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SMU-DDE-Assignments-Scheme of Evaluation PROGRAM SEMESTER SUBJECT CODE & NAME BK ID DRIVE MARKS Q.No 1 A 2 A MSC BIOINFORMATICS 2 BI0029 MOLECULAR BIOLOGY B0827 WINTER 2015 60 Criteria Marks Total Marks Discuss the phenomenon of Rho-dependent and Rho-independent termination of transcription in prokaryotes. (Unit 3, Page No. 86) Explanation for Rho-dependent termination of transcription in 5 10 prokaryotes: The rho-dependent terminator received its name because it is dependent on a specific protein called a rho factor. This protein binds and runs along the mRNA towards the RNA polymerase. When ρ-factor reaches the RNAP, it causes RNAP to dissociate from the DNA, terminating transcription. Explanation for Rho-independent termination of transcription 5 in prokaryotes: The rho-independent termination is simpler of the two systems and as a result is also called simple termination. The rho-independent signal is found on the DNA template strand. It contains a stretch of sequences which is repeated again a few base pairs away in the inverted sequence. When this stretch is transcribed into an RNA sequence, the RNA can fold back and base pair with itself forming a hairpin loop terminating the transcription. Explain any six differences between DNA and RNA. Add a note on Griffith’s ‘Bacterial transformation experiment’. (Unit 1, Page No. 20, 22) Six of the following differences between DNA and RNA. 6X1 10 DNA RNA Double polynucleotide Single polynucleotide chains. chain. Larger molecular mass Smaller molecular mass. SMU-DDE-Assignments-Scheme of Evaluation Always a double helix May have a single or double helix. is Pentose sugar is ribose. Pentose sugar deoxyribose The bases are adenine, guanine, cytosine and thymine. Found entirely in the nucleus The bases are adenine, guanine, cytosine and uracil. Made in the nucleus but found throughout the cell. Permanent Temporary- exists for a short time. Exists in one form only Exists in many forms messenger, ribosomal and transfer RNA etc., Griffith’s ‘Bacterial transformation experiment’: Griffith carried out experiment on the bacterium Streptococcus pneumoniae. S. pneumoniae exists in two forms: Harmful form and safe form. His experiments can be summarized as follows: a. S-strain kills mouse; S-strain + Live mouse Dead mouse(S-strain recovered) b. R-strain does not kill mouse; R-strain + Live mouseLive mouse(No bacteria recovered) c. Heat killed S-strain does not kill mouse: Heat killed S-strain + Live mouseLive mouse(No bacteria recovered) d. R-strain + heat killed S-strain kills live mouse. Live S-strain Heat killed + R-strain +Live mouseDead mouse (Encapsulated strain recovered). 4 When live bacteria isolated from the dead mouse after mixed infection, S-type bacteria were obtained. The live R bacteria had been transformed into the harmful S bacteria. Griffith called the substance responsible for the transformation as the ‘Transforming principle’. 3 A Explain any five causes of cancer. Explanation for any five of the following causes of cancer: a. Retroviruses b. DNA viruses c. Hereditary predisposition (Unit 8, Page No. 234 ) 5X2 10 SMU-DDE-Assignments-Scheme of Evaluation 4 A d. Ionizing radiation e. Ultraviolet light f. Chemical mutagens Describe the process of RNA editing. Explain its types. Description for the process of RNA editing: RNA editing is a process in which the information content is altered in a RNA molecule through a chemical change in the base makeup. Till date, this process is observed in eukaryotes, not in prokaryotes. RNA editing occurs in the cell nucleus, cytosol, as well as in mitochondria and plastids, which are thought to have evolved from prokaryotic-like endosymbionts. Explanation for the types of RNA editing: a. Editing by insertion/deletion: RNA editing through the addition of Uracil has been found in mitochondria from kinetoplastid protozoa. This uses a guide RNA (gRNA) that is complementary to the region to be changed, with some differences. The gRNA binds to the region to be edited, and the differences are copied from the gRNA to mRNA. This is typically seen in mitochondria and the functional effect is often a frameshift. b. Editing by deamination: C-U editing: This type of editing involves Cytidine deaminase that deaminates a Cytosine base into a Uracil base. An example of C to U editing is with the apolipoprotein B gene in humans. Apo B100 is expressed in the liver and apo B48 is expressed in the intestines. The B100 form has a CAA sequence that is edited to UAA, a stop codon, in the intestines. It is unedited in the liver. A-I editing: this has been found in large genes with extensive areas of double stranded RNA. During translation, I pairs as if it is G. The enzymes responsible for A-to-I editing are called the adenosine deaminases. Long extended dsRNAs undergo massive editing, whereas RNA duplex structures with bulges and loops are subject to site-selective editing, as observed in several neurotransmitter receptor mRNAs ensuing (Unit 4, Page No. 128) 5 10 5 SMU-DDE-Assignments-Scheme of Evaluation 5 A 6 A single amino acid substitutions. The deficiency or mis-regulation of A-to-I RNA editing has been implicated in the etiology of neurological diseases, such as epilepsy, amyotrophic lateral sclerosis (ALS), and depression in mammals. Explain the four levels of eukaryotic gene regulation. (Unit 6, Page No. 192) Explanation for the four levels of eukaryotic gene regulation: 3+2+2+3 10 Regulation at Transcriptional Level. (3 Marks) Post-transcriptional Modification. (2 Marks) Translational control (2 Marks) Post translational control (3 Marks) Define genetic code. Describe any eight features of genetic code. (Unit 5, Page No. 158) Definition of genetic code: 2 10 Genetic code is a set of rules by which information encoded within genetic material is translated into proteins. Eight features of genetic code: 8 1. Each codon contains three bases that code for one aminoacid. 2. The codons do not overlap 3. Most of the aminoacids have more than one codon. Many codons that codes for only one aminoacid differ from each other by only the last base. 4. There are three stop codons. They are UAA, UAG, and UGA. 5. The genetic code is universal. It exists in prokaryotes and eukaryotes and even viruses. 6. There is one start codon, AUG. It signals the start of translation. 7. The AUG codon also codes for the incorporation of the aminoacid methionine. 8. The region between the start and the stop codons is called the coding region or the Open Reading Frame (ORF). *A-Answer Note –Please provide keywords, short answer, specific terms, specific examples (wherever necessary) **********