Only One DNA Strand Participates in Transcription, Why?

Transcription is considered as the first step in gene expression. It refers to the copying of DNA sequence into an RNA sequence. However, unlike DNA replication, only one strand is transcribed. The question is why both the DNA strands are not copied during transcription.

The DNA strand involved in transcription is called template DNA and the other strand which does not take part in transcription is called coding strand. Now, let's imagine, if both strands participate in transcription i.e., act as a template, they would code for RNA molecule with different sequences. Now, if these RNA strands code for proteins, they would be of different types. This means, one DNA strand would code for different proteins and this would result in complication in terms of the genetic information transfer machinery. Besides, if two RNA molecules are produced simultaneously, they would complement each other and would form a double stranded RNA. The double stranded RNA would eventually resist from being translated into proteins.

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DNA Replication Question Discussion

There are 15 questions on DNA replication. Some questions have been asked in previous medical entrance examinations while others are not. Please go through all these questions and find the right answer. We'll not provide answer key for the same, but on request, we'll provide the same.

Q1. During DNA replication, torques are relieved by enzymes

(a)    DNA ligase

(b)   DNA polymerase

(c)    DNA helicase

(d)   DNA gyrase

(C.O.M.E.D – K’s 2011) 

  

Q2. 1.7m double helical DNA will have base pairs

(a)    3.4 x 10⁹

(b)   5x 10⁹

(c)    1.7x 10⁹

(d)   1.7x 10⁵

(AMU 2011)

Q3. First step in DNA replication is:

(a)    Synthesis of Okazaki segments

(b)   Formation of DNA templates

(c)    Synthesis of RNA primers

(d)   Activity of ssBP

(M.H.T.CET 2009)

Q4. Okazaki fragments are formed in the direction of

(a)    3’-->  5’

(b)   5’-->  3’

(c)    5’-->  5’

(d)   3’ --> 3’

(W.B 2009)

Q5. In DNA molecule

(a)    Proportion of A to A varies with the organism

(b)   There are two antiparallel strands running in 5’--> 3’ and 3’ --> 5’

(c)    Amount of purine and pyrimidine nucleotides is not always equal

(d)   There are two parallel strands running in 5’--> 3’ direction

(C.B.S.E 2009)

Q6. RNA primer is used in

(a)    Translation

(b)   Replication

(c)    Conjugation

(d)   Transformation

(D.P.M.T 2008)

 

Q7.  DNA replication is semi-conservative as

(a)    Only non-parent strand acts as template

(b)   Both strands of new molecule are synthesized de novo

(c)    One of the strands in each new molecule is parental and the other one is new

(d)   Daughter strands are dispersive

(   (C.O.M.E.D- K’s 2008) 

      Q8. Okazaki fragments during DNA replication

(a)    Polymerize in 3’à 5’ direction and form replication fork

(b)   Prove semiconservative DNA replication

(c)    Polymerize in 5’à 3’ direction and explain 3’à 5’ DNA replication

(d)   Cause transcription

(C.B.S.E 2007)

Q9. DNA replication requires

(a)    DNA polymerase

(b)   DNA ligase

(c)    RNA polymerase

(d)   All of the above

(M.P.P.M.T 2007)

Q10. C-value paradox is

(a)    Diploid DNA content

(b)   Haploid DNA content

(c)    Variation in C-value

(d)   Constancy of C-value

(C.P.M.T 2007)

Q11. Which of the enzymes of DNA replication require ATP

(a)    Helicase

(b)   Ligase

(c)    DNA polymerase

(d)   All of the above

(

Q11. How many OriC are found in E.coli

(a)    1

(b)   2

(c)    3

(d)   4

(

Q12. DNA replication in Bacteria is:

(a)    Unidirectional

(b)   Bidirectional

(c)    Multidirectional

(d)   None

Q13. Which of the following enzyme is absent in DNA Pol II complex of Bacteria

(a)    3’à 5’ exonuclease

(b)   5’à 3’ exonuclease

(c)    Both

(d)   None

Q14. How many base pairs are present in OriC region

(a)    250 bp

(b)   100 bp

(c)    300 bp

(d)   400 bp

Q15. Dna B protein is also called as:

(a)    Ligase

(b)   Protease

(c)    Helicase

(d)   Gyrase

 

 

 

 

 

 

 

 

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