DNA replication

In a Nutshell

Polymerases and Nucleases

Polymerases are enzymes that synthesize nucleic acids by forming phosphodiester (PDE) bonds.

Nucleases are enzymes that hydrolyze PDE bonds.

Exonucleases remove nucleotides from either the 5’ or the 3’ end of a nucleic acid.

Endonucleases cut within the nucleic acid and release nucleic acid fragments.

DNA polymerase Vs RNA polymerase

1. RNA primer required in DNA polymerase
2. reads 3' to 5' in both
3. adds/ grows to 3' end in both
4. high energy Phosphates (Nuleotide tri-phosphates) are required
5. Pauses and checks & repair occur in DNA but not in RNA

Note

Telomerase

• Completes the replication of the telomere sequences at both ends of a eukaryotic chromosome
• Present in embryonic cells, fetal cells, and certain adult stem cells; not present in adult somatic cells
• Inappropriately present in many cancer cells, contributing to their unlimited replication

Telomerase

A ribonucleoprotein that adds TTAGGG repeats to the 3' end of chromosomes (telomere region). It is similar to other reverse transcriptase enzymes in that it synthesizes single-stranded DNA using single-stranded RNA as template (RNA-dependent DNA polymerase).

has 2 major subunits:

1. TERT = telomerase reverse transcriptase subunit