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Molecular Biology2.7 DNA Replication, transcription and translation
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DNA to Protein Synthesis The function of most genes is to specify
the sequence of amino acids in a particular polypeptide.
Two processes are needed to produce a polypeptide using the base sequence of a gene. Transcription Translation
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Transcription Transcription is the synthesis
of mRNA copied from the DNA base sequences by RNA polymerase.
The enzyme RNA polymerase binds to a site on the DNA at the start of a gene
The RNA polymerase separates the double strand of DNA and pairs up RNA nucleotides with complementary bases.
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Transcription The RNA polymerase
forms covalent bonds between the nucleotides
Transcription stops at the end of the gene. The completed mRNA is released.
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Transcription The completed mRNA has
a base sequence that is complementary to the template DNA strand. Note: Uracil replaces
Thymine
Complete the transcription portion of the practice sheet
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Translation Translation is synthesis
of polypeptides on ribosomes
Ribosomes are complex structures that consist of a small and large sub-unit with binding sites for each of the molecules used in translation.
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Translation The amino acid
sequence of polypeptides is determined by mRNA according to the genetic code
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Translation Codons of three bases
on mRNA correspond to one amino acid in a polypeptide
“Genetic Code” = The translation “dictionary” that enables the cellular machinery to convert the base sequence on mRNA into the amino acid sequence
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Translation There are 20 amino
acids and only 4 nucleotide bases.
Living organisms use a triplet code with 3 bases coding for an animo acid.
The sequence of 3 bases on the mRNA = CODON
Examine the list of codons
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Translation There are 3 “stop”
codons that code for the end of translation.
Different codons can code for the same amino acid. The code is
“degenerate”
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Translation Translation depends on
complementary base pairing between codons on mRNA and anticodons on tRNA
The amino acids are carried on tRNA
The tRNA has a 3 base ANTICODON complementary to the mRNA codon
Complete the translation portion of the worksheet