Biol 3130 Session 13: Post-transcriptional Regulation & Epigenetics

Flashcards covering post-transcriptional regulation, RNA interference, microRNAs, and epigenetic control of gene expression including DNA methylation and histone modifications, based on the Biol 3130 Session 13 lecture notes.

Post-transcriptional Regulation

Control of gene expression occurring after transcription, including mRNA processing, mRNA degradation, and RNA interference in eukaryotes.

RNA Interference (RNAi)

A mechanism in which small RNAs target homologous transcripts for degradation, leading to gene silencing.

Short Interfering RNAs (siRNAs)

Small RNA molecules (21-23 nucleotides) derived from double-stranded RNAs (e.g., RNA viruses or repetitive transcripts) that are processed by Dicer and incorporated into RISC to induce gene silencing.

MicroRNAs (miRNAs)

Small RNA molecules (around 22 nucleotides) encoded by genes, processed by Dicer, and incorporated into RISC to regulate gene expression by blocking translation or promoting mRNA degradation.

RNA-Induced Silencing Complex (RISC)

A protein complex that acts on both siRNAs and microRNAs to dock at target mRNA sequences and induce silencing, containing an enzyme called Slicer (Argonaute).

Dicer

An enzyme that processes double-stranded RNAs into single-stranded miRNAs or siRNAs (each ~21-25 nucleotides long) to trigger RNAi.

Slicer (Argonaute)

An enzyme within the RISC complex that cleaves target mRNA during RNA interference.

Epigenetics

The study of heritable changes to chromosomes that modify gene expression without altering the underlying DNA sequence.

Epigenetic Marks

Changes to chromatin structure that affect gene expression, such as DNA methylation, histone modifications, and RNA molecules, which are often heritable.

Mutation

A change to the DNA code (e.g., sequence, inversion, duplication) which alters the information present in the genetic material.

DNA Methylation

A covalent modification involving the addition of a methyl group to the cytosine nucleotide (forming 5-methylcytosine), often occurring at CpG islands in promoters and typically leading to reduced gene expression.

5-methylcytosine

The product of DNA methylation, where a methyl group is added to the cytosine nucleotide.

DNA Methyltransferases (DNMT)

Enzymes that add methyl groups to DNA, particularly important for maintaining DNA methylation patterns across generations by adding methyls to newly synthesized strands.

CpG Islands

Regions in mammal promoters rich in CG sequences where DNA methylation often occurs, leading to gene silencing when methylated.

Euchromatin

A relaxed chromatin conformation that is generally associated with low DNA methylation and active gene transcription, allowing access for transcriptional machinery.

Histone Modifications

Post-translational modifications of histone proteins, typically on their 'tails,' such as addition of phosphates, methyl groups, or acetyl groups, which can alter DNA accessibility and gene expression.

Histone Acetylation

The addition of acetyl groups to histone tails, which removes their positive charge, causes them to 'let go' of DNA, relaxes the nucleosome, and thereby stimulates transcription.

Histone Deacetylation

The removal of acetyl groups from histone tails, which restores their positive charge, causes them to bind tightly to DNA, condenses the nucleosome, and thereby represses transcription.

Epigenome

The collection of epigenetic marks on DNA and histones in a given cell or cell type, which varies across cell types and over an organism's lifespan and impacts specific gene expression.

Barr Body

An inactivated X chromosome found in all cells having two or more X chromosomes, formed through X-chromosome inactivation mediated by long non-coding RNA (Xist gene).

Transgenerational Epigenetic Effects

Epigenetic changes that are passed down through multiple generations, influencing phenotypes in subsequent offspring without changes to the primary DNA sequence, often in response to environmental factors.

Writers (Epigenetics)

Enzymes that add histone modifications or DNA methylation.