Steps of DNA Synthesis

1) 3' -OH acts as a nucleophile in nucleic acid elongation; pyrophosphate (PPi) is released after dNTP attack and is cleaved to orthophosphate (Pi) to force reaction to be irreversible

2) DNA polymerase holds the template and the primer in the active site; dNTP diffuses to active site to base pair with the template

3) Magnesium ion shields negative charges and activates the 3' -OH, synthesis continues in 5' to 3' direction

4) DNA polymerase may correct mistakes along the way due to their nuclease activity and ability to remove incorrect basics

1) retroviruses begin with two copies of a single-stranded RNA molecule that enter the cell

2) upon cell entry, RNA is copied into DNA via reverse transcriptase (acts as both a polymerase and an RNase)

3) following DNA version of viral genome can be incorporated into chromosomal DNA and is replicated like normal DNA

4) viral genome is later expressed to form viral proteins and RNA that assemble into new viral particles

dna synthesis

retroviruses

1) no primer is needed since 3' -OH attacks inner phosphoryl group of incoming dNTP

2) beginning near a promoter, RNA polymerase synthesizes 5' to 3' powered by hydrolyzing PPi to Pi

3) resulting mRNA has the same sequence as the coding strand but is synthesized complimentary as all U bases become T

4) synthesis ends at a terminator point