Lesson 5: Control of Gene Expression Flashcards
Gene expression
The process of transcription and translation are collectively known as gene expression, in the eukaryotes it’s controlled by several processes
Transcriptional regulation, Post-transcription regulation, Translation regulation
Transcriptional regulation
Prevent transcription
Post-transcriptional regulation
Control of mRNA after it has been produced
Translation regulation
Prevents translation
More on Transcription Regulation pt 1
Transcription can be regulated by nucleosomes and by binding proteins. Nucleosomes are the result of DNA packaging, e/ nucleosome consists of DNA wound around 8 histones
-Nucleosomes can prevent gene expression by blocking the activators and enzymes involved in transcription from binding to certain regions of the DNA
-DNA in nucleosomes may be wrapped or unwrapped and doesn’t need to be completely released in order to be transcribed. This allows for DNA site exposure.
More on Transcription regulation pt 2
RNA polymerase requires the presence of transcription factors before transcription can begin. Many different transcription factors have been found and e/ one is able to recognize and bind to a specific sequence of DNA. A specific combination of factors is necessary to activate a gene.
-activators (a type of transcription factor) must bind to a section of DNA known as the enhancer, it may be some distance from the gene
-other proteins must bind in order to bend the DNA so that the enhancer region is brought close to the promoter region— an initiation complex is created when this occurs and transcription can begin.
More on Transcription regulation pt 3
Transcription factors are controlled by signals from other molecules such as hormones, transcription factors may also be controlled by other molecules in the environment of the cell. Both the organism’s internal/external environment might influence gene expression:
Temperature, light, chemicals, sex of organism
Example of environmental control: Drugs
Thalidomide in the 1950s was prescribed to pregnant women to treat morning sickness. It had no effects on gene expression in adults but prevented gene expression during limb formation in the fetus
Example of environmental control: Sex
Male pattern baldness is activated by the presence of both testosterone and dihydrotesterone
Example of environmental control: Temperature
The Himalayan rabbit which has a gene for pigmentation. Inactive above 35 degrees but very active between 15-25 degrees.
More on Transcription regulation pt 5
Chemical modification to the DNA itself can also regulate transcription. The addition of a methyl group to cytosine doesn’t alter the sequence but in areas that are heavily methylated transcription doesn’t occur. Removal of the methyl groups reactivates the gene.
Post-transcriptional regulation
Post-transcriptional regulation involves modification of the mRNA. Sequences of DNA that are transcribed but don’t appear in the mature mRNA called introns. The introns are removed from the mRNA sequence leaving only the exons which are joined together to create the mature mRNA that will be translated.
-This allows for a gene to code for more than one protein. It’s thought that the avg human gene can code three proteins
Translational regulation
There are many proteins involved in the start of polypeptide synthesis, these proteins may prevent from occurring. The mRNA will eventually be recycled by enzymes
