Name: ______________________________________________  Period: _____

 

Gene Mutations Activity

Background: There are two types of mutations, small-scale gene mutations and large-scale chromosomal mutations.  In this activity you will be learning about gene mutations.  There are two basic types of gene mutations, point (base substitution) and frameshift (insertions and deletions).  In frameshift mutations, an insertion or deletion of a base changes the reading frame of the sequence since mRNA is read in groups of three nitrogen bases (codons).  This causes several amino acids to be affected unless the deletion or insertion is a group of three.  There are very few examples of frameshift mutation diseases in organisms because they are usually fatal to the organism because the proteins do not function.  In point mutations, a simple base substitution does not change the reading frame because one nitrogen base is simply substituted with a different nitrogen base, so only one amino acid is affected unless there are several base substitutions.

 

Part 1: Frameshift Mutations

Example 1: Insertion Frameshift

DNA Sequence Sentence:       THE BOY CUT HIS LIP AND ATE THE HOT DOG

                

Affect of Insertion:                  THE BOY CUT HIS SLI PAN DAT ETH EHO TDO

                       

                         Insert a nitrogen base

 

Example 2: Deletion Frameshift

                                                                                                Delete a nitrogen base

                         ↓

DNA Sequence Sentence:      THE BOY CUT HIS LIP AND ATE THE HOT DOG

                 

Affect of Deletion:                 THE BOY CUT HIS LIP ANA TET HEH OTD OG

 

The insertion shifts the reading frame to the right.  The deletion shifts the reading frame to the left.  Complete the following lines for frameshift mutations. 

 

Write each codon per line:

 

DNA Sequence:     THE BOY CUT HIS LIP AND ATE THE HOT DOG

 

Insertion:                THE BOY _____   _____   _____   _____   _____   _____   _____   _____

                                                    

Insert a nitrogen base

 

Deletion:                THE BOY CUT _____   _____   _____   _____   _____   _____   _____  

             ↑

             Delete a nitrogen base

 

 

 

 

 

 

 

Part II:  Now use a real DNA sequence and transcribe and translate it into the correct amino acids.  In the original DNA code put the insertion frameshift mutation in the FOURTH CODON by inserting a G after the C in TCT. Please use the mRNA codon chart below to find the corresponding amino acids. 

http://wiki.ctl.sri.com/download/attachments/819221/chart.jpg

 

Write each codon per line and circle the mutated nitrogen base where the mutation took place and the amino acid.

 

Original DNA                             TAC   GGA    CGA   TCT  CAG   GAG   CCT   ATA   ATC

 

Insertion Mutation          ____   ____    ____    ____   ____   ____   ____   ____   ____ 

 

Mutated mRNA              ____   ____    ____    ____   ____   ____   ____   ____   ____ 

 

Mutated Amino Acids     ____   ____    ____    ____   ____   ____   ____   ____   ____ 

 

Original Amino Acid

            Sequence              Met     Pro       Ala      Arg     Val      Leu    Gly     Try     STOP

 

In the original DNA code put the deletion frameshift mutation in the THIRD CODON by deleting the C of CGA. Please use the mRNA codon chart provided to find the corresponding amino acids.  Write each codon per line and circle the mutated nitrogen bases where the mutation took place and the amino acid.

 

Original DNA                             TAC     GGA   CGA   TCT   CAG   GAG   CCT   ATA   ATC

 

Deletion Mutation           ____    ____    ____    ____   ____   ____   ____   ____    ____ 

 

Mutated mRNA              ____    ____    ____    ____   ____   ____   ____   ____    ____ 

 

Mutated Amino Acids     ____   ____    ____    ____   ____   ____   ____   ____     ____ 

 

Original Amino Acid

            Sequence              Met     Pro       Ala        Arg    Val      Leu       Gly   Try    STOP

Part III: Point (Base Substitution) Mutations

A different type of gene mutation is called a point (base substitution) mutation.  It is the simplest type of mutation where a nucleotide pair is replaced with a different nucleotide pair.  There are three types of point mutations: missense, silent, and nonsense. 

 

Example 1:  Missense Point Mutation

A missense mutation occurs when one nitrogen base is substituted for another nitrogen base causing a different amino acid than previously to occur in the protein sequence. There are two types of missense mutations: Transversions and Transitions.

                       

1A:  A Transversion Missense Point Mutation: A transversion mutation is when one purine (A, G) is swapped with a pyrimidine (C,T).

Purine → Pyrimidine              GAC → TAC

Pyrimidine → Purine              GAC → GAG

 

Use the DNA code below to demonstrate purine → pyrimidine transversion missense mutation.  All you have to do is change the DNA base in the SECOND CODON from CAT to GAT. Write each codon per line and circle the mutated nitrogen base and amino acid.

 

 Original DNA               TAC     CAT   GCA   GAT   CTG   GCC   CAG   TTC   ATC

 

Transversion Mutation   ____    ____    ____    ____   ____   ____   ____   ____   ____ 

 

Mutated mRNA             ____    ____    ____    ____   ____   ____   ____   ____   ____ 

 

Mutated Amino Acids   ____    ____    ____    ____   ____   ____   ____   ____   ____ 

 

Original Amino Acid

            Sequence            Met      Val      Arg      Leu   Asp A   Arg      Val     Lys     STOP

 

1B:  Transition Missense Point Mutation:  A transition mutations are the opposite of transversions.  Transition mutations happen when one purine is swapped with the other purine or one pyrimidine with the other pyrimidine. 

 

Purine → Purine                      GAC → AAC

Pyrimidine → Pyrimidine         GAC → GAT

 

Use the DNA code below to demonstrate a purine → purine transition missense mutation.  All you have to do is change the DNA base in the FIFTH CODON from CGG to CAG. Write each codon per line and circle the mutated nitrogen base and amino acid.

 

Original DNA                             TAC     GTC      GCT     CAA    CGG    GAC    CTG    ACC     ACT

 

Transition  Mutation       ____     ____     ____     ____     ____     ____    ____     ____     ____ 

  

Mutated mRNA               ____    ____     ____     ____     ____     ____    ____     ____     ____ 

  

Mutated Amino Acids     ____     ____     ____    ____      ____     ____   ____      ____     ____ 

 

Original Amino Acid

            Sequence              Met     Glu      Arg       Val     Ala      Leu     Asp A   Trp     STOP

 

Example 2: Silent Point Mutation

A silent mutation happens when one base in a codon is changed but both code for the same amino acid. 

 

DNA Codon       CTT →  CTC

mRNA codon     GAA →GAG

Amino Acid        Glu A → Glu A

 

Use the DNA code below to demonstrate a silent mutation.  All you have to do is change one DNA base in the THIRD CODON from TCT to TCC. Write each codon per line and circle the mutated nitrogen base and amino acid.

 

Original DNA                             TAC     CAT      TCT     CGG    TGT     AAA     AGG     GCG    ATT

 

Silent  Mutation               ____     ____    ____    ____      ____     ____     ____      ____     ____ 

  

Mutated mRNA                ____    ____    ____    ____      ____     ____     ____      ____     ____ 

 

Mutated Amino Acids     ____     ____    ____     ____     ____     ____      ____      ____     ____ 

 

Original Amino Acid

            Sequence              Met     Val      Arg       Ala     Thr      Phe      Ser     Arg     STOP

 

Example 3: Nonsense Point Mutation

A base mutation that creates a new stop codon in place of an amino acid causing a premature stopping of translation is called a nonsense mutation.

 

DNA codon                ATA → ATT

mRNA            codon              UAU → UAA

Amino Acid                Tyr → STOP

 

Use the DNA code below to demonstrate a nonsense mutation.  All you have to do is change one DNA base to create a new amino acid sequence with a premature stop codon in the FIFTH CODON by changing ATA to ATT. Write each codon per line and circle the mutated nitrogen base and amino acid.

 

Original DNA                             TAC     GGT   AAT   CAA    ATA   GAA    CCT    GAG    ACT

 

Nonsense  Mutation         ____   ____    ____    ____   ____     ____    ____   ____     ____     

 

Mutated mRNA               ____   ____    ____    ____   ____     ____    ____   ____     ____    

 

Mutated Amino Acids     ____   ____    ____    ____   ____      ____   ____    ____     ____    

 

Original Amino Acid

            Sequence              Met     Pro      Leu       Val     Tyr      Leu      Gly      Leu     STOP

 

 

 

 

 

 

 

 

 

 

Analysis Questions:

 

1.       How many amino acids were affected in the point mutations?

 

 

2.      How many amino acids were affected in the frameshift mutation?

 

 

3.      Explain the difference between a frameshift mutation and a point mutation.

 

 

 

 

 

4.      Which type of mutation, a frameshift or a point mutation, has more effect on the organism?  Why?

 

 

 

 

5.      Usually a frameshift mutation results in the synthesis of a nonfunctional protein.  Why do you think mutated proteins might not be functional?

 

 

 

 

6.      Which type of point mutation would be insignificant to the organism?  Why?

 

 

 

7.      Which type of point mutation would have the greatest affect on the organism?  Why?

 

 

 

8.      Which type of point mutation would most likely cause major changes to physical structures of the organism?