Chemistry

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Food Additives of Chemistry In Everday Life

Have you ever noticed the ingredients that is printed on the cover of the packed food materials such as biscuits, chocolates etc… You might have noticed that emulsifiers such as 322, 472E, dough conditioners 223 etc… are used in the preparation, in addition to the main ingredients such as wheat flour, edible oil, sugar, milk solid etc… Do you think that these substances are necessary? Yes. These substances enhance the nutritive, sensory and practical value of the food.

They also increase the shelf life of food. The substances which are not naturally a part of the food and added to improve the quality of food are called food additives.

Important Categories of Food Additives

• Aroma compounds
• Food colours
• Preservatives
• Stabilizers
• Artificial Sweeteners
• Antioxidants
• Buffering substances
• Vitamins and minerals

Advantages of Food Additives:

1. Uses of preservatives reduce the product spoilage and extend the shelf-life of food
2. Addition of vitamins and minerals reduces the mall nutrient
3. Flavouring agents enhance the aroma of the food
4. Antioxidants prevent the formation of potentially toxic oxidation products of lipids and other food constituents

Preservatives:

Preservatives are capable of inhibiting, retarding or arresting the process of fermentation, acidification or other decomposition of food by growth of microorganisms. Organic acids such as benzoic acid, sorbic acid and their salts are potent inhibitors of a number of fungi, yeast and bacteria. Alkyl esters of hydroxy benzoic acid are very effective in less acidic conditions. Acetic acid is used mainly as a preservative for the preparation of pickles and for preserved vegetables.

Sodium metasulphite is used as preservatives for fresh vegetables and fruits. Sucrose esters with palmitic and steric acid are used as emulsifiers. In addition that some organic acids and their salts are used as preservatives. In addition to chemical treatment, physical methods such as heat treatment (pasteurisation and sterilisations), cold treatment (chilling and freezing) drying (dehydration) and irradiation are used to preserve food.

Antioxidants:

Antioxidants are substances which retard the oxidative deteriorations of food. Food containing fats and oils is easily oxidised and turn rancid. To prevent the oxidation of the fats and oils, chemical BHT (butylhydroxy toluene), BHA(Butylated hydroxy anisole) are added as food additives.

They are generally called antioxidants. These materials readily undergo oxidation by reacting with free radicals generated by the oxidation of oils, thereby stop the chain reaction of oxidation of food. Sulphur dioxide and sulphites are also used as food additives. They act as anti-microbial agents, antioxidants and enzyme inhibitors.

Sugar Substituents:

These compounds that are used like sugars (glucose, sucrose) for sweetening, but are metabolised without the influence of insulin are called sugar substituents. Eg. Sorbitol, Xylitol, Mannitol.

Artificial Sweetening Agents:

Synthetic compounds which imprint a sweet sensation and possess no or negligible nutritional value are called artificial sweeteners. Eg. Saccharin, Aspartame, sucralose, alitame etc…

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Chemistry In Everday Life of Drug and its Types

The word drug is derived from the French word “drogue” meaning “dry herb”. A drug is a substance that is used to modify or explore physiological systems or pathological states for the benefit of the recipient. It is used for the purpose of diagnosis, prevention, cure/relief of a disease.

The drug which interacts with macromolecular targets such as proteins to produce a therapeutic and useful biological response is called medicine. The specific treatment of a disease using medicine is known as chemotherapy. An ideal drug is the one which is nontoxic, bio-compatible and bio-degradable, and it should not have any side effects.

Generally, most of the drug molecules that are used now a days have the above properties at lower concentrations. However, at higher concentrations, they have side effects and become toxic. The medicinal value of a drug is measured in terms of its therapeutic index, which is defined as the ratio between the maximum tolerated dose of a drug (above which it become toxic) and the minimum curative dose (below which the drug is ineffctive). Higher the value of therapeutic index, safer is the drug.

Classification of Drugs:

Drugs are classified based on their properties such as chemical structure, pharmacological effect, target system, site of action etc. We will discuss some general classifications here.

Classification Based on the Chemical Structure:

In this classification, drugs with a common chemical skeleton are classified into a single group. For example, ampicillin, amoxicillin, methicillin etc.. all have similar structure and are classified into a single group called penicillin.

Similarly, we have other group of drugs such as opiates, steroids, catecholamines etc. Compounds having similar chemical structure are expected to have similar chemical properties. However, their biological actions are not always similar. For example, all drugs belonging to penicillin group have same biological action, while groups such as barbiturates, steroids etc.. have different biological action.

Penicillins

Classification Based on Pharmacological Effect:

In this classification, the drugs are grouped based on their biological effect that they produce on the recipient. For example, the medicines that have the ability to kill the pathogenic bacteria are grouped as antibiotics.

This kind of grouping will provide the full range of drugs that can be used for a particular condition (disease). The physician has to carefully choose a suitable medicine from the available drugs based on the clinical condition of the recipient.

Examples:

Antibiotic drugs: amoxicillin, ampicillin,cefiime, cefpodoxime, erythromycin, tetracycline etc..
Antihypertensive drugs: propranolol, atenolol, metoprolol succinate, amlodipine etc…

Classification Based on the Target System (Drug Action):

In this classifiation, the drugs are grouped based on the biological system/process, that they target in the recipient. This classification is more specific than the pharmacological classification. For example, the antibiotics streptomycin and erythromycin inhibit the protein synthesis (target process) in bacteria and are classified in a same group. However, their mode of action is different. Streptomycin inhibits the initiation of protein synthesis, while erythromycin prevents the incorporation of new amino acids to the protein.

Classification Based on the Site of Action (Molecular Target):

The drug molecule interacts with biomolecules such as enzymes, receptors etc,, which are referred as drug targets. We can classify the drug based on the drug target with which it binds. This classification is highly specific compared to the others. These compounds often have a common mechanism of action, as the target is the same.

Drug-Target Interaction:

The biochemical processes such as metabolism (which is responsible for breaking down the food molecules and harvest energy in the form of ATP and biosynthesis of necessary biomolecules from the available precursor molecules using many enzymes), cell-signaling (senses any change in the environment using the receptor molecules and send signals to various processes to elicit an appropriate response) etc… are essential for the normal functioning of our body.

These routine processes may be disturbed by any external factors such as microorganism, chemicals etc.. or by a disorder in the system itself. Under such conditions we may have to take medicines to restore the normal functioning of the body.

These drug molecules interact with biomolecules such as proteins, lipids, etc.. that are responsible for different functions of the body. For example, proteins which act as biological catalysts are called enzymes and those which are important for communication systems are called receptors. The drug interacts with these molecules and modify the normal biochemical reactions either by modifying the enzyme activity or by stimulating/suppressing certain receptors.

Enzymes as Drug Targets:

In all living systems, the biochemical reactions are catalysed by enzymes. Hence, these enzyme actions are highly essential for the normal functioning of the system. If their normal enzyme activity is inhibited, then the system will be affected. T is principle is usually applied to kill many pathogens.

We have already learnt that in enzyme catalysed reactions, the substrate molecule binds to the active site of the enzyme by means of the weak interaction such as hydrogen bonding, van der Waals force etc… between the amino acids present in the active site and the substrate. When a drug molecule that has a similar geometry (shape) as the substrate is administered, it can also bind to the enzyme and inhibit its activity.In other words, the drug acts as an inhibitor to the enzyme catalyst.

These type of inhibitors are of en called competitive inhibitors. For example the antibiotic sulphanilamide, which is structurally similar to p-aminobenzoic acid (PABA) inhibits the bacterial growth. Many bacteria need PABA in order to produce an important coenzyme, folic acid.

When the antibiotic sulphanilamide is administered, it acts as a competitive inhibitor to the enzyme dihydropteroate synthase (DHPS) in the biosynthetic pathway of converting PABA into folic acid in the bacteria. It leads to the folic acid deficiency which retards the growth of the bacteria and can eventually kill them.

In certain enzymes, the inhibitor molecule binds to a different binding site, which is commonly referred to as allosteric site, and causes a change in its active site geometry (shape). As a result, the substrate cannot bind to the enzyme. This type of inhibitors are called allosteric inhibitors.

Receptor as Drug Targets:

Many drugs exert their physiological effects by binding to a specifi molecule called a receptor whose role is to trigger a response in a cell. Most of the receptors are integrated with the cell membranes in such a way that their active site is exposed to outside region of the cell membrane.

The chemical messengers, the compounds that carry messages to cells, bind to the active site of these receptors. This brings about the transfer of message into the cell. These receptors show high selectivity for one chemical messenger over the others.

If we want to block a message, a drug that binds to the receptor site should inhibit its natural function. Such drugs are called antagonists. In contrast, there are drugs which mimic the natural messenger by switching on the receptor. These type of drugs are called agonists and are used when there is lack of chemical messenger.

For example, when adenosine binds to the adenosine receptors, it induces sleepiness. On the other hand, the antagonist drug caffine binds to the adenosine receptor and makes it inactive. This results in the reduced sleepiness (wakefulness). The agonist drug, morphine, which is used as a pain killer, binds to the opioid receptors and activates them. This supress the neuro transmitters that causes pain.

Thrapeutic Action of Different Classes of Drugs:

The developments in the field of biology allowed us to understand various biological process and their mechanism in detail. This enabled to develop new safer efficient drugs. For example, to treat acidity, we have been using weak bases such as aluminium and magnesium hydroxides. But these can make the stomach alkaline and trigger the production of much acid. Moreover, This treatment only relives the symptoms and does not control the cause.

Detailed studies reveal that histamines stimulate the secretion of HCl by activating the receptor in the stomach wall. This findings lead to the design of new drugs such as cimetidine, ranitidine etc.. which binds the receptor and inactivate them. These drugs are structurally similar to histamine. In this section, we shall discuss the therapeutic action of a few important classes of drugs.

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Biomolecules of Hormones

Hormone is an organic substance (e.g. a peptide or a steroid) that is secreted by one tissue. it limits the blood stream and induces a physiological response (e.g. growth and metabolism) in other tissues. It is an intercellular signalling molecule.

Virtually every process in a complex organism is regulated by one or more hormones: maintenance of blood pressure, blood volume and electrolyte balance, embryogenesis, hunger, eating behaviour, digestion – to name but a few.

Endocrine glands, which are special groups of cells, make hormones. The major endocrine glands are the pituitary, pineal, thymus, thyroid, adrenal glands, and pancreas. In addition, men produce hormones in their testes and women produce them in their ovary.

Chemically, hormones may be classified as either protein (e.g. insulin, epinephrine) or steroids (e.g. estrogen, androgen). Hormones are classified according to the distance over which they act as, endocrine, paracrine and autocrine hormones.

Endocrine hormones act on cells distant from the site of their release. Example: insulin and epinephrine are synthesized and released in the bloodstream by specialized ductless endocrine glands.

Paracrine hormones (alternatively, local mediators) act only on cells close to the cell that released them. For example, interleukin-1 (IL-1).

Autocrine hormones act on the same cell that released them. For example, protein growth factor interleukin-2 (IL-2).

Only those cells with a specific receptor for a given hormone will respond to its presence even though nearly all cells in the body may be exposed to the hormone. Hormonal messages are therefore quite specifically addressed.

Most commonly, hormones are categorized into four structural groups, with members of each group having many properties in common:

• Peptides and proteins
• Steroids
• Amino acid derivatives
• Fatty acid derivatives – Eicosanoids

Some hormones that are products of endocrine glands are proteins or peptides, others are steroids. (The origin of hormones, their physiological role, and their mode of action are dealt with in the article hormone). None of the hormones has any enzymatic activity.

Some examples of protein hormones include growth hormone, which is produced by the pituitary gland, and follicle-stimulating hormone (FSH), which has an attached carbohydrate group and is thus classified as a glycoprotein.

Chemically, hormones may be classified as either proteins or steroids. All of the hormones in the human body, except the sex hormones and those from the adrenal cortex, are proteins or protein derivatives.

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Nucleic Acids Types and its Functions

The inherent characteristics of each and every species are transmitted from one generation to the next. It has been observed that the particles in nucleus of the cell are responsible for the transmission of these characteristics.

They are called chromosomes and are made up of proteins and another type of biomolecules called nucleic acids. There are mainly two types nucleic acids, the deoxyribonucleic acid (DNA) and ribonucleic acid (RNA). They are the molecular repositories that carry genetic information in every organism.

Composition and Structure of Nucleic Acids

Nucleic acids are biopolymers of nucleotides. Controlled hydrolysis of DNA and RNA yields three components namely a nitrogenous base, a pentose sugar and phosphate group.

Nitrogen Base

These are nitrogen containing organic compounds which are derivatives of two parent compounds, pyrimidine and purine. Both DNA and RNA have two major purine bases, adenine (A) and guanine (G). In both DNA and RNA, one of the pyrimidines is cytosine (C), but the second pyrimidine is thymine (T) in DNA and uracil (U) in RNA.

Pentose Sugar:

Nucleic acids have two types of pentoses. The recurring deoxyribonucleotide units of DNA contain 2’-deoxy-D-ribose and the ribonucleotide units of RNA contain D-ribose. In nucleotides, both types of pentoses are in their β-furanose (closed five membered rings) form.

Phosphate Group

Phosphoric acid forms phospho diester bond between nucleotides. Based on the number of phosphate group present in the nucleotides, they are classified into mono nucleotide, dinucleotide and trinucleotide.

Nucleosides and Nucleotides:

The molecule without the phosphate group is called a nucleoside. A nucleotide is derived from a nucleoside by the addition of a molecule of phosphoric acid. Phosphorylation occurs generally in the 5’ OH group of the sugar. Nucleotides are linked in DNA and RNA by phospho diester bond between 5’ OH group of one nucleotide and 3’ OH group on another nucleotide.

Sugar + Base → Nucleoside
Nucleoside + Phosphate → Nucleotide
nNucleotide → Polynucleotide (Nucleic Acid)

Double Strand Helix Structure of DNA

In early 1950s, Rosalind Franklin and Maurice Wilkins used X-ray diffraction to unravel the structure of DNA. The DNA fibers produced a characteristic diffraction pattern. The central X shaped pattern indicates a helix, whereas the heavy black arcs at the top and bottom of the diffraction pattern reveal the spacing of the stacked bases.

The structure elucidation of DNA by Watson and Crick in 1953 was a momentous event in science. They postulated a 3-dimensional model of DNA structure which consisted of two antiparallel helical DNA chains wound around the same axis to form a right-handed double helix.

The hydrophilic backbones of alternating deoxyribose and phosphate groups are on the outside of the double helix, facing the surrounding water. The purine and pyrimidine bases of both strands are stacked inside the double helix, with their hydrophobic and ring structures very close together and perpendicular to the long axis, thereby reducing the repulsions between the charged phosphate groups. The offet pairing of the two strands creates a major groove and minor groove on the surface of the duplex.

The model revealed that, there are 10.5 base pairs (36 Å) per turn of the helix and 3.4 Å between the stacked bases. They also found that each base is hydrogen bonded to a base in opposite strand to form a planar base pair.

Two hydrogen bonds are formed between adenine and thymine and three hydrogen bonds are formed between guanine and cytosine. Other pairing tends to destabilize the double helical structure. This specific association of the two chains of the double helix is known as complementary base pairing. The DNA double helix or duplex is held together by two forces,

• Hydrogen bonding between complementary base pairs
• Base-stacking interactions

The complementary between the DNA strands is attributable to the hydrogen bonding between base pairs but the base stacking interactions are largely non-specific, make the major contribution to the stability of the double helix.

Types of RNA Molecules

Ribonucleic acids are similar to DNA. Cells contain up to eight times high quantity of RNA than DNA. RNA is found in large amount in the cytoplasm and a lesser amount in the nucleus. In the cytoplasm it is mainly found in ribosomes and in the nucleus, it is found in nucleolus.

RNA molecules are classified according to their structure and function into three major types

• Ribosomal RNA (rRNA)
• Messenger RNA (mRNA)
• Transfer RNA (tRNA)

rRNA

rRNA is mainly found in cytoplasm and in ribosomes, which contain 60% RNA and 40% protein. Ribosomes are the sites at which protein synthesis takes place.

tRNA

tRNA molecules have lowest molecular weight of all nucleic acids. They consist of 73 – 94 nucleotides in a single chain. The function of tRNA is to carry amino acids to the sites of protein synthesis on ribosomes.

mRNA

mRNA is present in small quantity and very short lived. They are single stranded, and their synthesis takes place on DNA. The synthesis of mRNA from DNA strand is called transcription. mRNA carries genetic information from DNA to the ribosomes for protein synthesis. This process is known as translation.

Difference between DNA and RNA

More to Know

DNA finger printing Traditionally, one of the most accurate methods for placing an individual at the scene of a crime has been a fingerprint. With the advent of recombinant DNA technology, a more powerful tool is now available: DNA fingerprinting is (also called DNA typing or DNA profiling).

It was first invented by Professor Sir Alec Jeffrey sin 1984. The DNA finger print is unique for every person and can be extracted from traces of samples from blood, saliva, hair etc… By using this method we can detect the individual specific variation in human DNA.

In this method, the extracted DNA is cut at specific points along the strand with restriction of enzymes resulting in the formation of DNA fragments of varying lengths which were analysed by technique called gel electrophoresis. This method separates the fragments based on their size.

The gel containing the DNA fragments is then transferred to a nylon sheet using a technique called blotting. Then, the fragments will undergo autoradiography in which they were exposed to DNA probes (pieces of synthetic DNA that were made radioactive and that bound to the fragments).

A piece of X-ray film was then exposed to the fragments, and a dark mark was produced at any point where a radioactive probe had become attached. The resultant pattern of marks could then be compared with other samples. DNA fingerprinting is based on slight sequence differences (usually single base-pair changes) between individuals. These methods are proving decisive in court cases worldwide.

Biological Functions of Nucleic Acids

In addition to their roles as the subunits of nucleic acids, nucleotides have a variety of other functions in every cell such as,

(i) Energy Carriers (ATP)

(ii) Components of enzyme cofactors (Example: Coenzyme A, NAD⁺, FAD)

(iii) Chemical messengers (Example: Cyclic AMP, cAMP)

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Biomolecules of Vitamins and Their Functions

Vitamins are small organic compounds that cannot be synthesised by our body but are essential for certain functions. Hence, they must be obtained through diet. The requirements of these compounds are not high, but their deficiency or excess can cause diseases. Each vitamin has a specific function in the living system, mostly as co enzymes.

They are not served as energy sources like carbohydrates, lipids, etc. The name ‘Vitamin’ is derived from ‘vital amines’, referring to the vitamins earlier identified amino compounds. Vitamins are essential for the normal growth and maintainance of our health.

Classification of Vitamins

Vitamins are classified into two groups based on their solubility either in water or in fat.

Fat Soluble Vitamins:

These vitamins absorbed best when taken with fatty food and are stored in fatty tissues and livers. These vitamins do not dissolve in water. Hence they are called fat soluble vitamins. Vitamin A, D, E & K are fat-soluble vitamins.

Water Soluble Vitamins:

Vitamins B (B₁, B₂, B₃, B₅, B₆, B₇, B₉ and B₁₂) and C are readily soluble in water. On the contrary to fat soluble vitamins, these can’t be stored. The excess vitamins present will be excreted through urine and are not stored in our body. Hence, these two vitamins should be supplied regularly to our body. The missing numbers in B vitamins are once considered as vitamins but no longer considered as such, and the numbers that were assigned to them now form the gaps.

Table 14.2: Vitamins, their Sources, Functions and their Deficiency Disease

A diverse range of biomolecules exist,

Including:

Small Molecules:

Lipids, fatty acids, glycolipids, sterols, monosaccharides. Vitamins.

Biological Function of Vitamins

Once growth and development are completed, vitamins remain essential nutrients for the healthy maintenance of the cells, tissues, and organs that make up a multicellular organism; they also enable a multicellular life form to efficiently use chemical energy provided by food it eats, and to help process
the proteins, All of the biomolecules that make up our cells are made up of strings of monomers.

For example, proteins are made up of strings of amino acids and nucleic acids are strings of nucleotides. The term for a long string of monomers is a polymer. The biomolecules, proteins, carbohydrates and nucleic acids are all polymers.

Vitamins and minerals are considered essential nutrients-because acting in concert, they perform hundreds of roles in the body. They help shore up bones, heal wounds, and bolster your immune system. They also convert food into energy, and repair cellular damage.

Vitamin, any of several organic substances that are necessary in small quantities for normal health and growth in higher forms of animal life. Vitamins are distinct in several ways from other biologically important compounds such as proteins, carbohydrates, and lipids.