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Translation
Chapter 10: DNA, RNA and
Protein Synthesis
The Genetic Code
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The Genetic Code is the term for the rules
that relate how a sequence of nitrogenous
bases in nucleotides corresponds to a
particular amino acid.
In the Genetic Code, three adjacent
nucleotides (“letters”) in mRNA specify an
amino acid (“word”) in a polypeptide.
Codon
A sequence of three nucleotides that encode
for an amino acid or signifies a start or stop
signal.
Examples:

UUU = phenylalanine
AUG = start
The Genetic Code
Examine the sequence of three
bases: UAC
Codons
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There are 64 possible codons corresponding
to 20 amino acids
Each amino acid has more than one possible
codon.
There are Start and Stop signals built into the
code.
The Start codon corresponds to the amino
acid methionine.
Flow of Information

The sequence of nitrogenous bases in DNA
becomes complementary to the sequence of
bases in the mRNA molecule during
TRANSCRIPTION.

tRNA molecules bring amino acids to the
ribosome and match up their complementary
bases to the mRNA molecule during
TRANSLATION.
Translation
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The making of a protein by stringing together
amino acids to make a polypeptide chain.
Information flows from DNA to mRNA and
then tRNA brings the corresponding amino
acid.
Peptide bonds are formed between adjacent
amino acids and a polypeptide chain is
formed.
Translation
- What is it?
The making of a protein
- Where does it take place?
Prokaryotes = cytoplasm
Eukaryotes = cytoplasm
- What is needed?
mRNA, 2 ribosomal subunits, tRNA and
amino acids
Steps of Translation
 Initiation:
The ribosomal subunits, the mRNA,
and the tRNA carrying methionine
bind together.
Initiation
Elongation
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The tRNA carrying the amino acid sequence
specified by the next codon binds to the
codon.
A peptide bond forms between adjacent
amino acids
The ribosome moves the tRNA and mRNA.
Elongation
(Continued Elongation)
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The first tRNA detaches and leaves its amino
acid behind.
Elongation continues.
The polypeptide chain continues to grow.
Elongation (continued)
Termination
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The process ends when a stop codon is
reached.
A stop codon is one for which there is no
tRNA molecule that has a complementary
anticodon.
Disassembly

The ribosome complex falls apart. The newly
made polypeptide is released.
Summary
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Information flows from DNARNAProteins
RNA serves as the intermediary between DNA and
proteins.
There are three types of RNA. mRNA, rRNA and
tRNA.
The Genetic Code represents 64 possible codons
corresponding to 20 different amino acids, start
signal and stop signals.
The process of TRANSLATION takes place within
the cytoplasm on a ribosome.
The process of TRANSLATION involves: initiation,
elongation and termination.