Molecular Biology Questions

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Molecular Biology

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

SECTION A Short – Answer Questions  

 

  1. The available evidence indicates that each eukaryotic chromosome (excluding polytene chromosomes) contains a single giant molecule of DNA. What different levels of organization of this DNA molecule are apparent in chromosomes of eukaryotes at various times during the cell cycle?

 

  1. In molecular biology, two identical molecules with different linking number are said to be topoisomers. Describe how a circular DNA molecule can be converted from one topoisomer into another if there are no free ends?                                                                   

 

  1. Look at below illustration of an origin of replication and answer the following questions.                                                                                                                              
  • Add the following primer (5’– GCUAUCG –3’) to its complementary sequence at the given diagram and show the direction of replication by an arrow.
  • Why this primer is needed in the process?
  • If the replication fork moves to the right, will the primer be used to create the leading strand of replication or the lagging strand? Explain your answer.
  • If you answered lagging strand, explain why this leads to discontinuous replication. If you answered leading strand, explain how this leads to continuous replication.

 

  1. Transcription is the process of making mRNA from a gene in the DNA, answer the following;                                                                                                                  
    • Explain briefly how mRNA would be transcribed from DNA? What is the key enzyme for this process? 
    • How does the enzyme know where to start and stop the transcription?
    • Below sequence is a short strand of double-helix DNA. The start of RNA transcription is shown with the number +1. Identify each of the following characteristics.

 

  1. Template strand
  2. Coding strand
  • Identity of base number +3
  1. Identity of base number -4
  2. What is the identity of the base five nucleotides upstream from +1?
  3. What is the identity of the base two nucleotides downstream from +1?

 

 

 

SECTION B Long – answer Questions  

 

 

 

5.      Evidence favoring DNA as the genetic material was first obtained during the study of bacteria and bacteriophages, answer the following questions                            a.      How did the transformation experiment of Griffith differ from those of Avery and his associates?

  1. What was the significant contribution of each?
  2. Why Griffith’s work was not an evidence for DNA as the genetic material, whereas the experiments of Avery and coworkers provided direct proof that DNA carried the genetic information?

In regards to Hershey and Chase experiment, answer the following:

  1. What was the objective of the experiment carried out by Hershey and Chase?
  2. How was the objective accomplished?
  3. What is the significance of this experiment?

 

 

 

6.      In regard to how organisms might replicate their DNA, answer the following questions and use the illustration to answer                                                                                       

  1. What were the main competing models for the mechanism of DNA replication?
  2. What technique did Meselson and Stahl use to test whether any of these models appeared to be at work? What were the goals of the control experiments of Meselson and Stahl?
  3. Show how many generations of DNA replication must be examined to reach a definitive conclusion? Do Meselson and Stahl’s results point to a particular model of DNA replication?

 

 

7.      Assume that the following polynucleotide is part of long DNA molecule. Answer the following questions and use the illustration whenever necessary  to answer                                                                                                                                      

 

a)   Write out the product would be obtained from its replication as double stranded molecule and the product would be obtained from its transcription.b)   Distinguish between; (i) unidirectional and bidirectional synthesis, and (ii) continuous and discontinuous synthesis of DNA.c)    During replication, what would be the consequences of the loss of functions of;                                                                       i.      single-stranded binding proteins,                                                                      ii.      DNA ligases,                                                                    iii.      DNA topoisomerases, and                                                                    iv.      DNA helicases? 

 

THE END J