Replication of human genome

Question 1

Is the polymer symmetric ?

Answer 1

It is asymmetric

Question 2

What is on the 5’ end and 3’ end ?

Answer 2

5' = Phosphate 
3' = Hydroxyl

Question 3

What bases are Pyrimidines and Purine ?

Answer 3

Pyrimidines = Cytosine, Thymine and Uracil 
Purines = Adenine and Guanine

Question 4

What kind of ring do Pyrimidines have ?

Answer 4

They have a single hexametric ring of C and N atoms

Question 5

What kind of ring do Purines have ?

Answer 5

They are made of two rings

Question 6

DNA replication is semi-conservative. Meaning ?

Answer 6

Each double-stranded DNA molecule is made of one parental and one newly-synthesised strand

Question 7

During replication, what strand is continuous and discontinuous ?

Answer 7

• Leading strand replication proceeds continuously

- Lagging strand replication is discontinuous

Question 8

The daughter DNA strand is assembled from smaller fragments called ?

Answer 8

Okazaki Fragments

Question 9

The lagging strand is synthesised discontinuously, in a series of small fragments called Okazaki fragments, which are then ?

Answer 9

Processed by fill-in and ligation to yield the final continuous DNA strand

Question 10

Polymerisation by DNA polymerases requires ?

Answer 10

A primer, which can be DNA or RNA

Question 11

In genomic DNA replication this primer is made of ?

Answer 11

RNA

Question 12

What polymerase initiates synthesis in the initiation of DNA synthesis ?

Answer 12

DNA polymerase α

Question 13

Both the leading strand and Okazaki fragment synthesis is initiated from ?

Answer 13

RNA primers made by the primase, and elongated by DNA polymerase alpha

Question 14

While DNA pol epsilon then takes over from alpha in the leading strand, DNA pol delta ?

Answer 14

Does so at the lagging strand

Question 15

RNA primers are then removed by

Answer 15

The combined action of DNA pol, helicase, nuclease and ligase

Question 16

The ends of linear DNA cannot be fully replicated due to ?

Answer 16

The polarity of DNA synthesis (5’ to 3’ only) and the fact that DNA synthesis requires an RNA primer

Question 17

A terminal gap is left on the daughter molecule end replicated by ?

Answer 17

Lagging strand, due to inability to fill-in the gap after RNA primer removal

Question 18

Human telomeres are made of ?

Answer 18

Hexa-nucleotide repeats (5’-TTAGGG-3’) arrayed in a tandem arrangement for 2-10 kb at the chromosome terminus

Question 19

The lagging telomere experiences terminal sequence loss due to ?

Answer 19

RNA primer removal and lack of fill-in

Question 20

Because the RNA primers are short (7-12 nucleotides), a correspondingly small amount of ?

Answer 20

Sequence is lost at each division

Question 21

However, the leading telomere is also shortened, in this case due to ?

Answer 21

• Lack of template in correspondence of the single-stranded overhang
• This shortening is much more significant, in the order of 100-200 nucleotides

Question 22

What is Telomerase ?

Answer 22

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.