E5. Nucleic acid structure and DNA replication Flashcards
which bases are the pyrimidines and the purines?
purines- adenine and guanine
pyrimidines- uracil, thymine, cytosine
-structure on one note
ATP structure?
adenine (nitrogenous base), a ribose sugar and three phosphate groups ONE NOTE FOR STRUCTURE
how are nucleic acid sequences synthesised?
synthesised 5’ to 3’ end- structure on one note
Describe the nucleosome
-composed of highly basic proteins
-DNA is wound twice around nucleosome
Describe DNA polymerase
-replicate and repair DNA
-DNA polymerases only synthesise from 5’ to 3’
-DNA polymerases need the 3’ end of a nucleic acid strand to add on to. This can be DNA or RNA and is called a primer
Explain DNA replication
-helicase enzyme unwinds the double strand
-DNA replication requires synthesis of RNA primers and hydrolysis of triphosphates
-DNA replication is completed after RNA primers are replaced with DNA
-DNA polymerase continues to synthesise DNA until it hits the 5’ end of another RNA primer
-RNA primers are removed
DNA replication is usually followed by mitosis (cell division) in which what happens?
-During DNA replication, the nucleosomes are also duplicated
-The ends of the chromosome protected by telomeres
-after DNA replication, duplicated chromosomes stay attached at a single point. Duplicated chromatin is packed tightly, shortening length, reducing chance of tangles or breaks
Describe cancer drugs in DNA synthesis
-Inhibition of thymidine monophosphate synthesis
(fluorouracil, aminopterin, methotrexate)
-Does affect RNA synthesis, because thymidine is only used in DNA: toxicity limited to effects on tissues with DNA replication
anti- microbial drug targets in DNA synthesis
-Many antibiotic and antiviral drugs inhibit the DNA metabolism of the microbe/virus, but not of the host
-Inhibition of bacterial thymidine monophosphate synthesis
-(Fluorocytosine, Trimethoprim)
Inhibition of reverse transcription (RNA dependent DNA synthesis) in HIV infection (azidothymidine, AZT)
