Transcription and translation

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DNA is so important to the subject of Biology that the “Central Dogma of Biology” describes the two step process of protein synthesis and can be represented by: GENE RNA PROTEIN

The first step of protein synthesis is called transcription The first step of protein synthesis is called transcription. In transcription, a copy of a gene is made in the form of mRNA.

An enzyme called RNA polymerase is responsible for separating the two DNA strands of a gene and adding matching RNA nucleotides until the sequence is copied.

For example: DNA- T A C C G G G C A C G A A C T mRNA-

For example: DNA- T A C C G G G C A C G A A C T mRNA- A U G G C C C G U G C U U G A

Remember, the DNA of a cell cannot leave the nucleus, but mRNA can Remember, the DNA of a cell cannot leave the nucleus, but mRNA can. The mRNA travels to a ribosome so the “code” of the gene can be translated into a protein.

The second step of protein synthesis is, thus, called translation The second step of protein synthesis is, thus, called translation. In translation, the mRNA message is translated into a sequence of amino acids, the building blocks of proteins. Translation occurs at a ribosome.

The mRNA sequence is read three letters at a time The mRNA sequence is read three letters at a time. Each set of three letters is called a codon. mRNA- A U G G C C C G U G C U U G A Codon 1 Codon 2 Codon 3 Codon 4 Codon 5 Each codon is the “code” for one amino acid.

Once the mRNA has arrived at a ribosome, its code can be translated Once the mRNA has arrived at a ribosome, its code can be translated. A type of RNA called tRNA brings specific amino acids to the ribosome, and connects them in the exact sequence dictated by the mRNA code.

The charts below can be used to determine the amino acid that corresponds to each codon.

mRNA- A U G G C C C G U G C U U G A amino acid-

mRNA- A U G G C C C G U G C U U G A amino acid- Methionine Alanine Arginine Glycine Stop

Although a particular protein is made of thousands of amino acids in a specific sequence, the first amino acid is always methionine. The stop codon tells the RNA when the protein is complete.

When the chain of amino acids is complete, the protein will be directed to other organelles (rough E.R. and Golgi) to be folded into its correct shape. It can then perform its function for your cells.