Biochemical Reactions

The Active Cell

Biological Reactions

• Metabolism is a term used to refer to all the chemical reactions that take place in a living organism

• Two main categories of metabolic reactions– Catabolic reactions are those that break large

molecules into small ones

• E.g. – digestion of proteins– respiration

– Anabolic reactions are those that build larger molecules

• E.g. photosynthesis

Metabolism Summary

Gibbs Free Energy and Metabolism

• Gibbs free energy measures the likelihood that a reaction will proceed spontaneously

• A calculation based on the energy required to break the bonds between the atoms of the reactants as compared to the products

Catabolic reactions

• Most catabolic reactions release energy

• This energy is available to do work (physical definition of work)

• These types of reactions are called exothermic in chemistry – energy is released at once in the form of heat

• Ea = activation energy

• ΔG = Gibbs Free Energy

Catabolic Reactions

• In biological system, a sudden release of heat energy in the living cell will cause it to die

• Therefore, energy is released in a controlled manner through a variety of chemical intermediates

• Thus, in biology, we call these exergonic reactions

Anabolic Reactions

• These are chemical reactions that result in larger molecules

• Usually require a large energy input

• In chemistry, these are called endothermic reactions – energy input in the form of heat

Anabolic Reactions

• As with catabolic reactions, these process are highly controlled in the living cell– Cannot add energy directly by heating the reactants

– Must do so in small controlled amounts

• These types of reactions are called endergonic

Reaction Energy Summary

ATP – Energy Molecule of the Cell

Enzymes

• Enzymes are functional proteins in that they are the main chemical drivers of life

• These are protein molecules that accelerate and control biochemical reactions by reducing the activation energy of a reaction

• The organic equivalent of a catalyst

Catalysis

• Refers to the process by which a chemical reaction proceeds with the assistance of a helper compound or molecule

• The helper is not consumed in the reaction• General form is:

Reactants + Catalyst

Reactants/Catalyst complex

Products + Catalyst

Enzymes

• Similar pathway for reactivity• Reactants are called substrates

Substrates + Enzyme

Activated Enzyme Substrate complex

Products + Enzyme

Enzymes

• As with catalysts, enzymes reduce the amount of activation energy needed to start a reaction.

• The energy curve of an enzyme mediated reaction will have a lower activation energy than that without the enzyme

Enzymes

• Note that ΔG for an enzyme mediated reaction does not change

• Only the activation energy is changed – reduced by a factor

• Enzymes work in one of two ways– Catabolic enzymes have an active site that will place

stress on a specific bond causing it to break

– Anabolic enzymes have an active site that will bring two molecules together in a configuration that permits bonding

Enzyme Action

Controlling Enzyme Activity

• Enzymes are reusable• Active enzymes will continue to function as long

as substrate is available to react• Often, it is essential to control when an enzyme is

active and when it is not• Such controls are important in controlling how

and when biochemical reactions take place

Controlling Enzyme Activity

• Several methods by which enzyme action is controlled

• Co-Enzymes and Co-Factors– These are molecules or minerals that are essential

for the enzyme to function properly

• Inhibitors– These are molecules that interfere with the

functioning of the enzyme

– Two types

• Competitive inhibitors

• Allosteric inhibitors

• Biochemical Pathways

Co-Enzymes and Co-Factors

Enzyme Inhibitors -

Enzyme Inhibitors - Applications

Metabolic Pathways