There are segments in our DNA called genes that code for the proteins needed to carry out cellular functions. These genes are a sequence of nucleotides; adenine (A), thymine (T), cytosine (C) and guanine (G) and the specific sequence of these nucleotides is what conveys the information needed to produce a given protein. In humans, the smallest gene is 252 nucleotides long, whereas the largest is more than 2 million nucleotides long! The genetic code is used to decipher the sequence of nucleotides into a sequence of amino acids. The code uses a series of three-nucleotide sequences called codons. Each different codon codes for an amino acid and it is this specific sequence of amino acids that determines what protein is formed.
DNA is found in our nucleus, yet our proteins are synthesized in the cytoplasm. A gene must first be transcribed into a form that can leave the nucleus. Transcription is the process in which a sequence of DNA used to synthesize a complementary strand of messenger RNA (mRNA). This mRNA acts a template and is used to translate the original DNA sequence into a protein, based on the information in its codons and the Genetic Code.
For example, the DNA sequence ATG-CGT-TAG-CGT-ATTC would be transcribed into the mRNA sequence UAC-GCA-AUC-GCA-UAA. Then, using Fig 10.11 on p 180 in your book, you can determine that this mRNA would be translated into the amino acid sequence Tyrosine-Alanine-Isoleucine-Alanine-Stop.
In Exercise 1, you will have the opportunity to demonstrate your understanding of transcription and translation. You will be using the following website; be sure that you are able to access and use the site:
University of Utah. No date. Transcription and Translation
https://learn.genetics.utah.edu/content/basics/txtl/ (Links to an external site.)
In Exercise 2, you will apply what you learned in Exercise 1 and evaluate the effect that different types of mutations have on the outcome of transcription and translation. You’ll want to review these mutations on pp 186-187 of your book and in our online lecture on DNA before starting. You will be using the following website; be sure that you are able to access and use the site:
McGraw Hill. No date. Virtual Lab: DNA and Genes
http://glencoe.mheducation.com/sites/dl/free/0078802849/383936/BL_26.html (Links to an external site.)
Finally, in Exercise 3, you will complete a series of calculations to determine the probability of a mutation occurring within a gene that results in a change in protein structure. These are straight-forward math calculations; do not let them overwhelm you.