Question

Complete the following sentences: "Replication forks from the same origin of replication extend __________. __________ DNA strand is used as template for the leading strand at one fork and for the lagging strand at the second fork. New DNA is synthesized from 5' to 3' on the __________."
a. unidirectionally, A different, both the leading and lagging strands
b. bidirectionally, The same, leading strand
c. bidirectionally, The same, lagging strand
d. unidirectionally, A different, leading strand
e. bidirectionally, The same, both the leading and lagging strands

Answer 1

Answer:

Replication fork from the same of origin of replication extend bidirectionally. The same DNA strand is used as template for the leading strand at one fork and for the lagging strand at the second fork. New DNA is synthesized from $5'$ to $3'$ on the both leading and lagging strands.

Explanation:

DNA replication is the process of producing two identical replicas of DNA from an original DNA molecule. The process begins by the unwinding and separation of strands of DNA at the origin of replication to form a 'Y' shaped replication fork by the DNA helicase enzyme.

In eukaryotic cells, DNA replication is bidirectional. The two strands of DNA are complementary, and they are oriented in opposite directions to each other. One strand is in the  $3'$ to $5'$ direction, while the opposite runs antiparallel ($5'$ to $3'$). The former produces a leading strand, while the latter produces a lagging strand (Okazaki fragments). The formation of Okazaki fragments is due to the action of DNA polymerase. It polymerases the new strand by joining the $5'$phosphate group of the newly adding nucleotide to the $3'$-OH group of the parent chain. Hence, the synthesis of new strands will always occur in the $5'$ to $3'$ direction.

Answer 2

Replication forks from the same origin of replication extend bi-directionally, the same, leading strand (b).

• A replication fork is formed when the helicase enzyme separates the DNA strands at the origin of replication.
• The Y-shaped structure that is formed is called a replication fork. This fork contains two strands that are the leading strand and the lagging strand.
• The leading strand is in the direction of 5' to 3' and the lagging strand is in the direction 3' to 5'.
• DNA polymerase is able to add nucleotides at 5' to 3' direction resulting in the formation of a new strand.