Question

1. mutations

sometimes errors, called mutations, occur during dna replication. a mutation is a random and
physical change in the nucleotide sequence of a dna molecule. most mutations occur in somatic
cells over the course of our lifetimes. the only mutations that are passed on to the next generation
are mutations that occur in the gametes, or germ cells.
some mutations are \silent\ and cause no change in the protein expressed by a gene; however, many
other mutations result in the production of abnormal protein products. these abnormal proteins
can potentially be harmful because they can be so misshapen that they are unable to perform their
intended function within the cell.
mutations can occur as base substitutions or frameshift mutations. base substitutions are muta-
tions in the dna sequence in which one nucleotide is substituted for a different nucleotide (e.g.,
a is replaced with g). there are three types of base substitutions: silent, missense, and nonsense. a
silent mutation does not result in a change in the amino acid sequence of a protein. a missense
mutation causes one amino acid in a protein to be replaced with a different amino acid. a nonsense
mutation changes an amino acid - coding codon to a stop codon. frameshift mutations are the
result of one or more nucleotides being deleted or inserted in a gene (e.g., act becomes acct).
frameshift mutations alter the reading frame of the mrna molecule, causing a change in all codons
downstream of the mutation.
procedure

1. work in pairs to consider how a variety of mutations alter the protein produced by gene

expression. an original dna sequence and its mrna transcript are listed below. these are
the original dna and mrna sequences as they should be, prior to any mutations that might
occur during dna replication. use table 8 - 1 to determine the sequence of amino acids that
should be produced during translation.

1. simulate a mutation by deleting the eighth nucleotide. transcribe this new dna sequence into

mrna, and then translate it into an amino acid sequence.

Explanation:

Step1: Transcribe DNA to mRNA

DNA sequence after deletion: \(3'\)-T A C G T C G A C T C G G T A C T-\(5'\)
mRNA is transcribed as \(5'\)-A U G C A G C U G A G C C A U G A-\(3'\) (using base - pairing rules: A - U, T - A, C - G, G - C)

Step2: Translate mRNA to amino acids

Using the genetic code (codon - amino acid mapping):

• The first codon \(AUG\) codes for Methionine (MET)
• The second codon \(CAG\) codes for Glutamine (Gln)
• The third codon \(CUG\) codes for Leucine (Leu)
• The fourth codon \(AGC\) codes for Serine (Ser)
• The fifth codon \(CAU\) codes for Histidine (His)
• The sixth codon \(GA\) is a partial codon. But if we consider the reading frame, and assuming the codons are read in triplets, the last two bases \(GA\) along with the next non - existent base (if we follow the frame) is not a complete codon. However, if we consider the existing codons: \(AUG\) (MET), \(CAG\) (Gln), \(CUG\) (Leu), \(AGC\) (Ser), \(CAU\) (His)

Answer:

Methionine (MET), Glutamine (Gln), Leucine (Leu), Serine (Ser), Histidine (His)