Cell Biology: Transcription, RNA Processing, and Cancer Cell Review

Vocabulary practice flashcards covering transcription termination, eukaryotic RNA post-transcriptional modifications, splicing mechanisms, and cellular/cancer biology review concepts.

Hairpin Loop (Transcription Termination)

An RNA secondary structure formed by self-complementary base pairing that puts mechanical weight near a sequence of weak $A\text{-}U$ base pairs, pulling the mRNA transcript off the DNA template and RNA polymerase.

Promoter

A DNA sequence located upstream of the coding region that is not transcribed into RNA, functioning as the binding site for RNA polymerase and general transcription factors.

$5'$ Cap

A methylated GTP molecule attached to the $5'$ end of eukaryotic pre-mRNA via a unique $5'$ to $5'$ bond, which is required for nuclear export and the initiation of translation.

Polyadenylation Sequence

An $AAUAAA$ sequence located near the $3'$ end of eukaryotic pre-mRNA that directs poly-A polymerase to cleave the transcript and add a tail of $150$ to $250$ adenine ribonucleotides without a DNA template.

Introns

Noncoding RNA sequences within eukaryotic genes that are typically $10$ times larger than coding regions and are excised from the pre-mRNA transcript during splicing.

Exons

Protein-coding segments of eukaryotic genes and pre-mRNA transcripts that are preserved and joined together after intronic sequences are removed.

Alternative Splicing

The differential selection and joining of exons and introns within a pre-mRNA transcript, occurring in approximately $94\%$ of human genes to produce distinct protein isoforms from a single gene.

Spliceosome

A large ribonucleoprotein complex that recognizes conserved splicing sequences to excise introns and ligate exons together.

snRNPs

Small nuclear ribonucleoproteins composed of RNA and proteins that locate pre-mRNA cis-elements, such as the $5'$ splice site and branch point, via complementary base pairing.

Branch Point A

A conserved adenine nucleotide located within an intron near the $3'$ end that carries out a nucleophilic attack on the $5'$ splice site to initiate lariat formation.

Lariat Structure

A transient loop intermediate created during pre-mRNA splicing when the severed $5'$ end of an intron covalently bonds to the $2'$ hydroxyl of an internal branch point adenine.

Exon Junction Complex

A group of proteins that binds to the junction where two exons are ligated together, serving as a quality-control tag indicating that splicing has occurred.

Nuclear Pore

A protein channel in the nuclear envelope that inspects transcripts for cap-binding proteins, exon junction complexes, and poly-A binding proteins before permitting nuclear export.

Sarcoma

A cancer originating from transformed cells of mesenchymal origin rather than epithelial tissue.

Warburg Metabolism

A metabolic state in cancer cells characterized by elevated glucose and lactate transport and high rates of glycolysis, generating only $2\text{ ATP}$ per glucose compared to $36\text{ ATP}$ from complete respiration.

Constitutive Heterochromatin

Permanently condensed, transcriptionally silent chromatin found in regions such as centromeres that does not alternate between heterochromatic and euchromatic states.

DNA Hypermethylation

An epigenetic modification that converts open euchromatin into condensed heterochromatin, silencing gene expression and leading to a loss of function when occurring in tumor suppressor genes.

Lactate Dehydrogenase (LDH)

An enzyme that converts pyruvate to lactate; its pharmacological inhibition causes pyruvate accumulation, feedback inhibition of glycolysis, depletion of cellular ATP, and death of cancer cells.