The ends of the linear chromosomes of eukaryotes cannot be replicated by DNA polymerase. This problem is overcome through the us
e of telomerase, an enzyme implicated in aging and cell lifespan. Telomerase contains a noncoding RNA that acts as a moving template to add a repetitive DNA sequence at the chromosome tip, preventing the loss of essential DNA. In mammals, the ends of the chromosomes fold back to form a circular structure called a T‑loop. Select the answers that correctly describe telomeres and the actions of telomerase.
a) Telomerase is a specialized reverse transcriptase and its presence within eukaryotic cells indicates that an early eukaryote was infected by a retrovirus.
b) Inappropriate activation of telomerase can result in cellular immortality, one of the cellular changes implicated in the development of cancer.
c) Telomerase activity is turned off in most human cells, causing the telomeres to gradually shorten as the individual ages.
d) The T-loop protects the chromosome ends from degradation by nucleases and double-strand break repair enzymes.
e) Telomerase activity results in a telomere that is completely double-stranded with no single-stranded region that would be susceptible to nucleases.
The first option indicates an early retroviral colonization of large double-stranded DNA viruses, which are the presumed ancestors of the eukaryotic nucleus; and then inappropriate activation of the telomerase can be implicated in the development of cancer by continous elongation of the telomere length without control.
Its activity can also be turned off leading to continuous shortening during replication and bringing about senesence and aging. the T-loops formed by the activity of the telomerase protects the ends of the chromosomes from being recognized as being broken and degradation.
The water has a dipole that causes it to act like a magnet, attracting other water molecules to it. Adhesion is the attractive forces that cause water to "stick" to a surface other than its own. ... The salt water has a much lower cohesion than plain water so it's attractive forces are less than plain water.
When an individual muscle fiber receives a threshold stimulus, it contracts as much as possible. ... a threshold stimulus is the minimum amount of energy needed to make a muscle fiber contract.
