The genetic code is used as a blueprint to make proteins. We have looked at DNA. But how is this genetic code actually used for anything? Lets See! See!

Proteins are widely used in cells to serve diverse functions. Some proteins provide the structural support for cells while others act as enzymes to catalyze certain reactions. But, where do proteins come from?

Since the beginning of evolution, cells have developed the ability to synthesize proteins. They can produce new proteins either for reproduction or to simply replace a degraded one.

To manufacture proteins, cells follow a very systematic procedure that first transcribes DNA into mRNA transcribes DNA into mRNA and then translates the mRNA and then translates the mRNA into chains of amino acids. into chains of amino acids. The amino acid chain then folds into into specific specific proteins. proteins.

has only a single strand of nucleotides instead of two strands contains a different sugar (ribose instead of deoxyribose) contains the nitrogen base uracil (U) instead of thymine (T) (Transcribed is a fancy way of saying “copied.”) RNA is very similar to DNA except that it:

Messenger RNA (mRNA) copies DNA’s code & carries the genetic information to the ribosomesMessenger RNA (mRNA) copies DNA’s code & carries the genetic information to the ribosomes Ribosomal RNA (rRNA), along with protein, makes up the ribosomesRibosomal RNA (rRNA), along with protein, makes up the ribosomes Transfer RNA (tRNA) transfers amino acids to the ribosomes where proteins are synthesizedTransfer RNA (tRNA) transfers amino acids to the ribosomes where proteins are synthesized

The “m” in “mRNA” stands for “messenger,” because mRNA copies genetic information from DNA (which is found in the nucleus) and carries it to another part of the cell (the ribosomes).

Codon O.K., we’ve gone from DNA to mRNA. How do proteins fit into all this? Think of the genetic code the mRNA is carrying as a series of three-letter “words.” Each of these three-letter words is called a codon.

Different codons code for different amino acids. For example, the codon for the amino acid methionine is AUG (adenine, uracil, guanine). The codon for the amino acid serine is UCA (uracil, cytosine, adenine).

Another type of RNA, called tRNA (“t” stands for “transfer”) matches the codons in mRNA to the correct amino acids. As the mRNA strand moves along the ribosome, the amino acids are joined in the correct sequence to form a protein. This process is called translation.

C C U Proine U C G Serine U C C Tryptophan G G A Proine Codon U C G Serine G U U Valine G

The diagram below shows a codon chart. A codon chart shows which codons code for which amino acids.

Suppose a DNA mutation led to a change in a single mRNA codon. Now suppose this codon changed from GCC to GCG. By looking at the codon chart, you can see that both of these codons code for the amino acid alanine. So even though the DNA and mRNA have changed, there is no change in the protein!

This chart shows the amino acids coded for by each of the 64 possible mRNA codons. To find which amino acid the codon CAA codes for, follow these steps. (1) Look on the left side of the chart to find the large row of codons that begin with C. (2) Move across this row until you get to the column of codons whose second base is A. (3) Move down this column until you get to the row of codons whose third base is A. The codon CAA codes for the amino acid glutamine.