Practice Set 2 Flashcards
When comparing the three key models of DNA replication, the model that included the
synthesis of a brand new double stranded DNA molecule from an original molecule was
named:
conservative replication.
When comparing the three key models of DNA replication, the model that included the
separation of the two strands of the original DNA (template) and using those strands as
templates to synthesize two new DNA strands is called:
semiconservative replication.
In 1959, Arthur Kornberg isolated DNA polymerase activity from Escherichia coli
cells, revealing its ability to copy DNA by mixing ___________________ in a tube and
measuring synthesis of a DNA strand.
dATP, dGTP, dTTP, dCTP, template DNA, and pure DNA polymerase enzyme
Examine Figure 7-16, recalling that DNA synthesis by DNA polymerases always occurs
in the 5’ to 3” direction. The predominant location of small Okazaki fragments during
DNA replication occurs at the:
lagging strand of replication.
The replisome contains a protein subunit responsible for unwinding the double helix to
enable DNA replication. This subunit/enzyme is named:
helicase.
The replisome contains a protein subunit responsible for attaching free ends of DNA on
the newly formed strand. This subunit/enzyme is named:
ligase.
Topoisomerase and helicase have distinct functions that include which of the following?
Helicase is responsible for unwinding the double helix (separating strands).
The complexity of lagging strand replication is necessary because:
as polymerization occurs only in the 5’ to 3’ direction, the lagging strand must be
synthesized in consecutive small fragments.
When replicating the end of a chromosome, the lagging strand cannot copy the last ~10
nucleotides at the end of the chromosome. As a result, chromosomes contain telomere
sequences at their ends, which are defined as:
non-coding, repetitive sequences that can be copied independent of the replisome.
Telomerase activity relies upon ________________ for appropriate priming.
a short, telomeric RNA sequence that is carried within its structure
Telomeres regulate the replication of the ends of chromosomes in eukaryotes. Why is
this structure implicated in human aging?
Telomeres are structures at the ends of eukaryotic chromosomes that contain tandem
DNA sequences added to the 3’ ends by the enzyme telomerase. Telomeres stabilize
chromosomes by preventing the loss of genomic information after each round of DNA
replication. Human somatic cells contain little or no telomerase, and those that do
contain it get progressively shorter and enter premature senescence. People with
diseases of premature aging such as Werner syndrome and dyskeratosis congenital have
shorter telomeres than healthy people.
How are primase and telomerase similar?
- Both use RNA primers for addition of nucleotides that match single-stranded DNA
sequences. Primase is important in chromosome replication, while telomerase
completes the duplication of telomeres at the ends of chromosomes.
Telomeres have been a recent focus in experiments regarding both aging and cloning.
For example, it has been shown that in the absence of telomerase, the chromosome
becomes shorter and shorter after each cell division. When chromosomes reach a
certain length the cell may cease to divide and die. Hence, maintaining telomerase
action could be a “fountain of youth” for a cell.
Excess telomerase activity is associated with cancer cells, providing unlimited numbers
of cell divisions (immortality) to these cells and presenting a dangerous threat to the
organism.
Find a recent news or research article on telomeres and discuss what its experiments tell
you about the role of telomerase in the cell. Could activation of this enzyme in humans
be beneficial with regard to age-related disease?
- Responses to this question will vary depending upon the article selected. This question
would work well with a take home exam, or a class assignment. Telomerase activity
has been the focus of aging research for over 20years, as scientists examine the role
chromosome ends play in this fascinating process. Some recent papers have reported
success in extending lifespan by manipulating the activity of telomerase. Cancer cells
often gain unlimited cell division cycles through activation of telomerase during the
process of becoming cancerous. Student investigation into this topic will provide some
interesting insight into numerous characteristics of genetics and chromosomes.
