Class Chemistry English Volume · Part

C ∫ G as complementary base pairing. The DNA double helix or duplex is held together by two forces, a ) Hydrogen bonding between complementary base pairs b ) 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 i. Ribosomal RNA (rRNA) ii. Messenger RNA (mRNA) iii. Transfer RNA (tRNA) rRNA rRNA is mainly found in cytoplasm and in ribosomes, which contain % RNA and % 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 – 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 Table . Difference between DNA and RNA DNA RNA It is mainly present in nucleus, mitochondria and chloroplast It is mainly present in cytoplasm, nucleolus and ribosomes It contains deoxyribose sugar It contains ribose sugar Base pair A = T. G ≡ C Base pair A = U. C ≡ G Double stranded molecules Single stranded molecules It's life time is high It is Short lived It is stable and not hydrolysed easily by alkalis It is unstable and hydrolyzed easily by alkalis It can replicate itself It cannot replicate itself.

It is formed from DNA. 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 Jeffreysin .

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. Chromosomal DNA (e.g., Suspect ) Cleave with restriction endonuclease. DNA fragments DNA markers DNA markers DNA markers Suspect Suspect Victim Evidence DNA markers Suspect Suspect Evidence Victim Separate fragments by agarose gel electrophoresis (unlabeled). Radiolabeled DNA probe Denature DNA, and transfer to nylon membrane.

Incubate with probe, then wash. Expose X-ray film to membrane. Figure . DNA finger printing .

. 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) Sugar Nitrogenous base (adenine) Phosphate group O - P O - ii. Components of enzyme cofactors (Example: Coenzyme A, NAD + , FAD) HS NH N C N C P P P ' ' ' ' ' Pantothenic acid Coenzyme A '-Phosphoadenosine diphosphate ( '-P-ADP) -Mercaptoethylamine iii.

Chemical messengers (Example: Cyclic AMP, cAMP) ' ' CH Adenosine ', '-cyclic monophosphate (cyclic AMP; cAMP) Adenine P