Metabolism: All the chemical processes of the cell. Catabolic Pathways:
Produce energy
sugars
Anabolic pathways:
CO2 + H2O
+ release energy
Absorption of energy
build amino acids (a.a.) A.A.
Protein
Nucleotides (NT) Photosynthesis:
DNA or RNA CO2 + H2O
hv
Sugars
04-07-16: Lecture 4
Bioenergetics:
All metabolic pathways are subject to the 1st and 2nd laws of thermodynamics
1st:
Energy can be transferred or transformed, but it can not be created or destroyed
2nd:
Every process in the universe increases Disorder (Entropy) Na+
Na+
Entropy
Diffusion
Diffusion
04-07-16: Lecture 4
Bioenergetics:
Chemical reactions in the cell
•All controlled , stepwise fashion •Compartmentalized •Requires enzymes (proteins) •Serve as a catalyst – can be re-used •Increase entropy •Increase rate of the reaction (rxn) Chemical RXNs
Spontaneous: Non-Spontaneous: ΔG = Gibbs free energy Free energy of a reaction: difference between the final state and the initial state
04-07-16: Lecture 4
ΔG = ΔH – TΔS •ΔG = Gibbs free energy – amount of energy that is capable of doing work during a reaction at constant pressure and constant temperature. •When a system changes to possess less energy (free energy is lost) than the free energy change (ΔG) is negative and the reaction is exergonic (spontaneous)
•Enthalpy: the heat content of a system (H). When a chemical reaction releases heat it is exothermic and has a negative (ΔH). •Entropy: Randomness or disorder of a system. When the products of a reaction are less complexed and more disordered than the reactants, the reaction proceeds with a gain in entropy (ΔS).
04-07-16: Lecture 4
Bioenergetics: ΔG = Gibbs free energy
Free energy of a reaction from the final state and the initial state ΔG : free energy (amount of energy that can do work) ΔH : Enthalphy (heat) ΔH < 0 ΔH > 0 T - temp : constant ΔS Entropy ΔS < 0 ΔS > 0
04-07-16: Lecture 4
Bioenergetic: Enthalpy and Entropy constant
ΔG = ΔH – TΔS ΔG < 0
Will be spontaneous because:
Give up enthalphy (H decreases) Give up order (S increases) 1 or both have to happen for a reaction to be spontaneous
ΔG = ΔH – TΔS ΔG = ΔH – TΔS ΔG = ΔH – TΔS
04-07-16: Lecture 4
Bioenergetics: Chemical Equilibrium and Metabolism reactant
A
product
Reversible!
B
Cells live in an open system! Cell: OPEN system
Every rxn in the cell is potentially Reversible!
In a closed system: reach equilibrium
Energy Environment
Matter
ΔG = 0
Cells are an open system: Metabolism never reaches equilibrium – Defining feature !!!
04-07-16: Lecture 4
Bioenergetics: ΔG = Gibbs free energy
ΔG = Gibbs free energy – Made Easy! Bond Energy* It takes energy to break chemical bonds Energy is released as chemical bonds form Many forms of energy Electrical Mechanical Chemical All forms are ultimately converted into heat therefore biologist measure energy in unit of heat: Kilocalorie (kcal) – amount of heat to warm 1 liter of water 1˚C 2H2O 2H2 + 02 440 kcal consumed when 4 (0-H bonds) are broken 322 kcal released when form 2(H-H) and 1 (O-O) bond Where is the energy gone?
*Note: also see: http://www.biologypages.info/B/BondEnergy.html
04-07-16: Lecture 4
Bioenergetics:
ΔG = Gibbs free energy – Made Easy!
2H2O 2H2 + 02
440 kcal 322 kcal (consumed) (released) It is now Chemical Energy stored in the bonds of 2H2 + 02. This is called free energy. ΔG = BEreactants – BEprodcuts ΔG = 440 kcal - 322 kcal = 118 kcal ΔG = + 118 kcal – we’ve added 118 kcal to the chemical system.
ΔG = -686 kcal exergonic Lost as heat 6CO2 + 6H2O Course of rxn
Oxidation of glucose is highly controlled – stepwise fashion; compartmentalized – to maximize ability to recoup some of the lost free energy in the form of:
04-07-16: Lecture 4
Bioenergetics:
ΔG = Gibbs free energy – Made Even Easier! Cellular Respiration C6H12O6 + 602 6CO2 + 6H2O ; ΔG = -686 kcal 2878 kcal (consumed)
Need to release 2878 kcal to balance amount consumed
The conversion of CO2 + H2O glucose is strongly endergonic – would never happen without the environment (photosynthesis). So how do endergonic reactions take place in the cell?
ATP!
04-07-16: Lecture 4
Bioenergetics:
ΔG = Gibbs free energy – Made Even Easier! Photosynthesis 6CO2 + 6H2O C6H12O6 + 602 ; ΔG = +686 kcal 3564 kcal (consumed)
2878 kcal (released)
But actually release only 2878 kcal
Heat infused Release Released
Free Energy 0 (ΔG)
Consume
3564 kcal
ΔH
3564 kcal
Course of rxn To balance equation
ΔG = ΔH – TΔS
Free energy gain
Need to release 3564 kcal to balance amount consumed
04-07-16: Lecture 4
Bioenergetics: Enzymes (E) speed up reactions reactant
product
B
A
Enzymes
reactant
product
B
A
ΔG < 0
ΔG > 0
•Increase rate of the reaction (rxn) •Serve as a catalyst – can be reused •Allows for the influx of energy
A+E
Reactant-Enzyme Transitional State
[A●E]
Enzyme is recycled
B+E
04-07-16: Lecture 4
reactant
A
reactants
product
B
Free Energy (ΔG)
reactant
product
B
A
products
Free Energy (ΔG) products Course of rxn
reactants Course of rxn
04-07-16: Lecture 4
Bioenergetic: Reactions inside a living cell reactant
product
Transitional state
B
A
A●E
ΔG < 0 reactants Free Energy (ΔG)
Ea
Energy of activation Energy of activation With enzyme
A + E ΔG B + E products Course of rxn
∆G < 0 – so the reactions looks spontaneous but actually requires and enzyme!
04-07-16: Lecture 4
reactants
Bioenergetic: Reactions inside a living cell
ΔG > 0 Endergonic
reactants
Speeds up rxn Lowers Energy of activation (Ea) ∆G is unchanged Works for forward and reverse rxns
Free Energy (ΔG)
Enzymes (E):
ΔG < 0 Exergonic
products
products Course of rxn
Chemistry takes place here
A+E
Reactant-Enzyme Transitional State
[A●E]
Product-Enzyme Transitional State
Enzyme is recycled
[B●E]
Course of rxn
B+E
04-07-16: Lecture 4
Bioenergetic: Enzymes are substrate specific (SPECIFICITY) There can be > 1 in a reactions. Substrate is acted on by the enzyme.
Basic Properties of Enzyme Active Site: pocket on enzyme where substrate can bind Specificity: compatible fit between enzyme and substrate (remember R-groups - chemical toolbox) Induced Fit: substrate binding induces 3D structural change of Enzyme Chemistry takes place with reactants (transitional states)
04-07-16: Lecture 4
Catalytic cycle of an Enzymes (Reactant)
Sucrose
Sucrase(E)
1 molecule
(products)
Glucose
+ Fructose
2 molecules
E + Sucrose + H20
[E●SH20]
Binding at active site
•Bound complex •Induced fit •Chemistry •Break bonds
