How to Crack the Code

 

DNA - the Blueprint of Life

 

Every living organism contains within itself the information it needs to build a new organism. This information, you could think of it as a blueprint of life, is stored in the organism's genome. The genome is made up of a material called DNA, which stands for deoxyribonucleic acid. If you take a really, really close look at the DNA molecule you will see that it looks like an ordinary ladder, although somewhat twisted. The steps that connects the two strands in this ladder are composed of four different molecules of the same type, called nucleotides. In DNA they are A, T, C and G; where A stands for adenine, T for thymine, C for cytosine and finally G for guanine.

 

 

 

 

 

 

RNA - a Blueprint Copy

 

When an organism needs to use the data stored in the genome, e.g. to build components of a new cell, a copy of the required DNA part is made. This copy is called RNA and is almost identical to DNA. Just like DNA, RNA is an abbreviated form of a chemical name which in the case of RNA is ribonucleic acid. Unlike the double stranded DNA, RNA is only made up of a single strand. Furthermore, the base T, thymine, is replaced by U, uracil in RNA. This RNA string is used by the organism as a template when it builds protein molecules, sometimes called the building blocks of the body. For example, your muscles and hair are mostly made up of proteins.

 

 

 

Amino Acids Make Up the Protein

Proteins can vary in length and size and look very different, but they are all composed of smaller units, i.e. molecules called amino acids. Inside our body there are 20 amino acids all with different chemical and physical properties. In the table below their names and abbreviations can be found.

Name	Abbrev.	Short Abbrev.
alanine	Ala	A
arginine	Arg	R
asparagine	Asn	N
aspartic acid	Asp	D
cysteine	Cys	C
glutamine	Gln	Q
glutamic acid	Glu	E
glycine	Gly	G
histidine	His	H
isoleucine	Ile	I
leucine	Leu	L
lysine	Lys	K
methionine	Met	M
phenylalanine	Phe	F
proline	Pro	P
serine	Ser	S
threonine	Thr	T
tryptophan	Trp	W
tyrosine	Tyr	Y
valine	Val	V

 

But how does the organism know how to assemble these proteins compromising of the different amino acids? How can the organism "read" the RNA, the blueprint copy, and how is the information written in the RNA?

 

The RNA Message

The alphabet in the RNA molecule contains 4 letters, i.e. A, U, C, G as previously mentioned. To construct a word in the RNA language, three of these letters are grouped together. This three-letter word are often referred to as a triplet or a codon. An example of such a codon is ACG. The letters don't have to be of different kinds, so UUU is also a valid codon. These codons are placed after each other in the RNA molecule, to construct a message, a RNA sequence. This message will later be read by the protein producing machinery in the body.

The RNA part to the left contains 39 letters and since each codon contains 3 letters, 13 codons are present (39 letters divided by 3 letters equals 13 words or codons.)

But how does these RNA words get interpreted by the organism into the final product, the protein?

Can you decode the message in the RNA string?

 

Interpreting the Message

Every organism has an almost identical system that is able to read the RNA, interpret the different codons and construct a protein with various combinations of the amino acids mentioned previously. In fact every RNA word or codon, corresponds to one single amino acid. These codons and their correlation with the amino acids in a protein sequence is what defines the genetic code. Below is a schematic animation of this process displayed.

 

Visualizing the Code

One way to visualize the genetic code, the connection between a codon and an amino acid, is with a table. In the example below, the letter in the outermost left column represents the first letter in the codon. The letters in the top row represents the second codon letter and finally the letters in the outermost right column represents the third codon letter.

	U C A G   U Phe Ser Tyr Cys U Phe Ser Tyr Cys C Leu Ser STOP STOP A Leu Ser STOP Trp G C Leu Pro His Arg U Leu Pro His Arg C Leu Pro Gln Arg A Leu Pro Gln Arg G A Ile Thr Asn Ser U Ile Thr Asn Ser C Ile Thr Lys Arg A Met Thr Lys Arg G G Val Ala Asp Gly U Val Ala Asp Gly C Val Ala Glu Gly A Val Ala Glu Gly G

 

The genetic code is an important key in the understanding of the process in the body when the DNA copy - RNA, is translated into the functional molecules, the proteins.

 

First published 7 July 2004

 

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