Question

Question 2 1 pts What happens at the telomere once the RNA primer is removed? Think carefully about this answer! The question in my presentation had a mistake. DNA poll replaces the RNA primer at the 5' end of the new strand with DNA. DNA poll replaces the RNA primer at the 3' end of the new strand with DNA. None of the above

Answer 1

The DNA polymerase needs a RNA primer on the leading strand to be able to start polymerization. Afterwards this is not needed anymore, since the replication goes on without a break. On the lagging strand polymerization replication can only work between the replication fork and the next region of double-stranded DNA. See the figure

3 Helicases and Daughter DNA Topoisomerases 5 Double Strand - RNA Primer Parental DNA - Leading Strand Double Strand RNA Primers Okazki Fragments 3 Replication Fork 5 Lagging Strand <3' Double Strand RNA Primer Daughter DNA Double Strand 3 ' New Strand 5' Old Strand 1 W Overall Direction of Replication

The reason for the need for RNA primers is located in the function of the enzymes. While the DNA polymerase can only work on a double stranded template (add nucleotides to the 3'OH-end of the strand) the DNA Primase (actually an RNA polymerase) can work on single stranded targets and thus add the RNA primer there. Then, in the very end of the synthesis of this strand (called lagging strand) one last fraction will not be copied from the template as even if the last primer is set in the very end of the chromosome, once this RNA is degraded a void space is going to remain invisible for DNA polymerase.

Question 2: none of the above.

Question 4:Elongating the 5' to 3' newly replicated DNA strand.

Question 6: Transcription

Question 7: DNA

Explanation:

Q.2: Every RNA primer synthesized during replication can be removed and replaced with DNA strands except the RNA primer at the 5′ end of the newly synthesized strand. This small section of RNA can only be removed, not replaced with DNA. Enzymes RNase H and FEN1 remove RNA primers, but DNA Polymerase will add new DNA only if the DNA Polymerase has an existing strand 5′ to it ("behind" it) to extend. However, there is no more DNA in the 5′ direction after the final RNA primer, so DNA polymerse cannot replace the RNA with DNA. Therefore, both daughter DNA strands have an incomplete 5′ strand with 3′ overhang. This is the reason why telomeres exist, to avoid the important, coding DNA from being shortened. Instead, the repetitive telomere sequences are shortened, which does not affect gene expression

Q3. The enzyme binds to a special RNA molecule that contains a sequence complementary to the telomeric repeat. It extends (adds nucleotides to) the overhanging strand of the telomere DNA using this complementary RNA as a template. When the overhang is long enough, a matching strand can be made by the normal DNA replication machinery (that is, using an RNA primer and DNA polymerase), producing double-stranded DNA.The purpose of Telomerase is to keep the DNA strand from degrading after many subsequent replications. When DNA is copied, the bits on the end are unable to be replicated because polymerase always needs an RNA primer to catalyze its synthesis of new DNA. Once this primer is removed, it always leaves a small gap which the polymerase is unable to fill due to the fact that the primer was removed. Therefore, telomerase is a different kind of polymerase enzyme that adds complimentary RNA bases to the 3' end of the DNA strand. This extends the sequence and allows the length of the DNA strand to remain relatively constant even after many replications of the sequence. The material added usually follows a repeating sequence of base pairs which forms the structure known as a telomere. This protects the DNA from degradation by other enzymes in the cell and also by the limitations of DNA replication. The issue of aging is often associated in the breakdown of telomere enzymes which shortens or eliminated telomeres. This causes the shortening of the DNA strand which means important genetic information is lost, eventually resulting in the breakdown of cellular functions.

alGottlocullo AATICIMAATICAATA ||GIG GTTAG CA AU COCA AUC Bases are added using the telomerase RNA as a template.

Q.6: Sort of a weird question since gene expression involves all all 3 steps to go from DNA to protein, but I would choose transcription as gene expression is measured most commonly by measuring RNA levels, which indicate if a DNA is bound by histones and thus not expressing a gene or vice versa.

Q:7: While individual proteins and mrna last hours in a cell, the half life of a DNA molecule is around 521 years . This makes sense as RNA and proteins come from DNA, and with so many different types of proteins in the body, DNA must have a long lifespan in order to provide the blueprint for the daily transcription/translation of these proteins.