Lecture 15: Transcription

Comprehensive vocabulary flashcards covering the key concepts, mechanisms, and structures involved in eukaryotic and prokaryotic transcription, the genetic code, telomeres, and gene expression from Lecture 15 of Bio 93.

Telomeres

Special repetitive nucleotide sequences ($\text{TTAGGG}$ in humans) at the ends of eukaryotic chromosomal DNA molecules that postpone the erosion of genes near the ends.

Telomerase

An enzyme that catalyzes the lengthening of telomeres in germ cells, preventing essential genes from being lost during repeated rounds of DNA replication.

Werners Syndrome

An inherited premature aging disease proposed to be connected to abnormal telomere shortening and degradation.

Mutations

Permanent alterations in DNA nucleotide sequences that escape proofreading repair and serve as the ultimate source of genetic variation on which natural selection operates.

Genotype

The complete genetic makeup of an organism, which is contained and carried within its sequence of nucleotide bases.

Phenotype

The observable physical and physiological traits of an organism, determined directly as a consequence of expressed proteins.

Gene Expression

The biological process by which inherited DNA sequences direct protein synthesis, occurring in two stages: transcription and translation.

Central Dogma

The cellular chain of command in molecular biology stating that genetic information flows from $\text{DNA} \rightarrow \text{RNA} \rightarrow \text{Protein}$.

Primary Transcript

The initial RNA transcript generated directly from any gene before undergoing post-transcriptional modifications or RNA processing.

Transcription

The DNA-directed synthesis of an RNA molecule, specifically producing messenger RNA ($\text{mRNA}$) from a DNA template.

Translation

The ribosome-mediated synthesis of a polypeptide sequence specified by the sequence of codons in an $\text{mRNA}$ molecule.

Coupled Transcription and Translation

The cellular phenomenon in prokaryotic cells where ribosomes attach to and begin translating an $\text{mRNA}$ molecule while transcription is still underway, enabled by the lack of a nuclear membrane.

Codon

A triplet sequence of nucleotide bases in DNA or $\text{mRNA}$ that codes for a specific amino acid or acts as a translational stop signal.

Template Strand

The DNA strand oriented in the $3'$ to $5'$ direction that provides the complementary nucleotide pattern during RNA transcription.

Reading Frame

The correct grouping of non-overlapping nucleotide triplets in an $\text{mRNA}$ transcript that must be read in sequence to produce the specified polypeptide.

Redundancy of the Genetic Code

The property of the genetic code in which multiple different codons can specify the same amino acid, with $61$ coding triplets coding for $20$ amino acids.

Lack of Ambiguity in the Genetic Code

The characteristic of the genetic code wherein each codon specifies one and only one amino acid, meaning no triplet codes for multiple amino acids.

Universality of the Genetic Code

The conservation of the genetic code across almost all life forms, allowing genes from one organism to be transcribed and translated successfully when inserted into another species.

Start Codon

The specific codon $\text{AUG}$ that serves as the initiation signal for translation and codes for the amino acid methionine ($\text{Met}$).

Stop Codons

The three codons ($\text{UAA}$, $\text{UAG}$, and $\text{UGA}$) that do not designate an amino acid but instead signal the termination of translation.

RNA Polymerase

The enzyme that opens the double helix of DNA and links ribonucleotides together into an RNA strand complementary to the DNA template.

Promoter

The specific DNA sequence located upstream of a gene where RNA polymerase binds and initiates the transcription process.

Transcription Unit

The complete stretch of DNA that is transcribed into a functional RNA molecule by RNA polymerase.

Transcription Factors

Proteins in eukaryotic cells that mediate and direct the binding of RNA polymerase to the promoter region to initiate transcription.

Transcription Initiation Complex

The fully assembled eukaryotic molecular apparatus consisting of transcription factors and RNA polymerase II positioned at the promoter.

TATA Box

A crucial conserved eukaryotic promoter DNA sequence involved in recruiting transcription factors and forming the transcription initiation complex.

Initiation of Transcription

The initial stage of transcription during which RNA polymerase recognizes the promoter, unwinds the DNA duplex, and begins transcribing ribonucleotides.

Elongation of Transcription

The stage of transcription where RNA polymerase travels downstream along the template, unwinding $10\text{ to }20$ base pairs at a time and elongating RNA at approximately $40\,\text{nucleotides per second}$.

Termination of Transcription

The concluding step of transcription wherein the newly synthesized pre-mRNA is cleaved and the RNA polymerase enzyme dissociates from the DNA template.

RNA Processing

The nuclear modification steps applied to the eukaryotic primary transcript ($\text{pre-mRNA}$) to generate a mature $\text{mRNA}$ molecule before cytoplasmic transport.