Module #8: Changes to the Genetic Code

Module #8: Changes to The Genetic Code

(Mechanisms of Genetics)

6E: (Readiness Standard) Identify and illustrate changes in DNA and evaluate the significance of these changes.

Purpose: understanding how genetic mutations can cause certain disorders.

Procedures:

-Define the following terms

-Answer the following questions

-Do the given activities provided

Terms:

1. Mutation

2. Point Mutation

3. Frame-shift mutation

4. Codons (Start/ Stop)

5. Purines and Pyramidines

6. Nitrogen Base pairs

7. peptide bonds

Essential Question:

-Humans have approximately 75,000 to 100,000 genes in a typical cell. A single gene contains about 10,000 nitrogen base pairs. How is it possible for a single mutation to one of these base pairs to cause a life-threatening condition?

Activities and Questions:

1.Using the mRNA Genetic Code chart, determine the name of the amino acid each codon represents. Write the name under the codon.

A U G C C A A C A G U G A G A U U A C A G A AA U C G U A A

2. Attach each codon to the next until all 10 have been connected. This is a model of a sequence of codons; it will serve as the Original Sequence for the remainder of this activity. What does this long chain of amino acids represent?

3. Some genetic mutations are caused by changes in the bases of some codons. Examine the sequence of codons below.

In Sequence A below, uracil (U) from the Original Sequence has been replaced with cytosine (C) in one of the codons.

Sequence A

A U G C C A A C A G C G A G A U U A C A G A AA U C G U A A

A similar change has occurred in one of the codons in Sequence B shown below: The adenine in the Original Sequence has been replaced with guanine. These types of mutations are called point mutations.

Sequence B

A U G C C A A C A G U G A G A UUG C A G A AA U C G U A A

What effect do the point mutations have on the protein strands coded in Sequences A and B?

4. Locate the sequence of codons assembled for Question 1. Find the codon GUG. Add one additional uracil base to the beginning of the GUG codon. It now reads UGU—the G base shifts to the next codon, causing all the subsequent codons to shift one of their bases to the next codon as well. This type of mutation is called a frame-shift mutation.

Rearrange all the plastic codons to reflect the frame-shift mutation described—that is, after you’ve added a uracil base to the beginning of the GUG codon, shift the last base of each remaining codon to the next codon, all the way to the end of the strand.

Write the new codon arrangement below and identify the amino acids using the mRNA Genetic Code Chart.

(Insertion of new base)

A U G C C A A C A U G U G A G A U U A C A G A A A U C G U A A

______

5. What is the significance of this frame-shift mutation for the structure of the protein?

6. Sickle cell anemia results from a mutation at the Number 6 codon that causes the beta globin gene to be misread, which results in the production of abnormal hemoglobin. Use the information on the Genetic Mutation Cards and the mRNA Genetic Code Chart to fill in the protein strand with the mutation that could cause this type of anemia. (use the figure provide for you in the folder to write your answer.)

7. How does this mutation change the type of hemoglobin produced?

8. Which of the Genetic Mutation Cards represent mutations that are considered beneficial to humans? Why are these mutations considered beneficial?