Upload
others
View
4
Download
0
Embed Size (px)
Citation preview
04-07-16: Lecture 4
Bioenergetics:
Metabolism: All the chemical processes of the cell.
Catabolic Pathways:
Anabolic pathways:
Cell as a Chemical Factory
Produce energy
Absorption of energy
sugars + release energy
build amino acids (a.a.)
A.A. Protein
Nucleotides (NT) DNA or RNA
Photosynthesis: CO2 + H2O Sugarshv
CO2 + H2O
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+
Diffusion
Entropy
04-07-16: Lecture 4
Na+
Diffusion
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 = 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).
ΔG = ΔH – TΔS
04-07-16: Lecture 4
Free energy of a reaction from the final state and the initial state
ΔG = Gibbs free energyBioenergetics:
ΔGΔH
ΔH < 0ΔH > 0
T - tempΔS Entropy
ΔS < 0 ΔS > 0
: free energy (amount of energy that can do work): Enthalphy (heat)
: constant
04-07-16: Lecture 4
Bioenergetic: Enthalpy and Entropy
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
constant
04-07-16: Lecture 4
Cells live in an open system!
Cell: OPEN system
Environment
Energy
Matter
Bioenergetics: Chemical Equilibrium and Metabolism
A Breactant product
Reversible!
Every rxn in the cell is potentially Reversible!
In a closed system: reach equilibrium
ΔG = 0
Cells are an open system:Metabolism never reaches equilibrium – Defining feature !!!
04-07-16: Lecture 4
ΔG = Gibbs free energy – Made Easy!
Bond Energy*It takes energy to break chemical bondsEnergy is released as chemical bonds form
Many forms of energyElectricalMechanicalChemical
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 broken322 kcal released when form 2(H-H) and 1 (O-O) bond
Where is the energy gone?
Bioenergetics: ΔG = Gibbs free energy
04-07-16: Lecture 4
*Note: also see: http://www.biology-pages.info/B/BondEnergy.html
2H2O 2H2 + 02
Bioenergetics: ΔG = Gibbs free energy – Made Easy!
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.
440 kcal 322 kcal(consumed) (released)
04-07-16: Lecture 4
2H2 + 02 2H20
Bioenergetics: ΔG = Gibbs free energy – Made Easy!
ΔG = BEreactants – BEprodcuts
So ΔG = 322 kcal – 440 kcal = -118 kcal
ΔG = - 118 kcal : we’ve lost 118 kcal from the chemical system.
322 kcal 440 kcal(consumed) (released)
04-07-16: Lecture 4
Bioenergetics: ΔG = Gibbs free energy – Made Easy!
Where did this free energy go:
But heat does us no good if we can’t use it!
Cells have solved a way to oxidized molecules and harvest the free energy loss
Cellular RespirationC6H12O6 + 602 6CO2 + 6H2O ; ΔG = -686 kcal
2878 kcal 3564 kcal(consumed) (released)
Photosynthesis6CO2 + 6H2O C6H12O6 + 602 ; ΔG = +686 kcal
3564 kcal 2878 kcal(consumed) (released)
04-07-16: Lecture 4
ΔG = ΔH – TΔS
ΔG < 0 (spontaneous)
ΔG = ΔH – TΔS
ΔG > 0 (non spontaneous)
ΔG = BEreactants – BEprodcuts
Bioenergetics: ΔG = Gibbs free energy – Made Easy!
Free Energy(ΔG)
Course of rxn
C6H12O6 + 602 6CO2 + 6H2O ; ΔG = -686 kcal
Breakdown (oxidizing) glucose
C6H12O6 + 602
6CO2 + 6H2O
ΔG = -686 kcalexergonic
Lost as heat
Cellular Respiration
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!
Free Energy(ΔG)
Course of rxn
0
Cellular RespirationC6H12O6 + 602 6CO2 + 6H2O ; ΔG = -686 kcal
2878 kcal 3564 kcal(consumed) (released)
Rele
ase
Need to release 2878 kcal to balance amount consumed
Con
sum
e
2878 kcal
Rele
ased
3564 kcal
But actually 3564 kcal released
To balance equation ΔG = ΔH – TΔS
ΔH
Lose heat from chemical system to environment
Free energy lost
04-07-16: Lecture 4
Bioenergetics: ΔG = Gibbs free energy – Made Easy!
Free Energy(ΔG)
Course of rxn
Synthesis of glucose
C6H12O6 + 602
6CO2 + 6H2O
ΔG = +686 kcalendergonic
Added : able to do work
6CO2 + 6H2O C6H12O6 + 602 ; ΔG = +686 kcalPhotosynthesis
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!
Free Energy(ΔG)
Course of rxn
0
Release
d
But actually release only 2878 kcal
Rele
ase
3564 kcal
Need to release 3564 kcal to balance amount consumed
To balance equation ΔG = ΔH – TΔS
Con
sum
e
3564 kcal
ΔH
Heat infused
Photosynthesis6CO2 + 6H2O C6H12O6 + 602 ; ΔG = +686 kcal
3564 kcal 2878 kcal(consumed) (released)
Free energy gain
04-07-16: Lecture 4
Bioenergetics: Enzymes (E) speed up reactions
A Breactant product
ΔG < 0 ΔG > 0
A Breactant product
•Increase rate of the reaction (rxn)•Serve as a catalyst – can be re-used•Allows for the influx of energy
Enzymes
A + E [A●E] B + E
Reactant-EnzymeTransitional State
Enzyme is recycled
04-07-16: Lecture 4
Free Energy(ΔG)
Course of rxn
products
reactants
Free Energy(ΔG)
Course of rxn
A Breactant product
A Breactant product
products
reactants
04-07-16: Lecture 4
Free Energy(ΔG)
Course of rxn
products
reactants
ΔG
Ea
A + E
A●E
B + E
Energy of activation
Transitional state
A Breactant product
ΔG < 0
Bioenergetic: Reactions inside a living cell
Energy of activationWith enzyme
∆G < 0 – so the reactions looks spontaneous but actually requires and enzyme!
04-07-16: Lecture 4
Bioenergetic: Reactions inside a living cell
Enzymes (E):
Speeds up rxnLowers Energy of activation (Ea)∆G is unchangedWorks for forward and reverse rxns
A + E [A●E] B + E
Reactant-EnzymeTransitional State
Enzyme is recycled
[B●E]
Product-EnzymeTransitional State
Fre
e E
nerg
y(Δ
G)
Course of rxn
products
react
ant
s
Course of rxn
products
react
ant
s
Chemistry takes place here
ΔG < 0Exergonic
ΔG > 0Endergonic
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
SucroseSucrase(E)
Glucose Fructose+(products)
E + Sucrose + H20 [E●SH20] E + Glucose + Fructose
Binding at active site •Bound complex•Induced fit•Chemistry•Break bonds
1 molecule 2 molecules
(Reactant)
04-07-16: Lecture 4