Unit 4: Transcription

What are the three phases of transcription?

initiation, elongation, termination

Where does transcription take place in the cell?

nucleus

What direction is an mRNA molecule made?

5' to 3'

When we say a nucleic acid is made 5' to 3', what do we mean by that?

New nucleotide monomers are added to the 3' carbon of the sugar group in the backbone.

What is a transcription bubble?

The opened up section of DNA that is currently being copied by the RNA polymerase

What protein is responsible for synthesizing the mRNA during transcription?

RNA polymerase

What monomer is needed during transcription?

free RNA nucleotide triphosphates (NTPs)

What is the product of transcription?

messenger RNA (mRNA)

What is mRNA?

a complementary RNA copy of the DNA template strand at a specific point in the sequence (a gene)

What is the DNA sequence that identifies where transcription initiation should begin called?

a Promoter sequence

Promoters are recognized by what protein in prokaryotes?

Sigma Factor

Promoters are identified by what protein in eukaryotes?

Transcription Factors/TATA-binding proteins

Are promoters unique to each gene or the same across all genes?

Both! There is a conserved section and a unique section of the sequence.

Can RNA Polymerase initiate transcription on it's own?

No. It needs other proteins to help it recognize the initiation site.

How does transcriptional initiation begin?

A Transcription Factor or Sigma Factor protein recognizes and binds to a promoter sequence in the DNA. Then recruits an RNA Polymerase.

What is a promoter?

A sequence of DNA to which proteins bind to initiate transcription of a single RNA transcript from the DNA downstream of the promoter

What is the conserved section of the promoter sequence found in eukaryotes called?

TATA box

What is the conserved promoter sequence found in prokaryotes called?

Pribnow Box [TATAAT]

What occurs during transcriptional elongation?

RNA polymerase separates the DNA helix and synthesizes a new strand of mRNA in its active site

Which strand of DNA is referred to as the "template strand"?

The one that forms complementary base pairings with the RNA nucleotides as mRNA is synthesized.

What kind of bond is made to link RNA nucleotides together?

phosphodiester bond (covalent)

What kind of intermolecular force is essential for the process of transcription? Why?

Hydrogen bonding. It happens between the nitrogenous bases in the DNA template strand sequence and the nitrogenous bases in the RNA nucleotides in order to make sure the RNA polymerase is copying the correct sequence.

What does the elongation phase of transcription entail?

Elongation involves attaching free RNA NTPs to the DNA via hydrogen bonding, then creating the phosphodiester bonds along the RNA backbone via dehydration synthesis.

Does the coding strand hydrogen bind to the mRNA?

No. The Coding strand is the DNA strand that DOES NOT hydrogen bind to the RNA strand as it's being made, but its sequence is the same as the RNA strand (except U replaces T in the sequence)

If the coding strand on the DNA has the sequence 5'-ATGCGACTA-3', what will the mRNA transcript read?

5'-AUGCGACUA-3'

what occurs during the termination phase of transcription?

the RNA polymerase stops transcribing mRNA from the DNA template.

How does termination happen in bacteria?

the RNA molecule pairs with itself and forms a hairpin structure that boots the RNA polymerase off the DNA

What is an exon?

Any part of a gene sequence that will form a part of the final mature RNA product

What is an intron?

any nucleotide sequence within a gene that is not expressed or operative in the final RNA product.

What is a UTR?

UTR stands for "UnTranslated Region". They are found at the 5' and 3' ends of mRNA transcripts.

What is polyadenylation?

Adds an adenine tail ("AAAAAAAA") to mRNA transcripts.

What purpose does polyadenylation serve?

The adenine tail also helps export mRNA from the nucleus, and protects it from breaking down.

Do exons or introns code for proteins?

Exons

What is alternative splicing?

The process when different mRNA transcript molecules can be chopped up differently and thus different proteins can be coded into the same gene.

After the mRNA has been post-transcriptionally processed, what does the mRNA look like?

5' cap—5' UTR—AUG(start)—coding sequence—End—3' UTR—PolyA tail

What does the 5' cap do for an mRNA transcript?

increases mRNA transcript stability.

What is a 5' cap?

a specially altered nucleotide added on the 5′ end of an mRNA transcript.