CELS 191 Lecture 16

Select the statements that apply to prokaryotic DNA

Select the statements that apply to eukaryotic DNA

What is the role of the primase enzyme in DNA replication

What is the role of the DNA Polymerase III enzyme in DNA replication

What is the role of the Helicase enzyme in DNA replication

What is the role of the Topoisomerase enzyme in DNA replication

What is the role of single stranded binding proteins in DNA replication

What is the role of Ligase in DNA replication

The overall direction of DNA synthesis on the lagging strand is in the 3'-5' direction

How are errors in DNA sequence corrected during replication?

[blank_start]During[blank_end] DNA replication, errors in DNA sequence are corrected with [blank_start]exonuclease[blank_end] activity of DNA polymerase [blank_start]III[blank_end]. It checks the newly added bases against the [blank_start]template[blank_end], removes it and replaces it so synthesis can continue as normal.

[blank_start]After[blank_end] DNA replication, any errors in the sequence are corrected by [blank_start]endonuclease[blank_end] activity of DNA polymerase [blank_start]II[blank_end]. it removes the incorrect bases and some either side, [blank_start]DNA polymerase[blank_end] corrects the mistake, then [blank_start]Ligase[blank_end] [blank_start]joins[blank_end] the newly synthesised sequence to the pre-existing sequence with [blank_start]phosphodiester bonds[blank_end].

Failure to [blank_start]correct[blank_end] mistakes in DNA sequence will lead to [blank_start]permanent[blank_end] changes in [blank_start]DNA[blank_end] sequence, in turn leading to a [blank_start]mutation[blank_end]

PCR (P[blank_start]olymerase[blank_end] C[blank_start]hain[blank_end] R[blank_start]eaction[blank_end]) [blank_start]amplifies[blank_end] a gene so you can have [blank_start]multiple[blank_end] copies of the [blank_start]same[blank_end] gene. There are no [blank_start]lagging[blank_end] strands (unlike prokaryotic replication) as both strands are synthesised [blank_start]continuously[blank_end].

Select the key components of PCR

At what temperature does Denaturation of double stranded DNA occur during PCR?

At what temperature does Annealing of DNA templates occur during PCR?

At what temperature does extension/elongation occur during PCR?

What is the role of DNA polymerase I during DNA replication

DNA replication begins with [blank_start]Helicase[blank_end] unwinding the DNA strands from an [blank_start]AT[blank_end] rich origin of replication, with [blank_start]Single[blank_end] [blank_start]Stranded[blank_end] [blank_start]Binding[blank_end] [blank_start]Proteins[blank_end] (SSBP) protecting the strands from [blank_start]degradation[blank_end] and stopping them from coming back together again. Topoisomerase releases [blank_start]tension[blank_end] at the replication fork by cutting and gluing the strands back together again. [blank_start]Primase[blank_end] adds an [blank_start]RNA[blank_end] primer with a chemically reactive [blank_start]3[blank_end]’ hydroxyl group, then DNA Polymerase [blank_start]III[blank_end] adds complimentary [blank_start]nucleotides[blank_end] from that hydroxyl group. On the leading strand, synthesis happens [blank_start]continuously[blank_end] in the [blank_start]5'-3'[blank_end] direction, however on the lagging strand this occurs [blank_start]discontinuously[blank_end] in the overall [blank_start]3'-5'[blank_end] direction in [blank_start]Okazaki[blank_end] fragments. RNA primers are added intermittently along the strand, with DNA Polymerase III adding the complementary nucleotides in the 5’-3’ direction. DNA Polymerase [blank_start]I[blank_end] then comes and removes the RNA primers on the leading and lagging strands, and fills in the gaps with [blank_start]complimentary[blank_end] nucleotides. [blank_start]Ligase[blank_end] forms the bonds between 3’ hydroxyl and 5’ phosphate groups, completing DNA synthesis.