Chapter 8 Flashcards
Transcription involves synthesis of RNA From a DNA template by a protein called ____________
RNA polymerase
What are the seven main types of RNA
1) messenger RNA: encodes sequence of amino acids in polypeptides
2) ribosomal RNA: forms large and small ribosomal subunits
3) transfer RNA: carries amino acids to ribosomes during translation
4) small nuclear RNA: forms spliceosomes
5) micro RNA: base pair with mRNA, altering stability & translation
6) small interfering RNA: regulate mRNA stability & translation
7) telomerase RNA: helps elongate telomere length of chromosomes
In what ways do DNA & RNA differ?
1) DNA has thymine, RNA has uracil
2) DNA has deoxyribose sugar (H @ 2’ carbon), RNA has ribose sugar (OH @ 2’ carbon)
Four steps of Bacterial Transcription
1) Promoter recognition
2) Transcription initiation
3) Chain elongation
4) Chain termination
Bacterial promoters have two consensus sequences ____ & _____ that are recognized by the _____________________________
(-10 - Pribnow box, -35), RNA polymerase holoenzyme
T or F: bacterial translation can begin before transcription is finished and one gene can even have multiple RNA polymerases generating multiple strands of RNA at the same time
True
What are the two ways bacterial transcription is terminated?
1) intrinsic
2) rho-dependent
both involve the formation of hairpins
Compare the main differences between bacterial and eukaryotic transcription
Bacteria
- transcription & translation both in the cytoplasm
- mRNA is not spliced, no introns (more or less)
Eukaryotes
- transcription is in nucleus, translation in cytoplasm
- more diversity in promoter sequences
- mRNA gets spliced before translation, exons & introns
- chromatin influences transcription
Describe the three eukaryotic RNA polymerases
1) RNA polymerase I: several rRNA genes
2) RNA polymerase II: protein coding genes & snRNA genes
3) RNA polymerase III: tRNA genes, one snRNA gene, one rRNA gene
A promoter is…
a region of DNA upstream of a gene - this region is recognized and bound to by RNA polymerase which then transcribes that gene
T or F: in bacteria, RNA polymerase typically binds to one promoter and transcribes several genes in an operon but in eukaryotes, usually each gene has its own promoter where binding of RNA polymerase requires the help of general transcription factors
True
What are the three main ways a promoter is identified?
1) Introduce mutations in upstream sequences - if mutations are in the promoter region, the mutation is expected to be expressed less
2) Band shift assay - if DNA contains a transcription factor binding domain, it will migrate more slowly since a protein is bound to it
3) DNA footprint protection assay - if DNA contains a transcription factor binding domain, it won’t be degraded by DNAse
The half-life of transcripts in bacteria is _________________ while in eukaryotes, it is _______________, demonstrating that eukaryotic mRNA is much more stable.
seconds to minutes, hours to days
What are the three main methods of post-transcriptional processing in eukaryotes?
1) 5’ capping - methylated guanine is added
2) 3’ polyadenylation - string of adenines are added
3) intron splicing
Explain the four types of introns (splicing mechanism & type of organism)
1) Group I: self-splicing in eukaryotes, bacteria, bacteriophages
2) Group II: self-splicing in eukaryotic organelles, bacteria, archaea
3) pre-mRNA: via spliceosome in eukaryotic nuclear genes
4) rRNA & tRNA: enzymatic in eukaryotes, bacteria, archaea
What are the three recognition sequences recognized by the spliceosome?
1) 5’ splice site: most introns begin w/ GU nucleotides
2) 3’ splice site: most introns end w/ AG nucleotides
3) branch site: near the end of an intron - where the lariat forms (branch point adenine)
small nuclear ribonucleoproteins (snRNPs) bind to intron recognition sequences and form a _______ structure, these snRNPs make up the _______________. Lariat formation involves a covalent bond called a ___________________________. Then, the lariat is cleaved at the 3’ end of the intron and degraded.
lariat, spliceosome, 2’ - 5’ phosphodiester bond,
Three mechanisms that explain why there are more proteins than genes
1) Alternative promoters
2) Alternative polyadenylation
3) Alternative pre-mRNA splicing
Bigger genomes result in _______ and ________ introns
more and bigger
In bacteria, a __________ transcript is produced by RNA-coding genes, then RNA cleavage releases _______ and _______.
30S pre-RNA, rRNA, tRNA
In humans, a ___________ transcript is produced, resulting in ______ rRNAs
45S pre-RNA, three (18S, 28S, 5.8S)
