Respiration Flashcards
Define cell respiration
Controlled release of energy from organic compounds to produce ATP
Explain why organisms need to respire
Provide energy in the form of ATP for:
- Active transport
- Anabolic reactions (e.g. building proteins from amino acids)
- Movement (e.g. cilia, flagella, muscles)
Write the word equation for aerobic respiration
Glucose + Oxygen → Carbon dioxide + Water
Write the symbol equation for aerobic respiration
C6H12O6 + 6O2 → 6CO2 + 6H2O
Where does aerobic respiration take place?
- Mitochondria
- Glycolysis occurs in cytosol
Describe the structure of the matrix
- Fluid found inside mitochondrion
- Contains enzymes needed in link reaction and Krebs cycle
What does the inner mitochondrial membrane contain?
Contains electron transport chain and ATP synthase (oxidative phosphorylation)
What is the cristae?
- Folds of inner mitochondrial membrane
- Increases surface area for oxidative phosphorylation
What does the outer mitochondrial membrane do?
Separates contents of mitochondrion from the rest of the cell
Describe how the structure of a mitochondrion is related to its function
- Intermembrane space between inner and outer membrane allows for a proton gradient to develop
- Cristae give large surface area for ATP synthesis
- ATP synthase generates ATP from ADP + phosphate
- Electron transport chains for generating a proton gradient
- Matrix contains enzymes for Krebs cycle
- Ribosomes and DNA for protein synthesis
What is phosphorylation?
- Transfer of a phosphate group to a molecule (e.g. hexose)
- Makes the molecule less stable and more reactive
- Prevents diffusion out of the cell
- Phosphate can be transferred from ATP or as inorganic phosphate (Pi)
List the stages of aerobic respiration
- Glycolysis
- Link reaction
- Krebs cycle
- Oxidative phosphorylation
What is the substrate in glycolysis?
Glucose
Where does glycolysis take place?
Cell cytoplasm
Outline the process of glycolysis
- Takes place in cytoplasm/cytosol
- Glucose is phosphorylated
- Two molecules of ATP are used
- Produces hexose bisphosphate
- Hexose sugar converted into two (3C) triose phosphate molecules (lysis)
- 3C molecules oxidised to form pyruvate
- Small net gain of two ATP
- Formed by substrate-level phosphorylation
- Net gain of two NADH (reduced NAD)
Summarise the link reaction
- Pyruvate produced by glycolysis is absorbed by mitochondrion
- Enzymes in matrix of mitochondrion remove hydrogen and carbon dioxide from pyruvate
- Removal of hydrogen is oxidation
- Removal of carbon dioxide is decarboxylation
- Whole process = oxidative decarboxylation
- Hydrogen accepted by NAD+ to form reduced NAD (NADH)
- Product is an acetyl group
- Acetyl group is attached to Coenzyme A to form Acetyl CoA
Where does the link reaction take place?
Mitochondrial matrix
From which substrate is the first carbon dioxide molecule released during cellular respiration?
Pyruvate
Outline the role of coenzyme A in aerobic respiration
- Binds to acetyl group
- Passes acetyl group to Krebs cycle
Outline the Krebs cycle
- Occurs in the mitochondrial matrix
- Series of enzyme controlled reactions that break down Acetyl CoA into CO2
- Acetyl group (2C) from Acetyl CoA combines with oxaloacetate (4C) to make citrate (6C)
- Citrate is decarboxylated and oxidised to give a 5C compound, CO2 and reduced NAD
(NADH) - Further decarboxylation and oxidation gives the 4C compound oxaloacetate, CO2, NADH,
reduced FAD (FADH2) and ATP - ATP produced by substrate-level phosphorylation
- Oxaloacetate combines with a new molecule of acetyl CoA and cycle starts again
What name is given to the removal of a hydrogen from a compound?
Dehydrogenation
Name one compound that undergoes dehydrogenation during the Krebs cycle
Citrate
Define substrate level phosphorylation
Production of ATP from ADP
- Via transfer of a phosphate group from a reactive intermediate
In which stages of respiration does substrate level phosphorylation occur?
- Glycolysis
- Krebs cycle
Explain the difference between substrate level phosphorylation and oxidative phosphorylation
Substrate level
- Direct transfer of phosphate group
- From a reactive intermediate
- Occurs in glycolysis and Krebs cycle
- Produces small amounts of ATP
Oxidative
- Requires electron transport, chemiosmosis and ATP synthase
- Inorganic phosphate added to ADP
- Produces large amounts of ATP
What are NADH and FADH2?
Coenzymes
What is the role of NADH and FADH2 in aerobic cell respiration?
- Electron carriers
- Provide electrons and H+ required for chemiosmosis
- Produced in glycolysis, link reaction and Krebs cycle
Where is the electron transport chain located?
Mitochondrial inner membrane (cristae)
What is the role of electron transport chain?
- Proteins in the inner mitochondrial membrane
- Energy from electrons used to pump protons into intermembrane space
- Establishes proton gradient across inner membrane
What is the role of ATP synthase?
- Enzyme located in inner mitochondrial membrane
- Energy released as protons diffuse down the gradient through ATP synthase
- ATP synthase converts ADP to ATP
What is the final electron acceptor in oxidative phosphorylation?
- Oxygen
- Combines with an electron and H+ ions to form water
Explain how oxidative phosphorylation occurs by means of chemiosmosis
- Electrons from NADH/FADH2 passed along electron transport system in inner membrane of
mitochondria - Energy released as electrons move from one carrier to next
- Carrier is oxidised as it loses an electron to the next carrier, which becomes
reduced - Energy released during electron transport causes proton pumping
- H+ pumped against concentration gradient from matrix to intermembrane space
- H+ provided by NADH and FADH2
- H+ diffuses down concentration gradient back through ATP synthase
- Passage of H+ through ATP synthase causes production of ATP from ADP + Pi
When is the majority of ATP produced during aerobic respiration?
- Oxidative phosphorylation
- Produces ~32 ATP molecules per 1 glucose molecule
What are the products of aerobic respiration?
- Carbon dioxide
- Water
Why does aerobic respiration yield fewer molecules of ATP than the theoretical maximum?
- Some ATP used to transport pyruvate into mitochondrion
- Some energy released in electron transport chain is not used to transport H+
- Not all the H+ movement back across membrane is used to generate ATP
- Not all the NADH is used to feed into the electron transport chain
When does anaerobic respiration occur?
When no oxygen is present
Which stage is common to both aerobic and anaerobic respiration?
Glycolysis
- Takes place in cytoplasm
- Does not require oxygen
- Small net gain of ATP
Define anaerobic respiration
- Doesn’t require oxygen
- Gives small yield of ATP from glucose
- Allows cellular processes to continue (e.g. active transport)
Products: - Lactate (humans)
- Ethanol + carbon dioxide (yeast)
Give the word equation for anaerobic respiration in animals
Glucose → Lactate
Describe what happens to pyruvate during anaerobic respiration in an animal cell
- Pyruvate produced by glycolysis
- Pyruvate accepts hydrogen from NADH
- Catalysed by lactate dehydrogenase
- NAD+ regenerated
- Allows glycolysis to continue
- Limited amount ATP can continue to be produced
- Pyruvate converted to lactate
- No oxygen to act as final electron acceptor
- Link reaction, Krebs cycle and oxidative phosphorylation cannot take place
Why is it necessary for NAD+ to be regenerated during anaerobic respiration in an animal cell?
- Limited amount of NAD+ in the cell
- Regeneration of NAD+ allows glycolysis to continue
- Some ATP can continue to be formed
Why can anaerobic respiration in animal cells not continue indefinitely?
- Reduced quantity of ATP produced not sufficient to maintain vital processes
- Lactic acid causes pH to fall
- Leads to proteins denaturing
- e.g. respiratory enzymes, muscle filaments
Where is lactate (lactic acid) converted back into glucose?
- Liver
- Carried there in the blood
What is required to convert lactic acid into glucose?
Oxygen
Define oxygen debt
The oxygen required to convert the lactic acid built up into glucose
Explain why anaerobic respiration produces less ATP than aerobic respiration
- In anaerobic respiration:
- Conversion of glucose into pyruvate during glycolysis occurs
- Produces 2 molecules of ATP (net)
- Only substrate level phosphorylation occurs
- Oxygen not available as final electron acceptor
- Pyruvate (animals) and ethanal (yeast) used to regenerate NAD+ for glycolysis
- Krebs cycle and oxidative phosphorylation do not occur
Give the word equation for anaerobic respiration in yeast
Glucose → Ethanol + Carbon dioxide
Describe the process of anaerobic respiration in yeast
- Non-reversible
- Pyruvate converted to ethanal
- Catalysed by pyruvate decarboxylase
- Ethanal accepts hydrogen atom from NADH
- Converts ethanal to ethanol
- NAD+ regenerated for glycolysis to continue
Why can anaerobic respiration in yeast cells not continue indefinitely?
- Ethanol is toxic to yeast cells
- Yeast unable to survive if levels rise too high
Explain why the anaerobic respiration pathway in animal cells can be reversed, but the anaerobic respiration pathway in yeast cells cannot
In animals:
- Pyruvate is converted lactic acid
- Can be reversed as no other product formed
- Lactate dehydrogenase enzyme can reverse the reaction
In yeast
- Pyruvate converted to ethanol and carbon dioxide
- Cannot be reversed as carbon dioxide is lost
- Decarboxylase enzyme cannot reverse the reaction
Describe the use of yeast in the baking industry
- Yeast is added to flour at the start of the baking process
- Aerobic respiration of yeast produces carbon dioxide
- Carbon dioxide bubbles help dough rise
Describe the use of yeast in the brewing and biofuels industry
- Fermentation
- Anaerobic respiration of yeast produces ethanol and carbon dioxide
- Yeast die when ethanol concentration reaches 15%
Define respiratory substrate
Molecule that can be used in respiration to produce ATP
What is the primary respiratory substrate?
Glucose
What other molecules can be used as respiratory substrates?
- Lipids
- Proteins
Explain how lipids can be used as respiratory substrates
Triglycerides hydrolysed to fatty acids and glycerol
- Fatty acids enter the Krebs cycle
- Glycerol converted to pyruvate
Explain how proteins can be used as respiratory substrates
- Hydrolysed into amino acids
- Amino acids deaminated in liver
- Remaining molecule enters respiratory pathway
- As pyruvate
- Process requires ATP
- Reduces net production of ATP
Why do lipids produce more ATP than glucose during respiration?
Lipids contain greater proportion of carbon-hydrogen bonds
Why aren’t fats and proteins used as the substrate in glycolysis?
- Lipids are harder to transport and digest (although will yield more energy per gram)
- Proteins release potentially toxic nitrogenous compounds when broken down
- Deamination and conversion to pyruvate requires ATP
How is the respiratory quotient calculated?
RQ = CO2 produced / O2 consumed
