ASCP Molecular Biology Certification Exam
Questions & Answers Latest Version 2024
A+Grade
What would you call the polymer of DNA? How many strands are there and why would
they be described as antiparallel?
Polynucleotide- There are two strands
One DNA strand goes in an opposite direction to the other in the double helix strand.
How do two nucleotides join together?
The bottom monomers phosphate joins with the deoxyribose pentose sugar of the top
monomer in a condensation reaction.
The bond is called a phosphodiester bond.
The enzyme is called DNA polymerase.
Three theories of DNA replication
conservative, dispersive, semiconservative
Meselson-Stahl Experiment
First green bacteria in a solution containing a heavy form of nitrogen this meant that when
the scientists obtained the DNA from these bacteria would be heavy.
The bacteria was then put in a light solution which produced medium bacteria.
The bacteria was then put back in a light solution and this produce a range between light
and medium bacteria.
This experiment proved the semi-conservative replication.
DNA replication steps 1 and 2
- DNA helicase will break the hydrogen bonds between the complementary base pairs.
-The DNA is split into two stands with the bases now exposed.
- DNA is a very long molecule so whilst the two strands are being separated by DNA helicase.
Free nucleotides come in and match up by complementary base pairing.
, - Also importantly short strands of RNA, complementary to the bases at the start of the DNA
strands are paired up- DNA primers.
-New H bonds form between the bases.
-Primers are needed as DNA polymerase III can only extend an existing polynucleotide, so
primers are needed as a starting point for DNA polymerase to form the new strand.
DNA replication step 3
-The free nucleotides that have been paired up on the template strand are now joined
together by DNA polymerase III.
-This process happens simultaneously as helicase unwinds the DNA double helix. The place
where helicase is working is called the replication fork.
-DNA polymerase III only works in the 5'-3' direction so one strand is called the leading
strand.
-However, the other strand is antiparallel to the direction of the replication fork (3'-5'),
therefore there will always be a lagging strand created by short fragments of DNA called
Okazaki fragments.
DNA replication step 4
The DNA primers need to be removed, this is done by the DNA polymerase which hydrolyses
each phosphodiester bond and removes the DNA primers.
They are replaced with the correct DNA nucleotides and joined to form the final DNA strand.
For the lagging strand, as the primers are removed and replaced, the separated Okazaki
fragments are joined together by DNA ligase.
DNA ligase joins the phosphodiester backbones of these fragments together in a
condensation reaction.
Transcription
The DNA double helix unwinds and the hydrogen bonds holding the two strands are broken
by the enzyme DNA helicase.
One of the separated strands of DNA, the antisense strand, acts as a template for the
formation of mRNA.
Free RNA nucleotides present in the nucleus pair up with the exposed nucleotides on the
Questions & Answers Latest Version 2024
A+Grade
What would you call the polymer of DNA? How many strands are there and why would
they be described as antiparallel?
Polynucleotide- There are two strands
One DNA strand goes in an opposite direction to the other in the double helix strand.
How do two nucleotides join together?
The bottom monomers phosphate joins with the deoxyribose pentose sugar of the top
monomer in a condensation reaction.
The bond is called a phosphodiester bond.
The enzyme is called DNA polymerase.
Three theories of DNA replication
conservative, dispersive, semiconservative
Meselson-Stahl Experiment
First green bacteria in a solution containing a heavy form of nitrogen this meant that when
the scientists obtained the DNA from these bacteria would be heavy.
The bacteria was then put in a light solution which produced medium bacteria.
The bacteria was then put back in a light solution and this produce a range between light
and medium bacteria.
This experiment proved the semi-conservative replication.
DNA replication steps 1 and 2
- DNA helicase will break the hydrogen bonds between the complementary base pairs.
-The DNA is split into two stands with the bases now exposed.
- DNA is a very long molecule so whilst the two strands are being separated by DNA helicase.
Free nucleotides come in and match up by complementary base pairing.
, - Also importantly short strands of RNA, complementary to the bases at the start of the DNA
strands are paired up- DNA primers.
-New H bonds form between the bases.
-Primers are needed as DNA polymerase III can only extend an existing polynucleotide, so
primers are needed as a starting point for DNA polymerase to form the new strand.
DNA replication step 3
-The free nucleotides that have been paired up on the template strand are now joined
together by DNA polymerase III.
-This process happens simultaneously as helicase unwinds the DNA double helix. The place
where helicase is working is called the replication fork.
-DNA polymerase III only works in the 5'-3' direction so one strand is called the leading
strand.
-However, the other strand is antiparallel to the direction of the replication fork (3'-5'),
therefore there will always be a lagging strand created by short fragments of DNA called
Okazaki fragments.
DNA replication step 4
The DNA primers need to be removed, this is done by the DNA polymerase which hydrolyses
each phosphodiester bond and removes the DNA primers.
They are replaced with the correct DNA nucleotides and joined to form the final DNA strand.
For the lagging strand, as the primers are removed and replaced, the separated Okazaki
fragments are joined together by DNA ligase.
DNA ligase joins the phosphodiester backbones of these fragments together in a
condensation reaction.
Transcription
The DNA double helix unwinds and the hydrogen bonds holding the two strands are broken
by the enzyme DNA helicase.
One of the separated strands of DNA, the antisense strand, acts as a template for the
formation of mRNA.
Free RNA nucleotides present in the nucleus pair up with the exposed nucleotides on the
