Respiration Flashcards
Which Pi releases energy?
When the 3rd phosphate group detaches.
What do we need energy for?
Metabolism; movement; active transport; maintenance, repair and division; production of substances; homeostasis; activation of molecules.
What is the energy currency in cells?
ATP - adenosine triphosphate
What is the energy from respiration used for?
To synthesise more ATP.
Structure of ATP
Ribose sugar, adenine base, a phosphate group.
How are bonds broken in ATP?
Bonds are broken by ATPase and when broken, it releases large amounts of energy.
Equation for phosphorylation
ATP + H2O = ADP + Pi + Energy
Continual process and some body parts require more ATP.
Why is energy released?
Due to the resynthesis of ATP
The equation for respiration
C6H12O6 + 6O2 = 6CO2 + 6H2O
How are the phosphates detached?
Via a hydrolysis reaction - addition of water to break molecules down.
Why is ATP used to release energy instead of glucose?
The energy from ATP can be released more quickly in a simple hydrolysis reaction.
A smaller amount is closer to the amount required in cellular reactions.
Larger amounts of energy released would be more difficult to control.
The molecule’s easily moved around the cell but can’t leave the cell.
Phosphorylation
The addition of a phosphate
Metabolic processes
Building macromolecules such as proteins and polysaccharides.
Movement
Provides energy for muscle contraction.
Active Transport
Carrier proteins need the energy to change shape in the plasma membrane.
Activation in molecules
Allows enzyme catalysed reactions to occur more easily.
Coenzymes
Molecules that bind with a specific enzyme or substrate, helping to catalyse a reaction.
Breaking the bonds between coenzyme and product after a reaction is…
Crucial, otherwise coenzyme concentration will drop, limiting respiratory rate.
3 major coenzymes
NAD - nicotinamide adenine dinucleotide
CoA - Coenzyme A
FAD - flavine adenine dinucleotide
NAD
Accepts a hydrogen molecule, forming reduced NAD (NADH).
Used to regenerate ADP in the electron transport chain (ETC).
Coenzyme A
Aids the transition between glycolysis and the Krebs cycle, by converting pyruvate to acetyl coenzyme A.
FAD
Can accept hydrogen to form reduced FAD (FADH2).
Where does respiration occur?
Occurs in all living cells.
In eukaryotes, early stages of respiration occur in the cytoplasm.
The later stages are restricted to the mitochondria.
What does mitochondria possess?
Highly folded inner membranes; provision of an isolated optimum; have their own DNA and ribosomes.
Effect of highly folded inner membranes
Holds key respiratory proteins (includes the enzyme that makes ATP) over a large surface area.
Effect of provision of an isolated optimum
Maintains optimum conditions for respiration.
Effect of having own DNA and ribosomes
Can manufacture their own respiratory enzymes.
Describe how ATP acts as a supplier of energy to power metabolic reactions.
Hydrolysis of ATP to ADP + Pi
Name the immediate source of energy used to reform ATP from ADP molecules.
Glucose
Process of re-energising ADP into ATP molecules.
Phosphorylation
Explain in what way the ATP/ADP system can be likened to a rechargeable battery.
Alternates between high energy and low energy. The addition of phosphates recharges the ADP for cellular work.
Aerobic respiration.
Requires oxygen and produces carbon dioxide, water, and much ATP.
Anaerobic respiration.
Takes place in the absence of oxygen and produces lactate (in animals) or ethanol and carbon dioxide (in plants and fungi) but only a little ATP.
Aerobic respiration involves 4 stages:
Glycolysis, Link reaction, Krebs cycle, Oxidative phosphorylation (electron transport chain)
Glycolysis.
The splitting of the 6-carbon glucose molecule into two 3-carbon pyruvate molecules.
Link reaction.
3-carbon pyruvate is oxidised into carbon dioxide and acetylcoenzyme A - a 2-carbon molecule.
Krebs cycle.
Acetylcoenzyme A enters a cycle of redox reactions that produce ATP and a large number of electrons stored in reduced NAD and FAD.
Oxidative phosphorylation (ETC).
The electrons stored in reduced NAD from the Krebs cycle are used to generate ATP, with water as a waste product.
What stage is glycolysis in aerobic and anaerobic respiration?
Initial stage and occurs in the cytoplasm of all living cells.
Steps of glycolysis.
- PHOSPHORYLATION - Glucose (6C) is phosphorylated by 2 ATP to form phosphorylated glucose.
- LYSIS - The phosphorylated glucose splits into two molecules of triose phosphate (3C).
- OXIDATION - Hydrogen is removed from each molecule of triose phosphate and transferred to coenzyme NAD to form 2 reduced NAD.
- DEPHOSPHORYLATION - Phosphates are transferred from the intermediate substrate molecules to form 4 ATP through substrate-linked phosphorylation.
- PYRUVATE is produced as the end product of glycolysis which can be used in the next stage of respiration.
The overall yield from 1 glucose molecule undergoing glycolysis is therefore:
2 ATP; 2 reduced NAD; 2 pyruvate.
Role of coenzyme A.
Helps an enzyme carry out its function.
Consists of a nucleotide and a vitamin.
Link reaction - pyruvate from glycolysis enters the…
mitochondrial matrix by active transport.
Process of link reaction.
- Pyruvate is oxidised to form acetate, producing reduced NAD, and releasing a molecule of carbon dioxide.
- Acetate combines with CoA to produce acetyl coenzyme A.
What happens to acetyl coenzyme A prior to entering the Krebs cycle?
Acetyl coenzyme A reacts with a 4C compound to produce a 6C compound which enters the Krebs cycle, releasing coenzyme A.
Location of Krebs cycle.
Mitochondrial matrix.
During the Krebs cycle, what is generated?
3 reduced NAD, 1 reduced FAD and ATP through a series of redox reactions and substrate-level phosphorylation.
What is lost in the Krebs cycle?
Carbon dioxide.
What enters the Krebs cycle?
Other respiratory substrates; deaminated amino acids (with NH2) enter directly; acetates, from the breakdown of fatty acids from lipids, can enter the Krebs cycle via coenzyme A.
What does the Krebs cycle consist of? What is it also known as?
The citric acid cycle and consists of enzyme-controlled reactions.
Krebs cycle - process.
2 carbon - Acetyl CoA enters the circular pathway from the link reaction in glucose metabolism.
4C - oxaloacetate accepts the 2C acetyl fragment from acetyl CoA to form the 6 carbon (6C) citrate; CoA released in the reaction.
Citrate is then converted back to oxaloacetate through a series of redox reactions.
What is released in the decarboxylation of citrate?
Release of 2 CO2 as waste gas.
What is substrate-linked phosphorylation?
Phosphate is transferred from one of the intermediates to ADP, forming 1 ATP.
What do coenzymes do in photosynthesis and respiration?
Carry hydrogen atoms from one molecule to another.
Which is the most important coenzyme in respiration?
Works with dehydrogenase enzymes that catalyse the removal of hydrogen atoms from substrates and transfer them to other molecules involved in oxidative phosphorylation.
Significance of Krebs cycle.
Breaks down macromolecules into smaller ones.
Produces hydrogen atoms that are carried by NAD to the electron transport chain and provide energy for oxidative phosphorylation; leading to the production of ATP.
Regenerates 4C molecule that combines with acetyl coenzyme A, which would otherwise accumulate.
Source of intermediate compounds used by cells in the manufacture of other important substances.
Oxidative phosphorylation
Last stage of aerobic respiration.
Takes place at the inner mitochondrial membrane.
Results in the production of many molecules of ATP and production of water from oxygen.
The current model for oxidative phosphorylation is the chemiosmotic theory.
The model states that energy from electrons passed through a chain of proteins in the membrane (ETC) is used to pump protons (hydrogen ions) up to their concentration gradient into their intermembrane space.
The hydrogen ions are then allowed to flow by facilitated diffusion through a channel in ATP synthase into the matrix.
The energy of the hydrogens flowing down their conc gradient is harnessed resulting in phosphorylation of ADP into ATP by ATP synthase.
Process of oxidative phosphorylation.
Hydrogen atoms are donated by reduced NAD (NADH) and reduced FAD (FADH2) from the Krebs Cycle.
Hydrogen atoms split into protons (H+ ions) and electrons.
The high-energy electrons enter the electron transport chain and release energy as they move through the electron transport chain.
The released energy is used to transport protons across the inner mitochondrial membrane from the matrix into the intermembrane space.
A concentration gradient of protons is established between the intermembrane space and the matrix.
The protons return to the matrix via facilitated diffusion through the channel protein ATP synthase.
The movement of protons down their concentration gradient provides energy for ATP synthesis.
Oxygen acts as the ‘final electron acceptor’ and combines with protons and electrons at the end of the electron transport chain to form water.
The electron transport chain.
Made up of series of membrane proteins/ electron carriers.
Positioned close together allowing the electrons to pass from carrier to carrier.
The inner membrane of the mitochondria is impermeable to H+ ions so these electron carriers are required to pump the protons across the membrane to establish the concentration gradient.
What is the role of respiration?
To provide energy in the form of ATP to living cells.
Why can glycolysis take place in both types of respiration?
Doesn’t require energy.
Location of glycolysis.
Cytoplasm.
How many molecules of ATP are used in glycolysis?
2
Why is ATP required for glycolysis?
To activate glucose/ make glucose more reactive.
How many molecules of ATP are generated by glycolysis?
4
How many molecules of NADH are produced by glycolysis?
2
After glycolysis, what happens to pyruvate in animals cells during anaerobic respiration?
Converted to lactate with the addition of hydrogen from reduced NAD.
What happens to lactate after anaerobic respiration?
When oxygen becomes available, lactate is converted back to pyruvate or converted to glycogen in the liver.
What happens to pyruvate and reduced NAD in yeast cells during anaerobic respiration?
Pyruvate is converted to ethanol and carbon dioxide and reduced NAD is re-oxidised to NAD.
What is the net gain of ATP from one molecule of glucose during anaerobic respiration?
2 molecules.
What is the role of the Krebs cycle?
To generate reduced NAD and reduced FAD, which can then be used to transfer hydrogen atoms to the electron transport chain.
In addition to pyruvate, what other substances can be used to generate reduced coenzymes via the Krebs cycle?
Amino acids and fatty acids.
Why is the oxygen called the final electron acceptor?
Oxygen is the final substance that accepts electrons as they finish passing through the electron transport chain.
Write a definition of chemiosmosis.
The diffusion of ions through a partially permeable membrane which is linked to the generation of ATP.
When hydrogen atoms become available at different points during respiration, NAD and FAD…
Accept these hydrogen atoms.
When coenzymes gain hydrogen, they are…
Reduced.
Anaerobic pathways.
Some cells are able to oxidise the reduced NAD produced glycolysis so it can be used for further hydrogen transport.
This means that glycolysis can continue and small amounts of ATP are still produced.
Ethanol fermentation.
Reduced NAD transfers its hydrogens to ethanal to form ethanol.
1. Pyruvate is decarboxylated to ethanol, producing CO2.
2. Ethanal is reduced to ethanol by the enzyme alcohol dehydrogenase.
Ethanal - the electron acceptor.
Ethanol can’t be further metabolised - a waste product.
Lactate fermentation.
Reduced NAD transfers its hydrogens to pyruvate to form lactate.
1. Pyruvate is reduced to lactate by the enzyme lactate dehydrogenase.
Pyruvate - hydrogen acceptor.
The final product lactate can be further metabolised.
During exercise, lactate can…
Build up in muscles, causing cramp and muscle fatigue. Lactate must be oxidised back to pyruvate, to enter the link reaction, or be converted into glycogen in the liver.
During anaerobic respiration, one molecule of glucose generates…
2 molecules of ATP (by glycolysis).
