happens in the dehydrogenation and formation of ATP in glycolysis ?
- Two triose bisphosphate molecules are oxidised by the removal of hydrogen atoms
- Forming two pyruvate molecules
What happens to the two hydrogen molecules that are released from the dehydrogenation of Triose Bisphosphate ?
- NAD coenzymes accept the removed hydrogens
- They are then reduced and form two reduced NAD molecules
How many ATP molecules are produced in glycolysis ?
4
What is the overall net ATP yield of glycolysis ?
2
What is glycolysis an example of ?
Substrate level phosphorylation
What is substrate level phosphorylation ?
The formation of ATP without the involvement of an electron transport chain
Where do the remainder of the aerobic reactions of cellular respiration take place ?
They take place in the mitochondria
What is the role of the outer mitochondrial membrane ?
- It separates the contents of the mitochondrion from the rest of the cell
- It creates a cellular compartment with ideal conditions for aerobic respiration
What is the role of the matrix ?
- It contains enzymes for the Krebs cycle and the Link reaction
- It contains mitochondrial DNA
What is the role of the inner mitochondrial membrane ?
It contains electron transport chains and ATP synthase
What is the role of the intermembrane space ?
- Proteins are pumped into this space by the electron transport chain
- The space is small so the concentrations build up quickly
What are the cristae ?
They are projections of the inner membrane which increase the surface area available for oxidative phosphorylation
What is the first step in the aerobic respiration ?
Oxidative decarboxylation
What is oxidative decarboxylation sometimes called ?
The link reaction
Why is it called the link reaction ?
It is the step that links anaerobic glycolysis to the aerobic steps of respiration
Where does pyruvate enter into ?
Mitochondrial matrix
How would pyruvate enter the mitochondrial matrix ?
Active transport via specific carrier proteins
What does pyruvate undergo once in the mitochondrial matrix ?
Oxidative decarboxylation
What is oxidative decarboxylation ?
Carbon dioxide is removed along with hydrogen
What happens to the hydrogen that is removed from pyruvate ?
It is accepted by NAD
What does NAD turn into once it accepts the hydrogen from pyruvate ?
- Reduced NAD
- NADH
What is left after oxidative decarboxylation occurs ?
Acetyl group
What happens to the acetyl group that is left?
- It is bound to coenzyme A
- This forms Acetylcoenzyme A
What is the role of Acetyl CoA ?
It delivers the acetyl group to the Krebs Cycle
Where is the NADH used ?
In oxidative phosphorylation to synthesise ATP
What happens to the carbon dioxide that was produced as a result of the decarboxylation ?
It will either diffuse away and be removed or be used as a raw material in photosynthesis
Where does the krebs cycle take place ?
Mitochondrial matrix
What does each krebs cycle result in ?
The breakdown of an acetyl group
What processes are involved in the Krebs cycle ?
- Decarboxylation
- Dehydrogenation
- Substrate level phosphorylation
What picks up the H atoms that are released in the krebs cycle ?
Coenzymes NAD and FAD
What happens to the CO2 released in the krebs cycle ?
It is a by product
What happens to the ATP released in the krebs cycle ?
It is available for use by energy requiring processes within the cell
When are the reduced NAD and reduced FAD used ?
In oxidative phosphorylation (the final oxygen requiring step of aerobic respiration)
What does acetyl combine with when it enters the krebs cycle ?
Oxaloacetate (4C molecule)
What does the reaction between acetyl and oxaloacetate form ?
A six carbon molecule called citrate
What happens to the citrate molecule once it is formed ?
It undergoes decarboxylation and dehydrogenation
What is formed after the decarboxylation and dehydrogenation of a citrate molecule ?
- One reduced NAD
- CO2
- 5 carbon compound
What happens to the 5 carbon molecule in the krebs cycle ?
It undergoes further decarboxylation and dehydrogenation reactions
What is eventually regenerated in the krebs cycle ?
Oxaloacetate
What is released in one cycle of Krebs ?
- 2 CO2
- 1 ATP
- 1 FADH2
- 3 NADH
What is released in two cycle of Krebs ?
- 4 CO2
- 2 ATP
- 2 FADH2
- 6 NADH
Why will two cycle of Krebs occur ?
Because there were originally 2 pyruvate molecules
Why are coenzymes required in respiration ?
To transfer protons, electrons and functional groups between the enzyme catalysed reactions
Which reactions are necessary in respiration ?
Redox reactions
Why are coenzymes really important in redox reactions ?
Without coenzymes transferring electrons and protons between these reactions many respiratory enzymes would be unable to function
What are the two main coenzymes in the Krebs Cycle ?
- NAD
- FAD
What do FAD and NAD do ?
They accept protons and electrons released during the breakdown of glucose in respiration
What are the differences between NAD and FAD ?
- NAD takes part in all of cellular respiration whereas FAD only takes part in the krebs cycle
- NAD accepts one hydrogen and FAD accepts two hydrogens
- NADH results in the synthesis of 3 ATP molecules whereas FADH2 results in the synthesis of 2 ATP molecules
Where are coenzymes normally derived from ?
Vitamins
Where do the hydrogens from reduced NAD and reduced FAD go ?
They are delivered to ETCs
Where are the electron transport chains in oxidative phosphorylation ?
They are present in the membranes of the cristae of the mitochondria
What do hydrogen atoms dissociate into at the cristae ?
Hydrogen ions and high energy electrons
What are electrons used for after they dissociate from hydrogen atoms ?
They are used in the synthesis of ATP by chemiosmosis
How is energy released at the cristae ?
During redox reactions as the electrons reduce and oxidise electron carriers as they flow along the ETC
What is energy used to create in oxidative phosphorylation ?
A proton gradient leading to the diffusion of protons through ATP synthase resulting in the synthesis of ATP
What happens at the end of the ETC ?
The electrons combine with hydrogen ions and oxygen to form water
What is the final electron acceptor in the ETC ?
- Oxygen
- The ETC cannot operate unless oxygen is present
What is oxidative phosphorylation ?
The phosphorylation of ADP to form ATP, this is dependent on electrons moving along ETCs, which is dependent on the presence of oxygen
What is substrate level phosphorylation ?
The production of ATP involving the transfer of a phosphate group from a short lived, highly reactive intermediate
How is oxidative phosphorylation different from substrate level phosphorylation ?
Oxidative phosphorylation couples the flow of protons down the electrochemical gradient through ATP synthase to the phosphorylation of ADP to produce ATP
Comparison of ATP production between aerobic respiration and fermentation
- Aerobic respiration is 38 molecules of ATP
- Fermentation is 2 molecules of ATP
What are obligate anaerobes ?
They cannot survive in the presence of oxygen
What category do obligate anaerobes fall under ?
Almost all of them are prokaryotes
What are facultative anaerobes ?
They synthesis ATP by aerobic respiration if oxygen is present, but can switch to anaerobic respiration in the absence of oxygen
Give an example of a facultative anaerobe
Yeast
What are obligate aerobes ?
They can only synthesise ATP in the presence of oxygen
What is fermentation ?
It is the process by which complex organic compounds are broken down into simpler inorganic compounds, without the use oxygen or the involvement of an ETC
How much ATP does fermentation produce ?
- Much less than aerobic respiration
- 2 ATP molecules compared to 38 ATP
How is the ATP in fermentation produced ?
Via substrate level phosphorylation
What is alcoholic fermentation ?
- It occurs in yeast and some plant root cells
- end products are ethanol and carbon dioxide
What is lactate fermentation ?
- It results in the production of lactate
- Carried out in animal cells
What does no oxygen at the end of the ETC lead to ?
- No final electron acceptor
- No synthesis of ATP as chemiosmosis stops
- NAD and FAD can no longer be regenerated
- Decarboxylation and oxidation of pyruvate stops
- Krebs cycle comes to a halt as there are no coenzymes
What does pyruvate act as in mammals ?
- It can act as a hydrogen acceptor
- Taking the H from NADH
What enzyme catalyses the formation of reduced NAD in lactate fermentation ?
Lactate dehydrogenase
What is the pyruvate converted to in lactate fermentation ?
Lactate (Lactic Acid)
What is regenerated in lactate fermentation ?
NAD
What can lactate be converted back into ?
Glucose
Where is lactate taken to ?
Liver
What are the two reasons that mean that lactate fermentation cannot occur indefinitely ?
- Reduced quantity of ATP produced would not be enough to maintain vital processes for a long period of time
- Accumulation of lactic acid causes the pH to fall and proteins to denature
- e.g. respiratory enzymes and muscle filaments
Is alcoholic fermentation a reversible process ?
No
What happens in alcoholic fermentation ?
- Pyruvate is converted into ethanal
- The ethanal then accepts a H from NADH to become ethanol
Which enzyme catalyses alcoholic fermentation ?
Pyruvate decarboxylase
What is regenerated in alcoholic fermentation ?
NAD
What does NAD act as once regenerated in alcoholic fermentation ?
It can continue to act as a coenzyme and glycolysis can continue
What are respiratory substrates ?
Substrates that can be broken down in order to release energy for the synthesis of ATP
Give an example of a respiratory substrate
Triglycerides
What happens to the glycerol before undergoing oxidative decarboxylation ?
- It is first converted to pyruvate
- Producing an acetyl group which is picked up by coenzyme A, forming acetyl CoA
What do the fatty acids in a triglyceride lead to the formation of ?
50 acetyl CoA molecules result in the synthesis of up to 500 ATP molecules
Compare the energy release between alcohol, carbohydrates, lipids and proteins
- Alcohol contains more energy than carbohydrates but less than lipids
- Proteins are roughly equivalent to carbohydrates
What is a respiratory quotient ?
It is calculated by dividing the volume of carbon dioxide released by the volume of oxygen taken in during respiration of that particular substrate
How is a respiratory quotient measured ?
Using a simple piece of apparatus called a respirometer
Why do lipids produce more ATP in respiration than carbohydrates ?
This is because they have a greater proportion of carbon-hydrogen bonds than carbohydrates
What do lipids need to break them down, given that they have more bonds ?
- They need more oxygen to break them down
- They release relatively less carbon dioxide
Relative RQ’s for carbs, proteins and lipids
- Carbs = 1
- Protein = 0.9
- Lipids = 0.7
How can we identify the type of substrate being used for respiration ?
By measuring the volume of oxygen taken in and carbon dioxide released, and calculating RQ
What is the RQ range during normal activity ?
0.8 to 0.9
What is the RQ range during anaerobic respiration ?
Increases above 1
What happens to proteins before they enter the respiratory pathway ?
They have to be hydrolysed to amino acids and then the amino acids have to be deaminated before they enter
How do deaminated amino acids enter the respiratory pathway ?
Via pyruvate
