Replication of human genome Flashcards
Is the polymer symmetric ?
It is asymmetric
What is on the 5’ end and 3’ end ?
5' = Phosphate 3' = Hydroxyl
What bases are Pyrimidines and Purine ?
Pyrimidines = Cytosine, Thymine and Uracil Purines = Adenine and Guanine
What kind of ring do Pyrimidines have ?
They have a single hexametric ring of C and N atoms
What kind of ring do Purines have ?
They are made of two rings
DNA replication is semi-conservative. Meaning ?
Each double-stranded DNA molecule is made of one parental and one newly-synthesised strand
During replication, what strand is continuous and discontinuous ?
- Leading strand replication proceeds continuously
- Lagging strand replication is discontinuous
The daughter DNA strand is assembled from smaller fragments called ?
Okazaki Fragments
The lagging strand is synthesised discontinuously, in a series of small fragments called Okazaki fragments, which are then ?
Processed by fill-in and ligation to yield the final continuous DNA strand
Polymerisation by DNA polymerases requires ?
A primer, which can be DNA or RNA
In genomic DNA replication this primer is made of ?
RNA
What polymerase initiates synthesis in the initiation of DNA synthesis ?
DNA polymerase α
Both the leading strand and Okazaki fragment synthesis is initiated from ?
RNA primers made by the primase, and elongated by DNA polymerase alpha
While DNA pol epsilon then takes over from alpha in the leading strand, DNA pol delta ?
Does so at the lagging strand
RNA primers are then removed by
The combined action of DNA pol, helicase, nuclease and ligase
The ends of linear DNA cannot be fully replicated due to ?
The polarity of DNA synthesis (5’ to 3’ only) and the fact that DNA synthesis requires an RNA primer
A terminal gap is left on the daughter molecule end replicated by ?
Lagging strand, due to inability to fill-in the gap after RNA primer removal
Human telomeres are made of ?
Hexa-nucleotide repeats (5’-TTAGGG-3’) arrayed in a tandem arrangement for 2-10 kb at the chromosome terminus
The lagging telomere experiences terminal sequence loss due to ?
RNA primer removal and lack of fill-in
Because the RNA primers are short (7-12 nucleotides), a correspondingly small amount of ?
Sequence is lost at each division
However, the leading telomere is also shortened, in this case due to ?
- Lack of template in correspondence of the single-stranded overhang
- This shortening is much more significant, in the order of 100-200 nucleotides
What is Telomerase ?
Telomerase is a reverse transcriptase with its own associated RNA which serves as the template for the synthesis of telomeric DNA repeats to the chromosome end, to counterbalance the loss of terminal sequences.
