Question

The following DNA sequence occurs at the start of a DNA strand: 3′—AATTGCAGATTCA—5′. Which of the sequences below would most likely bind to this sequence to initiate DNA replication through the formation of RNA ?

A.    5′—TTAACGTCTAAGT—3′

B.    3′—TTAACGTCTAAGT—5′

C.    3′—UUAACGUCUAAGU—5′

D.    5′—UUAACGUCUAAGU—3′

Answer 1

Answer- D) 5'-- UUAACGUCUAAGU --3'

DNA replication is the process of synthesizing identical copies of double stranded DNA. During this process, the double stranded DNA unwinds into two and each strand act as templates for the synthesis of new daughter strands on it by the help of the enzyme DNA polymerase. A short segment of RNA, called a primer, is then synthesized and acts as a starting point for DNA polymerase to start replication. This RNA primer is later replaced with DNA to complete the process of DNA replication.

So the strand that bind to the given strand would be complementary to it and also would be in the opposite polarity. Complementarity means guanine (G) will bind with cytosine (C) and vice versa. Similarly thymine (T) in the given DNA strand pairs with adenine (A) where as adenine in the given DNA strand will be complementary to uracil (U). This is because the nitrogenous base thymine is replaced with uracil in RNA. Polarity of nucleic acids are represented by 5' and 3' ends. The two strands of nucleic acids are anti-parallel to each other. Hence the 3' end of one strand pairs with the 5' end of another strand. When we consider these factors, we can conclude that the sequence most likely bind to the given DNA sequence will be 5'-- UUAACGUCUAAGU --3'