Molecular exam Essay | Online Homework Help

Section A

*word limit: 150 words for all Section A (+10% limit)*

• Explain what is meant by a ‘restriction endonuclease’. (2 marks)

• You are given an 8 kb intact circular plasmid miniprep (pSIB2003). You do not know its sequence but want to assess if it has any useful restriction sites and their relative locations, in case the pSIB2003 can be used as a cloning vector. You undertake single or double (combined) restriction digests of your miniprep using the restriction enzymes EcoRI, XhoI and Hin You then analyse the resulting fragments by 0.8% agarose gel electrophoresis, visualised using ethidium bromide (or Sybr Safe) and UV light. The resulting gel is below:

State how many times (if any) that each restriction enzyme cuts pSIB2003. Draw apossible resulting restriction map of pSIB2003 (i.e. mark the relative location of the restriction sites on the plasmid), determined from the gel. (5 marks)

Turn Over

• No restriction enzyme was included in the last (right hand side) lane – explain what the two bands are and why they do not run at the same expected size as pSIB2003 (8 kb). (1 mark)

• You later perform another restriction digest with NotI which recognises and cuts an 8 bp sequence in pSIB2003, forming cohesive ends with 5’-overhangs of 4 nucleotides, shown by the diagram below. The two shades show the cohesive ends.

What sort of enzyme could be used to fill in the cut fragment’s cohesive ends to produce a flush/blunt end?(2 marks)

Section B (answer ALL questions, each question carries 5 marks)

*word limit: 150 words each question (+10% limit)*

5)Outline the major steps involved in the maintenance of accuracy of DNA replication both during and after DNA synthesis.

6) Describe two ways of making expression of a lac operon constitutive.

Section C(question carries 20 marks)

*word limit: 500 words (+10% limit)*

7) Give an account of chromatin structure, with particular emphasis on how chromatin is modulated to switch genes on and off.

4P Double spaced