ew Go Tools Window Help More review for Final.pdf (page 21 of 22) 15: How do you
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ew Go Tools Window Help More review for Final.pdf (page 21 of 22) 15: How do you deactivate a transposon? (Pull its plug?) Name two good things and two bad things about transposons What is the relationship between C-value and cDNA? None; one is the amount of DNA in an organism, the other is a type of DNA that is all-coding and lacks introns. Name two safe-havens for transposable elements. Introns, intergenic spacers (5' upstream and 3' downstream) With what you learned this semester, are those truly 'safe' havens? What would expand the genome, cut and paste or copy and paste? Why is our genome bigger than that of E. coli Who was Barbara McClintock? Explain a direct terminal repeat vs. an inverted repeat. 8 8 9 0Explanation / Answer
Excessive Transposable Element(TE) activity can damage exons, many organisms have acquired mechanisms to inhibit their activity. Bacteria may undergo high rates of gene deletion as part of a mechanism to remove TEs and viruses from their genomes, while eukaryotic organisms typically use RNA interference to inhibit TE activity. Nevertheless, some TEs generate large families often associated with speciation events. Evolution often deactivates DNA transposons, leaving them as introns.
Two good things:
- Tn mutants are also quite stable ; once the Tn has been inserted, the frequency of the movement of that element is quite low. When Tn inserts into a gene, there is a complete loss of function in the interrupted gene ; nonleaky mutations.
- Tn mutants also revert by precise excision of the transposon and one of the duplicated target site sequences.
Two bad things:
- Transposable elements are rather large and therefore not preferable to work with when doing fine detail analysis (single nucleotides).
- Transient siRNA expression and low and variable transfection efficiency.
C- value and c DNA are not related.
The C-value is the amount of DNA in the haploid genome of an organism.
The term cDNA refers to complementary DNA. cDNA is synthesized from an mRNA or messenger RNA template. It is synthesized in a reaction that is catalyzed by the reverse transcriptase and DNA polymerase enzymes.
Safe havens—regions of the genome where they will do minimal harm. Safe havens include duplicate genes such as tRNA or rRNA genes.
Safe haven-is a site in the genome where the insertion of a transposable element is unlikely to cause a mutation, thus preventing harm to the host.In this region of genome there are few genes
Ans; Copy and paste mechanism.
Reason:
Retrotransposons are genetic elements that can amplify themselves in a genome and are ubiquitous components of the DNA of many eukaryotic organisms. These DNA sequences use a "copy-and-paste" mechanism, whereby they are first transcribed into RNA, then converted back into identical DNA sequences using reverse transcription, and these sequences are then inserted into the genome at target sites. The retrotransposons' replicative mode of transposition by means of an RNA intermediate rapidly increases the copy numbers of elements and thereby can increase genome size. Retrotransposon amplification has been a major cause of genome expansion.
Human genome bigger than E.coli:
A lot of the human genome is made up of regulatory regions that don't contain genes, and gene regulation. most human (and eukaryotic) genes are divided into introns and exons which allows alternative splicing, that can make more than one protein from a single gene.Exons make up about 3% of the human genome while introns are about 25%. E coli and most prokaryotes have few if any genes with introns.
Roughly 98% of our genome is "noncoding", meaning that it does not code for a polypeptide product; only 20% (on average) of prokaryotic DNA is noncoding.
This noncoding DNA was termed and considered "Junk DNA", whuch may have the ollowing functions.
Some of it is regulatory elements to determine which gene is turned on and when.
Sometimes the RNA product is almost immediately degraded into siRNA and miRNA, which performs other functions as RNA molecules within the molecule.
Still more can be used as Ribozymes, or RNA based enzymes to perform catalytic functions within the cell.
Some of it is part of a still somewhat enigmatic process known as "transposition", which is when segments of DNA are essentially "cut-pasted" from one part of the genome to another for various functions.
More of it is part of the "telomeres" on the ends of DNA strands, which functions as a "cap" to prevent DNA degradation during replication.
Transposons were first discovered in corn (maize) during the 1940s and '50s by American scientist Barbara McClintock, whose work won her the Nobel Prize for Physiology or Medicine in 1983.
A direct repeat occurs when a sequence is repeated with the same pattern downstream. There is no inversion and no reverse complement associated with a direct repeat.It may or may not have intervening nucleotides.
An inverted repeat is a single stranded sequence of nucleotides followed downstream by its reverse complement.The intervening sequence of nucleotides between the initial sequence and the reverse complement can be any length including zero. When the intervening length is zero, the composite sequence is a palindromic sequence.
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