Transcription, translation, & the genetic code (Basic science review)

1. Introduction
2. The structure of DNA, RNA and proteins
3. The two types of RNA
4. The genetic code
5. Transcription
6. Translation

Introduction

• DNA contains the genetic information needed to create proteins.
• Transcription is the process of converting that information into RNA.
• Translation is the process of using the RNA to create a protein.

The structure of DNA, RNA and proteins

• DNA, RNA and proteins are all polymers.
• The monomers in DNA are the bases: adenine, guanine, cytosine, and thymine.
• The monomers in RNA are the bases: adenine, guanine, cytosine and uracil.
• The monomers in proteins are amino acids.
• DNA has two strands. One strand is used to code the genes. The other strand is used to duplicate the coding strand.
• The bases always associate in a specific way: adenine with thymine, and guanine with cytosine. (An easy mnemonic is that A & T both have only straight lines, and G & C have curves.)

The two types of RNA

• There are two main types of RNA: messanger RNA (mRNA) and transfer RNA (tRNA).
• mRNA is a long strand that mirrors the DNA that was used to make the mRNA.
• tRNA is a short strand of RNA that guides an amino acid into place on the developing strand of protein.

The genetic code

• There are only 4 bases in DNA, but there are 20 different amino acids used in proteins.
• Because of this, it takes 3 bases to code for one amino acid. The sequence of 3 bases is called a codon.
• However, DNA is not used directly to code proteins. Instead, DNA is used to make a strand of RNA which is then translated into a protein.
• Because RNA contains uracil instead of thymine, the genetic code is written with a U instead of a T.

Transcription

• The coding strand of DNA is used to make a strand of RNA.
• On the DNA strand, an A (adenine) indicates a U (uracil) should be added to the RNA strand, a G (guanine) indicates a C (cytosine) should be added, a C indicates a G should be added, and a T (thymine) indicates an A should be added.
• This occurs in the nucleus of the cell.

Translation

• The RNA then leaves the nucleus and attaches to a ribosome which uses the genetic code to translate the sequence of bases in the RNA into a sequence of amino acids in the protein.