(19-21) Eukaryotic mRNA synthesis and Promoter

The globin gene is [] nucleotides long. Its mRNA is approximately [] nucleotides long. The protein is [] amino acids long. This equates to about [_] nucleotides of mRNA that is translated

589; ~700; 146; 438

Every addition of a RNA nucleotide costs how many phosphate groups?

2

What three regions does the Globin gene consist of? (names and length)

5’ NCR (56 nucleotides), coding region (438 nucleotides), and 3’ NCR (95 nucleotides)

5’ NCR

noncoding region at the 5’ end of a gene. Functions as the ribosome binding site in a mRNA molecule. Approximately the first 50 nucleotides of a gene. First 56 nucleotides in the globin gene.

3’ NCR

noncoding region at the 3’ end of a gene. Poly A tail attaches here.

What post-transcriptional modifications occur as or after a gene is transcribed?

G-cap, poly-A tail, intervening sequence (introns and exons)

G-cap (describe and draw an example of it)

guanosine cap. Post transcriptional modification in which a guanosine nucleotide is added to the 5’ end of the mRNA. Unusual in that there is a 5’ to 5’ linkage between this guanosine and the nucleotide at the 5’ end of the mRNA. Functions in stabilizing the mRNA by protecting it from exonucleases.

What is the termination sequence for RNA polymerase II in eukaryotes?

there is no termination sequence. It over transcribes past the gene. There is however a SIGNAL sequence called the AATAAA sequence which is the target of a UsnRNP to cut off the over transcript of a gene.

over transcript

RNA polymerase II transcribes past the end of a gene. It can go up 1500 nucleotides past the end of the gene (as is the case in the globin gene).

What signal sequence indicates the end of the gene? (where on the gene is this?, why does it indicate the end of the gene?)

the AATAAA sequence is located about 10 nucleotides from the 3’ end of the gene. On mRNA, this sequence is AAUAAA, and is the target for UsnRNP and poly A synthetase.

UsnRNP

catalytic ribonucleoprotein which is formed from proteins and Uracil rich snRNA (UsnRNA). Recognizes the AAUAAA signal sequence and cuts the over transcript of the gene off about 10 nucleotides downstream from that sequence.

Poly A synthetase

enzymatic protein which recognizes the AAUAAA signal sequence after UsnRNP cuts off the over transcript. Creates a poly A tail on the 3’ end of the transcript. This poly A tail consists of about 110 adenine nucleotides being added to the end of the globin transcript.

poly-A tail

post transcriptional modification in which multiple adenine nucleotides are added to the 3’ end of a mRNA transcript. May be 60-120 nucleotides long. Protects the 3’ end and it serves as a marker for nuclear pore proteins to move the mRNA from the nucleus to the cytoplasm of the cell.

t/f all mRNA in eukaryotes receives a G-cap

true

t/f all mRNA in eukaryotes receive a Poly-A tail

false

About [] % of mRNA in eukaryotes receive a poly-A tail. If they don't have this, there is instead a [] in its place.

85; hairpin loop

t/f prokaryotic mRNA may be translated in a eukaryote if it receives a poly-A tail

false; it must be a G-cap, not a poly-A tail

Mature mRNA

mRNA with a G-cap, poly-A tail, and removed intervening sequences (introns)

Immature mRNA

any mRNA which has not undergone all the post transcriptional modifications necessary for it to go off into the cytoplasm and be translated

Spliceosome

UsnRNP responsible for cutting out introns/intervening sequences from a transcript then splicing the two ends of the mRNA back together

When a spliceosome acts on a immature mRNA, the removed sections are called [_] and the sections that remain in the transcript are known as []

introns; exons

Introns

mRNA that is removed by a spliceosome

Exons

mRNA that is not removed by a spliceosome

What benefit is there to mRNA having introns and exons?

introns may be selectively left in or out of a transcript to create different proteins from one singular gene. This allows multiple proteins to be made from one gene.

t/f introns must be removed from a gene in order for it to become a mature mRNA

false; the wording here is wrong because it should be a TRANSCRIPT not a gene.

Name the conserved sequences of the eukaryotic promoter and where they are relative to the gene and/or each other

TATA box (20-30 nucleotides upstream of gene). CAAT box (70-80 nt upstream from gene).

TATA box

conserved sequence of eukaryotic promoters. 20-30 nucleotides upstream of the gene. Role is helping RNA polymerase II to identify the first nucleotide of a gene

CAAT box

conserved sequence of eukaryotic promoters. 70-80 nucleotides upstream of the gene. Role is determining how often RNA polymerase II transcribes a gene. Does this by being the binding site of transcription factors.

Transcription factors

molecules which bind to DNA which regulates gene expression by controlling the rate of transcription.

Enhancer regions

regions which may be 100s or even 1000s of nucleotides upstream (or downstream← don't worry about in this class) from a gene. Works to increase the transcription of a gene, often by opening up the promoter region of the gene.