Question

2. Describe transcription in your own words clearly but concisely enough that someone could visualize what is happening.

Answer 1

Ans:- process which involves transformation of DNA to RNA is called a transcription. the complementary principle is applied here in this case also adenine forms new base pair with uracil instead of thymine. in this process one strand of the DNA called coding strand is copied to RNA. the process is catalyzed by an enzyme called RNA polymerase. the immediate product of transcription is called as primary transcript and it is processed to yield a single type of mRNA encoding a single protein. transcription starts from the first base pair called the start point.

The process of transcription can be divided into three stages: initiation, elongation and termination which are discussed under the following headings;

Initiation:- the enzyme RNA polymerase binds the promoter and starts the initiation reaction by foming a closed binary complex closed in sense means the DNA is duplex. the DNA is then opened to form the open complex by melting a short sequence of DNA within the squence bound to the enzyme now the incorporation of first two nucleotides takes place and phosphodiester bond forms between them this generates the teritiary complex comtainning DNA, RNA and enzyme.

Elongation:- it involves the movement of the transcription bubble by disruption of DNA structure. the enzyme moves and extends the growing RNA chain as the enzyme moves it unwinds the DNA helix to expose new segment of the DNA and nucleotides are covalently added to 3' end o the growing chain, forming the DNA, RNA hybrid. During elongation when RNA polymerase transcribes DNA unwinding and rewinding occurs. the overalll reaction rate is 40 nucleotides per second at 37 degree celcius.

Termination;- it involves the recognition of the point at which no further bases should be added to the chain the sequences which are required for these reactions is called the terminator. At this point enzyme stops adding nucleotides to the growing RNA chain releases the completed product and dissociates from the DNA template. there are various concepts which describe the termination process and are intrinsic termination and Rho-dependent termination.