|
HOW IN THE WORLD CAN ONLY 20 AMINO ACIDS CREATE THE PRACTICALLY INFINITE NUMBER OF PROTEINS PRESENT IN THE BODY?!!??
It seems impossible, doesn't it? The key to all the variety is that the 20 amino acids can be linked in different combinations and in different numbers. For example,
alanine-valine-tryptophan........serine
is a different protein than
valine-serine-tryptophan........alanine
because the sequence is different, even though the same amino acids are represented. Similarly, a protein made of 200 amino acids is quite different than a protein that is 2000 amino acids. The reason for this is because a protein's function is directly related to its shape (which is related to its amino acid sequence). Thus, if you change a protein's amino acid sequence, then you change its shape; and if you change the protein's shape, you change its function!
So, the key to remember here is that the FUNCTION OF THE PROTEIN IS DIRECTLY RELATED TO THE SEQUENCE OF AMINO ACIDS ! To go one step further, the sequence of amino acids is related to the code on the mRNA molecule, which is determined by the code on the DNA molecule itself! This is how DNA eventually codes for proteins!!
Now you know WHY it's so important that the DNA code stays intact (no mutations) because if you change the DNA, you change the mRNA, you change the amino acids coded for, and thus, you change the protein! The problem is if you change the protein, it usually renders the protein biologically inactive (in other words, it won't work properly!).
As the term "anticodon" on tRNA implies, it is complementary to the codon on mRNA. The codon is ALSO a set of three bases, but because the codon is found on the mRNA molecule, it is called something different. So, let's review this…
 A series of three nucleotide bases on a DNA molecule is called a triplet;
A set of three nucleotide bases on an mRNA molecule is called a codon; and
A set of three nucleotide bases on a tRNA molecule is called an anticodon.
You might be saying to yourself, "Isn't this just a case of the same thing being called a different name depending on where it is?" YES, YOU ARE CORRECT! Try to compare yourself to this example: You may be called by your first name here at school, by a nick-name by someone you know well, and Mr. or Ms. on a job interview. So, you are still the same person, you're just called a different name depending on where you are!
Protein synthesis occurs in three stages: Initiation, Elongation and Termination.
|
