Unit 14- RNA Flashcards
gene organization
- concept of colinerarity and noncolinearity
- # of nucleotides in a gene should be proportional to the # of amino acids in encoded protein
- DNA much longer than mRNA (hybridization)
- bacteria = colinear; eukaryotes = noncolinear (loops)
colinearity
continuous seq of nucleotides in DNA encodes a continuous sequence of amino acids in a protein
introns
- eukaryotes have introns and exons
-later REMOVED by RNA processing - # and size vary between genes
- common in eukaryotes; uncommon in bacteria
group 1 introns
- Location: some rRNA genes
- mechanism: self-splicing
group 2 introns
- Location: protein-encoding genes in mitochondria and chloroplast
- mechanism: self-splicing
nuclear-premRNA introns
- Location: protein-encoding genes in the nucleus of eukaryotes
- mechanism: spliceosomal (snRNA)
tRNA introns
- Location: tRNA genes
- mechanism: enzymatic
gene
- DNA sequences that code for all exons and introns
- Sequences at the beginning and end of the RNA are not translated into a protein
-The promoter
-The terminator
structure of RNA
- mature mRNA contains 5’ untranslated region (5’ UTR, or leader seq)
- Shine-Dalgarno seq (prokaryotes)
- protein-coding region
- 3’ untranslated region
(3’ and 5’: stability and reg of translation NOT aa encoding)
start codon
AUG (met)
stop codons
- UAA
- UAG
- UGA
pre-mRNA processing
- addition of 5’ cap: nucleotide with 7-methylguanine; 5’-5’ bond to 5’ end
- addition of poly(A) tail: 50-250 adenine nucleotides added to 3’ end
5’ cap
facilitates bingind of ribosomes to 5’ end of mRNA, increasing mRNA stability
3’ clevage and addition of poly(A) tail
inc stability of mRNA, facilitates binding of ribosomes
RNA splicing function
removes noncoding introns, facilitates mRNA export to cytoplasm, allows mult protein production from alt splicing
RNA editing
alters nuckeotide seq of mRNA
RNA splicing
consensus seq
- 5’ consensus seq: GU(A/G): 5’ splice site
- 3’ consensus seq: CAGG
- branch point: adeine “A”: ~18-40 nucleotides upstream of 3’-splicing site
spliceosome: five RNA molecules +300 proteins
steps of splicing
- 5’ end cleaves from the upstream exon and attatched to branch point to form a LARIAT
- 3’ end of intron is cleaved from downstream exon, and ends of the 2 exons are spliced together
- takes place in spiceosome
nuclear organization
- intron removal, mRNA processing, and transcription take place at same site in nucleus
minor splicing
- 2-tpes of self-splicing introns: group 1 and 2 (due to complez secondary structure)
- occur in some protist rRNA and in fungi mitochondria
alt processing pathways for processing pre-mRNA
- enables exons to be spliced together in different combinations to yield different proteins
- due to Multiple 3’ cleavage sites
RNA editing
- guide RNA pairs with mRNA
- template for addition, deletion, or alteration of bases
structure of tRNA
- rare modified RNA nucleotide bases (robothymine and pseudouridine)
- produced by chem alt of standard bases
- common secondary structure: cloverleaf
- anticodon
structure of ribosome
- large ribosome subunit
- small ribosome subunit
ribosomal RNA is processed after transcription
- methyl groups added
- RNA cleaved into several pieces
- trimmed
- mature rRNA molecules(subunits) produced
RNA interfering
limits the invasion of foreign genes and censors the expression of their own genes
Long Noncoding RNAs
- do not encode proteins
- control gene expression
- enhancer RNAs are transcribed from enhancers and control gene expression
