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Investigation DNA Proteins and Mutations
Evolutionary Biology (BIOL 320)
California State University East Bay
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Name: Mahir Patel
Investigation: DNA, Proteins, and Mutations
Below are two partial sequences of DNA bases (shown for only one strand of DNA) Sequence 1 is from a human and sequence 2 is from a cow. In both humans and cows, this sequence is part of a set of instructions for controlling a bodily function. In this case, the sequence contains the gene to make the protein insulin. Insulin is necessary for the uptake of sugar from the blood. Without insulin, a person cannot use digest sugars the same way others can, and they have a disease called diabetes.
Instructions:
-Using the DNA sequence, make a complementary RNA strand from both the human and the cow. Write the RNA directly below the DNA strand (remember to substitute U's for T's in RNA).
-Use the codon table in your book to determine what amino acids are assembled to make the insulin protein in both the cow and the human. Write your amino acid chain directly below the RNA sequence.
*Note: This is not the real sequence for insulin, which actually contains 51 amino acids. Uniprot provides full sequencing information on insulin and known variants. uniprot/uniprot/P
HUMAN DNA
DNA CCA TAG CAC GTT ACA ACG TGA AGG AAA
RNA GGU AUC GUG CAA UGU UGC AGU UCC UUU
Amino Acid
Glycine Isoleucine Valine Glutamine Cysteine Cysteine Threonine serine Phenylalan ine
COW DNA
DNA CCA TAG CAT GTT ACA ACG CGA AGG GAC
RNA GGU AUC GUG CAA UGU UGC GCU UCC CUC
Amino Acid
Glycine Isoleucine Valine Glutamine Cysteine Cysteine Alanine Serine Leucine
Analysis
- Compare the DNA Sequence and circle any single base that is different in the cow and human sequences. How many bases are different? 6 bases First two different bases: C (human) and T (Cow), Second two different bases: T (Human) and C (Cow), Third two different bases: A (Human) and G (Cow)
Examine the amino acids produced. Highlight in yellow any amino acids that are different in the two sequences. How many are there? 4 In human: Threonine and Phenylalanine, In Cow: Alanine and Leucine
- Could two humans (or two cows) have some differences in their DNA sequences for insulin, yet still make the exact same insulin proteins? Explain.
Yes two humans or cows can have some differences in their DNA sequences for insulin and still
make the exact same insulin protein because more than amino acid can codify for the same protein
so if there is a little different in the sequence, it could still make the same protein.
- Examine the codon chart and list all of the codons that code for the amino acid leucine. List them:
All the Codons that code for leucine are UUA, UUG, CUU, CUC, CUA, CUG.
MUTATIONS
Diabetes is a disease characterized by the inability to break down sugars. Often a person with diabetes has a defective DNA sequence that codes for the making of the insulin protein. This mutation is called a POINT MUTATION because only one base is affected.
When the amino acid in a sequence has been changed, the shape of the protein changes and can become less functional (or not function at all.)
4 a person has a mutation in their DNA, and the first triplet for the gene coding for insulin is T A T (instead of C C A). Determine what amino acid the new DNA triplet codes for. Will this person be diabetic? Explain Normal DNA TAG-AUC Isoleucine Mutant DNA TAT-AUA Isoleucine
Both normal and mutant dna have mrna codon for isoleucine. Since there is no change in amino acid
sequence, the protein folding remains unaffected. As a result the protein insulin remain functional
and the person with the mutant protein is not diabetic.
- A SILENT MUTATION occurs when the nucleotide changes, but the resulting amino acid is the same. The protein that is made from this new DNA will have no functional difference from the original.
A FRAMESHIFT MUTATION occurs when a base is added (or removed) from a DNA/RNA sequence.
- Determine the amino acid chain coded for by the following sequence. Suppose a mutation occurs where another A is added after the first codon. What would the new sequence of amino acids be?
Normal DNA: T G G A G T C G A G G T
Normal RNA: ACC UCA GCU CCA
Amino Acids: Thr Ser Ala Pro
Mutant DNA: T G G A A G T C G A G G T
Mutant RNA: ACC UUC AGC UCC A
Amino Acids. Thr Phe Ser Ser
Why are frameshift mutations likely to cause more problems than a point mutation?
Point mutation does not alter the reading frame of amino acid in a growing polypeptide chain. Also,
there is a chance that point mutations might code for the same amino acid, but a frameshift mutation
completely alters the reading frame coding for entirety different amino acids. Therefore, frameshift
mutations are likely to cause more problems than point mutation.
- A NONSENSE MUTATION occurs when a codon is changed to a STOP codon. Many proteins are thousands of amino acids in length. At the end of the gene, the cell reaches the stop codon. If a codon is changed to STOP, the building of the amino acid terminates and the protein is incomplete.
Why would a Nonsense mutation be less damaging if it occurred at the end of the gene rather than the beginning?
If nonsense mutation is at the end of the sequence, it is most likely that the entire protein was
accurately coded. However, if the nonsense mutation is in the beginning of the protein coding
sequence, the protein cannot be entirely coded.
Gene Sequences Across Species
- DNA sequences are often used to determine relationships between organisms. DNA sequences that code for a particular gene can vary widely. Organisms that are closely related will have sequences that are similar.
Below is a list of sequences for a few organisms:
Human: CCA TAG CAC CTA Chimpanzee: CCA TAA CAC CTA
Pig: CCA TGG AAA CGA Cricket: CCT AAA GGG ACG
--Based on the sequences, which two organisms are most closely related? Human + Chimpanzee
Investigation DNA Proteins and Mutations
Course: Evolutionary Biology (BIOL 320)
University: California State University East Bay
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