On pages 177-178, Dr. Moalem discusses how promoters and
repressors can regulate gene expression, which relates to Big Idea 3 (Living
systems store, retrieve, transmit, and respond to information essential to life
processes), as gene expression mechanisms constantly respond to the body’s
needs.
First of all, explain how promoters and repressors work
together to regulate gene expression at the molecular level. How does this
regulation system relate to tolerance to certain drugs? Dr. Moalem discusses
DNA methylation and promoters/repressors as two mechanisms that regulate gene
expression; however, Unit 10 in the AP Biology curriculum discusses many other
mechanisms by which gene expression is regulated. Name two other methods by
which gene expression is regulated, and explain how the mechanisms work at a
molecular level.
Inside our bodies, there is a system of promoters and repressors that determine how much a particular gene expresses itself. This whole system regulates whether or not a given gene will be transcribed into mRNA and then translated into a protein and thus “amounts to an internal regulator that can turn on, turn off, or even crank up production of specific proteins in response to the body’s changing needs” (178). By regulating gene expression to accommodate for our body’s changing needs, this regulation system allows us to build up tolerance to certain drugs. For example, some people - when first prescribed a new drug - experience unwanted side effects, but eventually their bodies overcome these unpleasant side effects, and the side effects go away after a couple of weeks. This eventual accommodation is an example of the promoter/repressor system at work: the body adapts to the presence of the drug by “promoting or suppressing the expression of specific genes that [help] process it” (178). Therefore, the promoter/repressor system in our bodies turns on certain genes, turns off others, and sometimes “increases the volume control” by making more of a certain protein in order to make the body tolerant to drugs or alcohol.
ReplyDeleteBut this promoter/repressor system along with DNA methylation (which are the two mechanisms in which gene expression is regulated that Dr. Moalem discusses in his book) are not the only mechanisms that regulate gene expression. Another way that gene expression is regulated in eukaryotic cells is through histone acetylation. The DNA of eukaryotic cells is packaged with proteins in a complex called chromatin; the basic unit of chromatin is the nucleosome. Histone tails protrude outward from a nucleosome, and amino acids found on the ends of these histone tails are available and can be accessed for chemical modification. A region of chromatin where nucleosomes (histones) are unacetylated (removal of acetyl groups) forms a compact structure of chromatin in which the eukaryotic DNA cannot be accessed and thus cannot be transcribed. On the other hand, a region of chromatin where nucleosomes (histones) are acetylated (addition of acetyl groups) forms a less compact structure of chromatin in which the eukaryotic DNA can be transcribed (because it is more accessible in this chromatin structural organization). Thus, histone acetylation stimulates transcription. In addition, another way in which gene expression is regulated in eukaryotic cells is through the organization of a typical eukaryotic gene. Activator proteins bind to distal control elements grouped as an enhancer in the DNA upstream of the promoter. Then, a DNA-bending protein brings the bound activators on the enhancer closer to the promoter region of the DNA. Next, the activator proteins bind to certain mediator proteins and general transcription factors that are nearby, helping them form an active transcription initiation complex on the promoter. With the transcription initiation complex in place, RNA polymerase has a high affinity for the promoter region on the DNA, so it binds to the promoter and stimulates transcription of the eukaryotic genes into mRNA.
(Tina Moazezi - tmoazez4@students.d125.org)