5.7 - Respiration Flashcards
Respiration def
The release of chemical potential energy form organic molecules inside mitochondria
What is ATP?
Adenosine Triphosphate
Uses of ATP and respiration
Used in active transport - sodium/potassium ion pump
Metabolic reactions
Protein synthesis
Endocytosis/pinocytosis/phagocytosis
Exocytosis - secretion of large molecules from cells
DNA Replication
Cell division
Movement
Activation of chemicals
Synthesis of large molecules, e.g. proteins such as collagen, etc
Why ATP is a good energy currency?
- ATP is relatively stable when in solution in cells
- ATP is readily hydrolysed by enzyme catalysis
- Whilst in solution, it can be easily moved from place to place within a cell
Anabolic reaction def
Metabolic reactions where large molecules are synthesised from smaller molecules
Catabolic reaction def
Metabolic reactions involving the hydrolysis of large molecules to smaller molecules
What is phosphorylation?
- When one or more phosphate groups are added to a molecule(e.g. ATP)
- Makes a molecule more unstable, so I easier to hydrolyse
What happens in glycolysis?
simple
- Anaerobic process
- Occurs in cytoplasm of the cell
- 10 reactions occur, each catalysed by a different enzyme, some with the help of the coenzyme, NAD.
- First stage of respiration, converts glucose to pyruvate
4 stages of respiration
What happens in them(simple)?
- Glycolysis - glucose(6C) is broken down to produce 2 molecules of pyruvate(3C)
- The link reaction/oxidative decarboxylation - pyruvate is dehydrogenated and decarboxylated and converted to acetate
- The Krebs Cycle - acetate is dehydrogenated and decarboxylated
- Oxidative phosphorylation - ADP is phosphorylated to AMP
Glycolysis mechanism(simple)
- Phosphorylation of glucose(6C) to hexose biphosphate
- Splitting each hexose biphosphate molecule into two triose phosphate molecules
- Oxidation of triose phosphate to 2 pyruvate molecules
What is NAD?
-NAD(Nicotinamode Adenine Dinucleotide) is an non-protein molecule that helps dehydrogenase enzymes to carry out oxidation reactions
In what stages of respiration does NAD function?
NAD oxidises substrate molecules during:
- Glycolyis
- The link reaction
- The Krebs Cycle
What is FAD?
- Flavine Adenine Dinucleotide
- It is a coenzyme involved in respiration
- More info needed
What are the three main stages of glycolysis?
- Phosphorylation
- Splitting the hexose biphosphate
- Oxidation of triose phosphate to pyruvate
Glycolyis full mechanism
Phosphorylation:
- One molecule of ATP is hydrolysed and the released phosphoryl group is added to glucose to make hexose Monophosphate
- Another molecule of ATP is hydrolysed and the phosphoryl group is added to the hexose phosphate to form a molecule of hexose bisphosphate
- The energy from the hydrolysed ATP molecules activated the hexose sugar and prevents it from being transported out of the cell
Splitting the hexose bisphosphate:
-Each molecule of hexose biphosphate is split into two three-carbon molecules, triose phosphate, each with a phosphate group attached
Oxidation of triose phosphate to pyruvate:
- Dehydrogenase enzymes, aided by coenzyme NAD, remove hydrogens from triose phosphate
- The two molecules of NAD accept the hydrogen atoms(protons and electrons) and become reduced
- At this stage, two molecules of NAD are reduced for every molecule of glucose undergoing glycolysis
- Also at this stage, four molecules of ATP are made for every two triose phosphate molecules undergoing oxidation by substrate level phosphorylation
OVERALL:
2 ATP produced
2NADH produced(reduced NAD)
2 pyruvate produced
Why does glucose undergo phosphorylation in glycolysis?
- Glucose is a hexose sugar, so contains six carbon atoms and is very stable.
- So it needs to be phosphorylated in order to become less stable so it can be broken down by hydrolysis into two three-carbon compounds
What are the products of glycolysis?
From each molecule of glucose, at the end of Glycolyis there are:
- Two molecules of ATP(net gain, as four were made, but two were used ‘kick start’ the process, so net gain is two molecule of ATP)
- Two molecules of reduced NAD
- Two molecules of pyruvate
What can pyruvate be used for after glycolysis?
- actively transported into mitochondria for link reaction (aerobic conditions)
- converted into lactate (anaerobic conditions)
- converted into ethanol (anaerobic conditions)
Hydrolysis of ATP
ATP —> ADP + Pi + H2O —> AMP + Pi + H2O—> Addnosine + Pi
Pi - phosphate group
How much energy does hydrolysis of ATP, ADP and AMP release?
ATP - 30.5kJ mol-1
ADP- 30.5kJ mol-1
AMP-13.8kJ mol-1
Where does aerobic respiration take place in the cells
Mitochondria
Individual structures in mitochondria
- Matrix
- Cristae
- Inner Membrane
- Outer Membrane
- Intermembrane space
- Stalked particles(ATP synthase)
Function of the matrix in mitochondria
The matrix is where the link reaction and Krebs cycle takes place
Matrix contains:
-Enzymes that catalyse stages of link reaction and Krebs cycle
-Molecules of coenzymes NAD and FAD
-Oxaloacetate - four carbon compound that accepts the acetyl group from the link reaction
-Mitochondrial DNA - some of which codes for mitochondrial enzymes and other proteins
-Mitochondrial ribosomes, which are structurally similar to prokaryotic ribosomes.
This is where proteins synthesis occurs
Function of outer membrane in mitochondria
-Contains proteins, some of which form channels or carriers that allow the passage of molecules, such as pyruvate, into the mitochondrion
Function of inner membrane in mitochondria
- Lipid bilayer in inner membrane is less permeable to small ions such as hydrogen ions(protons) than the outer membrane
- The folds, cristae, in inner membrane give a large surface area for the electron carriers and ATP synthase embedded in them
- Electron carriers are proteins arranged in electron transport chains
- Electron transport chains are involved in oxidative phosphorylation
Function of intermembrane space
- Between the outer and inner layers of the mitochondrial envelope - involved in oxidative phosphorylation
- Inner membrane in close contact with mitochondrial matrix, so the molecules of reduced NAD and FAD can easily deliver hydrogens to the electron transport chain
Function of cristae in mitochondria
Provides a large surface area for electron carrier proteins and ATP synthase
Outline events in the electron transport chain
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Info about ATP synthase/ ATPase
- Large
- Protrude from the inner membrane into the matrix
- Protons can pass through them
Structures in ATP synthase
- Proton channel - channel through centre of base piece that allows protons to move through
- Base piece - protrudes through phospholipid bilayer in inner mitochondrial membrane
- Stalk or axle - connects proton channel to headpiece
- Headpiece
Decarboxylation def
-Removal of a carboxyl group from a substrate molecule
Dehydrogenation def
-Removal of hydrogen atoms from a substrate molecule
Substrate-level phosphorylation def
Production of ATP from ADP and Pi during glycolysis and the Krebs cycle
Pyruvate info
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Link reaction mechanism
- Pyruvate is decarboxylated and dehydrogenated, catalysed by pyruvate dehydrogenase, which catalyses the sequence of reactions that occur during the link reaction
- No ATP is produced during this reaction
- The carboxyl group is removed and is the origin of some of the CO2 produced during respiration
- Decarboxylation and dehydrogenation of pyruvate produces and acetyl group (dehydrogenation and then decarboxylation)
- The acetyl group combines with coenzyme A(CoA) to become acetyl CoA
- The coenzyme NAD becomes reduced (==> 3ATP)
- Coenzyme A accepts the acetyl group and forms CoA acetyl
- CoA acetyl carries the acetyl group on to the Krebs cycle
Is ATP produced during the link reaction?
No ATP is produced
Outline simple mechanism of Krebs cycle
- Krebs cycle takes place in the mitochondrial matrix
- Krebs cycle is a series of enzyme-catalysed reactions that oxidises the acetate from the link reaction to two molecules of CO2
- All done while conserving energy by reducing the coenzymes NAD and FAD
- These reduced coenzymes then carry the hydrogen atoms to the electron transport chain on the cristae, where they will be involved in the production of many more ATP molecules
Krebs cycle mechanism
- The acetyl group released from acetyl CoA combines with a four-carbon compound, oxaloacetate
- This forms a six-carbon compound, citrate
- Citrate is dehydrogenation and decarboxylated
- This produces a five-carbon compound, one molecule of CO2 and one molecule of reduced NAD
- This pentose compound is further dehydrogenation and decarboxylated
- This produces a four-carbon compound, one molecule of CO2 and one molecule of reduced NAD
- This four-carbon compound combines temporarily with, and is then released from, coenzyme A.
- At this stage, substrate-level phosphorylation takes place, producing one molecule of ATP
- The four-carbon compound is dehydrogenated, producing a different four-carbon compound and a molecule of reduced FAD
- Rearrangement of the atoms in the four-carbon compound, catalysed by an isomerase enzyme, followed by further dehydrogenation, regenerate a molecule of oxaloacetate
- So the cycle can continue
- For every molecule of glucose there are two turns of the Krebs cycle
Products of link reaction
Reduced NAD - 2
Reduced FAD - 0
CO2 - 2
ATP - 0
Products of the Krebs cycle
Reduced NAD - 6
Reduced FAD - 2
CO2 - 4
ATP - 2
Chemiosmosis def
Flow of protons, down their conc gradient, across a membrane, through a channel associated with ATP synthase
Oxidative phosphorylation def
- The formation of ATP using energy released in the electron transport chain and in the presence of oxygen.
- It is the last stage in aerobic respiration
Where does oxidative phosphorylation take place?
Why?
- Takes place in the mitochondria, in the cristae
- This is because the folded cristae give a large surface area for the electron carrier proteins and the ATP synthase enzymes
Oxidative phosphorylation mechanism
- Reduced NAD and reduced FAD are reoxidised when they deliver their hydrogen atoms to the electron transport chain
- The hydrogen atoms released from the reduced coenzymes split into protons and electrons
- The protons go into solution in the mitochondrial matrix
Electron transport chain info
- Electrons from the hydrogen atoms pass along the chain of electron carriers.
- Each electron carrier protein has an iron ion at its core
- The iron ions can gain an electron, becoming reduced to Fe2+
- The reduced iron ion can then donate the electron to the iron ion in the next electron carrier in the chain, becoming deoxidised to Fe3+
- As electrons pass along the chain, they release energy, some of which is used to pump protons across the inner mitochondrial membrane, into the intermembrane space in the mitochondria
Proton gradient and chemiosomosis mechanism
- As protons accumulate in the intermembrane space, a proton gradient forms across the membrane
- Proton gradients generate a chemiosomotic potential that is also known as a proton motive force(PMF)
- They are a source of potential energy
- ATP is made using the energy of the proton motive force
- Protons cannot easily diffuse through the lipid bilayer of the mitochondrial membranes
- This is due to the outer membrane having a low degree of permeability to protons and the inner membrane is impermeable to protons
- Protons, though, can diffuse through the protein channels associated with ATP synthase enzymes that are in the inner membrane.
- As protons diffuse down their conc. gradient through these channel, the flow of protons causes a conformation shape change in the ATP synthase enzyme
- This change allows ADP and Pi to combine, forming ATP.
- This flow of protons is known as chemiosmosis.
- It is coupled to the formation of ATP
- Oxygen is the final electron acceptor
- It combines with electrons coming off the electron transport chain and with protons, diffusing down the ATP synthase channel, forming water, equation below:
- 4H+ + 4e- +O2 —> 2H2O
-Oxidative phosphorylation can produce 28 molecules of ATP per molecule of glucose
From 10 molecules of reduced NAD(25 ATP) and two molecules of reduced FAD(3ATP)
Why is oxidative phosphorylation oxidative?
ATP is formed in the presence of oxygen
Oxidative phosphorylation full mechanism better(?)
- Oxidative phosphorylation occurs upon the cristae
- NADH from the Krebs cycle and Glycolyis is oxidised by complex 1 to release electrons
- The electrons are passed along the chain of carrier proteins - Fe3+ ions
- Through a series of Redox reaction
- Electrons are then passed to the final electron acceptor oxygen
- 1/2O2 + 2H+ + 2e- —> H2O
- The energy of the redox reactions is used to shuttle protons from the matrix and into the intermembrane space
- This builds up a proton gradient
- The proton gradient drives ATP synthesis via ATP synthase
- 3H+ ions need to cross ATP synthase to generate 1 ATP
- ATP is made using the energy of the proton motive force
What is chemiosmosis?
- The creation of the chemical proton gradient in the intermembrane space
- Osmosis of protons across this gradient?
Why is cyanide a respiratory inhibitor?
- Cyanamide ions are CN-
- It acts as a dissipated of the protein gradient
- They can bind to the Fe3+ ions in the electron transport chain
- So electrons cannot bind to the Fe3+ ions
- Irreversible change
- So the electron transport chain breaks down, and aerobic respiration cannot occur
- Oxidative phosphorylation cannot occur in the mitochondria anymore
Mitochondrial diseases info to put here
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How many ATP is gained per stage of respiration theoretically?
Glycolysis - 2
The link reaction - 0
The Krebs cycle - 2
Oxidative Phosphorylation- 28
Total - 32 molecules of ATP produced per molecule of glucose
Why is the theoretical yield of ATP usually lower per molecule of glucose?
(2 Marks)
-Yield of ATP per glucose molecule is closer to 30 ATP molecules
This is because:
-Some ATP is used to actively transport pyruvate into the mitochondria
-Some ATP is used in a shuttle system that transports reduced NAD, made during glycolysis, into mitochondria
-Some ATP used to actively transport H+ ions from reduced NAD, formed in glycolysis, into the mitochondrion
-Not all the H+ ion movement in electron transport chains is used to generate ATP
-Not all the reduced NAD is used to feed into the Electron Transport Chain
-Some protons may leak out through the outer mitochondrial membrane
What is anaerobic respiration?
Respiration where oxygen is absent
What does ETC stand for?
Electron Transport Chain
What happens in respiration in the absence of oxygen?
3/4 Marks
-Oxygen cannot act as the final electron acceptor at the end of oxidative phosphorylation
-Protons diffusing through channels associated with ATPase are not able to combine with electrons and form water
-The concentration of protons increases in the matrix and reduces the proton gradient across the inner mitochondrial matrix
-Oxidative phosphorylation ceases
-Reduced NAD and reduced FAD are not able to unload their hydrogen atoms and cannot be reoxidised
-The Krebs Cycle stops
-The Link Reaction stops
-
Two different metabolic pathways to reoxidise reduced NAD
- Fungi
- Such as yeast, and plants use the ethanol fermentation pathway
- Mammals:
- Use the lactate fermentation pathway
What stage of respiration occurs in the absence of oxygen?
Glycolysis
Ethanol fermentation pathway
- Each molecule of pyruvate produced during glycolysis is decarboxylated and converted into ethanal
- This stage is catalysed by pyruvate decarboxylase, with a thiamine disphosphate coenzyme bound to it
- Ethanal accepts hydrogen atoms from reduced NAD, becoming reduced to ethanol
- The enzyme ethanol dehydrogenase catalysed this reaction
- Reduced NAD is re-oxidised and made available to accept more hydrogen atoms form triose phosphate,
- This allows Glycolyis to continue
Lactate fermentation pathway mechanism
What organism does it occur in?
-Occurs in mammals
- Pyruvate produced during Glycolyis accepts hydrogen atoms from the reduced NAD, also made during glycolysis
- Lactate dehydrogenase catalysed the reaction - There are two outcomes:
- Pyruvate is reduced to lactate
- The reduced NAD becomes reoxidised - Reoxidised NAD can accept more hydrogen atoms from triose phosphate during Glycolyis
- Glycolyis can continue to produce enough ATP to sustain muscle contraction for a short period
What can happen to the lactate produced during anaerobic respiration when more oxygen is abundant?
- Converted to pyruvate, which may enter the Krebs Cycle via the link reaction
- Recycled to glucose and glycogen
What would happen if lactate wasn’t removed from the muscle tissues?
- pH would be lowered
- This would inhibit action of many enzymes involved in glycolysis and muscle contraction
Why can’t protons leave the intermembrane space?
Outer membrane has low permeability to H+ ions
Benefits of anaerobic respiration to an organism
All takes place in lack of oxygen
- ATP is being produced
- NAD is recycled and can be used again
- Allows glycolysis to continue in lack of oxygen
Anaerobic respiration in yeast - simple
Pyruvate is converted into ethanol in anaerobic respiration
- Glucose undergoes glycolysis and is converted to pyruvate
- Pyruvate is decarboxylated to form ethanal - catalysed by pyruvate decarboxylase
- NADH donates hydrogens atoms to ethanal
- Removal of hydrogen atoms is catalysed by ethanol dehydrogenase
- NAD+ is regenerate and can be reused in further glycolysis reactions in the cell
Factors that could affect the size of a yeast population
- sugar/glucose conc. - as it is ides up amount decreases and levels could fall too low to allow anaerobic respiration
- production of ethanal could cause pH to fall too low - enzymes in yeast could denature
- high ethanol concentration could inhibit or damage yeast
Why is ethanol a primary metabolite of yeast?
- Ethanol is produced by yeast in anaerobic respiration all of the time
- Production of ethanol increases as heat population increases
Overall reaction for lactate fermentation
Glucose —> lactate + 2ATP
Overall reaction for ethanol fermentation
Glucose —> ethanol + 2CO2 + 2ATP
How many ATP can be made from 1NADH in the ETC?
3 ATP ( protons)
How many ATP can be made from 1FADH2 in the ETC?
2 ATP
Enzymes involved in lactate fermentation
- lactate dehydrogenase
Enzymes involved in ethanol fermentation
- Pyruvate decarboxylase
- Ethanol dehydrogenase
Why is yeast a facultative anaerobic?
- It can respire anaerobically in the presence of oxygen or can switch to fermentation if oxygen is not present
- yeast reproduce faster, though, during aerobic respiration, as more ATP is produced
Substrates that can be used in respiration
- process by which they are used
- carbohydrates - glycogen can be hydrolysed
- lipids - hydrolysed
- protein - deamination
Which substrates provide the most energy/ATP from respiration?
- Lipids
- Proteins
- Carbohydrates
Which substrate can only be used in the brain and erythrocytes?
- Glucose from carbohydrates
How is glucose stored?
- Glycogen in the liver in animals
- stored as starch in plants
Why is glycogen a good store of energy?
- Highly branched - easy to hydrolyse branches - quick release of energy
- Compact - more glycogen can be stored inside cells - more energy
Mechanism of lipid oxidation for ATP production in aerobic respiration
- Some energy from the hydrolysis of one molecule of ATP to AMP is produced
- This energy is used to aid the combine of each fatty acid with CoA
- Fatty acid CoA complex is transported to the mitochondrial matrix
- It is broken down into two-carbon acetyl groups, each attached to CoA
- The beta-oxidation pathway generates NADH and FADH2
- The acetyl groups are released from CoA and
- They enter the Krebs cycle by combining with the four-carbon oxaloacetate
- For every acetyl group oxidised in the Krebs cycle, the products are:
- 3 NADH
- 1 FADH2
- 1 ATP by substrate level phosphorylation
Products of one acetyl group in oxidation of one lipid molecule for ATP production
For every acetyl group oxidised in the Krebs cycle, the products are:
- 3 NADH
- 1 FADH2
- 1 ATP by substrate level phosphorylation
Protein in respiration mechanism
- starving effect on proteins in respiration?
- Amino acids are deaminated in the liver
- excess amino acids are removed in the kidneys
- the rest of the amino acids, a keto acid, entered the respiratory pathway as:
- pyruvate
- acetyl CoA
- oxaloacetic acid that enters Krebs cycle
- During fasting or prolonged exercise, there is insufficient amount of glucose or lipids for respiration
- protein from muscle can be hydrolysed to amino acids that can then be respired
- these amino acids can be converted to pyruvate or acetate and enter the Krebs cycle
Effect of number of hydrogen atoms in the molecule on energy value in respiration?
The greater the number of hydrogens in a molecule, the greater the energy value in respiration/ATP production
- as more hydrogens/protons can be donated to the ETC
Respiratory quotient
The ratio of volumes of oxygen absorbed to carbon dioxide being given off in respiration
What does respiratory quotient indicate?
Indicates which respiratory substrate is being resourced
Energy values of different substrates
Lipids -
Glucose/carbs -
Proteins/amino acids -
Respiratory quotient equation
CO2 produced/O2 consumed
Respiratory quotient values of different substrates
Glucose - 6/6 = 1
Lipids - 16/23 = 0.7
Proteins - 4/5 = 0.8
What does RQ value greater than 1 indicate?
- Indicates that some aerobic respiration is taking place
- Shows that more CO2 is being produced than O2 is being consumed
Which tissues can use lipids as a substrate for respiration?
All but RBCs and brain
- mostly muscles (including cardiac)
Pros and Cons of ATP
Pros:
- Single step hydrolysis
- As it is a reaction to release energy - so needs to be fast
- Release 30.5kJ mol-1
- This is just right for metabolic processes
- Can donate phosphate groups to enzymes and other molecules - activating them
- Can be regenerated from ADP and Pi
Negatives:
- Cannot be stored
Humans synthesis more than their body mass of ATP each day. Explain why it is necessary for them to synthesise such a large amount of ATP.
(2 Marks)
- ATP is unstable
- ATP cannot be stored
- Named process, (e.g. exocytosis) uses ATP
- ATP only release a small amount of energy at a time
Why is anaerobic respiration/ethanol fermentation important for the plant cell.
- (Extra) What are the products of this process?
(3 Marks)
- Releases NAD, to accept more Hydrogen
- This allows glycolysis to continue
- Some ATP can be available for cellular processes, e.g. active transport, exocytosis, protein synthesis, cell division, etc.
- May be useful in situation where there is low oxygen supply
Products:
- 2CO2
- 2x ethanol - 2C2H5OH
Suggest a reason for the difference in the rate of respiration between soaked and dry pea seeds.
- Reactions require an aqueous medium - they need to take place in solution
- Enzymes and substrates can move to collide in soaked seeds
- Soaked seeds need more ATP for protein synthesis, other metabolic reactions, etc.
What properties of the mitochondrial matrix allow chemiosmosis to occur?
(2 Marks)
- Mostly impermeable to H+ ions
- Large surface area for ATPase for oxidative phosphorylation
Explain why the incomplete breakdown of glucose in anaerobic respiration produces less ATP than aerobic respiration.
(5 Marks)
- In anaerobic respiration:
- One molecule of glucose is converted into two molecules of pyruvate
- This produces a net amount of 2 ATP
- This ATP is produced via substrate level-phosphorylation
- Oxygen is not available to act as the final electron acceptor in anaerobic conditions
- So Link reaction, Krebs cycle and Oxidative phosphorylation cannot occur
- Therefore, pyruvate undergoes the lactate fermentation pathway
- Pyruvate is converted into ethanal by pyruvate dehydrogenase
- Ethanal is then reduced by ethanal dehydrogenase into lactate
- This reoxidises and regenerates the NAD coenzymes
- So they can be reused in Glycolyis
- This allows Glycolyis to continue
Describe the role of ATP in the cell with reference to its structure
- ATP is the universal energy currency
- Phosphate groups can be removed by hydrolysis
- This release 30.5kJ of energy (13.8 when AMP produced)
- Energy released for metabolic processes, e.g. active transport, endococytosis, cell division
- ADP can attach a phosphate during respiration in substrate level-phosphorylation
- Energy released in small packets to prevent cell damage
Chronic fatigue syndrome (CFS) is a condition in which symptoms vary from individual to individual.
It is thought that a number of different malfunctioning processes can contribute to this condition in an individual.
CFS can affect every system in the body and is identified by symptoms that include fatigue, muscle weakness and aching muscles.
(i) It has been suggested that, in the cells of people with CFS, pyruvate may not be transferred into the mitochondria efficiently.
Outline the consequences of an inefficient transfer of pyruvate into mitochondria and link this to the symptoms of CFS stated above.
(3 Marks)
- Less pyruvate for link reaction
- Less Acetyl for the Krebs Cycle
- Less efficient oxidative phosphorylation
- Less ATP production for:
- Muscle contraction
- Resulting in muscle weakness
- For mental processes
- Anaerobic respiration takes place
- Lactate produced
- Causes a decrease in pH
- Causes aching muscles
Insects use glucose to generate ATP.
Outline the processes involved in the generation of ATP through chemiosmosis.
(6 Marks)
- occurs in mitochondria / on membrane
- involves inner membrane and matrix
- involves movement of hydrogen across membrane
- use of enzyme / channel protein / ATP synthase
- Hydrogen ions / H+ ions pumped out of matrix across membrane into intermebrane space
- H+ gradient is created
- proton motive force is created
- H+ ions pass from high concentration in matrix to low concentration in intermembrane space
- H+ ions pass through ATP Synthase
- ATP is produced when ADP and Pi are joined by conformational shape change of ATP synthase
- some H+ ions leak back into the matrix - process is not completely efficient
