Exonuclease activity

[Hemichordate]

Do human DNA polymerases only have the 3-5 exonuclease activity? And do bacteria have both 3-5 and 5-3 exonucleases?

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[ilovemcat]

Do human DNA polymerases only have the 3-5 exonuclease activity? And do bacteria have both 3-5 and 5-3 exonucleases?

Yes, you're right.

Prokaryotes have 3 different DNA Polymerases:

1. DNA Pol III: Main 5' to 3' Polymerase responsible for replication. Has 3' to 5' exonuclease Proofreading ability.
2. DNA Pol II: Unknown Function (although recent research shows it functions in DNA repair).
3. DNA Pol I: Same exact functions as DNA Pol III (5' to 3' Polymerase activity and 3' to 5' proofreading ability). BUT it also removes primers via 5' to 3' exonuclease activity.

Eukaryotes DNA pol is complex. You don't really need to know anything specific other than the primary functions of this enzyme:

1. Main 5' to 3' Polymerase responsible for replication.
2. It has 3' to 5' exonuclease Proofreading ability.

 

[docelh]

I know humans have a 5-3 exonuclease activity, for sure.

I think bacteria have both 3-5 and 5-3 as well.

 

[ilovemcat]

I know humans have a 5-3 exonuclease activity, for sure.

I think bacteria have both 3-5 and 5-3 as well.

Don't you mean 3' to 5' nuclease activity in Humans? Polymerization occurs from 5' to 3' and so if there was an incorrect base pair, the polymerase would backspace and replace it in a 3' to 5' direction. The 5' to 3' exonuclease activity is reserved for the removal of primers by separate enzymes.

 

[Don Draper]

I know humans have a 5-3 exonuclease activity, for sure.

maybe MCAT level (more likely to just understand there is a proofreading function).

I think bacteria have both 3-5 and 5-3 as well.

definitely beyond MCAT.

 

[Don Draper]

Yes, you're right.

Prokaryotes have 3 different DNA Polymerases:

1. DNA Pol III: Main 5' to 3' Polymerase responsible for replication. Has 3' to 5' exonuclease Proofreading ability.
2. DNA Pol II: Unknown Function (although recent research shows it functions in DNA repair).
3. DNA Pol I: Same exact functions as DNA Pol III (5' to 3' Polymerase activity and 3' to 5' proofreading ability). BUT it also removes primers via 5' to 3' exonuclease activity.

One thing I learned about the MCAT far too late is this:

Prokaryotes actually have 5 DNA polymerases. You don't need to know this. (they used to think 3).

Eukaryotes DNA pol is complex. You don't really need to know anything specific other than the primary functions of this enzyme:

1. Main 5' to 3' Polymerase responsible for replication.
2. It has 3' to 5' exonuclease Proofreading ability.

Good. Simple. The proofreading would occur on the new strand by backing up, which is made 5' to 3'

the polymerase would backspace and replace it in a 3' to 5' direction. The 5' to 3' exonuclease activity is reserved for the removal of primers by separate enzymes.

Again, going a bit too deep. The nucleophile in the polymerization is the OH on the 3' end, So... the base is removed and then a new base can be added.