Molecular Genetics
Overview
The information carried out by DNA is used to put amino acids in an order so that they can make proteins. DNA is in the nucleus of the cell, but ribosomes, the structures that make proteins, are the cell’s cytoplasm. Thus, a messenger must carry the information needed from the nucleus to the ribosomes in the cytoplasm. This messenger is called messenger RNA, or mRNA. RNA is made up of nucleotides like DNA, but RNA is typically single-stranded and shorter than DNA is. RNA also does not contain the base thymine, but it contains uracil, or U, instead. RNA also comes in the form of rRNA, which forms ribosomes, and tRNA, which brings the correct amino acids to the ribosome during protein synthesis.
Transcription
Translation
If a cell needs to make a protein it makes mRNA copies of the gene which codes for the protein. This process involves three steps:
1. DNA unzips at the start of the gene
2. New nucleotides fit into position by base-pairing. 'A' in DNA pairs with a 'U' in the new RNA.]
3. Enzymes join the new nucleotides together.
When the enzymes get to the end of the gene the completed mRNA is released and moves into the cytoplasm. This is called TRANSCRIPTION.
Ribosomes allow the information carried by mRNA to be used so the information can put amino acids in the correct order to make proteins.
Three bases code for one amino acid, and sometimes several bases codings will code for the same amino acid. Biologists have configured which base triplets, or CODONS, code for which amino acid. Protein synthesis will always begin with the start codon, AUG (therefore each protein begins with MET, or METHIONINE), and will always stop at the stop codons, UAA, UAG, or UGA. This process is called TRANSLATION. The chart below helps to “translate” codons for their amino acids.
