Biological Catalysts - Enzymes
Properties of Enzymes
Enzymes are large biological molecules responsible for the thousands
of chemical interconversions that sustain life. They are highly
selective catalysts, greatly accelerating both the rate and specificity of
metabolic reactions, from the digestion of food to the synthesis of DNA.
Most enzymes are proteins, although some catalytic RNA
molecules have been identified. Enzymes adopt a specific threedimensional structure, and may employ organic (e.g. biotin) and
inorganic (e.g. magnesium ion) cofactors to assist in catalysis.
In enzymatic reactions, the molecules at the beginning of the process,
called substrates, are converted into different molecules,
called products. Almost all chemical reactions in a biological cell need
enzymes in order to occur at rates sufficient for life. Since enzymes are
selective for their substrates and speed up only a few reactions from
among many possibilities, the set of enzymes made in a cell determines
which metabolic pathwaysoccur in that cell.
Metabolism
Metabolism is the set of life-sustaining chemical
transformations within the cells of living organisms.
These enzyme-catalyzed reactions allow organisms to grow
and reproduce, maintain their structures, and respond to their
environments. The word metabolism can also refer to all
chemical reactions that occur in living organisms, including
digestion and the transport of substances into and between
different cells, in which case the set of reactions within the cells
is called intermediary metabolism or intermediate metabolism.
Metabolism is usually divided into two
categories. Catabolism breaks down organic matter, for
example to harvest energy in cellular
respiration. Anabolism uses energy to construct components of
cells such as proteins and nucleic acids.
Catalysis
Catalysis is the change in rate of a chemical
reaction due to the participation of a substance
called a catalyst. Unlike other reagents that
participate in the chemical reaction, a catalyst is not
consumed by the reaction itself. A catalyst may
participate in multiple chemical transformations.
Catalysts that speed the reaction are called positive
catalysts. Substances that slow a catalyst's effect in
a chemical reaction are called inhibitors. Substances
that increase the activity of catalysts are called
promoters, and substances that deactivate catalysts
are called catalytic poisons.
Proteins Structure
Protein structure is the biomolecular structure of
a protein molecule. Each protein is a polymer – specifically
a polypeptide – that is a sequence formed from 20 possible L-αamino acids (also referred to as residues). By convention, a
chain under 40 residues is often identified as a peptide, rather
than a protein. To be able to perform their biological function,
proteins fold into one or more specific spatial conformations,
driven by a number of non-covalent interactions such
as hydrogen bonding, ionic interactions, Van der Waals forces,
and hydrophobic packing. To understand the functions of
proteins at a molecular level, it is often necessary to determine
their three-dimensional structure. This is the topic of the scientific
field of structural biology, which employs techniques such as Xray crystallography, NMR spectroscopy, and dual polarisation
interferometry to determine the structure of proteins.
How do enzymes act?
Enzymes are biological catalysts, each enzyme
has a specific shape of an active site (a cleft or
depression) that can only fit in its complementary
substrate molecule, the enzyme molecule hold
the substrate molecule in a way that makes it
easier for them to react so enzymes lower the
activation energy of a metabolic reaction. The
energy needed to start a metabolic reaction,
bonds are either made; condenation reactions
(removing a water molecule), or broken;
hydrolysation reactions(adding a water
molecule).
Denaturation
Denaturation is a process in which proteins or
nucleic acids lose the tertiary structure and secondary
structure which is present in their native state, by
application of some external stress or compound such
as a strong acid or base, a concentrated inorganic
salt, an organic solvent (e.g., alcohol or chloroform), or
heat. If proteins in a living cell are denatured, this
results in disruption of cell activity and possibly cell
death. Denatured proteins can exhibit a wide range of
characteristics, from loss of solubility to communal
aggregation.