NEET Chemistry Notes Biomolecules – Nucleic Acids
These are biological polymers. They function as the chemical carriers of cell’s genetic information.
DNA (Deoxyribose Nucleic Acid)
- DNA is the polymer of nucleotide.
- It is a genetic material.
- It has double helical structure.
- Nucleotide has deoxyribose sugar, phosphate and nitrogenous base.
- Nucleoside has deoxyribose sugar and nitrogenous base. A unit formed by the attachment of a base to l’-position of sugar is known as nucleoside.
- In nucleosides, the sugar carbons are numbered as l’,2′,3′ etc., in order to distinguish these from the bases. When nucleoside is linked to phosphoric acid at 5′-position of sugar moiety, we get a nucleotide.
- Nucleotides are joined together by phosphodiester linkage between 5′ and 3′ carbon.
RNA (Ribose Nucleic Acid)
- It is also a polymer of nucleotide units but in it the nucleotide unit contains ribose sugar instead of deoxyribose sugar.
- RNA has uracil (U) instead of thymine (T).
- RNA molecules are of three types, these are messenger RNA (mRNA), ribosomal RNA (rRNA) and transfer RNA (tRNA). They perform different functions.
Biological Functions of Nucleic Acids
- DNA has an ability of self duplication during cell division and identical DNA strand are transferred to daughter cell. In this way, DNA is responsible for maintaining the identity of different species of organisms over million of years.
- RNA molecules synthesised various types of nroteins in the cell but the message for the particular type of protein is present in DNA.
The communication among cells is established by certain biomolecules called hormones which act as messengers. Hormones are defined as a group of biomolecules which are produced in the ducUess (endocrine) glands and are carried to different parts of the body by the blood stream where they control various metabolic processes or show physiological activity which may be inhibitory or stimulatory. They are required only in very small amounts and are not stored in the body.
The communication among cells is established by hormones which act as messengers.
Classification of Hormones
- Steroid Hormones Steroids are a group of naturally compounds which are widely distributed in plants and animals. A part from hormones, the steroid nucleus is found in some vitamins, drugs, and bile acids, steroid alcohols are known as sterols. Cholesterol is the most common sterol present abundantly in animals. It is a part of all cell membranes and is the starting point for the synthesis of all other steroids.
Steroid hormones are of two types
- Sex hormones are one of the most important groups of steroid hormones. In males, steroid hormones originate in testes and adrenal cortex. Testosterone, dihydrotestosterone and androgens are the principal male sex hormones. Estrogens are female sex hormones. These are produced primarily in ovaries and are responsible for development of female sex characteristic during puberty. A third group of sex hormones are gestagens.- These are corpus luteum hormones. Common examples of gestagens are progesterone, pregnandiol etc. These sex hormones have significant effects on anabolic system.
- Adrenal cortex hormones or corticoids are produced by cortex of the adrenal glands. Cortisone, corticosterone and aldosterone are examples of corticoids. These hormones regulate metabolic process, control mineral and water balance. The deficiency of these hormones results the loss of fluids and their excess results is an increase in blood pressure.
Peptide Hormones These hormones are made up of α – amino acid units. Some examples of peptide hormones are insulin, oxytocin, vasopressin, angiotensin II glucagon, secretion etc. A few important peptide hormones are briefly discussed.
- Insulin Its function is to lower blood glucose level. Its deficiency in human beings causes diabetes.
- Oxytocin It is secreted by the posterior lobe of pituitary gland. It is a nanopeptide with the following amino acid sequence.
- Vasopressin It is also secreted by the posterior lobe of pituitary gland. It controls the reabsorption of water in the kidneys. It is a nanopeptide with the following amino acid sequence.
- Angiotensin It is present in blood plasma of persons with high blood pressure (hypertension). It leads to the constriction of blood vessels.
It is an octapeptide, i.e. consists of eight amino acid residues.
Amine Hormones These hormones are water soluble compounds. These are structurally derived from amino acids. Examples of amine hormones are adrenaline (epinephrine) and thyroid hormones such as thyroxine.
- Adrenaline It is secreted by adrenal medulla. It is needed to prepare animals including humans for emergency in several ways. It increases the heartbeat rate, the heart output and the blood pressure.
- Thyroid hormones such as thyroxine are secreted by thyroid gland. These control the metabolism of carbohydrates, proteins and lipids. The deficiency of hormones causes series of metabolic disturbances in the body such as diabetes, goitre etc.
An imbalance of sex hormones may result in malfunctioning of the sex organs.