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Chapter 104 -- Part 1: Regulation of Gene Expression
The operon is an excellent model for the regulation of genes.
Although every cell in your body contains the same 3 billion base pairs of DNA, a typical cell only expresses a small percentage of its genes at any one time.
Different mechanisms regulate the expression of genes.
The mechanisms are described below.
There are places where the expression of genes can be altered.
It is possible to describe the connection between the regulation of gene expression and observable differences within cells and between individuals in a population.
The basic unit of the nucleosome is the histones, which are packaged with Eukaryotic DNA.
Changes to the histone structure make it less accessible for transcription and expression.
The inhibition can be reversed.
Adding acetyl groups to histone tails helps loosen the structure of the chromatin.
There are acetyl groups that block transcription.
The DNA is silenced temporarily or for long periods of time when certain bases are added to it.
The reverse can turn genes on.
The long-term X-chromosome deactivation in females and the long-term deactivation of genes necessary for normal cell differentiation are likely caused by the switch off of genes.
Alterations to the genome that do not involve the nucleotide sequence are called Epigenetic inheritance.
These changes are not permanent.
Environmental factors like diet, stress, and prenatal nutrition can affect the expression of genes, but the mechanism behind epigenetics is not well understood.
One identical twin can develop schizophrenia, while the other one does not, which may be explained by Epigenetics.
It is a highly regulated process.
The promoter must be binding to the RNA polymerase.
The process requires the assistance of transcription factors.
Depending on whichRNA segments are treated as introns and which as exons, alternativeRNAs is an important means of regulating gene expression.
Cell types control intron-exon choices by binding to the primary transcript.
Most of the human-protein coding genes are subject to alternative splicing.
Gene expression can be regulated by the span of time after transcription.
Within minutes of their synthesis,bacteria are degraded.
The rapid degradation of mRNA may be the reason thatbacteria are able to adapt to changes in the environment.
Human mRNA can translate for hours or weeks.
Red blood cells can be translated multiple times with the help of stable Molecules of mRNA in developing red blood cells.
Recent data shows that as much as 90% of non-protein-coding DNA is transcribed into various kinds of noncodingRNA.
These ncRNAs help bind to and assist the Argonaute proteins.
Scientists are still learning about these regions, but they regulate a lot of our genes.
New information is published almost weekly and three types of ncRNA have been extensively studied.
MicroRNA is a small, single-strandedRNA that is about 22 nucleotides long.
It doesn't code for anything.
Instead, it targets specific mRNA molecules, which can either be degraded or blocked.
At least one-half of all human genes may be regulated by miRNA.
SiRNA is similar to miRNA in size and function.
The blocking of gene expression by siRNA is calledRNAi.
The discovery of how interferingRNA can play a role in the suppression of genes was the subject of the 2006 Nobel Prize in Physiology or Medicine.
This can be accomplished by binding to and destroying mRNA.
The piRNA is a large class of ncRNAs that guide PIWI proteins to complementaries which are derived from transposable elements.
Germ line cells are protected from attacks by transposons.
Following translation, there is a final opportunity to control gene expression.
After emerging from a ribosome, a newly madeProtein may spontaneously fold into its correct shape and begin "working" immediately.
Some newly made proteins have to be activated before they can function.
In an inactive form, a ribosome can be released from and only become an active hormone after being cleaved.
Taking two or more sources of DNA and combining them into one molecule is a form ofombinant DNA.
In nature, this occurs through viral transduction,bacterial transformation, and conjugate and when transposons or "jumping genes" move around the genome.
In the laboratory, scientists can manipulate and engineer genes.
Genetics or genetic engineering is a branch of science that uses recombinant DNA techniques for practical purposes.
Tools and techniques have been developed to manipulate genes.
There is a discussion of the uses for genetic engineering, an explanation of some techniques that are used, and a discussion of ethical issues within the field.
To make a large amount of humaninsulin in large quantities as an inexpensive pharmaceutical.
Gene therapy replaces a malfunctioning gene in a person's cells with a functioning one.
Clinical trials in this area have disappointing results.
The human subjects can become ill from the viral vector.
Sometimes, the gene is inserted successfully and begins to produce the required proteins, but it stops working in a short time.
Many lives will be improved if scientists can master this technique.
To prepare multiple copies of a gene.
The ability to make multiple copies of a single genes is a great research tool.
To clean up the environment.
One modified species can eat toxic waste.
The plasmid will be inserted into a cell that will carry it.
To take up a plasmid, a bacterium must be made competent.
The selected gene and the plasmid are being cloned as thebacteria reproduce themselves.
There are millions of copies of the gene.
Pick the bacteria that contain the selected gene and harvest them from the culture.
The late 1960s saw the discovery of restriction enzymes.
They are taken frombacteria which use them to fight off attacks.
There are specific recognition sites that are cut by restriction enzymes.
When these cuts are staggered, single-stranded sticky ends form a temporary union with other sticky ends.
The fragments that result from the cuts are called restriction fragments.
Explain how technologies can be used to manipulate heritable information.
Scientists have isolated hundreds of different restriction enzymes.
They were named after thebacteria in which they were found.
Eco RI is one of the examples.
Gene cloning is one of the uses of restriction enzymes.
The rate of movement of the large molecule of DNA is determined by the electric field created by the agarose gel.
The faster the molecule runs, the smaller it is.
Due to the presence ofphosphate groups in PO 4 3-, the DNA flows from the cathode to the anode.
The concentration of the gel can be changed to make it harder to separate smaller pieces.
It's also used to separate the two acids.
If the DNA is going to be run through a gel, it must be cut up by restriction enzymes into pieces small enough to migrate through the gel.
There are many ways in which the DNA can be analyzed.
The sequence of bases A, C, T, and G can be determined with the help of the gel.
The location of a specific sequence within the DNA can be identified with a DNA probe.
Three larger pieces and one short piece are in Lane 1.
There is a piece of uncut DNA in Lane 3.
The farther away the piece of DNA has traveled from the well.
A DNA probe is a single strand of nucleic acid molecule that is labeled with radioactivity.
The probe bonds to the sequence and radioactivity allows scientists to locate it.
A person with an inherited genetic defect can be identified by using the DNA probe.
A piece of DNA can be copied or amplified using a cell-free, automated technique called polymerase chain reaction.
Billions of copies of a fragment of DNA can be produced in a few hours.
In order to amplify the piece of DNA, it must be placed into a test tube with Taq polymerase, along with a supply of nucleotides and a primer.
These copies can be used in a comparison with other DNA samples.
In order to make the necessary primer, some information about the target DNA must be known in advance.
The piece that can be amplified must be small.
Contamination is a big problem.
Obtaining accurate results could be difficult or impossible if a few skin cells from the technician accidentally get into the sample.
A crime scene sample can have dire consequences if an error is made.
A restriction fragment is a segment of DNA.
The restriction fragment pattern is different in every individual and scientists discovered that when they compared noncoding regions of human DNA across a population.
A human's fingerprints look like a barcode after a RFLP analysis of their DNA.
RFLPs are unique to each person, except in identical twins.
They can be used in paternity suits to determine if a man is the father of a child because they are inherited in this way.
RFLPs are used to identify the perpetrators in rape and murder cases.
The suspect's DNA is compared against the victim's.
The cases can be solved with a high degree of certainty because of the accuracy of RFLP analysis.
In several instances, prisoners who have been imprisoned for a long time for violent crimes have been proven innocent by the use of DNA evidence.
The introns present a problem when scientists attempt to clone a human gene.
There is no way to edit introns after they are transcribed.
Scientists must insert a gene with no introns in order to clone a human gene.
Scientists extract fully processed mRNA from cells and then use the reverse transcriptase obtained from retroviruses to make DNA transcripts.
The complete coding sequence of interest but without introns is carried by the resulting DNA molecule.
The DNA produced by retroviruses is called cDNA.
The acronym stands for Clustered Regularly Interspersed Short Palindromic Repeats.
It is a tool that allows scientists to modify an organisms' genes.
There is a stretch of DNA that can be altered with the help of the Cas9 enzyme.
The whole unit is referred to as CRISPR-Cas9.
The naturally occurring genome editing system inbacteria was adapted for protection against viruses.
The genomes of invading viruses are captured by the bacteria and they use them to create segments of their own.
TheArrays allow thebacteria to remember the viruses.
If the viruses attack again, thebacteria produceRNA segments from the CRISPR array to target the viruses' genes.
The virus is disabled by the bacterium by cutting the DNA apart.
They were the first to propose that CRISPR-Cas9 could be used for gene editing.
Their work has been further developed by many research groups for the treatment of diseases.
In November of last year, the journal Science reported the first time that a person's genome was altered with the help of CRISPR.
Many people are worried about the consequences of genetic engineering.
Some of the concerns are discussed in this section.
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