Question

5a. For the replication fork shown below: - label the leading and lagging strands; - draw arrows to indicate which direction DNA synthesis is proceeding in for each of these strands; - label their 5' and 3' ends. Replication fork movement →→→ 5'-ATCTGGCAGTACGTACTGGATC CGUCAUGC GTCGAATCTGAC-3' CAGCTTAGACTG-5' ATCTGGCTATTCGT 3'-TAGACCGATAAGCATGACCTAG b. Okazaki fragments are generated during (leading / lagging) strand synthesis (circle the correct answer). c. Some U's are included in one of the strands in the figure. Why are there U's in a figure of DNA replication?

Answer 1

LAGGING STRAND a) 5'- ATCT GG CAG TAC GTACT G GATO - CGUCAUGO 31 GTC GAAT CT GAC 31 ICAGC TTAGACTG II 5 31 ATCTGG CT ATTCT 3' - TAGACCGATA A G CATGA CC TAG LEADING LAGAONG STRAND. be Okazaki fragments are generated during lagguig strand synthesis. The small fragments of DNA formed are called so in the name of Japanese scientist One new strand 5'- 3 auns towards the replication fork is made continuously because DNA polymerase moved in the same direction as replication fork. The other new strand 5'-3' away in the opposite direction of replication form. This stand is made in fragments because, as the fork moves forward DNA polymerase must come off and reattach to newly exposed DNA. C) DNA polymerase can only add uncleotides to the 3rend of an existing DNA srand (They use the free-OH group found at the 3 end as a "hook", adding a uncleotide to this group in the polymerization reaction). DNA polymerase also cannot add first nucleotide at a new wreplication So, an enzyme called primase, makes RNA primer that provides 3' end for DNA polymerase to · wo nke on Primer "prinnes" DNA synthesis. As the RNA is present as primer so 'U' curacie is visible in the new DNA strand which will be later cleaved off and ligated after replication.