ATP synthesis Flashcards
What are bioenergetics?
Quantitative study of energy transduction occurring in living cells
Study of the nature and function of the chemical processes that are reponsible for these energy transductions
What is the first thermodynamics?
First law states – for any physical or chemical change, the total amount of energy in the universe remains constant
Therefore energy cannot be created or destroyed but it can be converted from one form to another
What is free energy change? (deltaGibbs)
Gibbs free energy (G) is the amount of energy in a system available to do work
Free energy changes derive from -
Changes in heat content (detlaH) = enthalpy change
Changes in the state order (detlaS) = entropy change
DeltaG = deltaH – T. deltaS
What is meant by exergonic?
If deltaG is –ve, energy is liberated and the reaction is said to be exergonic
A reaction can occur spontaneously only if deltaG is –ve
(detla G = difference between substrate free energy and product free energy)
What is meant by endergonic?
If deltaG is +ve, the reaction is said to be endergonic
For the reaction to occur it will require an energy input
What is deltaG at equilibrium?
A system is at equilibrium and no net change can take place if deltaG is 0
The deltaG of a reaction is independent of the path of transformation
DeltaG provides no information on the rate of reaction
Why do we need energy?
Living organisms require contiual input of free energy as many biological processes are endergonic:
Mechanical work eg muscle contraction using myosin and actin require conversion of ATP to ADP
Active transport eg neurotransmission of Na+/K+ ECF/ICF
Synthesis of complex biomolecules from simple precursers
Also signal transduction (environmental responses) generation of light (fire flies) and electricity (eels)
How is energy derived from the environment by living organisms? (2 types)
Phototrophs – obtain energy by trapping light (photosynthesis)
Chemotrophs – obtain energy by oxidation of food stuffs (catabolism)
What is a chemoorganotrophs?
Extract energy from organic compounds by oxidation
Eg glucose + 6O2 – 6CO2 + 6H2O
Glucose oxidised to Co2 and water – releasing energy
Fats (9kcal/g), alcohol (7kcal/g), carbs and proteins (4kcal/g)
Why is controlled extraction of energy from food?
Regulation and control
Dont want to release all the energy at once
Dont want to increase body temperature excessively
Coupled reaction are more efficient
Not very mobile around body
Small carrier molecules are better
What are the 3 stages of energy extraction from food?
Extraction of energy from food
Stage 1 – large molecules broken down into smaller units. No useful energy captured
Stage 2 – small molecules degraded into a few simple units that play a role in central metabolism. Some ATP generated
Stage 3 – ATP produced from the complete oxidation of simple units by the final common pathways for oxidation of fuel
What are redox reactions? What is an electron donor and what is an electron acceptor?
As an organic compound is degraded (oxidised) electrons flow through intermediates to oxygen (the final electron acceptor) or are used to reduce other cellular components
In a redox reaction -
The electron donor is the reducing agent and is oxidised
The electron acceptor is the oxidising agent and is reduced
Redox reactions involve electron flow which can be made to do work just as they do in an electric circuit
What are the 4 biological redox reactions?
1) Direct electron transfer eg
Fe2+ + Cu2+ = Fe3+ + Cu+
2) Direct transfer of hydrogen ions eg
AH2 + B = A + BH2
3) Direct combination with oxygen as with mono-oxygenase reactions eg
R-CH3 + ½ O2 = R-CH2 OH
4) The most common involve dehydrogenation
What do dehydrogenases do?
Dehydrogenases oxidise organic compounds by abstracting 2H+ and 2e- and passing them to a mobile carrier in biodegration and energy abstraction (ie respiration)
Dehydrogenases can reduce organic compounds by adding 2H+ and 2e- from a mobile electron carrier typically in biosynthetic pathways
What is NADH?
Electron carriers
NADH – produced in catabolic reaction and by TCA cycle
Used in generation of ATP by OxPhos
Usually found inside the mitochondria
What is NADPH?
NADPH – produced by PPP
Used primarily for reductive biosynthesis (eg FA synthesis)
Usually found in the cytoplasm
What is FADH2?
FADH2 – produced in catabolic reactions by TCA cycle
Used in the generation of ATP by OxPhos (generates less energy than NADH)
Usually found inside the mitochondria
What is ATP?
ATP-energy currency of the cell
Any living organism must generate ATP to live – when they stop producing ATP they die
ATP is an energy rich molecule with high phosphoryl transfer potential
It contains 2 phosphoanhydride bonds on its triphosphate unit
What are the 2 energy producing equations using ATP? How is free energy linked to this?
ATP + H2O – ADP + Pi + energy
ATP + H2O – AMP + PPi + energy
Free energy (delta gibbs) is negative so thermodynamically unstable.
However kinetically stable (in absence of a catalyst, breakdown is very slow)
For ATP hydrolysis – deltaG = -7.3kcal mol-1 or –10.9kcal mol-1
What are the 3 unfavourable reactions that ATP drive?
Reaction 1 – glucose + Pi – G-6-P
DeltaG = +3.3kcal/mol
Reaction 2 – ATP + H20 – ADP + Pi
DeltaG = -7.3kcal/mol
Net reaction – glucose + ATP – G-6-P + ADP
DeltaG = -4kcal/mol
What is ATP-ADP cycle?
Fundamental mode of energy exchange in biological systems
ATP principle intermediate donor of free energy in biological systems rather than long-term storage form
Consumed within minutes of formation, very high turnover
Around 50Kg of ATP consumed in 24hr period
What is substrate level phosphorylation?
Transfer of phosphoryl group from metabolites with high-phosphoryl transfer potential to ADP producing ATP
What is oxidative phosphorylation?
Process of ATP formation as a result of transfer of electrons from fuels via electron carriers (NADH or FADH2) to the final electron acceptor oxygen
In animals over 90% of ATP formed by this method, carried out in the mitochondria
What are the 4 main functions of metabolism?
Highly coordinated cellular activity serves 4 main functions
Obtain energy eg ATP
Convert nutrients into own characteristics molecules
Polymerise monomeric precursors eg polysaccharides
Synthesise and degrade molecules required for special cellular functions eg intracellular messengers
Hundreds of different enzyme-catalysed reactions
Central metabolic pathways (few in number, highly conserved throughout nature)
