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BIOL 207 Exam -2 Questions And Answers Latest Update
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BIOL 207 Exam -2 Questions And Answers Latest Update
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2024/2025BIOL 207 Exam #2 Questions And
Answers Latest Update
describe--using drawings and text--how the three major modifications that happen to mRNA in
eukaryotes before it is exported to the cytoplasm
1) 5' cap: 5" to 5" G addition and methyl group
occurs shortly after transcription starts
important for stability of mRNA, translation initiation
protects mRNA from exonuclease activity
2) poly A tail added
50-250 As added (polyadenylation)
important for stability (protection from degradation by exonuclease activity), translation initiation,
transport to cytoplasm (hypothesis)
3) RNA splicing w/in coding region
exons encode amino acids, introns are intervening sequences
introns>exons in sequence length
using spliceosome (see below)
describe--using drawings and text--how the components of the spliceosome identify the exon/intron
boundaries of a mRNA in order to carry out splicing
Spliceosome: 5 small nuclear RNAs (snRNAs) + 300 proteins
Complimentary binding btwn snRNAs and consensus sequences
1) 5' splice site cut -> 5' end attaches to branch point (A) to form a lariat
2) 3' splice site cut -> exon ends joined
, 2024/2025
describe--using drawings and text--how alternative splicing can allow the production of related, but
not identical, proteins from the same gene
Alternative splicing allows more than one protein to be made from one gene, as shown above. The
spliceosome removes introns and the remaining exons are ligated to form mRNA. Exons are the
segments of RNA used to make mRNA while introns are often 'junk' RNA that gets degraded. Two
different mRNAs result in two different proteins and this contributes to protein diversity. In this
stylized example, Protein 1 has a helix contributed by exon 4, where as Protein 2 does not. The
proteins, made from the same gene, would be functionally distinct.
Proteins can block splice sites for certain genes
describe--using drawings and text--how the three major modifications that happen to mRNA in
eukaryotes are important for translation of the mRNA
see above
describe--using drawings and text--what a microRNA (miRNA) gene is and how it acts to regulate
the expression of other genes in eukaryotes
miRNAs (microRNAs) are short non-coding RNAs that regulate gene expression post-
transcriptionally. They generally bind to the 3'-UTR (untranslated region) of their target mRNAs and
repress protein production by destabilizing the mRNA and translational silencing.
double stranded RNA -> DICER cleaves it -> joins protein complex RISC (RNA-induced silencing
complex) -> not a perfect match but blocks translation
explain--using drawings and text--how a miRNA can inhibit translation even though it binds to the
3' UTR
By binding to specific sites within the 3′-UTR, miRNAs can decrease gene expression of various
mRNAs by either inhibiting translation or directly causing degradation of the transcript. The 3′-UTR
also has silencer regions which bind to repressor proteins and will inhibit the expression of the
mRNA.
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