Question

Differentiate Between the following:-
a. A leading strand and a lagging strand
b. Unidirectional and bidirectional DNA synthesis

Answer 1

Hint: - Both leading and the lagging strand are part of the replication process of the DNA (deoxyribonucleic acid). Various enzymes are involved in the process of DNA replication.
- DNA synthesis and different types of organisms (primitive and advanced) does not follow the same modes. The pattern of movement and growth of the replication eye is different in both.

Complete answer:
a. The key difference between the leading and lagging strands are as follows:

LEADING STRAND	LAGGING STRAND
Leading strand grows continuously	The lagging strand grows discontinuously.
The extension of the leading strand from primer by the action of DNA polymerase occurs without any interruption.	lagging strand involves its formation into segments.
Leading strand is formed without gaps	a lagging strand is formed by the okazaki fragments.
Leading strand does not involve any activity of DNA ligase for its formation.	lagging strand is formed by the activity of ligase
The formation of leading strand requires only one RNA primer	that of lagging strand requires many

b. Unidirectional DNA synthesis is only seen in a few prokaryotes whereas bidirectional DNA replication occurs in all eukaryotes and many prokaryotes.

The difference between unidirectional replication of DNA and bidirectional replication of DNA is as follows:

UNIDIRECTIONAL	BIDIRECTIONAL
In unidirectional synthesis, the replication process occurs in only one direction.	In bidirectional synthesis, the replication process occurs in two directions.
In unidirectional replication only one replication fork is formed.	In bidirectional replication two replication forks are formed
In unidirectional replication, only one end of the replication eye is moving or growing.	In bidirectional replication, both the ends are moving.

Note:
- DNA replication starts at a point or DNA sequence known as origin of replication. DNA replication occurs in cytoplasm in prokaryotes and it occurs in nucleus of eukaryotes but the basic process of the replication remains same in both eukaryotes as well as prokaryotes.
- Although DNA synthesis occurs in different directions in different organisms, the DNA polymerase acts in the same direction ie.5'-3' only.