bioenergetics: cell as a chemical factory produce energy...

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

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



So ΔG = 322 kcal – 440 kcal = -118 kcal

ΔG = - 118 kcal : we’ve lost 118 kcal from the chemical system.


04-07-16: Lecture 4


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


Photosynthesis6CO2 + 6H2O C6H12O6 + 602 ; ΔG = +686 kcal


04-07-16: Lecture 4

ΔG = ΔH – TΔS

ΔG < 0 (spontaneous)

ΔG = ΔH – TΔS

ΔG > 0 (non spontaneous)



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


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


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


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

bioenergetics: cell as a chemical factory produce energy...

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