DNA:
DNA – deoxyribo nucleotide is a genetic material which carries distinct characters and responsible for inheritance.
DNA is made up to two polynucleotide chains bonded with hydrogen bonds formed between their nitrogenous bases. The polynucleotide chains are wound helically around each other in such a way that maximum number of hydrogen bonds is formed between opposing nitrogenous bases. In short, molecules of DNA possess a complex structure.
Watson and Crick have proposed the model for DNA first time in 1953. According to them, DNA contains two polynucleotide chains arranged antiparallel. Adenine and thymine are joined with two hydrogen bond and guanine and cytosine are joined with three hydrogen bond in the structure of DNA. A complete helix covers a distance of 34 A° and winding of helix is right handed. The distance between opposing chains is 20 A° means the diameter of the molecules is 20 A°.
DNA replication:
The process by which two molecules of DNA are formed from the original DNA molecules is called DNA replication. Replication process is important for the growth of any organism and is controlled by DNA itself.
Semi conservative replication:
The process of DNA replication starts by breaking down the hydrogen bond between polynucleotide chains with the help of enzyme gyrase and helicase. The two chains move away from each other and new chain is synthesized. Each chain looks like a fork and is called replication fork. New chain synthesis starts at a specific site of parent chain and occurs in both the directions so also called as bidirectional.
At the end, two chains are developed in which one of each is of parental DNA and the other is a new one. Because of this, it is called as semi conservative replication. Each separated parent chain provides information for synthesis of new chain and is called as template chain. The sequence of nucleotide on new chain depends on the sequence of nucleotide on template chain. DNA polymerase-III is the enzyme responsible for synthesis of new chain.
RNA:
RNA – a rib nucleotide is also a genetic material and responsible for synthesis of protein. RNA contains single chain of polynucleotide. There are three types of RNA are present in the cell – messenger RNA (m-RNA), ribosomal RNA (r-RNA) and transfer RNA (t-RNA).
Messenger RNA acts as a messenger and provides information about sequence of amino acids to DNA during protein synthesis.
The act of transfer RNA is to collect amino acids from cytoplasm and bring them at proper places on ribosome for protein synthesis. Each t-RNA transfers one specific amino acid molecule only.
The RNA present in the ribosome is called ribosomal RNA and constitutes 60% of ribosome.
In the beginning of protein synthesis, m-RNA is synthesis from the specific DNA molecules and the process is called transcription. The enzyme responsible for this is transcriptase or DNA based RNA polymerase.
m-RNA contains a specific sequence of its nucleotide and based on that a specific protein is synthesis. This process is called translation.
Self study:
Example-1: What is the distance between opposing chains of polynucleotide in DNA?
a) 30 A°
b) 20 A°
c) 40 A°
d) 50 A°
Answer: The distance between opposing chains of polynucleotide in DNA is 20 A°
Example-2: What is the function of m-RNA?
a) Provide sequence of amino acids to DNA
b) Transfer amino acids to DNA
c) Formation of amino acids
d) Protein synthesis
Answer: m-RNA provides information about sequence of amino acids to DNA for protein synthesis.
Example-3: Name the enzyme responsible for synthesis of new chain of DNA?
a) Gyrase
b) Polymerase
c) DNA-Polymerase-III
d) Helicase
Answer: DNA polymerase-III is the enzyme responsible for synthesis of new chain of DNA.