Chapter 7 Translation
Translation is the conversion of the
information in the nucleic acid
sequence to polypeptides of a
specific amino acid sequence.
Crick的中心法则
DNA
1957年 transcription
RNA
translation
Protein
DNA
1970年Reverse
transcription
Protein
RNA
一,mRNA,
template for protein synthesis
mRNA carries information from DNA in
a triple codon
1,The genetic code has redundancy (多余
性 ),so codon is degenerate (简并的 ).
Section 1 The three roles of RNA
4 nucleotides taken 1 at a time could specified
only 4 different amino acid.
Two nucleotides taken at a time would permit
only 42 or 16 amino acids to be specified;
Any 3 adjacent nucleotides create 64 possible
codon (43),a number more than enough to
specify 20 different amino acids
。
1954年,G,Gamov 对破译密码首先提出了设想
2 Features of genetic codons
Stop codon UAA UAG UGA
Start codon AUG Met
UGG Trp
18 amino acids have more than one codon,called
synonymous codons (同义密码子 ),Generally they
differ only in their third position.
In all cases,if the third position is pyrimidine,the
codons specify the same AA,In most cases,if the
third position is a purine,the codons are also
synonymous.
The grouping of synonymous codons means that
the effects of mutations are minimized.
Transitions (碱基转换 ) are where a purine is
mutated into the other purine,or pyrimidine is
mutated into other pyrimidine,
Transversions(碱基颠换 ) are where a purine
changes to a pyrimidine or vice versa.
3 Effect of mutation
The effect of transition and transversion
on specified amino acid
Transition Transversion
Third position no effect,over half no effect
except Met,Trp
Second position effect on AA effect on both
species only AA species and type
first position a similar type of AA,in few cases,no effect
on AA species like Leu,Arg,Ser
4 The universality of genetic codons
Until recently,the standard genetic
code was considered universal,
however,some deviations are
found in mitochondria and some
unicellular.
硒代半胱氨酸
ORFS are suspected coding region
usually by computer in newly sequenced
DNA,They are continuous groups of
adjacent codons following a start codon
and ending at a stop codon.
5 Open reading frames(ORFS),读码框
Overlapping genes
The coding region of one gene partially or
completely overlaps that of another,For example:
AUG UAAAUG UAA
In prokaryotes,ribosomes can find the second
start codon to translate the overlapping gene
without detaching from the template,Eukaryotes
tend to make use of alternative RNA processing.
二,tRNAs,adopter molecules
tRNA are the adopter molecules (转接分子 )
that deliver amino acids to the ribosome
and decode the information in mRNA.
1 Primary structure of tRNA
Linear sequence,76nt (60~95nt);
Modified bases created post-transcriptionally,
accounting for 20% around of the total bases;
Four of these are very common:
T ( thymidine ),? ( pseuouridine ),
dihydrouridine ( D ) and I ( inosine )
2 tRNA secondary and tertiary structure
(1),AA activation
AA + ATP + E* Aminoacyl -AMP-E + PPi
E,aminonacyl-tRNA synthetase (ARS )
(2),The appropriate tRNA displaces the AMP
Aminoacyl-AMP-E + tRNA AA - tRNA + AMP +E
(3),Some ARS can carry out a proofreading step.
3 Aminoacylation of tRNAs
The computer-generated models of GlnRS and AspRS
The various ARS enzyme can be quite different
Four different classes,? ?2 ?4 ?2?2;
The length of polypeptide chains range from 334 to
1000AA;
They can be distinguished between 40 similarly
shaped,but different,tRNA molecules in cell,They
use identity elements (特征元件 ) of tRNAs,
including base pairs in the acceptor stem,except the
anticodon sequence.
?
Identity elements in
tRNA involved in
recognition by ARS
三,rRNA and ribosome
Ribosomes,protein-synthesizing machines
The interaction between codon and anticodon is
antiparallel in nature.
Wobble （摇摆） hypothesis, It was suggested
by Crick’ to explain the redundancy of the genetic
code,He realized,by model building,that the 5’-
anticodon base able to undergo more movement
than the other two bases and could thus form a
non-standard base pair as long as the distances
between the ribose units were close to normal.
1 codon - anticodon interaction and
wobble base pairs
Wobble base-pair
The base in the
third position of an
mRNA codon often
forms a
nonstandard base
pair with the base
in the first position
of a tRNA
anticodon
2 Ribosome binding site (RBS)
RBS is a sequence just upstream of the initiation
codon in prokaryotes mRNA, This sequence can
base pair with the 3’-end of the 16S rRNA in the
small subunit of the ribosome.
It is also called Shine-Dalgarno sequence,a
purine-rich sequence,5’- AGGAGGU.
Function,for the position of ribosome correctly
with respect to the initiation codon.
Translation is the conversion of the
information in the nucleic acid
sequence to polypeptides of a
specific amino acid sequence.
Crick的中心法则
DNA
1957年 transcription
RNA
translation
Protein
DNA
1970年Reverse
transcription
Protein
RNA
一,mRNA,
template for protein synthesis
mRNA carries information from DNA in
a triple codon
1,The genetic code has redundancy (多余
性 ),so codon is degenerate (简并的 ).
Section 1 The three roles of RNA
4 nucleotides taken 1 at a time could specified
only 4 different amino acid.
Two nucleotides taken at a time would permit
only 42 or 16 amino acids to be specified;
Any 3 adjacent nucleotides create 64 possible
codon (43),a number more than enough to
specify 20 different amino acids
。
1954年,G,Gamov 对破译密码首先提出了设想
2 Features of genetic codons
Stop codon UAA UAG UGA
Start codon AUG Met
UGG Trp
18 amino acids have more than one codon,called
synonymous codons (同义密码子 ),Generally they
differ only in their third position.
In all cases,if the third position is pyrimidine,the
codons specify the same AA,In most cases,if the
third position is a purine,the codons are also
synonymous.
The grouping of synonymous codons means that
the effects of mutations are minimized.
Transitions (碱基转换 ) are where a purine is
mutated into the other purine,or pyrimidine is
mutated into other pyrimidine,
Transversions(碱基颠换 ) are where a purine
changes to a pyrimidine or vice versa.
3 Effect of mutation
The effect of transition and transversion
on specified amino acid
Transition Transversion
Third position no effect,over half no effect
except Met,Trp
Second position effect on AA effect on both
species only AA species and type
first position a similar type of AA,in few cases,no effect
on AA species like Leu,Arg,Ser
4 The universality of genetic codons
Until recently,the standard genetic
code was considered universal,
however,some deviations are
found in mitochondria and some
unicellular.
硒代半胱氨酸
ORFS are suspected coding region
usually by computer in newly sequenced
DNA,They are continuous groups of
adjacent codons following a start codon
and ending at a stop codon.
5 Open reading frames(ORFS),读码框
Overlapping genes
The coding region of one gene partially or
completely overlaps that of another,For example:
AUG UAAAUG UAA
In prokaryotes,ribosomes can find the second
start codon to translate the overlapping gene
without detaching from the template,Eukaryotes
tend to make use of alternative RNA processing.
二,tRNAs,adopter molecules
tRNA are the adopter molecules (转接分子 )
that deliver amino acids to the ribosome
and decode the information in mRNA.
1 Primary structure of tRNA
Linear sequence,76nt (60~95nt);
Modified bases created post-transcriptionally,
accounting for 20% around of the total bases;
Four of these are very common:
T ( thymidine ),? ( pseuouridine ),
dihydrouridine ( D ) and I ( inosine )
2 tRNA secondary and tertiary structure
(1),AA activation
AA + ATP + E* Aminoacyl -AMP-E + PPi
E,aminonacyl-tRNA synthetase (ARS )
(2),The appropriate tRNA displaces the AMP
Aminoacyl-AMP-E + tRNA AA - tRNA + AMP +E
(3),Some ARS can carry out a proofreading step.
3 Aminoacylation of tRNAs
The computer-generated models of GlnRS and AspRS
The various ARS enzyme can be quite different
Four different classes,? ?2 ?4 ?2?2;
The length of polypeptide chains range from 334 to
1000AA;
They can be distinguished between 40 similarly
shaped,but different,tRNA molecules in cell,They
use identity elements (特征元件 ) of tRNAs,
including base pairs in the acceptor stem,except the
anticodon sequence.
?
Identity elements in
tRNA involved in
recognition by ARS
三,rRNA and ribosome
Ribosomes,protein-synthesizing machines
The interaction between codon and anticodon is
antiparallel in nature.
Wobble （摇摆） hypothesis, It was suggested
by Crick’ to explain the redundancy of the genetic
code,He realized,by model building,that the 5’-
anticodon base able to undergo more movement
than the other two bases and could thus form a
non-standard base pair as long as the distances
between the ribose units were close to normal.
1 codon - anticodon interaction and
wobble base pairs
Wobble base-pair
The base in the
third position of an
mRNA codon often
forms a
nonstandard base
pair with the base
in the first position
of a tRNA
anticodon
2 Ribosome binding site (RBS)
RBS is a sequence just upstream of the initiation
codon in prokaryotes mRNA, This sequence can
base pair with the 3’-end of the 16S rRNA in the
small subunit of the ribosome.
It is also called Shine-Dalgarno sequence,a
purine-rich sequence,5’- AGGAGGU.
Function,for the position of ribosome correctly
with respect to the initiation codon.
