Question

One DNA strand of a chromosome, the sequence of nucleotides below is present where the template strands separate to form a replication fork: 3' C C T A G G C T G C A A T C C 5' An RNA primer is formed starting at the underlined T (T) of the template. Which of the following represents the primer sequence?

A. 5' G C C T A G G 3'
B. 3' G C C T A G G 5'
C. 5' A C G U U A G G 3'
D. 5' A C G T T A G G 3'
E. 5' G C C U A G G 3'

Answer 1

The correct sequence for the RNA primer starting at the underlined T of the DNA template is 5' A C G U U A G G 3', which is complementary and antiparallel to the DNA strand, matching option C.

Step-by-step explanation:

The correct RNA primer sequence that will complement the given DNA template, beginning at the underlined T nucleotide, is 5' A C G U U A G G 3'. To determine this, remember that the RNA primer is built in the 5' to 3' direction and that RNA uracil (U) pairs with adenine (A) instead of thymine (T). Therefore, starting from the underlined T on the DNA template which is the 3' end of the primer, the complementary primer sequence runs opposite it in the 5' to 3' direction, resulting in a sequence complementary to the DNA strand from right to left. This gives us the sequence that begins with A (complementary to T) and ends with G (complementary to C), which is represented as option C: 5' A C G U U A G G 3'.

Nucleic acid sequences are written with the nucleotide having a free phosphate group (the 5' end) starting first. The DNA and RNA strands are antiparallel, and DNA polymerase can only extend a new strand in the 5' to 3' direction using a 3'-OH end as a starting point, provided by an RNA primer synthesized by primase.

Answer 2

The primer sequence is 5' A C G U U A G G 3'. Thus the correct option is (C).

Explanation :

When DNA replication occurs, the double-stranded DNA molecule separates into two single strands, forming a replication fork. One of these strands, called the template strand, serves as a guide for the synthesis of a new complementary strand. In this case, the sequence of nucleotides on the template strand is 3' C C T A G G C T G C A A T C C 5'. Thus the correct option is (C).

To initiate DNA replication, an RNA primer is synthesized by an enzyme called primase. This primer is complementary to the template strand and provides a starting point for DNA polymerase to synthesize the new DNA strand. In this example, the primer is synthesized starting at the underlined T (T) on the template strand.

The sequence of the RNA primer is determined by complementary base pairing between the RNA nucleotides and the template strand. Since RNA nucleotides have a uracil (U) instead of thymine (T), the primer sequence is 5' A C G U U A G G 3'. The first nucleotide of the primer is adenine (A), which pairs with thymine (T) on the template strand. The second nucleotide is cytosine (C), which pairs with guanine (G) on the template strand. This pattern continues until the end of the primer sequence. Once synthesized, the RNA primer is replaced with DNA nucleotides by DNA polymerase during elongation of the new DNA strand.