Lecture 9 — Transcription & Translation

What is the central dogma?

DNA → RNA → Protein.

What is gene expression?

Production of a functional gene product.

What is transcription?

Synthesis of RNA using DNA as a template.

What is translation?

Decoding mRNA to make a protein.

What enzyme performs transcription?

RNA polymerase.

What is a promoter?

DNA sequence where transcription machinery assembles and transcription begins.

What is a terminator?

Sequence that signals transcription to stop.

What are the three stages of transcription?

Initiation, elongation, termination.

What does sigma factor do in prokaryotic transcription?

Helps RNA polymerase recognize and bind the promoter.

Is sigma factor required throughout transcription?

No; it is mainly needed for initiation.

What do general transcription factors do in eukaryotes?

Help RNA polymerase recognize the promoter and begin transcription.

What does TFIID do?

Recognizes the promoter and begins assembly of the transcription machinery.

What protein within TFIID binds the TATA box?

TBP.

What does TFIIH do?

Helps open DNA and phosphorylates RNA polymerase II.

What is the pre-initiation complex?

RNA polymerase plus general transcription factors assembled at the promoter.

Why is RNA polymerase II phosphorylated?

It allows transcription to proceed into elongation.

What three processes modify eukaryotic pre-mRNA?

5′ capping, polyadenylation, and splicing.

What is added to the 5′ end of mRNA?

A methylated guanine cap.

What is added to the 3′ end of mRNA?

A poly-A tail.

What is an intron?

RNA sequence removed during splicing.

What is an exon?

RNA sequence retained in mature mRNA.

What removes introns?

The spliceosome.

What are snRNPs?

RNA-protein complexes that help form the spliceosome.

What is a codon?

Three mRNA nucleotides specifying an amino acid or stop signal.

What is an anticodon?

Three tRNA bases complementary to an mRNA codon.

What is a charged tRNA?

A tRNA attached to its correct amino acid.

What is the usual start codon?

AUG.

What amino acid does AUG encode?

Methionine.

What does the ribosome A site hold?

Incoming charged tRNA.

What does the ribosome P site hold?

tRNA carrying the growing polypeptide.

What happens at the ribosome E site?

Empty tRNA exits.

A = ?

Arrival of the next aminoacyl-tRNA.

P = ?

Peptide/growing protein.

E = ?

Exit.

What are ribosomes made of?

rRNA and proteins.

What are the two main parts of a ribosome?

Large and small subunits.

What is the Shine-Dalgarno sequence?

Prokaryotic ribosome-binding sequence used during translation initiation.

What is the Kozak sequence?

Eukaryotic sequence surrounding the start codon that assists translation initiation.

Where does a eukaryotic ribosome initially associate with mRNA?

The 5′ cap.

What happens during translation elongation?

tRNA enters A site, peptide bond forms, ribosome translocates.

What happens at a stop codon?

A release factor terminates translation and releases the protein.

What is wobble base pairing?

Flexible pairing that lets some tRNAs recognize more than one codon.

Given mRNA UUC-GAU-GUC, what is translated?

Phe-Asp-Val.