XII-CH-16-CHEMISTRY IN EVERYDAY LIFE NOTES
Medicines or Drugs
Chemicals which may be used
for the treatment of diseases and for reducing the suffering from pain are
called medicines or drugs. The branch of science which makes use of chemicals
for the treatment of disseases [therapeutic effect] is called chemotherapy.
How do drugs interact on its target
. Proteins which perform
the role of biological catalysts in the body are called enzymes
. Functions of enzymes:
(i) The first function of an enzyme is to hold
the substrate for a chemical reaction. Active sites of enzymes hold the
substrate molecule in a suitable position, so that it can be attacked by the
reagent effectively
(ii) The second function of
an enzyme is to provide functional groups that will attack the substrate and
carry out chemical reaction
. Main role of drugs is to
either increase or decrease role of enzyme catalysed reactions. Inhibition of
enzymes is a common role of drug action. Enzyme inhibitor is drug which
inhibits catalytic activity of enzymes or blocks the binding site of the enzyme
and eventually prevents the binding of substrate with enzyme. Drug can inhibit
attachment of substrate on active site of enzymes in following ways.
(a) Competitive Inhibition: Competitive Inhibitors are the drugs that compete with
the natural substrate for their attachment on the active sites of enzymes
(b) Non-Competitive Inhibition: Some drugs do not bind to the enzyme’s active site,
instead bind to a different site of enzyme called allosteric site. This binding
of inhibitor at allosteric site changes the shape of the active site in such a
way that substrate cannot recognise it. If the bond formed between an enzyme
and an inhibitor is a strong covalent bond and cannot be broken easily, then
the enzyme is blocked permanently. The body then degrades the enzyme-inhibitor
complex and synthesizes the new enzyme
7. Receptors as Drug Targets: Proteins which are vital for communication system
in the body are called receptors. In the body, message between two neurons and
that between neurons to muscles is communicated through chemical messengers.
They are received at the binding sites of receptor proteins. To accommodate a
messenger, shape of the receptor site changes which brings about the transfer
of message into the cell. Chemical messenger gives message to the cell without
entering the cell Receptors show selectivity for one chemical messenger over
the other because their binding sites have different shape, structure and amino
acid composition. Drugs that bind to the receptor site and inhibit its natural
function are called antagonists. These are useful when blocking of message is
required. Drugs that mimic the natural messenger by switching on the receptor
are called agonists. These are useful when there is lack of natural chemical
messenger.
Some important classes of
drugs are
Antacid
The chemical substances
which neutralize the excess acid in gastric juice and raise the pH to an appropriate
level in stomach are called antacids. The most commonly used antacids are weak
bases such as sodium bicarbonate [sodium hydrogencarbonate, NaHCO3),
magnesium hydroxide [Mg(OH)2] and aluminium hydroxide [Al(OH)3].
,,Generally liquid antacids are more
effective than tablets because .. have more surface area available for
interaction and neutralisation acid. ,,
Milk is a weak antacid.
Histamine stimulates the secretion of pepsin and hydrochloric acid. The drug
cimetidine [Tegamet] was designed to prevent the interaction of histamine with
the receptors present in the stomach Cimetidine binds to the receptors tbat triggers
the release of acid the stomach. This results in release of lesser amount of
acid. Now Ranitidine (zantac), omeprazole and lansoprazole are used
hyperacidity.
Tranquilizers
(Psychotherapeutic Drugs)
Chemical substances used for the treatment of
stress, anxiety, irritability and mild or even severe mental diseases, are
known as tranquilizers. ’’These affect
the central nervous system and induce sleep for the patients as well as
eliminate the symptoms of emotional distress. ’’They are the common constituents
of sleeping pills. Noradrenaline is one of the neurotransmitter that plays a
role in mood change. If the level of noradrenaline is low, the signal sending
activity becomes low, and the person suffers from depression. In such
situations antidepressant drugs are required. These drugs inhibit the enzymes
which catalyse the degradation of noradrenaline. If the enzyme is inhibited,
this important neurotransmitter is slowly metabolized and can activate its
receptor for longer, periods of time, thus counteracting the effect of
depression. Iproniazid and phenelzine are two such drugs. Barbituric acid and
its derivatives viz. veronal, amytal, nembutal, luminal, seconal are known as
barbiturates. Barbiturates are hypnotic, i.e., sleep producing agents. Equanil
is used to control depression and hypertension. Non-hypnotic chlorodiazepoxide
and meprobamate are relatively mild tranquilizers suitable for relieving
tension.
Analgesics
Medicines used for getting relief from pain
are called analgesics.
These are of two types :
1. Narcotics Drugs
which produce sleep and
unconsciousness are called narcotics. These are habit forming drugs. For
example, morphine and codeine. Morphine diacetate is commonly known as heroin.
2. Non-narcotics
These are non-habit forming chemicals which
reduce mild to moderate llatn such as headache, toothache, muscle and joint
pain, etc. These are also termed as non-addicti,ve. These drugs do not produce
sleep unconsciousness. Aspirin (2-acetoxybenzoic acid) is most commonly used analgesic
with antipyretic properties. Now these days because its anti-blood clotting
action, aspirin is widely used to heart-attacks.
”Aspirin is toxic for liver and sometimes also causes
bleeding from- stomach.’’ So,
naproxen, ibuprofen, paracetamol,dichlorofenac sodium are other widely used
analgesics.
Antipyretics
These are the chemical
substance which reduce body temperature during high fever. Paracetamol,
aspirin, phenacetin (4-hydroxy acetanilide), analgin and novalgin, etc., are
common antipyretics. Out of these, paracetamol (4-acetamidophenol) is most
common.
Antimicrobials
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