Genetic Code Chart Read from the center outwards to find out

Genetic Code Chart: Read from the center outwards to find out which of the 20 amino acids (Gly, Phe, Leu, etc.) each mRNA codon will cause to be added to a growing protein during the process of translation.

Explore the possible effects of mutation by answering the questions below about the same protein-coding gene that you analyzed above. But first, review the different causes, kinds, & consequences of DNA mutations at the Univ. of Utah’s Learn Genetics website: http://learn.genetics.utah.edu/content/basics/mutation/

       -TATAAAACGAGATGCTCGAGTTCAATCTAGATATATGAGGCTCAATAAA-

Template: -ATATTTTGCTCTACGAGCTCAAGTTAGATCTATATACTCCGAGTTATTT-

1) If the 18^th nucleotide (indicated in red) in the template strand of the same gene were altered by a point mutation which replaced the existing Cytosine (C) nucleotide with an Adenine (A) nucleotide, how would this affect the mRNA sequence transcribed, & the amino acid sequence of the protein being synthesized in translation? Explain.

      Would the mutation (C à A) above be considered a substitution, insertion, or deletion? Explain.

2) If instead, the 29^th nucleotide (indicated in green) in the template strand of the same gene were altered by a point mutation which replaced the existing Thymine (T) nucleotide with an Adenine (A) nucleotide, how would this affect the amino acid sequence of the protein? Explain.

Considering its effect on the protein, would the mutation (T à A) above be synonymous, or non-synonymous? Explain.

3) If instead, the 34^rd nucleotide (indicated in blue) in the template strand of the same gene were altered by a point mutation which replaced the existing Adenine (A) nucleotide with a Guanine (G) nucleotide, how would this affect the amino acid sequence of the protein? Explain.

Solution

Answer:

Template:

ATA-TTT-TGC-TCT-ACG-AGC-TCA-AGT-TAG-ATC-TAT-ATA-CTC-CGA-GTT-ATT-T

mRNA

UAU-AAA-ACG-AGA-UGC-UCG-AGU-UCA-AUC-UAG-AUA-UAU-GAG-GCU-CAA-UAA-A

Peptide

Tyr-Lys-Thr-Arg-Cys-Ser-Ser-Ser-Ile-STOP-Ile-Tyr-Glu-Ala-Gln-STOP

1).

Template:

ATA-TTT-TGC-TCT-ACG-AGA-TCA-AGT-TAG-ATC-TAT-ATA-CTC-CGA-GTT-ATT-T

mRNA

UAU-AAA-ACG-AGA-UGC-UCU-AGU-UCA-AUC-UAG-AUA-UAU-GAG-GCU-CAA-UAA-A

Peptide

Tyr-Lys-Thr-Arg-Cys-Ser-Ser-Ser-Ile-STOP-Ile-Tyr-Glu-Ala-Gln-STOP

UCG and UCU code for same amino acid, Serine. So even after mutation there would be no change in the peptide.

Replacement of one nitrogen base with another that is called substitution. Here cytosine (pyrimidine) is replaced by Adenine (purine), is called transversion.

2).

Template:

ATA-TTT-TGC-TCT-ACG-AGC-TCA-AGT-TAG-AAC-TAT-ATA-CTC-CGA-GTT-ATT-T

mRNA

UAU-AAA-ACG-AGA-UGC-UCG-AGU-UCA-AUC-UUG-AUA-UAU-GAG-GCU-CAA-UAA-A

Peptide

Tyr-Lys-Thr-Arg-Cys-Ser-Ser-Ser-Ile-Leu-Ile-Tyr-Glu-Ala-Gln-STOP

UAG codes for STOP codon whereas UUG codes for leucine. The peptide chain will be prolonged. The mutation is called nonsynonymous mutation as the mutation changed the existing amino acid by another amino acid.

3).

Template:

ATA-TTT-TGC-TCT-ACG-AGC-TCA-AGT-TAG-ATC-TAT-GTA-CTC-CGA-GTT-ATT-T

mRNA

UAU-AAA-ACG-AGA-UGC-UCG-AGU-UCA-AUC-UAG-AUA-CAU-GAG-GCU-CAA-UAA-A

Peptide

Tyr-Lys-Thr-Arg-Cys-Ser-Ser-Ser-Ile-STOP-Ile-His-Glu-Ala-Gln-STOP

UAU codes for tyrosine whereas histidine. The mutation is called nonsynonymous mutation as the mutation changed the existing amino acid by another amino acid.