TOPIC K: RESPIRATION Flashcards
What is the role of ATP?
ATP is an instant source of energy found in all living cells and is therefore known as the universal energy carrier or energy currency in living organisms.
Energy released during respiration is stored in the form of ATP molecules.
What is the structure of ATP?
ATP consists of a ribose sugar, an adenine base and 3 phosphate groups.
What are the properties of ATP?
ATP is soluble and can transport chemical energy to energy consuming processes anywhere within the cell.
Hydrolysis of ATP requires the addition of water and releases energy, converted to ADP and inorganic phosphate (Pi)
Phosphorylation of ADP can form ATP. This reaction releases water and is known as condensation. The enzyme that catalyses this is called ATP synthase, ADP is phosphorylated with Pi to form ATP.
What is the role of Nicotinamide Adenine Dinucleotide (NAD) and Flavin Adenine Dinucleotide (FAD)?
NAD and FAD are coenzymes to dehydrogenases involved in cellular respiration. Their ability to exist in the oxidised or reduced state allows them to function as proton and electron carriers. The reduced form is more energetically valuable.
What is NAD?
Nicotinamide adenine dinucleotide
During aerobic respiration, glucose is oxidised by a series of dehydrogenation reactions.
At each of these reactions in glycolysis, link reaction and Krebs cycle , protons and electrons are released and transferred to oxidised NAD (NAD+) to form reduced NAD. (NADH + H+)
What is FAD?
Flavin adenine dinucleotide.
During aerobic respiration, glucose is oxidised by a series of dehydrogenation reactions.
At each of these reactions in the Krebs cycle, protons and electrons are released and transferred to oxidised FAD (FAD) to form reduced FAD (FADH2)
What is the energy investment phase in glycolysis?
- Activation of glucose occurs to make it more chemically reactive.
Phosphorylation of glucose using ATP
Glucose —> Glucose-6-phosphate
Catalysed by hexokinase - Isomerisation of G6P to fructose-6-phosphate
- Phosphorylation of F6P using ATP
- F6P –> Fructose-1-6-bisphosphate
- Catalysed by phosphofructokinase - Cleavage of F16Bp into 2 triose phosphate which are dihydroxyacetone phosphate and glyceraldehyde-3-phosphate
- Isomerisation of dihydroxyacetone phosphate into glyceraldehyde-3-phosphate.
- At the end of step 5, 2 molecules of glyceraldehyde-3-phosphate have been formed from a single glucose molecule.
What is the energy payoff phase?
Subsequent conversion of each GALP to pyruvate via multiple steps: Generate 2ATP via substrate-level-phosphorylation
Releases protons and electrons via dehyrogenation which are transferred to 1 oxidised NAD to form 1 reduced NAD.
Since 2 molecules of GALP is formed from 1 glucose molecule, therefore, 2 pyruvate, 4ATP 2 reduced NAD are produced per glucose molecule.
What is substrate level phosphorylation?
Mode of ATP synthesis whereby an enzyme transfers a phosphate group from a substrate molecule to ADP.
Occurs in cytoplasm (during glycolysis) and in the mitochondrial matrix during Krebs cycle
Only a small amount of ATP is generated by SLP compared to oxidative phosphorylation.
What occurs during the link reaction?
1) Decarboxylation
Carboxyl group of pyruvate is removed and carbon dioxide is released.
First carbon dioxide produced from respiration
2) Oxidation (Dehydrogenation)
Remaining 2C molecule undergoes oxidation via dehydrogenation by transferring protons and electrons to oxidised NAD, therefore converting it to reduced NAD.
Acetate CH3COO- is produced
3) Addition of Coenzyme A (CoA)
Coenzyme A is attached to acetate to form acetyl-CoA.
What is the organisation of the electron transport chain (ETC)?
The ETC is composed of a collection of electron carriers embedded in the inner mito membrane.
Extensively folded inner mito membrane increase surface area to provide space for thousands of copies of the chain in each mitochondrion.
Electron carriers are numbered I through IV in decreasing levels of free energy.
What are the processes in the electron transport chain?
Reduced NAD and FAD transfer high energy protons and electrons to the ETC for synthesis of ATP.
Electrons are passed along the ETC from one electron carrier to the next, each with an energy level lower than the one preceeding it.
They alternate between reduced and oxidised state as they accept and donate electrons.
The last electron carrier passes the electrons to oxygen, which functions as the final proton and electron acceptor to form water, catalysed by CYTOCHROME OXIDASE
Oxidised NAD and FAD are regenerated in the process.
What is chemiosmosis?
As the electrons are passed from one electron carrier to the next, energy is released to pump protons from the matrix of the mitochondrion into the intermembrane space.
High concentration of H+ in the intermembrane space leads to a steep electrochemical proton gradient leads to proton motive force.
inner mito membrane is impermeable to H+, allowing it to be established.
Stalked particles each containing ATP synthase are embedded on inner mito membrane. H+ diffuses through them, down the electrochemical proton gradient back into the matrix.
This provides enough energy to synthesise ATP by the phosphorylation of ADP with Pi
What happens during alcoholic fermentation?
Pyruvate is converted into ethanol
Carbon dioxide is released from a pyruvate to produce acetaldehyde, catalysed by a decarboxylase.
Acetaldehyde is reduced to ethanol by reduced NAD catalysed by alcohol dehydrogenase. Thus oxidation of reduced NAD takes place and regenerates oxidised NAD, allowing glycolysis to continue.
What is lactate fermentation?
Pyruvate is reduced directly to lactate by reduced NAD. This occurs in a single step catalysed by lactate dehydrogenase.
Lactate has to be removed by the muscle cells to prevent muscle fatigue. Lactate accumulation can be hazardous to muscle tissue as it is acidic.
As lactate is a waste product which still contains a lot of energy, it is reconverted to pyruvate in the liver when oxygen supply is restored.
