protein synthesis
DESCRIPTION
Protein Synthesis. Revision. The Genetic Code. A gene is a sequence of bases in DNA that codes for the sequence of amino acids in a polypeptide (protein) The ‘language’ of a gene has only 4 letters - these are? A T C and G. The Genetic Code. The ‘language’ of a protein has 20 letters - PowerPoint PPT PresentationTRANSCRIPT
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Protein Synthesis
Revision
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The Genetic Code
A gene is a sequence of bases in DNA that codes for the sequence of amino acids in a polypeptide (protein)
The ‘language’ of a gene has only 4 letters- these are?
A T C and G
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The Genetic Code
The ‘language’ of a protein has 20 letters- these are?
The 20 different amino acids that make up proteins
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The Genetic Code
If 1 base coded for one amino acid in a protein then, only 4 amino acids could be coded for
If 2 bases coded for one amino acid in a protein then, only 16 amino acids could be coded for
If 3 bases coded for one amino acid in a protein then, 64 amino acids could be coded for – more than enough
41 = 4
42 = 16
43 = 64
The genetic code is a triplet code
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The Genetic Code
There are 20 amino acids to be coded for and 64 base triplets to use to code them
Each amino acid has more than one code word – that is the genetic code is degenerate.
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The Genetic Code
The genetic code is non-overlapping
ATTCGAGGCGGT is ‘read’ as
ATT CGA GGC GGT
Each base is a part of only one triplet.
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The Genetic Code is:
A triplet code Degenerate Non-overlapping Universal
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Protein synthesis
2 major processes involvedTranscriptionTranslation
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Transcription
The relevant gene in the DNA in the nucleus is ‘copied’ into a molecule of RNA called mRNA or messenger RNA
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Transcription
DNA double helix unzips as hydrogen bonds between complementary bases break and the two polynucleotide strands separate
A
G
C
T A
G
C
T
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Transcription
One strand called the sense strand acts as a template, free RNA nucleotides complementary base pair to the exposed bases on this strand by forming hydrogen bonds
RNA polymerase forms sugar-phosphate bonds between nucleotides
A
G
C
TA
G
C
U
A
G
C
T
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Transcription
The mRNA detaches from the sense strand The two DNA strands join together by complementary
base pairing The DNA molecules winds back up into a helix
A
G
C
TA
G
C
U
A
G
C
T
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Transcription
The sequences of 3 bases on the mRNA coding for amino acids are called CODONS.
Not all the bases in the DNA code for amino acids so the mRNA just transcribed contains non-coding regions known as INTRONS
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Transcription
exon intronintron exon exon
enzymes
These introns are removed by enzymes before the mRNA leaves the nucleusThis leaves just EXONS or coding regions of mRNA
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Transcription
exon exon exon
enzymes
intron intron
These introns are removed by enzymes before the mRNA leaves the nucleusThis leaves just EXONS or coding regions of mRNA
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nucleus
Transcription to translation
mRNA
ribosome
Following the removal of introns the mRNA moves out through a nuclear pore and attaches to a ribosome
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tRNA
GGG
aa2
Translation
AUG CCC GGG CGC ACA CGU UUC UGA
tRNA
UAC
aa1
start codon
anticodon
stop codon
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tRNA
GGG
aa2
AUG CCC GGG CGC ACA CGU UUC UGA
tRNA
UAC
aa1
peptide bond formed
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tRNA
GGG
aa2
AUG CCC GGG CGC ACA CGU UUC UGA
tRNA
UAC
aa1
‘empty’ tRNA leaves to pick up another specific amino acid
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tRNA
CCC
aa3
tRNA
GGG
aa2
AUG CCC GGG CGC ACA CGU UUC UGA
aa1
Ribosome moves along mRNA by one codon
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tRNA
CCC
aa3
tRNA
GGG
aa2
AUG CCC GGG CGC ACA CGU UUC UGA
aa1
peptide bond formed
‘empty’ tRNA leaves to pick up another specific amino acid
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tRNA
ACUAUG CCC GGG CGC ACA CGU UUC UGA
aa2aa1
This process is repeated until the ribosome reads a stop codon
aa4aa3 aa6aa5 aa8aa7