Respiration Flashcards
What is the structure of mitochondria?
All mitochondria have an inner and outer phospholipid membrane.
The inner membrane is folded into christae, giving it a large surface area. Between the inner and outer membranes is the intermembrane space.
The matrix is enclosed by the inner membrane. It is semi rigid and gel like.
Where do most of the reactions in aerobic respiration take place?
In the mitochondria
What does the matrix consist of?
A mixture of proteins and lipids. It also contains looped mitochondrial DNA, mitochondrial ribosomes and enzymes.
How are mitochondria adapted for respiration?
- The inner mitochondrial membrane is folded into cristae, which increases the membranes surface area to maximise respiration.
- there are lots of ATP synthase molecules in the inner mitochondrial membrane to produce lots of ATP in the final stage of respiration.
- the mitochondrial matrix contains all the reactants and enzymes needed for the krebs cycle.
What coenzymes are used in respiration and what do they do?
NAD and FAD are used to transport hydrogen from one molecule to another.
Coenzyme A transfers acetate between molecules
What are the four stages in aerobic respiration?
Glycolysis
The link reaction
The Krebs cycle
Oxidative phosphorylation
What do all of the stages of aerobic respiration do?
The first three stages, glycolysis, the link reaction and the Krebs cycle, are a series of reactions. The products from these are used in the last stage, oxidative phosphorylation, to produce a large amount of ATP.
What is respiration?
The process whereby energy stored in complex organic molecules is used to make ATP. It occurs in living cells
What do cells use to respire?
All cells use glucose to respire, but organisms can also break down other complex organic molecules (e.g. Fatty acids, amino acids), which can then be respired
What is the first stage of aerobic respiration?
Glycolysis
Where does glycolysis take place and why?
Glycolysis happens in the cytoplasm of cells, because glucose can’t cross the outer mitochondrial membrane. Pyruvate, the product of glycolysis, can cross the outer mitochondrial membrane, so the rest of the reactions in respiration occur within the mitochondria.
What is the purpose of glycolysis?
To make pyruvate from glucose
What are the two stages of glycolysis?
Phosphorylation and oxidation
What happens in the first stage of glycolysis, phosphorylation?
Glucose is phosphorylated by adding a phosphate from a molecule of ATP. This creates one molecule of hexose phosphate and one molecule of ADP. Hexose phosphate is phosphorylated again, using another molecule of ATP, to form hexose bisphosphate and another molecule of ADP. Hexose bisphosphate is split up into two molecules of triose phosphate.
What happens in the second stage of glycolysis, oxidation?
The two triose phosphate molecules are oxidised (they each lose a hydrogen), forming two molecules of pyruvate. NAD accepts the hydrogen ions, producing two molecules of reduced NAD. 4ATP are produced, but 2ATP were used up during phosphorylation, so there’s a net gain of 2ATP
What are the products of glycolysis?
2 reduced NAD
2 pyruvate
2 ATP (net gain)
What is used up during glycolysis?
One molecule of glucose
2 ATP
2 NAD
What happens to the reduced NAD produced during glycolysis?
It goes to oxidative phosphorylation
What happens to the pyruvate molecules produced in glycolysis?
They are actively transported into the matrix of the mitochondria for use in the link reaction
What happens to the ATP produced during glycolysis?
It is used by the cell for energy
What is the purpose of the link reaction?
To convert pyruvate to acetate
What happens in the link reaction?
Pyruvate is decarboxylated, meaning one carbon atom is removed, in the form of carbon dioxide, and then oxidised, giving a hydrogen to NAD to make reduced NAD. This changes pyruvate to acetate
What happens to acetate formed in the link reaction?
It is combined with coenzyme A (CoA) to form acetyl coenzyme A (acetyl CoA). The acetyl CoA is then taken to the Krebs cycle.
What are the products of the link reaction?
Acetyl CoA
Carbon dioxide
reduced NAD
How many times does the link reaction take place for every molecule of glucose?
Two times, because two molecules of pyruvate are formed from every molecule of glucose
Where does the link reaction take place?
In the matrix of mitochondria
What is the function of the Krebs cycle?
To produce reduced coenzymes FAD and NAD, as well as ATP
What happens to the carbon dioxide produced in the link reaction of respiration?
It is released as a waste product
What happens to the reduced NAD produced in the link reaction of respiration?
It is used in oxidative phosphorylation
How many times does the Krebs cycle happen for every molecule of glucose?
Twice
What happens during the Krebs cycle?
- acetate is released from CoA, which returns to the link reaction
- acetate combines with oxaloacetate to form citrate
- citrate, which has 6 carbons, is decarboxylated, releasing a molecule of CO2, and dehydrogenated, reducing a molecule of NAD, to produce a 5 carbon molecule.
- the 5C molecule is then decarboxylated and dehydrogenated, producing one molecule of reduced FAD, two of reduced NAD and CO2.
- ATP is produced by the direct transfer of a phosphate group from an intermediate compound to ADP. This is called substrate level phosphorylation.
- Citrate has now been converted back into oxaloacetate
What are the products of the Krebs cycle?
Oxaloacetate 2CO2 ATP 3 reduced NAD 1 reduced FAD
What happens to the oxaloacetate produced in the Krebs cycle?
It is reused in the next Krebs cycle
How many carbons does oxaloacetate have?
4
How many carbons does acetate have?
2
What happens to the 2 molecules of carbon dioxide produced in the Krebs cycle?
They are released as a waste product
What happens to the molecule of ATP produced in the Krebs cycle?
They are used by the cell for energy?
How is ATP produced in the Krebs cycle?
By substrate level phosphorylation - a phosphate group is directly transferred from an intermediate compound to a molecule of ADP
What happens to the 3 molecules of reduced NAD produced by the Krebs cycle?
They are used in oxidative phosphorylation
What happens to the molecule of reduced FAD produced by the Krebs cycle?
It is used in oxidative phosphorylation
What is substrate level phosphorylation ?
When a phosphate group is directly transferred from one molecule to another
Where does the Krebs cycle take place?
In the mitochondrial matrix
What is the function of oxidative phosphorylation?
To make ATP using the energy carried by electrons, from reduced coenzymes (NAD and FAD)
What are the two processes involved in oxidative phosphorylation?
The electron transport chain and chemiosmosis
Where does oxidative phosphorylation take place?
Across the inner mitochondrial membrane, using enzymes embedded in the membrane
What happens during oxidative phosphorylation?
- hydrogen atoms are released from reduced NAD and reduced FAD, which are oxidised to NAD and FAD. The hydrogen atoms are split into protons (H+) and electrons (e-).
- the electrons move along the electron transport chain, which consists of 3 electron carriers. They lose energy at each carrier.
- this energy is used by the electron carriers to pump protons from the matrix into the intermembrane space.
- there is a concentration gradient of protons from the intermembrane space to the matrix.
- protons flow down their gradient back into the matrix, through ATP synthase enzymes.
- this flow drives the synthesis of ATP from ADP and Pi. This is chemiosmosis.
- in the mitochondrial matrix, at the end of the transport chain, the protons, electrons, and oxygen from the blood combine to make water. Oxygen is said to be the final electron acceptor.
At what stage in respiration is oxygen used?
At the end of oxidative phosphorylation oxygen is combined with electrons and protons to make water
What happens to reduced NAD and reduced FAD in oxidative phosphorylation?
They are oxidised to form NAD and FAD. The hydrogen atoms that are released from them are split into protons and electrons
What happens to electrons in oxidative phosphorylation?
They pass through the chain of electron carriers, losing energy at each carrier, and are then combined with protons and oxygen to make water
What happens to the protons in oxidative phosphorylation?
They are pumped through the electron carriers across the inner mitochondrial membrane into the intermembrane space, using energy lost by the electrons. They then flow down their concentration gradient through ATP synthase enzymes back into the membrane. This flow is chemiosmosis and drives the synthesis of ADP and Pi to make ATP. The protons then combine with electrons and oxygen to make water.
What is the final electron acceptor in oxidative phosphorylation?
Oxygen
What is the total expected yield of ATP molecules from respiration?
32 per molecule of glucose
What is the structure of ATP?
ATP is a phosphorylated nucleotide, consisting of adenine, a ribose sugar and three phosphate groups.
Why is ATP used as a universal energy currency of cells?
Because the bonds between the second and third phosphate groups contain a very high level of energy (30.6kJmol-1)
Why is the actual yield of ATP from respiration lower than the expected yield?
- some of the reduced NAD formed during the first three stages of aerobic respiration is used for other reduction reactions in the cell, not oxidative phosphorylation
- some ATP is used up by actively transporting substances into the mitochondria during respiration, e.g. Pyruvate, ADP and phosphate.
- some protons may pass through the inner mitochondrial membrane into the matrix without going through ATP synthase, so they are not used to make ATP.
How were artificial vesicles used to provide evidence for the theory of chemiosmosis?
Artificial vesicles were created from phospholipid bilayers to represent the inner mitochondrial membrane. Proton pumps from bacteria and ATP synthase were added to the vesicles membranes. The proton pumps were light activated, so when light was shone on the vesicles they started to pump protons. The pH inside the vesicles decreased - protons were pumped into the vesicles from outside. When ADP and Pi were added to the solution outside the vesicles, ATP was synthesised. This shows that a proton gradient can be used to synthesise ATP, but doesn’t show that it happens in mitochondria.
How does the discovery that the intermembrane space in mitochondria has a lower pH than the matrix provide evidence for chemiosmosis?
This shows that the intermembrane space has a higher concentration of H+ ions, so a proton gradient exists between the intermembrane space and the matrix.
How does placing mitochondria in solutions of different pHs provide evidence to support the theory of chemiosmosis?
Mitochondria were put in a slightly alkaline solution and left until the whole of each mitochondrion (matrix and intermembrane space) became pH8, so there was no proton gradient across the membrane. When these mitochondria were given ADP and Pi, no ATP was produced.
The mitochondria were placed in a solution of pH4 (higher concentration of protons). The outer membrane of the mitochondrion is permeable to protons, so they moved into the intermembrane space, creating a proton gradient across the inner mitochondrial membrane. In the presence of ADP and Pi, ATP was produced. This experiment shows that a proton gradient can be used in mitochondria to make ATP.
What are uncouplers and how were they used to provide evidence for the theory of chemiosmosis?
Uncouplers are substances that destroy the proton gradient across the inner mitochondrial membrane. An uncoupler was added to mitochondria, along with reduced NAD, ADP and Pi. No ATP was made. This experiment shows that a proton gradient is required to synthesise ATP in mitochondria.
What is anaerobic respiration?
A type of respiration that doesn’t use oxygen. Like aerobic respiration it starts with glycolysis. However it doesn’t involve the link reaction, the Krebs cycle or oxidative phosphorylation.
Why does anaerobic respiration happen?
In conditions where oxygen is absent the electron transport chain cannot function, so the Krebs cycle and the link reaction also stop. This leaves only glycolysis as a source of ATP. The reduced NAD generated in glycolysis must be reoxidised so that glycolysis can continue. This increases the chances of the organism surviving under temporary adverse conditions.
What are the two pathways for the reoxidation of reduced NAD in anaerobic respiration?
- alcoholic fermentation, which occurs in fungi, such as yeast, and plant cells.
- lactate fermentation, which occurs in animals.
What happens during lactate fermentation?
Reduced NAD from glycolysis transfers it’s hydrogen to pyruvate, to form lactate, or lactic acid. The reduced NAD is reoxidised to form NAD, which can act as a hydrogen acceptor for glycolysis to continue
What happens to the lactate produced during lactate fermentation?
It is carried away from cells in the blood to the liver. When more oxygen is available it can be converted back to pyruvate and used in aerobic respiration.
What happens if lactic acid is allowed to build up in cells?
It causes a reduction in the pH of the cells, which reduces enzyme activity in the muscles, causing them to become fatigued.
What happens during alcoholic fermentation?
Under anaerobic conditions in yeast cells, each pyruvate molecule is decarboxylated, releasing a CO2 molecule. This means ethanal is formed. Reduced NAD then transfers its hydrogen to ethanal to form ethanol and NAD. The NAD can then be used in glycolysis.
Why is the ATP yield from anaerobic respiration always lower than from aerobic respiration?
Because anaerobic respiration only includes one energy releasing stage, which only produces 2ATP per glucose molecule, compared to 32ATP from aerobic respiration
What is a respiratory substrate?
Any biological molecule that can be broken down in respiration to release energy is called a respiratory substrate.
What substances other than glucose are respiratory substrates?
Other carbohydrates, lipids and proteins
At what point in respiration do proteins and lipids enter to be respired?
At the Krebs cycle
What is a respiratory quotient?
The volume of carbon dioxide produced when that substrate is respired, divided by the volume of oxygen consumed, in a set period of time.
What is the equation to calculate the respiratory quotient of a respiratory substrate?
RQ=volume of CO2 produced/volume of O2 consumed
OR
RQ=molecules of CO2 produced/molecules of O2 consumed
How do you work out the respiratory quotient for a whole organism?
By finding the average of all of the respiratory quotients for all of the different molecules the organism is respiring, or by measuring the volume of oxygen consumed and the volume of CO2 released by the organism, and using the equation to find the respiratory quotient.
Why is knowing the respiratory quotient for an organism useful?
Because it tells you what kind of respiratory substrate the organism is respiring, and what kind of respiration (aerobic or anaerobic) it is using.
What is the respiratory quotient for humans under normal conditions, and what does this tell us?
The usual RQ for humans is between 0.7 and 1. This shows that some fats (lipids) are being used for respiration, as well as carbohydrates like glucose. Protein isn’t usually used by the body for respiration, unless there’s nothing else.
What does a respiratory quotient of higher than 1 mean?
That an organism is short of oxygen, and is having to respire anaerobically as well as aerobically
Why might a plant have a low respiratory quotient?
Because the CO2 released may be used for photosynthesis, and not measured.
What is the respiratory quotient for a lipid?
0.7
What is the respiratory quotient for proteins or amino acids?
0.9
What is the respiratory quotient for carbohydrates?
1
