DECODING THE GENETIC CODE
The genetic code is made up of 4 chemical bases: Adenine, Cytosine, Guanine and
Thymine (or A, C, G, T). The code is based on the fact that A must join with T and C
must join with G.
What information does the genetic code contain?
Every coded message must carry information. The genetic code tells cells what proteins
the cell must make in order to function correctly.
How is this done?
The DNA bases are grouped in threes. Each group of three bases codes for a certain
amino acid. The code is also called a triplet code. When amino acids join together a
protein is made.
For example, the DNA bases ATA code for the amino acids tyrosine.
The table below shows the triplet code and the corresponding amino acids. Look at the
table carefully and answer the questions below:
Triplet codes and the amino acids they produce
DNA
coding
strand
AAA
AAG
AAT
AAC
GAA
GAG
GAT
GAC
TAA
TAG
TAT
TAC
CAA
CAG
CAT
CAC
Amino acid
phenylalanine
leucine
leucine
isoleucine
Start
valine
For example,
Base code
Amino acids
DNA
coding
strand
AGA
AGG
AGT
AGC
GGA
GGG
GGT
GGC
TGA
TGG
TGT
TGC
CGA
CGG
CGT
CGC
CGA
alanine
Amino
acid
serine
proline
threonine
alanine
AGA
serine
DNA
coding
strand
ATA
ATC
ATT
ATC
GTA
GTG
GTT
GTC
TTA
TTG
TTT
TTC
CTA
CTG
CTT
CTC
Amino acid
tryosine
stop
histidine
glutamine
asparagine
lysine
aspartic acid
glutamic acid
AAC
leucine
DNA
coding
strand
ACA
ACG
ACT
ACC
GCA
GCG
GCT
GCC
TCA
TCG
TCT
TCC
CCA
CCG
CCT
CCC
TCA
serine
Amino acid
cysteine
stop
tryptophan
arginine
serine
arginine
glycine
GCA
arginine
QUESTIONS
1.
2.
Amino acids do the following triplets code for:
a) TGT ________________
b) CCA ____________________
c) ACT _________________
d) GTA ____________________
e) GAG _________________
f) CCC ____________________
Write down the triplet combinations that could code for arginine.
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3.
What is the start sequence? _____________________
4.
What is the stop sequence? ( Hint there is more than one)
____________________________________________
5.
Why do you think a ‘start’ and ‘stop’ code is needed?
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6.
Write the amino acid sequence for the following bases:
TAC AAA CTG CCA GCC ATA ACT
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7.
Write down the amino acid sequence for the following tricky base code!
CCA TCT ACG TAC GAG AAT AAA CCC TTT ATC
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