Chapter 14 Flashcards
anatomy of RNA transcripts
- untranslated regions flank protein coding region; 3’ UTR affects the stability and translation of mRNA
- Shine-Dalgrano sequence in bacteria is right upstream of the start codon and is where the ribosome binds to mRNA for translation
- protein coding region is Madde up of codons that each specify an amino acid
- introns are non-coding regions that break up coding regions (axons) in eukaryotes
transcription and translation are ______ in eukaryotes
uncoupled
where does transcription and translation happen in eukaryotes?
transcription happens in the nucleus, translation happens in the cytoplasm
pre-mRNA
needs modification before its mature mRNA
what are some modifications of mRNA?
addition of 5’ cap
addition of 3’ poly A tail
splicing out of introns
alternative processing
RNA editing
addition of 5’ cap
guanine is added to the 5’ end of mRNA and is methylated
helps with mRNA stability, ribosome binding, and intron removal
addition of 3’ poly A tail
50-250 adenine nucleotides on 3’ end
helps with mRNA stability, ribosome attachment, and mRNA export to cytoplasm
splicing of introns
consensus sequences at exon/intron junctions and internal branch point guide splicing
spliceosome= RNA and proteins
alternative splicing
different combos of exons retained and spliced together
6-exon gene and 4-exon mRNA in thyroid cells makes calcitonin protein that regulates calcium levels
same 6-exon gene and 5-exon mRNA in brain cells makes CGRP protein that helps with pain transmission and blood vessel dilation
***different splicing can lead to differentiation of cells and function
what is alternative processing and what are the 2 ways to do it?
makes different proteins from the same gene
1. alternative splicing
2. multiple 3’ cleavage sites
multiple 3’ cleavage sites
proteins of different lengths can be produced from one gene
what does alternative processing effect?
can happen in 90% of human genes, can vary between people, and contributes organismal complexity
RNA editing
guide mRNA changes sequence of mRNA message
tRNA
each tRNA is specific for a different amino acid
incorporates rare modified bases
75-95 nt in length
processed after transcription
cloverleaf tertiary structure of tRNA
amino acid attachment site has conserved sequence where amino acid binds
anticodon is 3 nt long and interacts with codon in mRNA
aminoacyl-tRNa synthetase enzymes pair tRNA with the correct amino acid
*acceptor stem at one end, anticodon at the other end
rRNA
ribosomes are one of the most abundant molecular complexes in a cell
-made of RNA and protein
-one large and one small subunit
80% of total cellular RNA is in the ribosomes
rRNA genes
copy number varies across species
one long transcript may be methylated and cleaved to produce different functional rRNA molecules
small nucleolar RNAs and protein cleave and modify rRNAs and assemble them into mature ribosomes in eukaryotes
RNA interference
small interference RNAs (siRNAs) and microRNAa (miRNAs)
negatively regulate target genes via
1. degradation of mRNA
2. inhibition of transcripts (siRNA) or translation (miRNA)
3. chromatin modification
4. siRNA targets gene from which it was transcribed; miRNA targets other genes and thus has limited complementarity to them
mechanism of RNA interference
- double stranded RNA is cut by Dicer
- small piece of RNA joins with protein to form RNA-induced silencing complex
- RISC pairs with target mRNA and cleaves it (siRNA) or inhibits translation (miRNA)
what are other small RNAs?
piwi-interacting RNA- suppresses transponsons
CRISPR-bacterial defense and biotechnology
snRNAs and snoRNAS- post-transcriptional RNA processing
long noncoding RNAs- no known function typically
CRISPR mechanism
- bacteria put a piece of pathogen’s genome into their CRISPR array
- if the pathogen attacks again, they’ll transcribe their array
- transcript matching invader’s genome will pair with CAS protein to form effector complex
- effector complex cuts invader DNA
Xist
long noncoding RNA that coats the X chromosome destined for inactivation in bio. females
collinearity
number of nucleotides is proportional to number of amino acids- not completely true
how are introns removed from RNA?
via RNA splicing in the nucleus
shine-dalgrano sequence
ribosome binding site during translation in bacteria
what do small RNAs do?
transcription
translation
cancer
research
development
gene expression
formation of chromatin structure
defense against foreign DNA
