Foundation in Science Assessment 2022

NEWCASTLE UNIVERSITY
FOUNDATION IN SCIENCE
2019/2020
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Question 1
DNA replication
DNA replication entails a biological process where organisms undergo biological
inheritances aspects. DNA replication takes place in a process referred to as semi-
conservative method which yields double strands of DNA with parental strand and a
new daughter strand. The discovery of DNA by researches Watson and Crick on
double-strand helix ability to offer DNA replication offered a milestone in
understanding the dynamics of DNA action. In the cell division process, each DNA
molecule has to the copied so to produce identical molecules towards the daughter
cells. The double-strand structure of DNA entails that each strand can be reproduced
each acting as a template where it produces a new copy of complementary strand
thus generating two double-strand molecules from the original one (Méchali, 2010).
Various models have been advanced to understand the basis of the DNA replication
process, these models of replication entail conservative, semi-conservative and
dispersive. In the conservative avenue, two originals parental strands undergo base
pairing with each other after template usage in synthesizing new strands and the
new two strands referred to as daughter strands undergoing base pair with each
other. In this process, the outcomes yield two DNA molecules with characteristics of
'all old' and the other being 'all-new'. In semiconservative replication process, each of
the two parental DNA strands is able to act as the templates allowing the new
synthesis of DNA strands, after replication, each of the parental strands undergoes
base pairing with the complementary new synthesized strand. Birth doubles strands
will entail one parental or ‘old strand and one daughter also referred to as ‘new’
strand. In the dispersive process, when both copies have replicated, the new strands
would alternate the segments of the parental DNA somehow and the newly formed
DNA is on every two strands (Masai et al., 2010).
In demonstrating this process as observed in the picture, understanding of the
Meselson and Stahl model of replication is fundamental in this process. In Meselson
and Stahl focus is in their model were keen on understanding the processes of DNA
replication. This process entails the application of growing E. Coli generation in
heavy isotope media of nitrogen 15N which has nitrogen bases and eventually to the
DNA. The E. Coli was shifted into a light isotope medium containing isotope of
nitrogen with 14N and allowed for growth in one generation. After the elapse of this
period, the cells were harvested and the DNA isolated. The next step entailed
centrifugation of DNA at high speeds in a tube which there was known caesium
chloride density gradient. Some of the cells were allowed to go one more generation
further at 14N and centrifuged again (Raghuraman and Brewer, 2010).
During the density gradient ultracentrifugation, the researchers applied the use of
caesium chloride salt and spun at high speeds of about 50,000 to 60,000 rounds per
minute. In the centrifuge tube, the density gradient was created by the salt with
higher density allowing movement farther in the tube. During a point in this process,
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the molecules stopped the sedimentation process and formed stable bands. The
band molecules allow for closer identification of relative densities, these molecules
that formed in the lowest bands had the highest identities. This is a similar process
illustrated in the picture related to this question, the formation of bands are depicted
(Raghuraman and Brewer, 2010).
The rationale behind this signals that DNA from the 15N produces the lower band
than the DNA from the 14N, thus signalling higher density of the former compared to
the latter, due to the heavy isotope process. The researchers noted that after each
generational growth of 14N the DNA produces single-strand band intermediate in
DNA cells grown from the 15N and DNA cells exclusively in the 14N isotope. This
signalled a semi-conservative or dispersive replication mode. Had it been
conservative replication, then two bands would have been producing each
representing parental DNA with exclusive 14N located in its nitrogen bases, the single
observed demonstrates that there is an equal amount of both 15N and 14N in the DNA
molecules (Raghuraman and Brewer, 2010).
Analysis on this research by Meselson-Stahl’s demonstrates that cells are grown
from two generations in 14N yields two strands, one strand being at the intermediate
position between the 15N and 14N while the other corresponding to the 14N DNA
exclusively. This clearly demonstrates the observation seen in tube 3 contain the
generation in 14N isotope. This depicts a semi-conservative DNA replication. If it had
been a dispersive replication, then the single brand would be produced exclusively in
each new generation with slow movements of the band closer to the top of the 14N
band, thus ruling out dispersive process which is not observed in our figure (Amado,
2010).
Meselson and Stahl’s findings demonstrate that the DNA replication process offers
an avenue for two strands that make up the double helix are serving as the template
where the new strands are synthesized. The new strand will complement to the
parental or 'old while the new strand remains are base-paired on the old strand. Thus
each daughter DNA has old DNA strand and one new synthesized strand. Coping of
the two daughters DNA leads to identical sequence to one another and identical to
the parental DNA while the two daughter cells are further divided equally forming two
daughter cells, which are genetically identical to one another and genetically
identical to the parent cell.
Hence this illustrative depicts the scenarios observed in this question where there is
a semiconservative mode of DNA replication occurring in view of the application of
nitrogen pairs and process of centrifugation. This is an essential aspect in the
production of photocopy cells in organisms allowing duplicate production and genetic
similarities and differences occurrences.
Question 2
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Transcription process in a cell
Transcription process in the eukaryotic cell takes place in the membrane-bound
nucleus and organelles. The genes bound in the nucleus, they transport the mRNA
to the cytoplasm and must be protected from degradation before being translated.
Eukaryotic cells employ three key polymerases to perform the transcribing in
different subset genes and they are monogenetic specifying single protein.
Transcription entails the aspect of DNA information is copied into new molecules
messengers mRNA. The DNA safely has the ability to store genetic material in the
genetic nuclei to be sued as a referenced template. The mRNA used is similar to the
template carrying information as DNA but not used as long term storage and can exit
the nucleus easily. The mRNA has the same information but is not an identical copy
of the DNA due to its complementary sequence to the DNA template (Fatma, 2018).
The transcription process is carried out by the RNA polymerase and other
accessory proteins referred to as transcription factors. These factors are able to bind
to the specific sequence of DNA through the support of enhancers and promoters so
as to recruit the RNA polymerase to a site for the transcription process. The
transcription factors and the RNA polymerase forms complex transcription initiation.
This process begins with the synthesis of mRNA through matching with the original
DNA strand. The mRNA undergoes elongation after synthesization, thus terminating
the transcription. The newly formed mRNA gene copies are the blueprints of the
protein synthesis during the translation process (Puisieux, Brabletz and Caramel,
2014).
The underlying polymerase process in eukaryotic cells entails the aspects described
above entail the transcription factors which are able to bind the promoter area so as
to initiate appropriate polymerase. The eukaryotic mRNA synthesis is often complex,
the polymerase activity has 10 subunits in each of the three polymerases. Each
polymerase has a different transcription factors set to enable it to bring to the DNA
template.
RNA polymerase I is found in the nucleus, a substructure of the nucleus which
allows the ribosomal RNA to transcribed, processes and assembled into many
ribosome’s. The rRNA is categorized as the structural RNAs due to their cellular
roles but do not undergo a translation into the proteins. The ribosomal rRNAs are the
essential components which are fundamental in the translation process. The RNA
polymerase I is able to synthesize the rRNAs except for the 5S rRNA molecule. The
designation of 'S' denotes the 'Svedberg' units which characterize the centrifugation
speeds (Puisieux, Brabletz and Caramel, 2014).
In RNA polymerase II, synthesis of all protein-coding nuclear pre-mRNAs in the
nucleus, the pre-mRNAs undergo processing beyond the transcription phase with
mRNAs being the process for translating the mature processed molecules. RNA
polymerase II is essential in the transcription activity in many eukaryotic genes.
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