Bioenergetics and ATP synthesis Flashcards
What is bioenergetics ?
The quantitative study of energy transduction occurring in living cells
What is the first law of thermodynamics ?
It states that energy cannot be created or destroyed but it can be converted from one form to another
What is an exergonic reaction ?
- if ΔG is negative this means energy is liberated and the reaction is energetically favourable and so it is exergonic
- exergonic reactions can occur spontaneously
What is an endergonic reaction ?
- if ΔG is positive the reaction will require an energy input in order to occur and it is said to be endergonic
What does it mean if ΔG is 0 ?
- the system is at equilibrium
- no net change can take place
Describe ΔG in relation to reaction pathways and rates of reaction
- the ΔG of a reaction is the same no matter the pathway that the reaction takes
- ΔG doesn’t provide any information on the rate of reaction
Why do living organisms need energy ?
- living organisms require continual input of free energy because many biological processes are endergonic
Give some examples of biological processes which are endergonic
- muscle contraction
- active transport
- biosynthesis
- signal transduction
- generation of light and electricity
How do phototrophs obtain energy ?
- obtain energy by trapping light
e.g. photosynthesis
How do chemotrophs obtain energy ?
- obtain energy by oxidation of food
e.g. through catabolism
What is metabolism ?
anabolism + catabolism
How do chemoorganotrophs obtain energy ?
- obtain energy from organic compounds by oxidation
e.g. C6H12O6 + 6O2 → 6CO2 + 6H2O - this will yield ~ 30-32 ATP
What are the main energy sources for chemoorganotrophs specifically humans ?
- fats : 9 kcal/g
- carbohydrates : 4 kcal/g
- proteins : 4 kcal/g
- alcohol : 7 kcal/g
Why is it important that humans have controlled extraction of energy from food ?
- don’t want to release all the energy at once
- don’t want to increase body temperature excessively
How is energy extracted from food ?
Stage 1 - Large molecules broken down into smaller units. No useful energy is captured
Stage 2 - Small molecules are degraded into a few simple units that play a role in central metabolism. Some ATP is generated ~ 5-10%
Stage 3 - ATP (~90-95%) is produced from the complete oxidation of simple units by the final common pathways for oxidation of fuel. ~90-95%
What happens when an organic compound is degraded ?
when an organic compound is degraded (oxidised) :
- electrons flow through intermediates to oxygen (the final electron acceptor)
- or they are used to reduce other cellular components
What happens in a redox reaction ?
- the electron donor is the reducing agent and is oxidised
- the electron acceptor is the oxidising agent and is reduced
Give the different types of biological redox reactions with examples
- Direct electron transfer
e.g. Fe2+ + Cu2+ <> Fe3+ + Cu+ - Direct transfer of hydrogen ions e.g. AH2 + B <> A + BH2
- Direct combination with oxygen e.g. R-CH3 + ½O2 > R-CH2OH
- The most common involve dehydrogenation
How do dehydrogenase enzymes work ?
- oxidise organic compounds by abstracting 2H+ & 2 electrons and passing them to a mobile carrier in biodegradation and energy abstraction ( i.e. respiration)
- reduce organic compounds by adding 2 H+ & 2 electrons from a mobile electron carrier typically in biosynthetic pathways
Describe NADH
- produced in catabolic reactions and by the Krebs cycle
- used in the generation of ATP by oxidative phosphorylation
- usually found inside the mitochondria
Describe NADPH
- produced by PPP
- used primarily for reductive biosynthesis (e.g. FA synthesis)
- usually found in the cytoplasm
Describe FADH2
- produced in catabolic reactions and by the Krebs cycle
- used in the generation of ATP by oxidative phosphorylation
- usually found inside the mitochondria
Give some examples of electron carriers
- NADH
- NADPH
- FADH2
What is the energy currency of a cell ?
ATP
Describe the structure of ATP
- it is an energy rich molecule with high phosphoryl transfer potential
- it contains 2 phosphoanhydride bonds on its triphosphate unit
How does ATP release energy ?
the hydrolysis of bonds will yield energy which is used in endergonic processes
Describe the stability of ATP
- it is thermodynamically unstable because ΔG is negative
- it is kinetically stable because in the absence of a catalyst the breakdown is very slow
Describe the ATP-ADP cycle
- it is the fundamental mode of energy exchange in biological systems
- ATP is the principal immediate donor of free energy in biological systems rather than long-term storage form
- it is consumed within minutes of formation but it has a very high turnover
- around 50Kg of ATP is consumed in a 24h period
How is ATP produced ?
- substrate level phosphorylation : the transfer of a phosphoryl group from metabolites with high phosphoryl transfer potential to ADP which produces ATP
- oxidative phosphorylation : electrons are transferred from fuels via electron carriers to the final electron acceptor (oxygen)
Where does oxidative phosphorylation happen ?
- in the mitochondria
- in animals over 90% of ATP is formed by this method
What are the 4 main functions of metabolism ?
- obtaining energy e.g. ATP
- converting nutrients into own characteristic molecules
- polymerising monomeric precursors e.g. polysaccharides
- synthesising and degrading molecules required for special cellular functions e.g. intracellular messengers
What are the 2 classes of metabolic pathways ?
- catabolic reactions : transform fuels into usable cellular energy (breakdown)
- anabolic reactions : utilise the useful energy formed by catabolism to generate complex structures from simple ones (synthesis)
Give some differences between catabolic and anabolic reactions
- degradative v synthetic
- produces ATP v requires ATP
- exergonic v endergonic
- produces electrons v needs electrons
- generates NADH and FADH2 v uses NADPH
