To initiate translation, the $m$ RNA first binds to
the smaller ribosomal sub-unit
the larger ribosomal sub-unit
the whole ribosome
No such specificity exists
In E. coli, the lac operon gets switched on when
lactose is present and it binds to the repressor
repressor binds to operator
RNA polymerase binds to the operator
lactose is present and it binds to RNA polymerase
What is the function of histones in DNA packaging?
Functions of histones in DNA packaging are
(i) Histones as units of octamer participate in primary packaging of DNA.
(ii) Basic histone proteins neutralise the acidic DNA molecule.
Distinguish between heterochromatin and euchromatin. Which of the two is transcriptionally active?
Densely packed and dark stained chromatin regions are called hetorochromation, while, loosely packed light stained regions are called euchromatin.
Euchromation is transcriptionally active and is transcribed into mRNA. Due to very tight coiling heterochromatin can not be transcribed and is inert/inactive form.
The enzyme DNA polymerase in E.coli is a DNA dependent polymerase and also has the ability to proofread the DNA strand being synthesised Explain. Discuss the dual polymerase.
In bacteria, three types of DNA polymerases are there. All of them can add nucleotides in $5^{\prime} \rightarrow 3^{\prime}$ direction. They process exonuclease activity as well. DNA polymerase III can proofread the newly synthesised strand and senses the wrong base insertions.
It deletes wrong bases and helps correct the mistake by putting in the right one, DNA polymerase. The only mistake it cannot corrects substitution of uracil in place of thymin.
It can repair any damages done to DNA by UV exposure, etc., or the left over proofreading mistakes. It detects mutation caused by UV, removes mismatched pairs and puts back the right ones.