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