Eukaryotic Gene Expression Flashcards

A set of vocabulary flashcards covering the mechanisms, elements, and clinical correlates of eukaryotic gene expression from medical genetics lectures 7 and 8.

Epigenetics

Molecular factors or processes around the DNA that regulate genome activity independently of the DNA sequence, allowing for rapid adaptation to environmental changes.

Nucleosome

The lowest level of chromatin organization consisting of a 'core' particle of 8 small, positively charged basic histones with DNA wound around it twice.

Histone Acetyl Transferases (HATs)

Enzymes that add acetyl groups to histone tails to neutralize positive charges, destabilizing histone-DNA interactions and making the DNA more accessible for expression.

Histone Deacetylases (HDACs)

Enzymes responsible for removing acetyl groups from histones, leading to chromatin compaction and reduced gene expression.

Trans-acting elements

Factors, usually proteins, that can diffuse through the cytoplasm and act at target DNA sites on any DNA molecule in the cell.

Cis-acting elements

DNA sequences that can only influence the expression of adjacent genes on the same DNA molecule.

TFIID

A general transcription factor complex that includes the TATA Binding Protein ($TBP$) and must bind to the TATA box for transcription to begin.

TFIIH

A general transcription factor with helicase activity that unwinds DNA and phosphorylates RNA polymerase II to allow it to clear the promoter.

Promoter Proximal Elements (PPE)

Regulatory elements located further upstream from the start site (typically between $-50$ and $-500$), such as the CAAT box ($CCAAT$) and the GC box ($GGGCGG$).

Enhancers

Cis-acting DNA sequences that increase the rate of transcription initiation; they can be thousands of base pairs away, located either upstream or downstream of the gene.

Silencers

DNA sequences similar to enhancers that act over long distances to bind repressor proteins and reduce gene expression.

Zinc fingers

A type of DNA-binding domain structural motif found in the steroid hormone receptor family.

Leucine zippers

A DNA-binding domain structural motif characteristic of cAMP-dependent transcription factors like $Fos$, $Jun$, and $CREB$.

CREB (cAMP Response Element Binding protein)

A transcription factor activated by phosphorylation via Protein Kinase A that binds to the cAMP response element ($CRE$) to increase expression of target genes like $PEPCK$.

Alternative Polyadenylation (APA)

A post-transcriptional mechanism that generates mRNA with different 3' ends, affecting RNA stability, protein localization, or alternative splicing.

Alternative Splicing

A process where tissue-specific proteins are produced from the same pre-mRNA through mechanisms such as exon skipping, intron retention, or alternative splice sites.

RNA editing

A post-transcriptional modification involving specific nucleotide deaminases, famously exemplified by $Apo B$ mRNA where a Cytidine to Uridine change creates a stop codon in the intestine.

Iron-response elements (IREs)

Short hairpin loop structures in the 3' untranslated region ($UTR$) of transferrin receptor mRNA that are bound by iron regulatory proteins ($IRPs$) when iron is low to stabilize the mRNA.

P-bodies

Intracytoplasmic storage sites for mRNA where transcripts can be held in a translationally silent state or modified to promote degradation.

eIF-2

A eukaryotic translation initiation factor that, when phosphorylated in response to stress, inhibits global protein synthesis at the initiation step.

Ubiquitin

A protein used to label incorrectly folded or defective proteins for destruction by proteasomes in the cytoplasm.

Cystic Fibrosis (Phe 508 deletion)

A genetic disease where the deletion of Phenylalanine at position 508 results in improper protein folding, causing the chloride channel to be labeled for degradation in the proteasome.

Transposons

Mobile segments of DNA that move randomly from one site in the genome to another, mediated by the enzyme transposase.