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Chapter 8 DNA Answers Humane Life Cycles
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The answers to Chapter 8 DNA Human Life Cycles 1
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Hoofdstuk 8: Control of gene expression(82+83+84). The DNA sites to which eukaryotic gene activators bind are termed enhancers because
their presence dramatically enhances the rate of transcription. The DNA between the enhancer and
the promoter loops out, bringing the activator protein into close proximity with the promoter. The
DNA thus acts as a tether, allowing a protein that is bound to an enhancer—even one that is
thousands of nucleotide pairs away—to interact with the proteins in the vicinity of the promoter.
Often, additional proteins serve as adaptors to close the loop; the most important of these is a large
complex of proteins known as Mediator. Together, all of these proteins ultimately attract and
position the general transcription factors and RNA polymerase at the promoter, forming a
transcription initiation complex. This sequences is cis in relation to the gen that is read, because the
enhancer is part of the same molecule. The activator is it in trans in relation to the gene being read,
because the activator is unlike the enhancer, a different molecule and therefore acts in trans with
respect to the DNA it binds to.
(85+86+87). An activator is also called specific transcription factor. The enhancer brings the
activator protein to the complex of RNA polymerase and basal transcription. The distance between
the promoter to which the RNA polymerase II binds and the enhancer displayed is very large, the
enhancer does not have to be near the RNA polymerase II. Could even be on a completely different
chromosome.
(88). The protein that brings about just the opposite of an activator is a silencer / repressor /
inhibitor.
(89). In addition to physically bringing together the basal transcription factors and the RNA
polymerase II at the promoter, activator and repressor proteins affect the efficiency of transcription
in another way. Is the mechanism accessibility of chromatin to basal transcription factors and the
RNA polymerase II increase or decrease with it.
(90). Because acetyl groups bind to the histone proteins become negative, the DNA is also negative,
so this is going to repel each other. This creates more space in the chromatin, so for example a TATA
box can get on the left DNA, allowing transcription to take place, this is how the process of
transcription can be influenced. Repressor: HDAC, acetyl group of amino terminus tail of histone
proteins remove, minus - plus (DNA - histone), chromatin structure more closed, not accessible to
transcription machinery.
(93). The gene alpha-tropomyosin contains 14 exons. fibroblast mRNA 1: 1-3-5-6-7-9-10-11-12-14,
fibroblast mRNA 2: 1-3-5-6-7-8-10-11-12-14 occur in the two transcripts present in fibroblasts.
(94). Neurexin exon 4 splicing is a gene example of alternative splicing. Deletion of the nucleotides
encoding KTS at the end of exon 9 in the WT1 gene does not result in disruption of the reading frame
because it is a multiple of 3 nucleotides. If the reading frame is not maintained during alternative
splicing a frameshift occurs, this causes the translated sequence to be greatly altered from this point
and often shortened by a premature stop codon.
(95). Duchenne disease is an X-chromosome bound neuromuscular disorder that occurs in 1 in 3,500
boys. The disease is caused by deletions in the DMD (Duchenne muscular dystrophy) gene that codes
for dystrophin. When the deletion leads to a frameshift (reading frame shift), a non-functional
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