The roles of ATP in living cells and the mechanisms of production 1 Flashcards
Metabolism
Integrated set of enzymatic reactions comprising both anabolic and catabolic reactions
Anabolism
Synthesis of complex molecules from simpler ones (necessary energy usually derived from ATP)
Catabolism
Breakdown of energy rich molecules to simpler ones (CO2, H2O and NH3)
Energy is required for:
Motion (muscle contraction)
Transport (of ions/ molecules across membranes)
Biosynthesis of essential metabolites
Thermoregulation
Isothermal
Maintaining constant temperature
3 important thermodynamic quantities
Enthalpy- the heat content of the reacting system
Entropy- the randomness or disorder in a system
Gibbs free energy- energy capable of doing work at constant temperature and pressure
Exergonic reaction
Spontaneous
Free energy is defined as negative
Energy is liberated by the reaction
Catabolism
Endergonic reaction
Unfavourable
Free energy is defined as positive
Energy input is required to start the reaction
Anabolism
Coupling of reactions
Endergonic reaction driven in the forward direction by coupling it to an exergonic reaction through a common intermediate
Adenosine triphosphate
ATP provides most of the free energy required
Energy currency of the cell
Achieved by phosphate group transfer
Phosphate group transfer
Covalent participation by phosphate group transfer forms intermediate complex
Reaction between complex and another compound displaces the phosphate group to form product
ATP/ ADP Mg2+ complexes
ATP in the cytosol is present as a complex with Mg2+
Mg2+ interacts with the oxygens of the triphosphate chain making it susceptible to cleavage in the phosphoryl transfer reactions
Substrate level phosphorylation
Formation of ATP by phosphoryl group transfer from a substrate to ADP
Require soluble enzymes and chemical intermediates
Respiration linked phosphorylation
Involve membrane bound enzymes and transmembrane gradients of protons and require oxygen
Enzymes
Biological catalysts that accelerate the rate of chemical reactions
Create a new pathway for the reactions with a lower activation energy
Oxidoreductases
Classification of enzymes that transfer electrons
Transferases
Classification of enzymes that transfer functional groups
Co-enzymes
Non-protein cofactors
Most coenzymes derived from vitamins
Participate in the enzymatic reaction
Have a loose association with their enzyme
Diffuse from one enzyme to the next carrying e-
Regenerated to maintain cellular concentration
Prosthetic groups
Non-protein cofactor that is covalently bound to the enzyme
Not released as part of the reaction
Acts as a temporary store for e- or intermediates
Redox coenzyme/ posthetic groups
Major redox coenzymes/ prosthetic groups involved in transudation of energy from dietary foods to ATP: NAD+, FAD, FMN
Electrons transferred from dietary material to these carriers so coenzymes are reduced
In each case two electrons are transferred but the number of H+ moved varies
Nicotinamide adenine dinucleotide
NAD+ and NADP+ accept pairs of electrons to form NADH or NADPH
It is the nicotinamide that is the functional part of the molecule
NADH for ATP synthesis
NADPH for reductive biosynthesis
Re-oxidation of redox coenzymes
Recycling of NADH and FADH2 is via the respiratory chain in the mitochondria
This is coupled to ATP synthesis- process of oxidative phosphorylation
Glycolytic enzymes
Hexokinase- phosphorylation
PFK-1 - phosphorylation
Pyruvate kinase- phosphorylation
The fate of pyruvate
Two possible fates:
- under aerobic conditions, oxidation and complete degradation
- in hypoxic conditions, it an be reduced to lactate