Energy, ATP, and Enzymes

Energy The ability to do work, that is, to move

matter against opposing forces such as gravity and friction Kinetic energy- energy of motion Potential energy- stored energy, the capacity

to do work

Thermodynamics Study of energy transformation The First Law of Thermodynamics- energy can be

transferred and transformed, but it can neither be created nor destroyed The total energy of the universe is constant Mass is a form of energy

The Second Law of Thermodynamics- every energy transfer or transformation increases the entropy of the universe There is trend toward randomness Energy must be spent to retain order- this spending of

energy usually releases heat, increases the entropy elsewhere

Free Energy- the portion of a system’s energy that can perform work

It’s called “free” energy because this is the energy which can perform work, not because there is no energy cost to the system

Exergonic Reaction- a process with a net release of free energy Sometimes called spontaneous, but that doesn’t mean that it

will occur rapidly

Endergonic Reaction- a process which absorbs free energy from the surrounding

Most synthesis are endergonic

Energy Coupling- use of exergonic process to drive an endergonic process

The free energy released from the exergonic process is absorbed by the endergonic process

Types of Cellular Work Mechanical- beating of cilia, muscle

contractions, etc. Transport- pumping of molecules and

ions across a plasma membrane against their concentration gradient, etc.

Chemical- pushing endergonic reactions that would not occur spontaneously

ATP- Power to Drive Cellular Work Adenosine triphosphate – a close

relative to Adenine, a nucleotide found in DNA Contains 3 phosphate groups connected to

each other in sequence The bonds can be broken by hydrolysis

When the terminal phosphate bond is broken, a molecule of inorganic phosphate (Pi) is formed

This forms adenosine diphosphate, ADP + Pi

This generates free energy, which can be used by the cell to do work

ATP

Enzymes and Chemical Reactions Catalyst- a chemical agent that changes the

state of a reaction without being consumed in the reaction

Substrate- reactants in an enzyme-catalyzed reaction

Intermediate- compounds formed between initial reactants and products (i.e. enzyme-substrate complex)

Products- products Cofactors- helpers for enzymes Energy Carriers- sources of quick energy

(ATP)

Enzymes are protein catalysts 99% of all enzymes are proteins Speed up reactions Work for both forward and reverse

reaction They can become saturated They are highly selective

How Energy Relates to Reaction Initial State transition state final state

Substrate must overcome an energy barrier to react and form the products

An enzyme lowers the energy barrier, thus speeding up the reaction

http://www.uic.edu/classes/bios/bios100/lectures/enzymes01.html

Lock and Key Hypothesis There is only one active site which precisely

fits the reactants (more or less)

Enzymes are Substrate Specific Enzymes bind to the substrate or substrates when

there are two or more reactants Catalytic action of the enzyme converts the

substrate(s) to product(s) Enzymes can distinguish its substrate from similar

molecules and even isomers of the same molecules

Only a restricted region of the enzyme molecule actually binds to the substrate- active site This is not perfect- as enzyme and substrate come

together, a small conformation change occurs so that the action site fits even more snugly around the substrate Induced Fit

http://www.uic.edu/classes/bios/bios100/lectures/enzymes02.html

A Cell’s Physical and Chemical Environment Affect Enzyme Activity

Temperature: a measure of molecular motion As temp increases, reaction rate will increase However, as temp increases, the molecular

motion of the enzyme also increases Enzyme’s active site may become unstable and

function poorly Bond maintaining 2o, 3o, and 4o structure of

protein collapse denatured

Temperature optimum- temperature at which enzyme exhibits peak performance

pH- a measure of [H+] – acidic or basic pH optimum- peak performance at a certain pH Extreme pH, enzyme may denature

Cofactors A non-protein enzyme helper Aid in enzyme catalytic function May be inorganic (Zn or Cu) or organic coenzymes Stabilize transition state Most vitamins are coenzymes

Most Enzymes are Regulated1. Competitive Inhibition Other molecules is “competing” for space on the active site Interfere with substrate binding…slow down reaction rate

2. Allosteric Regulation Regulatory molecules (ligands) may bind to a location

other than the active site allosteric site Allosteric activation- shape change make active site

available Allosteric deactivation or non-competitive inhibition-

shape change makes active site unavailable

3. Feedback Inhibition (Negative Feedback) When the product of a pathway acts as an

inhibitor of the pathway Prevents too much buildup of product Provides a mean of self-regulating in a system