W9 Flashcards
What is the first level of control for gene expression?
At the chromosome. The coiled state of the the chromatin can inhibit physical access of the proteins necessary for transcription, therefor regulating whether a gene is expressed
Define chromatin
A complex of DNA, RNA and proteins that gives chromosomes their structure
What is chromatin remodeling?
The process in which nucleosomes are re positioned to expose different stretches of DNA to the nuclear environment
Ways in which chromatin remodeling can occur?
- Chemical modification of the histones
- Chemical modification of certain bases in the DNA
Explain the chemical modifications of histones as a way of chromatin remodeling
Individual amino acids in histone tails can be modified by the addition (or later removal) of different chemical groups (methyl or acetyl groups). The pattern of modifications of the histone tail constitutes a histone code that affects chromatin structure.
Explain the chemical modification of certain bases in the DNA as a way of chromatin remodeling
The most common is the addition of a methyl group to a cytosine base.DNA methylation recruits proteins that affect changes in chromatin structure, histone modification and nucleosome positioning that restrict access of transcription factors to gene promoters
Where does the methylation of cytosine bases usually occur?
In CpG islands, which are clusters of adjacent GC nucleotides located in or near the promoter of the gene
Define epigenetic
Descries the effect on gene description due to differences in DNA packaging, such as modifications in histones, or chromatin structures
True or false, epigenetic modifications can be inherited?
True. If they are present in sperm or eggs, they can transported from parents to offspring.
What is an example of an epigenetic form of gene regulation?
The manner in which mammals equalize the expression of X linked genes in XX females and XY males.
What is the relationship between gene dosage and gene expression?
The direct relationship means that as the number of copies of genes increases so does the expression of that gene because each copy of the gene is regulated independently
What is dosage compensation?
The differential regulation of X chromosomal genes in both females and males
What is X-Inactivation?
The process in mammals in which dosage compensation occurs through the inactivation of one X chromosome in each cell in females
What is the XIST gene?
X-inactivation specific transcript. A gene found in the XIC
What is the XIC (X inactivation center)
A small region on the X chromosome
What are the steps in X inactivation
- The Xist gene is transcribed and spliced, and Xist non-coding RNA binds with the Xic.
- Transcription of Xist continues and the X chromosome becomes coated in Xist RNA
- Eventually the entire chromosome becomes coated in Xist RNA
- Presence of Xist RNA triggers DNA methylation and other changes associated with transcriptional activity.
What is transcriptional regulation?
The mechanism that collectively regulates whether or not transcription occurs
What does transitional regulation in eukaryotic cells require ?
The coordinated action of many proteins that interact with one another and the DNA sequences near the gene
What are enhancers?
DNA sequenced that Regulatory transcription factors bind to that stimulate transcription.
What are silencers?
DNA sequences that regulatory transcriptions bind to that repress transcriptions
True or false a typical gene may be regulated by multiple enhancers and silencers of different types, each with one or more regulatory transcription factors that can bind with it?
True
Define combination control
Regulation of gene transcription by means of multiple transcription factors acting together
How does RNA processing contribute to gene regulation?
RNA splicing provides an opportunity for regulating gene expression because the same primary transcript can be spliced in different ways to yield different proteins in a process known as alternative splicing.
Why does alternative splicing occur?
Because what the spliceosome recognizes as an exon in some primary transcripts, it recognizes as an intron in others.
