Download The Genetic Code The nucleotide bases of the DNA strand

The Genetic Code
The nucleotide bases of the DNA strand determine the sequence of the nucleotide bases of the messenger
RNA strand (mRNA),
A Uracil complementing the Adenine
A Guanine
“
“ Cytosine
A Cytosine
“
“ Guanine
An Adenine
“
“ Thymine.
This step of assembling an RNA molecule according to the DNA sequence is called transcription – the
original information is now a message in form of an RNA strand.
This message is moving from the nucleus into the cytoplasm where it is read, employing the same principle
of complementary nucleotide bases. This time, however, small molecules with t h r e e nucleotide bases
have to complement the sequence on the mRNA. This RNA is called the transfer-RNA (tRNA), and it can
only accomplish a complementation, when all t h r e e bases find tree adjacent, matching bases on the
messenger RNA.
U
A
G
G
A
C
C
U
Using arrows, mark where the three letter sequence on the right might match up.
Once the tRNA has found it’s position along the mRNA it locks into a distinct place. The tRNA also carries
– as a specific correlation to its nucleotide sequence - one distinct amino acid. A tRNA is therefore distinct
for its three nucleotides at one end, and its proper amino acid at the other end of the molecule. Different
amino acids will be associated with different triplets of nucleotides, therefore accounting for different
molecules of tRNA. Different tRNA molecules will line up the different amino acids along the mRNA
strand. The amino acids, then, represents a specific protein that makes sense to the organism.
Exercise
The organism has to utilize the following information (DNA-code). You will need to transcribe it to
mRNA and then translate it to make the protein chain.
DNA: ACC TAA TGT TGG ACC TTT GTG TAA ACC TAA TGG CCG AGA TTG TAA ATT CCC
mRNA: UGG AUU
DNA: AAA AGA TTG GTA TAA TGT TGG TTG TAA CCA TTG TTT TTG TGT ACC CGC
mRNA:
DNA: TAA CGC CCC GTA TTG TAA
mRNA:
Since you cannot read off the amino acids, we have replaced each amino acid by a letter of the alphabet
only using those occurring in the message. If you then assemble the letters in the sequence in which the
amino acids would be lined up according to the information above, you will be able to read the information.
If the sentence is grammatically correct and all the words are spelled correctly, you did it right. If not, you
made a mistake (possible mutation) somewhere. Find your mistake and fix it.
Triplet in tRNA
CCG
CGC
GUA
UUG
CCA
UGG
ACC
GUG
amino A (letter)
A
C
D
E
G
H
I
K
Triplet in tRNA
AAA
UUU
CCC
AUU
UGU
AGA
UAA
amino A (letter)
L
N
O
S
T
V
end of word