Flashcards
Energy transduction
Cards in this deck (11)
- 1What is bioenergetics?The study of energy transduction in cells - three different types of pathways for transferring different things
1. Metabolic pathways - transfer matter
2. Energy transduction - transfer energy
3. Signal transduction - transfer information - consists of cycles connected by regulatory interactions - no matter or energy is transferred - 2Why do cells you need energy and why can this be problematic?- Need energy to concentrate substrate molecules to a high conc in the cell at low concs in environment, but exclude toxin molecules, also need to form ordered structures e.g. DNA, proteins and cells structure
-Problem is reactions go in the opposite direction as those that would be thermodynamically favourable - need net order of system and surrounding to increase
- Solution is - energy coupling and if deltaG1 + deltaG2 < 0 the reaction will occur
- New problem is that the driving reaction will soon run out - so use a chain of coupling reaction linked to spontaneous delta G<0
- Plants use light energy, animals oxidise organic substrates, some bacteria oxidise inorganic substrate e.g. thiobacillus ferrooxidans oxidises ferrous iron and reduced sulphur compounds or notifying bacteria oxidise ammonia - 3What are intermediates in In energy metabolismThree main types - 1. Electrons, measured by redox potential
2. Protons - measured by proton motive force
3. Phosphorylated groups - measured by phosphorylation potential - deltaGp
- These are not themselves energy intermediates - but they take part in reactions that are coupled by enzymes to form chains to distribute the energy - 4What does Gibbs free energy tell us about reactions?-Measure of the amount of work a system can do - if measured in kJ/mol is often called the chemical potential
- G depends on concentration -as they internal energy changes when the conc changes: G= constant + RT ln[C]
so if a reaction turns C into D delta G = DeltaG0(D-C) + RT ln ([D]/[C])
- The 0 means the reaction is conducted under standard conditions of 1M of all reagents - but when protons are used, not useful to use 1M, instead use 10^-7 M protons, i.e. pH 7 - given simple deltaG0' and are measured at pure water concentration 55M
- The delta0' of ATP hydrolysis is -31 kJ/mol, but because of the high ATP/ADP ratio -the actual free energy change is about -60 kJ/mol
- The delta g for ATP synthesis is sometimes called the phosphorylation potential deltaGp - phosphate donors with more negative deltaG0' s can phosphorylated ones with more positive values - 5What is redox potential and what does it tell us about a reaction?The free energy change of redox reactions - i.e. reactions where electrons are transferred between molecules is quantified using redox potential - measure for the affinity of molecules for electrons - if large and positive, high affinity for e-s, oxidising agent - so electrons flow from low redox potential to high ones
Eh = E0 + Rt/nF + ln[ox]/[red]
- The standard redox potential E0 is measured in a standard state ( 25 degrees, 1M concs ) relative to the hydrogen electrode
Em is the Eh when concentration are equal
- Delta Eh = Eh acceptor - Eh donor - delta G= -Fx deltaEh will be negative - 6What is the proton motive force and what does it tell us about reactions?Expression of delta G in millivolts instead of kJ aka deltaP = -deltaμ/F = deltaΨ - (2.3RT/F)deltapH, where delta Ψ is the change in electric potential acrosss the membrane - defined by the p phase (phase in which protons are pumped) minus the N-phsae (phase from which protons are pumped) - so normally has positive value, delta pH is also P-N pH, normally has -ve value
- Value for 2.3RT/F is about 60 - most bioenergetic membranes have delta P of about 200 mV - 7How is energy obtained and stored in photosynthetic organisms?- Energy input is light - energy of a single photon of light= hv, v=c/λ, a mole of photons is an Einstein and the total energy available in 1 mole of light is given by Ngv=Nh/λ, where N is Avogadro's number
- At 680 nm, 176 kJ/ einstein = 1.82 eV
- Main energy storage in in many organisms is polymerised reduced substrates e.g. fat, starch, glycogen and protein- but pCr is rapidly accessible, short-term store of phosphorylated groups - 8How do you know what couples reactions will work?-Stoichometry is important - need overall delta G to be positive
- e.g. 2 photons of light (1.2 eV) are needed to move one electron up the transport chain from H20 to NADP - 5 protons are pumped across for each electron, but only need 3 or 4 protons to make 1 ATP - the rest of the energy is lost as heat - makes the reaction irreversible
- Most of mitochondrial respiration is coupled to ATP synthesis, but significant fraction (about 20%) is lost by proton leak - ATP made is used mainly be actinomysin ATPase, protein synthesis and plasma membrane sodium pump (which about 20% each) - contribution of these calculated either by inhibiting them and seeing the decrease in oxygen consumption or measuring the rate of the process and multiplying by the known ATP requirement - 9What other respiratory chains are there?- In plant mitochondria they use an outward facing complex I and an alternative oxidase pathway where o2 is reduced to water from electrons from quinone but without electron pumping - may allow for variable efficiency of energy coupling and heat production
- Non-synthetic bacteria - many different electron transport chains - some with unusual electron donors like H2 and FE(ii) and acceptors like nitrate or fumarate
- Microbial fuel cells rely on bacteria passing electron to the outside world to create a external circuit - electrons can be transferred by direct contact, pili or endogenous mediators - 10—
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- Biology (Lecture notes ) Flashcards on Energy transduction , created by Jenna Robinson on 13/05/2017.
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- Jenna Robinson
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