Question

How many types of DNA ligases? and describe the (Weiss unit) used to determine the concentration these DNA ligases?

Answer 1

DNA ligase is also known as molecular glue. its join DNA molecule together by synthesising phosphodiester bond between nucleotide at the end of two different molecules or at the end of single molecule. OR we can also say that - to join okazaki fragment formed during replication , close repair and seal recombination fragment by phosphodiester bond . this is the enzyme that is responsible for the breaking down phosphate -sugar backbone of DNA .

In human beings, four type of DNA ligase are found. :-

1.DNA ligase I = these enzyme helps in joining of okazaki fragment during lagging strand DNA replication. these enzyme are phosphoprotein.

2. DNA ligase III = it is found in the mitochondria. it is complexes with the XRCC1 .it is the mammalian DNA ligase.

3. DNA ligase IV = it is complexes with XRCC4. it is extended carboxyl - terminal region of 300 amino acid.

3. DNA ligase II = the cellular role of DNA ligase II is not clear. it is more similar to the viccinia virus. encoded DNA ligase.

WEISS unit = the amount of ligase that catalyse of 1nmole of 32P from inorganic pyrophosphate to ATP in 20 minute at 37 degree celsious.