Question

deletion, insertion & substitution
there are several types of mutation:
➤ deletion (a base is lost/deleted)
➤ insertion (an extra base is added/inserted)
--- deletion & insertion may cause whats called a frameshift mutation, meaning the reading \frame\
changes, thus changing the amino acid sequence from this point forward
➤ substitution (one base is substituted for another)
--- if a substitution changes the amino acid, its called a missense mutation
--- if a substitution does not change the amino acid, its called a silent mutation
--- if a substitution changes the amino acid to a \stop,\ its called a nonsense mutation
complete the boxes below. classify each as deletion, insertion or substitution and as either
frameshift, missense, silent or nonsense (hint: deletion & insertion will always be frameshift).
original dna sequence: t a c a c c t t g g c g a c g a c t...
mrna sequence:
amino acid sequence:
mutated dna sequence #1 t a c a t c t t g g c g a c g a c t...
whats the mrna sequence? (circle the change)
amino acid sequence?
will there likely be effects? what type of mutation is this?
mutated dna sequence #2 t a c g a c c t t g g c g a c g a c t...
whats the mrna sequence? (circle the change)
amino acid sequence?
will there likely be effects? what type of mutation is this?
mutated dna sequence #3 t a c a c c t t a g c g a c g a c t...
whats the mrna sequence? (circle the change)
amino acid sequence?
will there likely be effects? what type of mutation is this?
mutated dna sequence #4 t a c a c c t t g g c g a c t a c t...
whats the mrna sequence? (circle the change)
amino acid sequence?
will there likely be effects? what type of mutation is this?

Answer:

Original DNA Sequence Analysis

Step 1: Transcribe DNA to mRNA (Original)

DNA uses bases A, T, C, G; mRNA uses A, U, C, G (T→U).
Original DNA: \( \text{T A C A C C T T G G C G A C G A C T} \dots \)
mRNA: \( \text{A U G U G G A A C C G C U G C U G A} \dots \) (complementary base pairing: A-U, T-A, C-G, G-C)

Step 2: Translate mRNA to Amino Acids (Original)

Use codon table:

• AUG: Met (start)
• UGG: Trp
• AAC: Asn
• CGC: Arg
• UGC: Cys
• UGA: Stop

Amino Acid Sequence: \( \text{Met - Trp - Asn - Arg - Cys - Stop} \)

Mutated DNA Sequence #1

Step 1: Identify Mutation

Original DNA: \( \text{T A C A C C T T G G C G A C G A C T} \dots \)
Mutated DNA: \( \text{T A C A T C T T G G C G A C G A C T} \dots \) (Change: \( \text{C} \to \text{T} \) at position 5)

Step 2: Transcribe to mRNA

Mutated DNA: \( \text{T A C A T C T T G G C G A C G A C T} \dots \)
mRNA: \( \text{A U G U A G A A C C G C U G C U G A} \dots \) (Circle \( \text{UAG} \))

Step 3: Translate to Amino Acids

• AUG: Met
• UAG: Stop (nonsense codon)

Amino Acid Sequence: \( \text{Met - Stop} \)

Step 4: Classify Mutation

• Type: Substitution (one base substituted: \( \text{C} \to \text{T} \))
• Effect: Nonsense (substitution creates stop codon)
• Frameshift? No (substitution, not insertion/deletion)
• Likely Effects? Yes (truncated protein)

Mutated DNA Sequence #2

Step 1: Identify Mutation

Original DNA: \( \text{T A C A C C T T G G C G A C G A C T} \dots \)
Mutated DNA: \( \text{T A C G A C C T T G G C G A C G A C T} \dots \) (Insertion: \( \text{G} \) added at position 4)

Step 2: Transcribe to mRNA

Mutated DNA: \( \text{T A C G A C C T T G G C G A C G A C T} \dots \)
mRNA: \( \text{A U G C U G G A A C C G C U G C U G A} \dots \) (Circle \( \text{CUG} \) (new codon))

Step 3: Translate to Amino Acids

• AUG: Met
• CUG: Leu
• GAA: Glu
• CCG: Pro
• CUG: Leu
• CUG: Leu
• A: (incomplete, but frameshift)

Amino Acid Sequence: \( \text{Met - Leu - Glu - Pro - Leu - Leu} \dots \) (frameshift, changes all codons after insertion)

Step 4: Classify Mutation

• Type: Insertion (extra base added)
• Effect: Frameshift (insertion causes reading frame shift)
• Likely Effects? Yes (drastic amino acid change)

Mutated DNA Sequence #3

Step 1: Identify Mutation

Original DNA: \( \text{T A C A C C T T G G C G A C G A C T} \dots \)
Mutated DNA: \( \text{T A C A C C T T A G C G A C G A C T} \dots \) (Change: \( \text{G} \to \text{A} \) at position 8)

Step 2: Transcribe to mRNA

Mutated DNA: \( \text{T A C A C C T T A G C G A C G A C T} \dots \)
mRNA: \( \text{A U G U G G A A U C G C U G C U G A} \dots \) (Circle \( \text{AAU} \))

Step 3: Translate to Amino Acids

• AUG: Met
• UGG: Trp
• AAU: Asn (original: AAC → Asn; new: AAU → Asn)
• CGC: Arg
• UGC: Cys
• UGA: Stop

Amino Acid Sequence: \( \text{Met - Trp - Asn - Arg - Cys - Stop} \) (no change in amino acid: silent)

Step 4: Classify Mutation

• Type: Substitution ( \( \text{G} \to \text{A} \))
• Effect: Silent (substitution does not change amino acid: AAC and AAU both code for Asn)
• Likely Effects? No (protein sequence unchanged)

Mutated DNA Sequence #4

Step 1: Identify Mutation

Original DNA: \( \text{T A C A C C T T G G C G A C G A C T} \dots \)
Mutated DNA: \( \text{T A C A C C T T G G C G A C T A C T} \dots \) (Deletion: \( \text{G} \) removed at position 13)

Step 2: Transcribe to mRNA

Mutated DNA: \( \text{T A C A C C T T G G C G A C T A C T} \dots \)
mRNA: \( \text{A U G U G G A A C C G C U G A U G A} \dots \) (Circle \( \text{UGA} \) (new codon))

Step 3: Translate to Amino Acids

• AUG: Met
• UGG: Trp
• AAC: Asn
• CGC: Arg
• UGA: Stop (premature stop)

Amino Acid Sequence: \( \text{Met - Trp - Asn - Arg - Stop} \) (truncated)

Step 4: Classify Mutation

• Type: Deletion (one base removed)
• Effect: Frameshift (deletion causes reading frame shift, leading to premature stop)
• Likely Effects? Yes (truncated protein)

Final Answers (Summarized)

Sequence	mRNA Sequence	Amino Acid Sequence	Effects?	Mutation Type	Subtype
Mutated #1	\( \text{AUG UAG AAC CGC UGC UGA} \dots \)	Met-Stop	Yes	Substitution	Nonsense
Mutated #2	\( \text{AUG CUG GAA CCG CUG CUG A} \dots \)	Met-Leu-Glu-Pro-Leu-Leu…	Yes	Insertion	Frameshift
Mutated #3	\( \text{AUG UGG AAU CCG CUG CUG A} \dots \)	Met-Trp-Asn-Arg-Cys-Stop	No	Substitution	Silent
Mutated #4	\( \text{AUG UGG AAC CGC UGA UGA} \dots \)	Met-Trp-Asn-Arg-Stop	Yes	Deletion	Frameshift