A few sentences of answer are enough. 2. The following question is about chromos

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A few sentences of answer are enough.

2. The following question is about chromosome. (a) Describe how DNA is packed into chromosome. (b) Distinguish between heterochromatin and euchromatin. (c) Describe how gene expression is regulated by chromatin remodeling. (6 marks) (2 marks) 4 marks) 3. The following question is about nucleic acids. (a) Describe how nucleic acid purity can be assessed by spectrophotometry. (b) What is hyperchromaxity of DNA? (c) Distinguish between Type II and Type IIS restriction endonucleases. d) List three precautions in total RNA extraction (e) In total RNA purification, which enzyme can be used to remove unwanted genomic DNA. ( Describe how RNA quality can be assessed by electrophoresis. (2 marks) (2 marks) ( mark) (3 marks) (1 mark) (3 marks)

Explanation / Answer

1) DNA is negatively charged and they bind to a protein which is positively charged called Histone proteins and it forms vast number of nucleosomes. Nucleosome forms beads on a string structure. Nucleosomes pack into a coil that twists and that twists into another larger coil and so forth and that produces condensed supercoiled chromatin fibers. The coils fold to form loops. Loops coil even further and that forms a chromosome.

B) Euchromatin is not densely packed, so it is available for transcription while heterochromatin is tightly packed and is not available for the transcription of genes.

C) When cells wants to switch on a gene from chromosome, cytosine are unmethylated or Histones are acetylated, so that dna detaches from Histones and genes can be expressed.

When cell wants to turn off the genes, cytosine of DNA are methylated and histones are deacetylated.

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