The Role of tRNA and the
Anticodon
•The anticodon is located on the
transfer RNA (tRNA)
•tRNA has a clover-leaf shape
Anticodon
Codon
•tRNA carreis an amino acid at one
end and carries the three letter code
of the anticodon on the other end
•tRNA picks up the
amino acid that
corresponds to the
mRNA codon and
delivers it to the
ribosome
Gene Expression Vocabulary
• GENE- a sequence of DNA that codes for a
protein and thus determines a trait
• GENETIC CODE - language of the mRNA
instructions as determined by the N-bases
• CODON- sequence of 3 nucleotides (or just the
N-bases) on mRNA that code for one amino acid
• POLYLPEPTIDES- proteins made by joining any
combination of the 20 amino acids during
Translation process of Protein Synthesis
Additional info about
Amino Acids
• There are 20 known amino acids present
in living things.
• How is it possible to get a group of four
letters to code for 20 things?
• Put them into groups of three…
– 43 = 64 codes
Number of members in a group of nitrogen bases
Number of nitrogen bases
Codon Review
• A codon is a sequence
of 3 bases on the
mRNA.
• How we determine
what amino acid each
codon codes for must
be read off of a codon
chart.
• This codon chart is
also known as the
Genetic Code.
Genetic Code (Codon) Chart
Second Base
U
A
G
Phenylalanine
Phenylalanine
Leucine
Leucine
Serine
Serine
Serine
Serine
Tyrosine
Tyrosine
Stop
Stop
Cysteine
Cysteine
Stop
Tryptophan
U
C
A
G
C
Leucine
Leucine
Leucine
Leucine
Proline
Proline
Proline
Proline
Histidine
Histidine
Glutamine
Glutamine
Arginine
Arginine
Arginine
Arginine
U
C
A
G
A
Isoleucine
Isoleucine
Isoleucine
Methionine
Threonine
Threonine
Threonine
Threonine
Asparagine
Asparagine
Lysine
Lysine
Serine
Serine
Arginine
Arginine
U
C
A
G
Valine
Valine
Valine
Valine
Alanine
Alanine
Alanine
Alanine
Aspartic Acid
Aspartic Acid
Glutamic Acid
Glutamic Acid
Glycine
Glycine
Glycine
Glycine
U
C
A
G
U
First
Base
C
G
Third
Base
Genetic Code (Codon) Code
Amino Acids and the Genetic Code
(Codon) Chart
• It is possible for some amino acids to have more
than one codon.
• There are three stop codons…they are UAA,
UGA and UAG (indicate end of protein
synthesis.
• There is also one START codon…AUG (indicate
start of protein synthesis).
TRANSLATION- Second Process of Protein
Synthesis
• mRNA message is used to make
proteins and amino acids are joined
• Occurs at the ribosome in the
cytoplasm
• Anticodon on the tRNA brings an
amino acid to the ribosome and
complements codon on mRNA
Steps of TRANSLATION
Ribosome
1. mRNA reaches
the ribosome
(rRNA)
How many amino acids
will be in the completed
protein?
TRANSLATION
2. The tRNA
brings the
anitcodon and
amino acid to
the ribosome
3. As the tRNA drops the
amino acid at mRNA,
the ribosome forms a
peptide bond between
the amino acids
TRANSLATION
TRANSLATION
TRANSLATION
TRANSLATION
TRANSLATION
TRANSLATION
TRANSLATION
TRANSLATION
TRANSLATION
TRANSLATION
Peptide Bond
TRANSLATION
Peptide Bond
TRANSLATION
Peptide Bond
TRANSLATION
Peptide Bond
TRANSLATION
Peptide Bond
TRANSLATION
Peptide Bond
TRANSLATION
Peptide Bond
TRANSLATION
Peptide Bond Peptide Bond
TRANSLATION
Peptide Bond Peptide Bond
TRANSLATION
Peptide Bond Peptide Bond
TRANSLATION
Peptide Bond Peptide Bond
TRANSLATION
STOP
Peptide Bond Peptide Bond
TRANSLATION
STOP
Peptide Bond Peptide Bond
TRANSLATION
STOP
TRANSLATION
4. Once the stop codon is reached, the
protein is complete. The protein will
now travel to the Golgi Apparatus.
STOP
Peptide Bonds hold the amino acids
together.
TRANSLATION
SUMMARY
Transcription
A
G
C
A
G
A
G
DNA
C
C
G
G
T
A
C
T
T
U
A
Translation
mRNA
tRNA
Protein
In summary…
• DNA contains the information needed to
make proteins.
• However, DNA is too large to leave the
nucleus.
• RNA acts as a set of working instructions
for ribosomes to make proteins.
• This process is also known as gene
expression.
Steps to Protein Synthesis and the Genetic Code
1. Obtain a DNA Template (a strand of DNA bases)
2. Transcribe DNA into mRNA (occurs in nucleus)
3. Translate mRNA into tRNA (occurs at ribosome)
4. Use the codons on mRNA to translate into amino acids
using Genetic Code Chart
Let’s Practice…
DNA
TAC
mRNA (Codon)
AUG
tRNA Strand
(anticodon)
UAC
Amino Acids
Methionine
DNA
ATG
mRNA (Codon)
UAC
tRNA Strand
(anticodon)
AUG
Amino Acids
Tyrosine
More practice needed?
DNA= GAT-TAC-GCC-ATC
AUG- CGG-UAG
mRNA= CUA________________
tRNA= ________________
GAU- UAC-GCC-AUC
LEU-METH-ARG-STOP
Amino Acids= _________________
Genetic Code (Codon) Code