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Protein Synthesis What is transcription? What is translation?
How are tRNA and mRNA involved in protein synthesis?
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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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ATTCGAGGCGGT is ‘read’ as ATT CGA GGC GGT
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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2 major processes involved
Protein synthesis 2 major processes involved Transcription Translation
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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
G C T A G C T DNA double helix unzips as hydrogen bonds between complementary bases break and the two polynucleotide strands separate
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Transcription A G C T A A G C T G C U
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
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Transcription A G C T A G C U A G C T
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
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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 intron exon intron exon enzymes
HL only exon intron exon intron exon enzymes These introns are removed by enzymes before the mRNA leaves the nucleus This leaves just EXONS or coding regions of mRNA
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Transcription intron intron exon exon exon enzymes
HL only intron intron exon exon exon enzymes These introns are removed by enzymes before the mRNA leaves the nucleus This leaves just EXONS or coding regions of mRNA
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Transcription to translation
Following the removal of introns the mRNA moves out through a nuclear pore and attaches to a ribosome nucleus mRNA ribosome
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Translation UAC GGG anticodon AUG CCC GGG CGC ACA CGU UUC UGA
tRNA UAC aa1 tRNA GGG aa2 anticodon AUG CCC GGG CGC ACA CGU UUC UGA start codon stop codon
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AUG CCC GGG CGC ACA CGU UUC UGA
peptide bond formed tRNA UAC aa1 tRNA GGG aa2 AUG CCC GGG CGC ACA CGU UUC UGA
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AUG CCC GGG CGC ACA CGU UUC UGA
aa1 tRNA GGG aa2 tRNA UAC AUG CCC GGG CGC ACA CGU UUC UGA ‘empty’ tRNA leaves to pick up another specific amino acid
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AUG CCC GGG CGC ACA CGU UUC UGA
tRNA CCC aa3 aa1 tRNA GGG aa2 AUG CCC GGG CGC ACA CGU UUC UGA Ribosome moves along mRNA by one codon
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AUG CCC GGG CGC ACA CGU UUC UGA
peptide bond formed aa1 aa2 tRNA CCC aa3 tRNA GGG AUG CCC GGG CGC ACA CGU UUC UGA ‘empty’ tRNA leaves to pick up another specific amino acid
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AUG CCC GGG CGC ACA CGU UUC UGA
aa6 aa5 aa8 aa7 aa2 aa1 aa4 aa3 tRNA ACU AUG CCC GGG CGC ACA CGU UUC UGA This process is repeated until the ribosome reads a stop codon
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