Genetics Chapter 16
Two ways that miRNA and siRNA regulate gene expression
- By inducing the binding of RISC which may inhibit translation - By inducing the binding of RISC which may direct degradation of the mRNA
Examples of epigeneics
- Covalent histone modification - DNA methylation - Localization of histone variants - Chromatin remodeling
What occurs following the binding of Xist RNAs to the Xi
- Covalent modification of specific sites in histone tails - Recruitment of protein complexes to Xo - Histone variant macroH2A is incorporated into the nucleosomes along the Xi - Recruitment of DNA methyltransferases to Xi
Which two complexes are the key regulators of epigenetic changes that occur during development?
- Polycomb group - Trithorax group
The Igf2 gene will be expressed if
- the ICR and DMR are methylated - the Igf2 gene can be stimulated by the enhancer
List the steps of how a gene may be targeted for silencing by PcG and TrxG complexes
1. PRE-binding protein binds to PRE and recruits PRC2 2. PRC2 catalyzes trimethylation of lysine 27 in histone H3 3. Transcription is inhibited by preventing binding of RNA polymerase 4. PCR1 may be recruited to inhibit transcription in various ways
Events of X chromosome inactivation in the correct sequence
1. X chromosomes pair briefly beginning at the Tsix gene. 2. A symmetry break shifts all pluripotency factors and CTCFs to a single chromosome 3. The Tsix gene of the chromosome without pluripotency factors and CTCFs is inhibited. 4. The inactivated chromosome is coated with Xist RNA. 5. Xist RNA recruitsproteins that epigenetically modifies specific sites within the Xi
Which type of exon is always found in mature mRNA?
Constitutive exon
What is the benefit of alternative splicing in the alpha-tropomyosin gene?
Different types of cells can regulate their degree of contractibility by producing variant gene products
How does iron regulatory protein exert its effect?
Iron regulatory protein (IRP) binds to the iron response element (IRE) in the 5' UTR inhibiting ferritin translation
What happens if polyA tail becomes less than 10-30 adenosines in length?
PolyA-binding protein cannot bind and the mRNA transcript will be degraded.
How do noncoding RNAs regulate gene expression in plants?
RNA-dependent DNA methylation forms bridges between specific sites in DNA and protein, altering the chromatin structure
In mammals, females (XX) and males (XY) express genes on the X chromosome at the same levels because of
X chromosome inactivation
What happens when pluripotency factors stimulate the expression of Tsix?
Xist is inhibited
The term for the mechanism that enables two or more different polypeptide sequences to be produced from a single gene is
alternative splicing
Epigenetic changes due to the actions of PcG complexes
are maintained in subsequent cell divisions.
X chromosome inactivation is an epigenetic event that occurs during
embryogenesis
What term explains the variation of gene expression that is not related to the variation of the DNA, is transmissible and is reversible?
epigenetics
The methylation of hemimethylated sites is called
maintenance methlyation
MicroRNAs play a key role in regulating gene expression
particularly during development in animals and plants
Splicing of pre-mRNA, altering mRNA stability and controlling the rate of translation are all examples of
postranscriptional gene regulation
AU-rich elements (AREs) are typically found in the 3' UTR of mRNAs with
short half-lives
Which type of RNA might originate in a virus?
siRNA
Proteins called ____ ____ are involved in the regulation of alternative splicing.
splicing factors
Binding of IRP to the 3' UTR
stabilizes the transferrin receptor mRNA
SR proteins & Splicing factors are involved in
the regulation of alternative splicing