STAAR Biology Assessments: Module 1
Changes to the Genetic Code
Mechanisms of Genetics
Changes to the Genetic Code
Student Pages
Purpose
The purpose of this station is to reinforce your understanding of how genetic
mutations can cause certain disorders.
Before You Begin . . .
Check to see that all the items are present and organized according to the
station information sheet. If you notice a problem, notify your teacher
immediately.
Materials
Station Information sheet
Codon cubes and base cubes
mRNA Genetic Code chart
Genetic Mutation cards
Activities and Questions
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?
1.
Locate the colored plastic cubes at this station. Arrange the cubes in the
order shown in the picture below. These cubes are arranged in groups of
three, and each group represents a codon.
Using the mRNA Genetic Code chart, determine the name of the amino acid
each codon represents. Write the name under the codon.
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?
Changes to the Genetic Code
3.
STAAR Biology Assessments: Module 1
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) has been replaced with cytosine (C) in one
of the codons.
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. 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.
STAAR Biology Assessments: Module 1
Changes to the Genetic Code
Write the new codon arrangement below and identify the amino acids
using the mRNA Genetic Code Chart.
Insertion of new base
continue with
new
sequence
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 codes chart to fill in the protein strand with the
mutation that could cause this kind of anemia.
7. How does this mutation change
the type of hemoglobin produced?
Changes to the Genetic Code
STAAR Biology Assessments: Module 1
8
Which of the Genetic Mutation cards represent mutations that are
considered beneficial to humans? Why are these mutations considered
beneficial?
9.
Now that you have completed these questions, return to the essential
question. Would you like to modify or change your answer? Write any
modifications to your answer below.
Practice:
The backbone of the double helix is made up of __________________ molecules and
____________________ groups, and the two chains are joined together by hydrogen
bonds between the __________________________________.
If the DNA of an organism contains 20% adenine, what is its percentage of guanine?
Which of the following represents the building block of a DNA molecule?
A. Nitrogen-containing base
B. Phosphate group
C. Deoxyribose sugar
D. Nucleotide
What would you expect to find in all organisms?
A. The same genetic information
B. The same sequence of DNA nucleotides in the DNA molecules
C. The same percentages of DNA base pairs
D. The same four DNA nucleotides
Note—Because other students are going to do the activity after you, be sure to put all the
materials at the station back as you found them. Sometimes there will be materials that need to
be renewed or replaced. If you need assistance or have any questions, ask your teacher.
Glossary for Changes to the Genetic Code
Mutation: change in an organism’s genetic material.
Point mutation: change to one or a few nucleotides in a codon.
Frame-shift mutation: occurs when one or more amino acids (C, G, U, or A) is deleted from or
inserted into a codon, altering the reading frame (pattern of reading triplet codons) in a
sequence.
Start codon: begins the translation of the first amino acid in the protein chain. The start codon
is methionine, AUG.
Stop Codon: A stop, or termination, codon can be any of three mRNA sequences: UGA, UAG, or
UAA. Stop codons do not code an amino acid, but rather signal the end of protein synthesis.