Title: 3 main types of RNA
13 main types of RNA
Transcription
- All are made from a DNA Template
- mRNA encode AA sequence of one of more
polypeptides from a gene or set of genes - tRNA reads info. In mRNA and transfers
appropriate AA to growing peptide chain - rRNA part of ribosome, cellular machines
synthesize proteins
2Synthesis
- Resembles DNA replication in its chemical
mechanism, polarity, use of template - Has initiation, elongation, termination phase
- Does not need a primer, only involves limited
segment of DNA molecule
3RNA Polymerase
- DNA directed RNA polymerase
- DNA template
- Nucleotides (ATP, CTP, UTP, GTP)
- Builds in the 5 to 3 direction
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5RNA Polymerase
6Binds to initiation site through sequences called
promoter elements that are recognized by ? factor
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9Once initiation occurs ? factor dissociates
10Recognized by ?70
Recognized by ?32
11RNA Polymerase has helicase activity
Gyrases/topoisomerases are needed to prevent
positive supercoiling ahead of the transcription
bubble
12An electron micrograph of three contiguous
ribosomal genes from oocytes of the salamander
Pleurodeles waltl undergoing transcription.
13Transcription is tightly regulated
Not all genes are transcribed equally
14Transcription Factor
- Upstream of RNAP II initiation site, different
combinations of specific DNA sequences each is
recognized by corresponding site specific DNA
binding protein - Each combination of DNA sequence and cognate DNA
binding protein represent a control module
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20The lac operon
21Eukaryotic transcription
Heterochromatin transcriptionally
inactive Euchromatin may be transcriptionally
active
Eukaryotic RNAP have almost no affinity for
promoters on their own
22Eukaryotic RNA Polymerases
- RNAP I synthesis of transcripts called
preribosomal RNA precursor 18s, 5.8s, 28s RNA - RNAP II synthesis of mRNA
- RNAP III synthesize tRNA
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24RNA Polymerase II
- Has 12 subunits
- Needs transcription factors that stimulate the
enzyme to bind to a nearby promoter - General TF required at every RNAP II promoter
25Functionally equivalent to ? factor
26Gaining access to the DNA template
Histones must be modified to access DNA
Histone acetyltransferases decrease
charge Histone deacetylases increase charge
27Lysine
Acetyllysine
28Gene Silencing
5 of cytidine residues are methylated at the 5
position
These are most often found at CG sequences
Hypermethylation is associated with
heterochromatin
29Recruiting RNA polymerase
30Regulated Transcription
31Regulated Transcription
32RNA Processing
- Most RNA is processed after synthesis
- Ribozymes catalyze post-transcriptional
processing - Primary Transcript newly synthesized RNA
molecule occurs in mRNA and tRNA contains
sequence encoding one gene but encoded
polypeptide not continuous - Noncoding Regions introns
- Coding Region exons
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37Post-transcriptional control
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40RNA Editing Changes the Meaning
41RNA Editing Changes the Meaning
C to U
A to I
42There are many ways to regulate the meaning of
genes after transcription
Prevent translation
43There are many ways to regulate the meaning of
genes after transcription
Degrade the message
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46Target the mRNA
47What about mistakes? Nonsense Mediated Decay