SCH2226 Human Molecular Genetics - Lecture 7: Gene Expression Transcription

Flashcards covering the fundamentals of gene expression transcription in prokaryotes and eukaryotes, including enzyme functions, promoter regions, and post-transcriptional modifications.

Central Dogma

The flow of information from $DNA \rightarrow RNA \rightarrow Protein$, a term coined by Francis Crick in 1956.

Transcription

The synthesis of an RNA molecule using a DNA template, where only one of the DNA strands is transcribed by the enzyme RNA polymerase.

Messenger RNA (mRNA)

RNA molecules that carry genetic information from DNA to the ribosome for protein synthesis.

Transfer RNA (tRNA)

RNA molecules involved in translation that contain anticodons and carry specific amino acids via an ester bond.

Ribosomal RNA (rRNA)

Structural and functional components of ribosomes; in eukaryotes, the major types are $28S$, $18S$, and $5.8S$.

Small Nuclear RNA (snRNA)

RNA molecules involved in splicing primary transcripts to form mature mRNA, often working within a spliceosome.

Sigma factor ($\sigma$)

A protein in E. coli that binds to the RNA polymerase core enzyme to form a holoenzyme, guiding the choice of genes to be transcribed.

Initiation

The first stage of transcription where RNA polymerase binds to the DNA promoter region; in prokaryotes, it involves binding to $-35$ and $-10$ regions.

Elongation

The stage of transcription where RNA polymerase adds nucleotides to the growing RNA chain in the $5' \rightarrow 3'$ direction while untwisting the DNA.

Termination

The final stage of transcription where specific DNA sequences signal the RNA polymerase to stop synthesis and dissociate from the DNA.

-35 Region

A prokaryotic promoter consensus sequence ($5'-TTGACA-3'$) located $35$ bases upstream from the transcription start site ($+1$).

-10 Region

A prokaryotic promoter consensus sequence ($5'-TATAAT-3'$) where RNA polymerase binds tightly and untwists approximately $17 \text{ bp}$ of DNA.

RNA Polymerase I

A eukaryotic enzyme located in the nucleolus that transcribes the three major ribosomal RNAs ($28S$, $18S$, and $5.8S$).

RNA Polymerase II

A eukaryotic enzyme located in the nucleus that transcribes messenger RNA (mRNA) and small nuclear RNA (snRNA).

RNA Polymerase III

A eukaryotic enzyme located in the nucleus that transcribes transfer RNA (tRNA), $5S$ rRNA, and some snRNAs.

TATA Box

A core eukaryotic promoter element located at $-30$ (sequence $TATAAAA$) that specifies where transcription begins.

TBP (TATA Binding Protein)

A $34 \text{ kDa}$ protein that binds to the TATA box and initiates the assembly of the transcription complex.

TFIID

A committed complex formed by the binding of TBP (TATA Binding Protein) and TAFs (TBP-associated factors) to the TATA box.

Enhancers

DNA sequences that regulate the rate of transcription initiation and are required for maximal transcription of a gene.

Activators

Proteins that bring enhancers close to the promoter to increase the rate of transcription.

Introns

Intervening, non-coding sequences in a primary transcript that are removed in the nucleus during splicing.

Spliceosome

A large machinery consisting of five snRNAs ($U1$, $U2$, $U4$, $U5$, and $U6$) and over $60$ proteins that facilitates intron splicing.

snRNP (Small Ribonucleoprotein)

A complex of snRNA and proteins, often called a 'snurp,' that helps position RNA segments for splicing.

5' Capping

A post-transcriptional modification where a $7\text{-methylguanosine}$ structure is added to the $5'$ end of mRNA to protect it from exonucleases.

Poly(A) Tail

A sequence of up to $200$ A residues added to the $3'$ end of mRNA by poly(A) polymerase after cleavage near the $AAUAAA$ recognition site.