Transcript DNA, RNA and Protein

RNA Molecules and
RNA Processing
Functions and Modifications
of RNA Molecules
Information Flow From DNA
replication
DNA
transcription
initial transcript RNA
processing
mature RNA
translation
Protein
Types of RNA Produced
by Transcription
• Messenger RNA
Contains the code words for the
sequence of amino acids in a specific
protein
CODON = group of three nucleotides
acting as a code word for an amino acid
Arrangement of
Codons on mRNA
Types of RNA Produced by Transcription
• Transfer RNA
– “Translates” the message by bringing a
specific amino acid into the correct position
on the growing protein chain
– Has ANTICODON = a group of three
nucleotides on a tRNA that recognizes a
mRNA codon
– Has amino acid attachment site
anticodon
Types of RNA Produced by Transcription
• Ribosomal RNA
One of the structural components of the
ribosome
Ribosome = organelle where protein
synthesis occurs
Has sites to bind both mRNA and tRNA
Interrupted Genes
Eukaryotic Genes have interruptions within
regions coding for protein
intron = interrupting sequence
exon = portion of coding region
Exon 1 intron 1 Exon 2
intron 2
Exon 3
Processing of the pre-mRNA is required
to remove introns and join exons.
Exon 1
Exon 2
Exon 3
Translated to Produce Protein
Coding Region
mRNA Processing
DNA
Untranslated
Region (UTR)
5’
In nucleus
UTR with
Transcription
consensus
sequence
Pre mRNA
Exon 1 intron 1 Exon 2
intron 2
Exon 3
3’
Add 5’ cap
m7G-P-P-P-
Exon 1 intron 1 Exon 2
Exon 3
intron 2
Cleave at 3’ end
Add 3’ poly-A tail
m7G-P-P-P-
Start
Codon
m7G-P-P-P-
Exon 1 intron 1 Exon 2
intron 2
Protein-coding Region
Exon 1
Exon 2
Exon 3
Exon 3
AAAAAA…..
Remove Introns
Splice Exons
together
AAAAAA……
Stop
Codon
Mature mRNA leaves for cytoplasm
Applying Your Knowledge
Which of the following molecules lacks
introns?
1. Pre-mRNA
2. DNA
3. Mature messenger RNA
4. All of these lack introns
5. None of these lack introns
Intron Removal for Ovalbumin mRNA
Addition of a
5’-Methyl
Guanine Cap
Cleavage and Polyadenylation of 3’ end
1. Pre-mRNA is cleaved 11-30 nucleotides
downstream of the AAUAAA consensus
sequence. (Rat1 will attach to 5’ end to terminate
transcription.)
2. 50-200 Adenine nucleotides are added
enzymatically to the resulting 3’ end.
Identifying Sites for Intron Removal
Steps in Splicing
Alternative Splicing
Multiple 3’ Cleavage Sites
RNA Editing
Applying Your Knowledge
A poly-A tail (repeating sequence of
adenine nucleotides) is added to
_____ of the primary transcript.
1. The 3’ end
2. The 5’ end
3. Either the 3’ end or the 5’ end
4. Both the 3’ end and the 5’ end
5. Neither the 3’ end nor the 5’ end
Applying Your Knowledge
Which molecule contains the information
for assembling the amino acids in the
correct order in the protein?
1. rRNA
2. tRNA
3. mRNA
4. All of these
5. None of these
tRNA Processing
Cleavage
Splicing
Nucleotide
Addition
Nucleotide
Modification
rRNA Processing
RNA Interference
(RNAi)
• Process by which small
RNA molecules regulate
gene expression
• Types of small RNAs
– Micro RNAs (miRNAs)
– Small Interfering RNAs
(siRNAs)
• Protein components
– Dicer
– Protein + RNA = RISC
(RNA-Induced Silencing Complex)
Producing Small RNAs
Interfering with RNA Function
Interfering with DNA
Function
• Some siRNAs can
inhibit transcription
• Protein components
– Protein + RNA = RITS
(RNA-Induced
Transcriptional Silencing)
– Methylating Enzyme
• Changes the chemical
characteristics of DNA or
chromatin histone
proteins to silence
transcription
siRNAs
From different RNA molecules
Gene Silencing by RNA Interference
Extra genes for a protein involved in
pigment production were introduced
into petunia plants. Silencing of both
the native and newly-introduced genes
led to white flower coloration.
Processes Affected by RNAi
• Genomic “Immunity”- protection from viral
and transposon genes observed in plants
and invertebrates
• Regulation of gene expression related to
– Development --miRNAs involved in the
timing of morphogenesis and maintenance of
stem cell populations
– Cell fate and proliferation
– Cancer
– Cell death