Energy and enzymes

Overview of metabolism

• breaking down glucose=cellular respiration
• C₆H₁₂6O₆+6O₂ -> 6CO₂+6H₂0+energy
• which energy captured by the ATP(adenosine triphosphate)
• which is the energy currency of the cell
• building up glucose=photosynthesis
• anabolic(building up) needs energy
• catabolic(breaking down) releases energy

Laws of thermodynamics

• types of energy: kinetic/thermal(constant moving of atoms or molecules)/potential/chemical... 
• types of system: open(energy, matter exchange)/closed(only energy)/isolated(both not exchange) system
• The first law of thermodynamics: energy cannot be created or destroyed, it can only change or be transferred
• The second law of thermodynamics: every energy transfer will increase the entropy of the universe(reduce the amount of usable energy) 
• the system will tend to move towards more disordered configuration bc it's statistically much more likely
• system hates temperature-separated(organized) configuration!

Free energy

• Gibbs free energy change equation: △G=△H-T△S
• G means the change in free energy of a system(from initial to final)
• △G<0 a reaction proceed spontaneously(without adding energy) △G>0 need an input of energy
• H means the enthalpy(energy stored in bonds) change. 
• △H<0 release heat, △H>0 absorb heat(from reactant to product)
• T means temperature
• S means the entropy change of the system
• △S<0 become ordered △S>0 become disordered(have more potential states)
• Endergonic reactions: require an input of energy(△G>0), non-spontaneous
• Exergonic reactions: release free energy(△G<0), spontaneous reactions
• ADP(adenosine diphosphate)+Pi+△G(=+7.3kcal/mol) -> ATP+H20 
• the energy needed to make ATP is provided, for example, glucose

ATP and reaction coupling

• ATP(Adenosine triphosphate) is unstable due to negative charges in its phosphate tail
• phosphoanhydride bonds: bonds between the phosphate groups, high-energy
• ATP+H20 <-> ADP+Pi+energy
• △G for the hydrolysis of 1 ATP into ADP(+Pi)=-7.3kcal/mol(=-30.5kJ/mol) @standard conditions
• -14kal/mol(=-57kJ/mol) @in a living cell 
• ATP in reaction coupling: the formation of sucrose
• the first reaction: a phosphate group is transferred from ATP to glucose, forming "glucose-P(glucose 6 phosphate)"
• Hexokinase: provides ions(Mg), make electrons(O- in phosphate tail) busy

• the second reaction: glucose-P intermediate reacts with fructose to form sucrose

Introduction to enzymes

• transition state: to break the bonds, molecules must be bent, unstable state, at higher energy level than both reactants and products
• activation energy(E_A): initial energy input to proceed the reaction(independent to whether it's endergonic, exergonic)
• catalyst=enzymes: lower the activation energy, increase reaction rate
• (enzyme's)substrate
• active site
• environmental effects on enzyme: temperature, pH(if both extreme, enzyme denature)
• induced fit

Enzyme regulation

• enzyme cofactor: non-protein part of an enzyme, help the enzyme do its function
• organic cofactor=coenzyme like NAD(NAD+H^-->NADH)
• regulatory molecules: molecules regulate enzyme. activator(encourage), inhibitor(discourage)
• competitive inhibition: substrate and inhibitor compete for the enzyme(active site). one attached, another can't. 
• allosteric competitive inhibition: inhibitor attach to a not-active site, which prevents substrate from attaching the active site
• noncompetitive inhibition: both can attach to an enzyme, but the activity doesn't happen. 

• V0(initial velocity): the amount of product/unit at the start of reaction
• Vmax(maximum velocity): the maximum rate of reaction, depends on enzyme concentration
• Vmax/2=Km: how quickly reaction rate increases with substrate concentration, altered by inhibitors
• with a competitive inhibitor: Vmax is unchanged(with more substrates, can reach the normal Vmax), Km is higher
• with a noncompetitive inhibitor: Vmax is lower than normal Vmax, Km is unchanged(bc inhibitors lower the number of (usable)enzyme)
• Michaelis-Menten equation