From Dna to Disorder

Name ______Per______

Lab: FROM DNA TO DISORDER

The fact that one little letter out of three billion can impairments and other complications in individuals really make a difference in the genetic makeup of an who inherit one copy of the gene. individual is often difficult to grasp. Molecular biology Although achondroplasia can be inherited as is a challenging topic to understand because people a dominant trait, approximately 80% of the cases struggle with drawing connections between four are due to new point mutations (see sidebar). letter codes and the complex diversity of organisms Approximately 98% of all cases of achondroplasia that inhabit Earth. are due to a G to A substitution at the 1138th One creative way to learn about molecular nucleotide with the remaining 2% a result of a G to biology is with the “From DNA to Disorder” activity, C substitution both mutations result in the which focuses on monogenetic diseases and replacement of the amino acid glycine by arginine, disorders. The activity offers a way to link molecular the 380th amino acid in the protein chain. This biology to the functions of cells, systems, organisms, mutation involves the FGFR3 gene, which is located inheritance, ecology, and evolution. Monogenetic on the short arm of human chromosome 4 and disorders and diseases are caused by one codes for the fibroblast growth factor receptor 3. identifiable gene. Scientists believe that FGFR3 mutations in achondroplasia have been approximately 6,000 monogenetic diseases and interpreted as gain-of-function mutations. The disorders exist, including Achondroplasia, Angelman mutation increases the activity of FGFR3, severely syndrome, Bukitt’s lymphoma, congenital adrenal limiting bone growth. Scientists look for genetic hyperplasia, cystic fibrosis, Duchenne muscular similarities among people who have the disorder dystrophy, fragile X, hemophilia, Huntington’s and another way of finding disorder genes is by disease, Marfan syndrome, Phenylketonuria, comparing gene sequences of people who do not retinoblastoma, sickle-cell anemia, spinal muscular express the disorder with people who do. atrophy, and Tay Sachs disease. In this lab, you are given six fragments of For the activity we will simulate how DNA suspected of having some relevance to scientists hunt for genes. We will also create a achondroplasia. Students compare and contrast the paper three-dimensional of the protein called segments in hopes of finding the gene that causes fibroblast growth factor receptor 3 (FGFR3), achondroplasia. which, when mutated, causes the disorder achondroplasia. Achondroplasia comes from MORE ON ACHONDROPLASIA Greek roots meaning “without cartilage formation” Two types of achondroplasia exist, de novo and and is one of the most common forms of dwarfism, a inherited. De novo mutations account for greater than genetic condition that usually results in an average 80% of achondroplasia cases; however, it can still be adult height of about 130 cm. A person with inherited. Over 80% of individuals with achondroplasia achondroplasia has an average sized trunk, have parents with normal stature and have disproportionately short arms and legs, a slightly achondroplasia as the result of a de novo gene mutation. enlarged head, and a prominent forehead. Such parents have a low probability of having another Achondroplasia only occurs in 1 per 16,000 to child with achondroplasia. 40,000 births, but can cause death in individuals An individual with achondroplasia who has a who inherit two copies of the gene and orthopedic partner with normal stature has a 50% probability in each pregnancy of having a child with achondroplasia. When DIRECTIONS both parents have achondroplasia, the probability of their In this lab you will be given six fragments of offspring having normal stature is 25%; of having mRNA suspected of having some relevance to achondroplasia, 50%; and of having homozygous achondroplasia. .You will compare and contrast these achondroplasia (a lethal condition), 25% Prenatal segments in hopes of finding the mutation that causes molecular genetic testing is available, but recommended achondroplasia. You will also create a three- only to detect the lethal homozygous form. dimensional (3-D) model of the normal and mutated Achondroplasia is inherited in an autosomal FGFR3 protein. dominant pattern, which means one copy of the altered gene in each cell is sufficient to cause the disorder. Most MATERIALS people with achondroplasia have average-size parents;  Tape these cases result from a new mutation in the FGFR3 gene. Other people with achondroplasia inherited an  Scissors altered FGFR3 gene from a parent who has the  mRNA codon chart condition.  mRNA transcript fragments  amino acid squares (2 copies)

PROCEDURES

1) You have been given DNA transcript fragments for fibroblast growth factor receptor 3 gene that causes Achondroplasia .Three strips (N1—N3) represent a segment from three individuals without achondroplasia (normal gene) and three strips (A1—A3) represent the same segment from three individuals with the achondroplasia gene.

2) Compare the DNA sequences within the normal and achondroplasia groups and then between the normal and achondroplasia groups.

3) Highlight the differences in the DNA stands

4) Transcribe each strand into mRNA

5) Use your mRNA codon chart to translate each of the mRNA sequences into an amino acid chain.

6) Write the amino acid sequences on the strips.

7) Compare the amino acid sequences within the normal and achondroplasia groups and between the normal and achondroplasia groups.

8) Using scissors cut out the amino acid squares.

9) Twenty different amino acids are used to synthesize proteins. a) Every amino acid has a central carbon attached to the central carbon are four things: i) an amino end (NH2/NH3+), ii) a carboxyl end (COOH/COO-), iii) a hydrogen (H) atom iv) One of the 20 different R group. Only the last portion of each R group is shown on your amino acid sheet.

10) Use the amino acid sequence that you just translated to make a paper version of your amino acid chain a) Make one amino acid chain for a normal protein and one for an achondroplasia protein. b) Use tape to link the carboxyl of one amino acid to the amino end of the next amino acid at the peptide bonds.

11) Proteins, like all organic compounds, are 3-D structures. Part of this shape is caused by hydrogen bonds. Hydrogen atoms can have partially positive charges. They are attracted to atoms with partially negative charges, such as oxygen (O), nitrogen (N), and sulfur (S). In a compound, hydrogen bends toward these negatively charged atoms, changing the shape of the molecule.

a) Look at the first amino acid in your chain. From there, count over three amino acids and look at the R group of the fourth amino acid. If the R group (see figure 1) is Negative (because it has N, O, or S), bend your amino acids so that you can tape the hydrogen group of the first amino acid to the negative R group of the fourth amino acid.

b) Make sure the writing of both amino acids is facing up.)

c) Continue this pattern (checking every third amino acid) until you have reached the end of your amino acid chain.

12) Although the actual folding of the protein is much more complex, you should now have the basic idea of how the amino acid sequence and bonding affects the shape a protein molecule.

Analysis Questions: 1) What does the term monogenic mean?

a) How many monogenic disorders are there currently?

b) What are (3) three other monogenic disorders?

2) What is the name of the protein for Achondroplasia?

3) What is the name of the gene for Achondroplasia?

a) What chromosome is the gene for Achondroplasia located on?

4) What does the word Achondroplasia mean?

5) What are the differences between a person who is heterozygous and someone who is homozygous dominant for achondroplasia?

6) What kind of inheritance do we see in Achondroplasia?

7) What is the minimum number of mutated alleles necessary for someone to express achondroplasia

8) Do a cross of a Normal mother and a dwarf father that is heterozygous for achondroplasia.

9) Complete the genotypes for this pedigree

10) How many variations were there

a) Within the Normal group?

b) Within the Achondroplasia Group?

c) Between Groups

11) What variations in the DNA sequences cause the disorder?

a) 98% ______

b) 2% ______

12) Which amino acid(s) do you think is responsible for the mutated protein? Explain:

13) Look at your decoded DNA sequences Can different nucleotide sequences result in the expression of the same gene? Explain:

14) How did hydrogen-bonding change the shape of your protein chain?

15) Is there a difference in shape between your normal protein and your achondroplasia protein? Explain!!!

16) How is it possible that different DNA sequences create the same amino acid sequence?

DNA Sequences N= Normal A=Achondroplasia CGGGCTGACTGG GACCCGTTCGGG GAACCCCTCCCG ACGAAGCCGGTC

CGGGCCGACTGG GACCCGTTCGGG GAACCCCTCCCG ACGAAGCCGGTC

CGGGCCAACTGG GACCCGTTCGGG GAACCCCTCCCG ACGAAACCGGTC

CGGGCCGACTGG GACCCGTTCGGG GAATCCCTCCCG ACGAAGCCGGTC

CGGGCCAACTGG GACCCGTTCGGG GATTCCCTCCCG ACGAAGCCGGTC

CGGGCCGACTGG GACCCGTTCGGG GAAGCCCTCCCG ACGAAGCCGGTC