CBSE Class 12-science Answered

Point of Difference

DNA Polymerase I

DNA Polymerase II

DNA Polymerase III

Structural gene

pol A

pol B

pol C

Number of subunits in the structure

1

Greater than or equal to 4

Greater than or equal to 10

Rate of Polymerisation

Low

(16-20 nucleotides/sec)

Low

(40 nucleotides/sec)

High

(250-1000 nucleotides/sec)

Processivity (nucleotides added before polymerase dissociates)

Low

(3-200)

Low

(1500)

High

Greater than or equal to 5,00,000

Proof-reading activity

3ˈ-5ˈ and 5ˈ-3ˈ exonuclease activities

3ˈ-5ˈ exonuclease activity

3ˈ-5ˈ exonuclease activity

Efficiency of primer removal

Best

Nil

Nil

Type of strand synthesised

Lagging strand

No role in strand synthesis

Leading and lagging strands

Role in DNA repair

Active

Active

No role

Biological functions in the cell

DNA replication,

Processing of Okazaki fragments, maturation

Excision repair

DNA replication,

DNA repair,

Translesion DNA synthesis

DNA replication,

DNA repair