Topic 10: How Enzymes Work Flashcards
Gibbs free Energy
Defined by the ability to do work
This is Gibbs free energy
Examples of work inside cells includes making
and breaking bonds, moving things around inside cells.
Potential vs Kinetic energy
the potential energy of objects at rest (e.g. a volume of water held in place by a
dam)
kinetic energy of objects in motion. In these examples mass/gravity are relevant. But in cells, everything is so small that gravity is not
considered. Chemical potential energy exists between atoms in a molecule, and can be released to perform work by molecules- such as catalyzing
a chemical reaction.
Energy flow
Plants transform radiant energy into chemical energy, which is consumed by animals, and lots of other organisms. Everything
is broken down by decomposers.
At the end there is only Thermal energy (heat), which cannot be used
for work
1st Law of Thermodynamics
Energy cannot be created and it cannot be destroyed. It can change forms (radiant to chemical) and move. The total energy of a closed system
does not change.
Entire universe as a closed system.
Observed universe as an open system. Open systems exchange energy and living organisms are open systems.
Gibbs free energy and heat equation
Delta G=DH-TDS
DS=change in free energy
DH=change in enthalphy (order)
T=temperature
DS=change in entropy
The change in free energy can be greater than or less than 0.
The reaction can break atoms apart (change in entropy is large; ΔS»ΔH, ΔG <0) and releasing free energy to perform work.
The reaction can bond atoms together (change in enthalpy is large; ΔH»_space;ΔS; ΔG >0)- in this case potential energy is stored rather than released.
Releasing free energy reduces order and increases entropy
2nd law of Thermodynamics
No transformation is 100% efficient. As a result creating order by moving chemical energy between atoms always increases entropy.
Happily
the observable universe is very large. Liquid is less ordered than a solid.
Entropy will increase unless free energy is available to increase enthalpy
(order) molecules. This is the challenge faced by cells- entropy- and disorder- is increased by every chemical reaction. Free energy must enter the
system (cell) to maintain the molecules that are required for life.
spontaneous reactions that
release free energy (like breaking a bond)
In the exergonic reaction, the free energy of the reactants»_space; than that of the products, and thus energy is released
reactions that are not spontaneous (like forming a bond
endergonic reaction, the free energy of the reactants is «_space;than the products, and energy has to be added to the system
Activation energy
There is a speed bump
This is the amount of free energy needed to overcome a unstable transition that as the reaction proceeds. For example, breaking a bond requires energy to separate the atoms. Forming a bond requires energy to bring the atoms together (e.g. a high energy collision) such that electrons can be shared (covalent) or stolen (ionic bonds) or allow a reaction between O and H
atoms (hydrogen bonds). If the reactants start with very little free energy (unhappy atoms with unfilled valence shells) a correspondingly large amount of free energy is needed.
how do biological systems
manage energy transfer?
cells need to store potential chemical energy. They can do this as ATP.
What is metabolism?
All the chemical reactions of an organism = organism’s metabolism
Using ATP
Free energy is released when ATP-ADP
this is used for work such as flagella
How do cells reduce the activation energy and speed up reactions?
The reaction is catalyzed by a molecule that increases the free energy available
to the reactants.
How doe enzymes catalyze reactions?
Enzymes catalyze chemical reactions by storing chemical potential energy. Free energy released from the ATP -> ADP +P reaction “activates” the enzyme by increasing its potential energy. This imposes order, moving atoms with the enzyme to create a active site- a favorable shape for reactants to bind to
the enzyme.
By binding the reactants in the enzyme’s active site, the energized enzyme can lower the energy barrier, as the atoms are now in a favorable
position for the chemical reaction.
While enzymes catalyze and speed up reactions, they do not create reactions that would not otherwise occur. After the products are released, enzymes are re-energized by ATP. Enzymes are not destroyed by the reaction.
Active site
The shape of the active site is also modified by the reactants (also called substrates) when they bind to the enzyme. This is called “induced fit”, and the change in shape lowers the energy barrier by transferring free
energy needed for the reaction.
