Classify the effects of the following mutations as missense, nonsense, or silent (use the genetic code table in the chapter to help you):
a. mRNA codon AUG is mutated to AUC
b. mRNA codon UAC is mutated to UAA
c. mRNA codon GGC is mutated to GGG
d. mRNA codon UAA is mutated to UAG
e. mRNA codon UGG is mutated to CGA

Verified step by step guidance

Step 1: Understand the definitions of mutation types: a missense mutation changes the codon to one that codes for a different amino acid; a nonsense mutation changes the codon to a stop codon, causing premature termination; a silent mutation changes the codon but still codes for the same amino acid.

Step 2: For each mutation, identify the original amino acid coded by the original mRNA codon using the genetic code table.

Step 3: Identify the amino acid or stop signal coded by the mutated mRNA codon using the genetic code table.

Step 4: Compare the original and mutated amino acids: if the mutated codon codes for the same amino acid, classify as silent; if it codes for a different amino acid, classify as missense; if it codes for a stop codon, classify as nonsense.

Step 5: Apply this process to each codon pair (original and mutated) given in parts a through e to classify each mutation accordingly.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Types of Point Mutations

Point mutations are changes in a single nucleotide of DNA or mRNA. Missense mutations alter a codon to code for a different amino acid, potentially changing protein function. Nonsense mutations convert a codon into a stop codon, leading to premature termination of translation. Silent mutations change a codon without altering the encoded amino acid, having no effect on the protein.

Genetic Code and Codon-Amino Acid Relationship

The genetic code consists of codons, three-nucleotide sequences in mRNA that specify amino acids. Each codon corresponds to one amino acid or a stop signal during protein synthesis. Understanding the codon table is essential to determine how mutations affect the amino acid sequence and classify mutation types.

Impact of Mutations on Protein Synthesis

Mutations can affect protein synthesis by altering the amino acid sequence or causing early termination. Missense mutations may change protein structure and function, nonsense mutations truncate proteins, and silent mutations do not affect the protein. Recognizing these effects helps predict mutation consequences on cellular function.

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Related Practice

Textbook Question

In eukaryotic cells, mRNA must be ___________ before it is ___________ into protein. In this process ___________ sequences are removed from the mRNA and ___________ are joined. A complex called the ___________ performs this process.

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Textbook Question

Select all the true statements about repressible operons:

a. By default they are on until turned off.

b. An example is the lactose operon.

c. An example is the arginine operon.

d. A repressor must bind to the operator in order for the operon to be turned off.

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Textbook Question

Which of the following helps to prevent mutations? Select all that apply.