MUTATIONS

Figure 10.15 Summary of transcription and translation. DNA mRNA is transcribed from a DNA template. 1 mRNA RNA polymerase Amino acid Translation Each amino acid attaches to its proper tRNA with the help of a specific enzyme and ATP. 2 Enzyme ATP tRNA Figure 10.15 Summary of transcription and translation. This figure is an overview of the processes, emphasizing the participation of enzymes and the requirement of an energy source. Beyond its use for attaching amino acids to tRNAs, phosphate-bond energy is also needed during initiation, elongation, and termination of translation. The need to obtain amino acids from the diet could be described along with this slide. If amino acids are present in sufficient amounts, they will be continually attached to tRNAs and available for protein synthesis. If one or more amino acids is low in quantity, the translation of any protein containing those amino acids will be terminated prematurely when the corresponding codon is reached and a tRNA fails to bind to the A site. For humans, animal protein sources have an appropriate profile of essential amino acids. Plant proteins can be combined to provide an adequate amino acid balance. Anticodon Initiator tRNA Large ribosomal subunit Initiation of polypeptide synthesis 3 The mRNA, the first tRNA, and the ribosomal sub-units come together. Start Codon Small ribosomal subunit mRNA

Mutations can change the meaning of genes A mutation is a change in the nucleotide sequence of DNA Mutations can be Spontaneous: errors in DNA replication or recombination (chromosomes) Induced by mutagens High-energy radiation Chemicals Student Misconceptions and Concerns 1. Beginning college students are often intensely focused on writing detailed notes. The risk is that they will miss the overall patterns and the broader significance of the topics discussed. Consider a gradual approach to the subjects of transcription and translation, beginning quite generally and testing comprehension, before venturing into the finer mechanics of each process. 2. Mutations are often discussed as part of evolution mechanisms. In this sense, mutations may be considered a part of a positive creative process. The dual nature of mutations, potentially deadly yet potentially innovative, should be clarified. Teaching Tips 1. A simple way to demonstrate the effect of a reading frame shift is to have students compare the following three sentences. The first is a simple sentence. However, look what happens when a letter is added (2) or deleted (3). The reading frame, or words, are re-formed into nonsense. (1) The big red pig ate the red rag. (2) The big res dpi gat eth ere dra g. (3) The big rep iga tet her edr ag. 2. The authors have noted elsewhere that “A random mutation is like a shot in the dark. It is not likely to improve a genome any more than shooting a bullet through the hood of a car is likely to improve engine performance!” Copyright © 2009 Pearson Education, Inc.

POINT MUTATION Replacement of one nucleotide with another Replacement of one nucleotide with another ONLY MATTERS IF: CHANGES Amino acid  CHANGES function of the protein Normal hemoglobin DNA Mutant hemoglobin DNA Sickle-cell hemoglobin Normal hemoglobin mRNA Val Glu Student Misconceptions and Concerns 1. Beginning college students are often intensely focused on writing detailed notes. The risk is that they will miss the overall patterns and the broader significance of the topics discussed. Consider a gradual approach to the subjects of transcription and translation, beginning quite generally and testing comprehension, before venturing into the finer mechanics of each process. 2. Mutations are often discussed as part of evolution mechanisms. In this sense, mutations may be considered a part of a positive creative process. The dual nature of mutations, potentially deadly yet potentially innovative, should be clarified. Teaching Tips 1. A simple way to demonstrate the effect of a reading frame shift is to have students compare the following three sentences. The first is a simple sentence. However, look what happens when a letter is added (2) or deleted (3). The reading frame, or words, are re-formed into nonsense. (1) The big red pig ate the red rag. (2) The big res dpi gat eth ere dra g. (3) The big rep iga tet her edr ag. 2. The authors have noted elsewhere that “A random mutation is like a shot in the dark. It is not likely to improve a genome any more than shooting a bullet through the hood of a car is likely to improve engine performance!” Copyright © 2009 Pearson Education, Inc.

DELETION INSERTION A BASE IS LOST AN EXTRA BASE IS INSERTED A BASE IS LOST INSERTION AN EXTRA BASE IS INSERTED RESULT: FRAME-SHIFT (HOW YOU READ); DOWNSTREAM AMINO ACID CHANGES WRONG PROTEIN NO PROTEIN Student Misconceptions and Concerns 1. Beginning college students are often intensely focused on writing detailed notes. The risk is that they will miss the overall patterns and the broader significance of the topics discussed. Consider a gradual approach to the subjects of transcription and translation, beginning quite generally and testing comprehension, before venturing into the finer mechanics of each process. 2. Mutations are often discussed as part of evolution mechanisms. In this sense, mutations may be considered a part of a positive creative process. The dual nature of mutations, potentially deadly yet potentially innovative, should be clarified. Teaching Tips 1. A simple way to demonstrate the effect of a reading frame shift is to have students compare the following three sentences. The first is a simple sentence. However, look what happens when a letter is added (2) or deleted (3). The reading frame, or words, are re-formed into nonsense. (1) The big red pig ate the red rag. (2) The big res dpi gat eth ere dra g. (3) The big rep iga tet her edr ag. 2. The authors have noted elsewhere that “A random mutation is like a shot in the dark. It is not likely to improve a genome any more than shooting a bullet through the hood of a car is likely to improve engine performance!”

The big red pig ate the red rag. The big res dpi gat eth ere dra g. INSERTION The big red pig ate the red rag. The big res dpi gat eth ere dra g. DELETION The big red pig ate the red rag. The big rep iga tet her edr ag.

SUBSTITUTION A SINGLE BASE CHANGES RESULT: A SINGLE BASE CHANGES RESULT: MISSENSE MUTATION- WRONG AMINO ACID WRONG PROTEIN SILENT MUTATION- SAME AMINO ACID CORRECT PROTEIN NONSENSE MUTATION- EARLY STOP CODON SHORTENED/WRONG PROTEIN Student Misconceptions and Concerns 1. Beginning college students are often intensely focused on writing detailed notes. The risk is that they will miss the overall patterns and the broader significance of the topics discussed. Consider a gradual approach to the subjects of transcription and translation, beginning quite generally and testing comprehension, before venturing into the finer mechanics of each process. 2. Mutations are often discussed as part of evolution mechanisms. In this sense, mutations may be considered a part of a positive creative process. The dual nature of mutations, potentially deadly yet potentially innovative, should be clarified. Teaching Tips 1. A simple way to demonstrate the effect of a reading frame shift is to have students compare the following three sentences. The first is a simple sentence. However, look what happens when a letter is added (2) or deleted (3). The reading frame, or words, are re-formed into nonsense. (1) The big red pig ate the red rag. (2) The big res dpi gat eth ere dra g. (3) The big rep iga tet her edr ag. 2. The authors have noted elsewhere that “A random mutation is like a shot in the dark. It is not likely to improve a genome any more than shooting a bullet through the hood of a car is likely to improve engine performance!”

The big red pig ate the red rag. The big res pig ate the red rag. MISSENSE The big red pig ate the red rag. The big res pig ate the red rag. NONSENSE The big red pig ate the red rag. The big re.

Normal gene mRNA Protein Base substitution Base deletion Missing Met mRNA Protein Met Lys Phe Gly Ala Base substitution Met Lys Phe Ser Ala Figure 10.16B Types of mutations and their effects. This figure contrasts the multiple amino acid changes caused by a deletion with the single amino acid change caused by a substitution. Base deletion Missing Met Lys Leu Ala His