Transcript PowerPoint Presentation - Foundations of Biology

Proverbs 3:1-3
1
2
3
My Son, forget not my law; but let
thine heart keep my commandments:
For length of days, and long life, and
peace, shall they add to thee.
Let not mercy and truth forsake thee:
bind them about thy neck; write them
upon the table of thine heart:
©2001 Timothy G. Standish
Messenger
RNA
Timothy G. Standish, Ph. D.
©2001 Timothy G. Standish
Introduction
The Central Dogma
of Molecular Biology
Cell
Transcription
Translation
Reverse
transcription DNA
mRNA
Ribosome
Polypeptide
(protein)
Information Only Goes One Way
The central dogma states that once “information”
has passed into protein it cannot get out again.
The transfer of information from nucleic acid
to nucleic acid, or from nucleic acid to protein,
may be possible, but transfer from protein to
protein, or from protein to nucleic acid, is
impossible. Information means here the precise
determination of sequence, either of bases in
the nucleic acid or of amino acid residues in
the protein.
Francis Crick, 1958
©2001 Timothy G. Standish
Transcription
Coding
(sense) strand
5’
3’
3’
5’
Template
(antisense) strand
©2001 Timothy G. Standish
Transcription
Coding
(sense) strand
5’
3’
3’
5’
5’
RNA
Pol.
Template
(antisense) strand
RNA
©2001 Timothy G. Standish
Transcription
Coding
(sense) strand
5’
3’
3’
5’
Template
(antisense) strand
RNA
Pol.
5’
©2001 Timothy G. Standish
RNA Polymerase
RNA Polymerase is a spectacular
enzyme, it performs the following
functions:
Recognition of the promoter region
Melting of DNA (Helicase +
Topisomerase)
RNA Priming (Primase)
RNA Polymerization
Recognition of terminator sequence
©2001 Timothy G. Standish
Products of Transcription
Transcription produces three major RNA
products:
1 Ribosomal RNA (rRNA) - Several rRNAs are
vital constituents of ribosomes
2 Transfer RNA (tRNA) - The molecule that
physically couples nucleic acid codons with
specific amino acids
3 Messenger RNA (mRNA) - The nucleic acid
messenger that carries encoded information from
genes on DNA to the protein manufacturing
ribosomes
©2001 Timothy G. Standish
Stages of Transcription
1.
2.
3.
Transcription can be logically
divided into three distinct
stages:
Initiation
Elongation
Termination
©2001 Timothy G. Standish
A “Simple” Gene
Transcription
Start Site
5’
5’ Untranslated Region
3’ Untranslated Region
Protein Coding Region
3’
RNA Transcript
Promoter/
Control Region
Terminator
Sequence
©2001 Timothy G. Standish
Transcription Initiation
Proteins called transcription factors bind
to the promoter region of a gene
If the appropriate transcription factors
are present, RNA polymerase binds to
form an initiation complex
RNA polymerase melts the DNA at the
transcription start site
Polymerization of RNA begins
©2001 Timothy G. Standish
Initiation
T. F.
Promoter
T. F.
RNA
Pol.
RNA
Pol.
RNA
5’
©2001 Timothy G. Standish
Transcription Termination
There are two types of termination:
Rho dependent requires a protein called
Rho, that binds to and slides along the RNA
transcript. The terminator sequence slows
down the elongation complex, Rho catches
up and knocks it off the DNA
Rho independent termination depends on
both slowing down the elongation complex,
and an AT-rich region that destabilizes the
elongation complex
©2001 Timothy G. Standish
Termination
Rho Independent
RNA
Pol.
RNA
Pol.
RNA
5’
RNA
Pol.
5’
RNA
5’
Terminator
©2001 Timothy G. Standish
Termination
Rho Dependent
Terminator
RNA
Pol.
RNA
5’
5’
r
Help, Rho
hit me!
r
RNA
Pol.
RNA
Pol.
RNA
5’
©2001 Timothy G. Standish
Differences
Between Transcription In
Prokaryotes and
Eukaryotes
©2001 Timothy G. Standish
Transcription And Translation
In Prokaryotes
5’
3’
3’
5’
RNA
Pol.
Ribosome
mRNA
Ribosome
5’
©2001 Timothy G. Standish
Eukaryotic Transcription
Cytoplasm
DNA
Transcription
RNA
RNA
Processing
mRNA G
G
AAAAAA
Nucleus
AAAAAA
Export
©2001 Timothy G. Standish
A “Simple” Eukaryotic Gene
Transcription
Start Site
3’ Untranslated Region
5’ Untranslated Region
Introns
5’
Exon 1 Int. 1
Promoter/
Control Region
Exon 2
3’
Int. 2 Exon 3
Terminator
Sequence
Exons
RNA Transcript
5’
Exon 1 Int. 1
Exon 2
Int. 2 Exon 3
3’
©2001 Timothy G. Standish
Processing Eukaryotic mRNA
5’ Untranslated Region
3’ Untranslated Region
Protein Coding Region
5’5’ G
3’
Int. 11 Exon
Int. 23 Exon 3 AAAAA 3’
Exon 1Exon
Exon22 Exon
5’ Cap
3’ Poly A Tail
RNA processing achieves three things:
 Removal of introns
 Addition of a 5’ cap
 Addition of a 3’ tail
l
This signals the mRNA is ready to move out of
the nucleus and may control its lifespan in the
cytoplasm
©2001 Timothy G. Standish
The 5’ Cap
5’ End of
hnRNA
O
H O
P
O H
N
O
GTP
H
C
C
H
C
N
C
O
C
H
C
H
C
C
O
O H
©2001 Timothy G. Standish
The 5’ Cap
O
H O
C
P
O
P
O
O
P
O H
N
N
O
C
C
O
H
N
C
OH
H
O
H
C
H
C
O
N
C
O
C
H
C
C
C
H O
H O
C
C
H
H
C
H
C
C
O H
O H
©2001 Timothy G. Standish
Transfer RNA (tRNA)
Acts as the adapter molecule between the genetic
code on mRNA and the protein “language”
75-85 bases long
A specific amino acid is covalently linked at the
3’ end
Elsewhere on the molecule is an anticodon
complimentary to the specific amino acid codon
on mRNA that codes for the amino acid carried
by the tRNA
Contain a number of modified bases
©2001 Timothy G. Standish
Transfer RNA (tRNA)
Acceptor Arm - A
specific amino acid is
attached to the 3’ end
16 Pu
17
9
A
17:1
13 12 Py 10
1
2
3
4
5
6
U* 7
Amino Acid
A
C
C
73
72
71
70
69
68
67
Py 59A*
66
65 64 63 62 C
D Arm - Contains
dihydrouridine
Py*
TyC arm - y stands
for pseudouridine
Pu
49 50 51 52 G T C
y
Py
G*
22 23 Pu 25
G
26
2020:120:2A
27
1
28
29
30
31
attachment site
47:16
47:15
43 44
42 45
41 46
47
40
47:1
39
38
Pu*
U
34 35 36
Anticodon
Extra Arm - May
vary in size
©2001 Timothy G. Standish
Aminoacyl-tRNA Synthetase
Aminoacyl-tRNA Synthetase enzymes
attach the correct amino acids to the
correct tRNA
This is an energy-consuming process
Aminoacyl-tRNA Synthetases recognize
tRNAs on the basis of their looped
structure, not by direct recognition of the
anticodon
©2001 Timothy G. Standish
Gly
P
P
Aminoacyl-tRNA
Synthetase
P
ATP
Gly
P
P
P
Aminoacyl-tRNA
Synthetase
Making
AminoacyltRNA
Pyrophosphate
Gly
P
Aminoacyl-tRNA
Synthetase
CCA
Gly
P
P
Making
AminoacyltRNA
Aminoacyl-tRNA
Synthetase
P
ATP
Gly
P
P
P
Aminoacyl-tRNA
Synthetase
Pyrophosphate
Gly
Aminoacyl-tRNA
Synthetase
Gly
Aminoacyl-tRNA
Synthetase
P
AMP
CCA
AminoacyltRNA
CCA
Note that the amino acid is not paired with the
tRNA on the basis of the anticodon. The correct
tRNA for a given amino acid is recognized on
the basis of other parts of
the molecule.
©1998 Timothy G. Standish
O
H
H N
C
Aminoacylation
of tRNA
O H
C
H O
H
H
R
C
H
O H
C
H
H
O H
H
C
H
C
O
N
C
3’
5’
H
O
O
H O
H
C
C
C
N
C
N
P
N
C
O
H
N
H
©2001 Timothy G. Standish
Class I Aminoacyl
Aminoacylation
O
tRNA Synthetases
attach amino acids to
of
tRNA
C
H
H N
Amino
acid
O
C
R
H
H
C
H
O H
C
H
H
O H
H
C
H
N
C
3’
5’
O
O
N
H
C
C
C
N
C
N
P
H O
tRNA
C
O
H
the 2’ carbon while
Class II attach to
the 3’carbon
C
O
H
N
H
©2001 Timothy G. Standish
Classification of AminoacyltRNA Synthetases
Aminoacyl-tRNA Class I - 2’ OH Class II - 3’ OH
Synthetases
Glu (a)
Gly (a b2
Gln (a)
Ala (a4
(ARS) may be
Arg (a)
Pro (a
mono or
Val (a)
Ser (a
multimeric.
Ile (a)
Thr (a
Two types of
Leu (a)
Asp (a ??
polypeptide
Met (a
Asn (a
chains are
Tyr (a
His (a
recognized:
(a
Lys (a
a and b.
©2001 Timothy G. Standish
Requirements for Translation
Ribosomes - rRNA and Proteins
mRNA - Nucleotides
tRNA
– The RNA world theory might explain these three
components
Aminoacyl-tRNA Synthetase,
– A protein, thus a product of translation and cannot be
explained away by the RNA world theory
L Amino Acids
ATP - For energy
This appears to be an irreducibly complex system
©2001 Timothy G. Standish
©2001 Timothy G. Standish