HMG Week 13: Gene Expression in Eukaryotes

Vocabulary flashcards covering eukaryotic operons, transcriptional regulation, chromatin remodeling, and post-transcriptional machinery based on the HMG Week 13 lecture notes.

Operon

A group of genes controlled together by a single promoter, a single operator, and multiple structural genes, all transcribed under the same regulatory region.

Caenorhabditis elegans (C. elegans)

A nematode species in which approximately $15\%$ of genes occur in operons that contain $2-8$ genes.

Polycistronic pre-mRNA

A single, large RNA transcript produced by RNA Polymerase II that contains multiple genes, characteristic of operons in C. elegans.

Trans-splicing

A process in eukaryotic operon regulation where special spliced leader (SL) RNAs are attached to individual gene transcripts.

Monocistronic mRNA

The separate mRNAs formed from a polycistronic transcript, each receiving a $5'$ cap and a poly(A) tail for independent translation.

Promoter

A regulatory DNA sequence located immediately upstream of a gene that controls the initiation of transcription.

Enhancer

Distal regulatory DNA elements that can be located thousands of base pairs away from the gene they regulate.

Activator proteins

DNA-binding proteins that bind to promoter or enhancer elements to recruit chromatin-modifying proteins and transcription machinery.

Nucleosomes

Structural units of chromatin where DNA is wrapped around histone proteins, often blocking access to promoter regions.

Histone Acetyltransferases (HATs)

Enzymes that add acetyl groups to lysine residues on histone tails to neutralize positive charges, loosening chromatin from a $30\,\text{nm}$ fibre to a $10\,\text{nm}$ fibre.

Histone Deacetylases (HDACs)

Enzymes that remove acetyl groups from histones, causing chromatin to condense and repress gene expression.

ATP-dependent nucleosome remodelling

The process of using specialized complexes and ATP to reposition nucleosomes, exposing promoter regions to transcription factors.

Combinatorial Gene Regulation

A mechanism where different specific combinations of enhancers, promoters, and activator proteins control thousands of genes using a limited number of factors.

Hormones

Effector molecules produced by one cell that cause responses in another cell, such as lipid-soluble steroid hormones.

Steroid Hormone Receptor (SHR)

The intracellular receptor that binds with lipid-soluble hormones like testosterone or cortisol after they diffuse through the cell membrane.

Hormone Response Elements (HREs)

Specific DNA sequences to which a hormone-receptor complex binds to activate or repress the transcription of target genes.

Alternative Polyadenylation

A post-transcriptional mechanism where different poly(A) sites are used to produce mRNA of different lengths, altering stability, localisation, or translation efficiency.

Alternative Splicing

A process where different combinations of exons are joined from a single gene to produce multiple protein isoforms.

RNA interference (RNAi)

A post-transcriptional mechanism that silences gene expression through small RNA molecules which lead to mRNA degradation or blocked translation.

miRNA (microRNA)

Small RNA molecules produced naturally by cells to participate in gene regulation and silencing.

siRNA (small interfering RNA)

Small RNA fragments often derived from viruses or experimental introduction used to trigger RNA interference.

Dicer

The enzyme that cuts double-stranded RNA into short fragments to be loaded into the RNA-Induced Silencing Complex (RISC).

RISC (RNA-Induced Silencing Complex)

A complex that uses small RNA fragments to identify and bind complementary target mRNA for degradation or translation blocking.

Antisense Oligonucleotides (ASOs)

Short synthetic single-stranded DNA or RNA molecules designed to bind target mRNA, blocking its translation or promoting degradation for treating genetic diseases.