Difference between cistron and an exon:
1. Cistron : A segment of DNA coding for a polypeptide ,chain; the structural gene in a transcription unit could be said as monocistronic (mostly in eukaryotes) or polycistronic (mostly in bacteria or prokaryotes).
2. Exon : The coding sequences or expressed sequences are defined as exons. Exons are said to be those sequences that appear in mature or processed mRNA.

Polarity of the two strands of the fork to be shown and polarity as well as arrow mark of the lagging and leading strands to be shown with correct labellings.

Prokaryotic structural genes are found in continuity without any non-coding region. In contrast, eukaryotic structural genes are divided into exons (coding DNA) and introns (non-coding DNA).

The enzymes involved in DNA replication other than DNA polymerase and ligase are listed below with their functions:

1. Lac is switched only adding lactose in the medium, as lactose acts as inducer and makes repressor inactive.
2. Due to this, \(\beta \) -galactosidase is formed which converts lactose into glucose and galactose. As soon as lactose is consumed, repressor again becomes active cause switching off of the system.

Dr.S.P.Rai Chaudhary and Dr.Lalji Singh

A complete set of gene contained in the haloid does of chromosomes and inherited as a unit from one parent is called geome

(a) In presence of an inducer(such as lactose or allolactose), the repressor is inactivated by intersection with the inducer.
(b) Transcription of lac mRNA stops when the repress of the operon is synthesised from the i gene.The repress protein binds to the operator region of the operon and stops transcription.
(c) The gene 'Z' codes for beta-galactosidase.

During RNA processing
(i)unwanted nucleotides are removed
(ii)useful regions are rejoined
(iii)certain nucleotides are added
(iv)some nucleotides are modified, and
(v)folding of molecule

First ribonucleotide in RNA chain is triphosphate, monophosphates

1.It is a DNA sequence that provides the binding site for RNA polymerase for transcription.
2.It is located towards the 5' end (upstream) of the structural gene (of the coding strand).

1.Hershey and Chase Experiment
2.They made two different preparations of bactoriophage.
3. In one, the DNA was made radioactive with \(^{ 32 }{ P }\)
4. In the second, the protein coat was made radioactive with \(^{ 35 }{ S }.\)
5. The DNA being heavier sediments and hence radioactivity was found in the pellet.
6.Protein coat being lighter the radioactivity was found in the supernatant.

Role of Ribosomes
(i) Ribosomes are the main cellular factory of protein synthesis the large subunit has two sites (P and A) for binding of amino acids,so that they are close to each other for formation of peptide bond.
(ii)They also act as catalyst (23s rRNA)in prokaryotes for formation of peptide bonds.ATP provides energy for the activation of amino acids.

(i) DNA-dependent DNA polymerase
 It catalyses the polymerisation of approximately 2000 bps in a second into DNA, with high degree of accuracy.
(ii) DNA-dependent RNA polymerase
It catalyses the formation of RNA from DNA.
(iii) In eukaryotes, there are three types of DNA
dependent RNA polymerase as follows
(a) RNA Polymerase-l Transcribes rRNAs.
(b) RNA Polymerase-II Transcribes precursor of mRNA, i.e. hnRNA.
(c) RNA Polymernse-lII Transcribes tRNA, srRNA and snRNAs.
(iv) Reverse transcriptase is used for the synthesis of complementary DNA over RNA template.