Mutations. Mutations may be either gene mutations or. These mistakes are called. mutations. Gene mutations produce a change

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1 What is a Mutation?

These mistakes are called. mutations Mutations may be either gene mutations or chromosome mutations.

2 Mutations On occasion cells make mistakes in copying. their DNA An incorrect nitrogen base may be inserted or a base may be skipped altogether. These mistakes are called. mutations Mutations may be either gene mutations or chromosome mutations. Gene mutations produce a change within a. single gene Chromosome mutations produce changes in the whole chromosome. Mutations are changes in the genetic material of a cell.

3 Mutation A permanent, heritable change in the DNA of an organism. One or several nucleotides can be added, deleted, or replaced. Most mutations are neutral, many are harmful, some are lethal, and a few are beneficial.

Point Mutations Point mutations are changes

There are two types of point mutations: a)

4 Point Mutations Point mutations are changes in just one base pair of a gene. These are called point mutations because they occur at a single point in the DNA sequence. There are two types of point mutations: a) base pair substitutions b) base pair insertions or deletions

5 Base Pair Substitutions 1. A base pair substitution is the. replacement of one nitrogen base with another 2. It would affect just that one amino acid coded for by that codon. 3. If the substitution is in the 3rd position, it may not have any effect on the organism since there is some redundancy of codons. For example: Alanine: GCU GCC GCA GCG A point mutation at the third position would have no effect whatsoever. The codon would still call for the amino acid. alanine These are called. silent mutations 4. If the substitution were in the first or second position, it would have a greater effect. The wrong amino acid would be called for and inserted into the polypeptide chain that is being manufactured. Only that one amino acid would be affected. 5. A switched amino acid may or may not have any effect on the proper functioning of that protein. If the alteration of a single protein is in a crucial area, such as the active site on an enzyme, the protein will not function properly.

6 Let s look at another example: What amino acid would be called for by the codon AAG? Answer: Lysine What would happen if an A was substituted at the third position in this codon? Answer: The codon AAA would still call for the amino acid lysine. There would be no effect on the protein being made. What would happen if a C was substituted at the third position in this codon? Answer: The codon AAC would call for the amino acid asparagine. The protein being made would be altered. What would happen if there was a substitution at the 1 st or 2 nd position in this codon? Answer: The wrong amino acid will be called for. The protein being made would be altered.

7 Insertions and Deletions 1. This is the: addition or deletion of a nitrogen base. 2. These have a disastrous effect on the resulting protein. 3. For example: AUG AAU GUU UGG UAU UAA If the G is deleted in the first codon, the codons would be read as follows: AUA AUG UUU GGU AUU AA The codons are still read in groups of three nitrogen bases. All of the nucleotides that are downstream of the deletion or addition will be improperly grouped into codons. The addition or deletion of a base would alter the reading of the entire rest of the mrna. 4.These are called frameshift mutations. 5.Frameshift mutations can alter a protein so much that it is unable to perform its normal functions.

8 A A U U A C U G C U C U G G A G A G U G U G A A U U U G U G Asn Tyr Cys Ser Gly Glu Cys Glu Phe Val Normal Protein Normal Function A A U U A C U G C U C U G G A G A G U G U G A A A U A U U U U G U G U G U U U Asn Tyr Cys Ser Gly Glu Shorter Protein Loss of Function

9 A closer look at Point Mutations Point mutation: a different nucleotide replaces the original Missense: results in a single amino acid change (altered protein) Nonsense: results in a premature stop codon (shortened protein) Silent: results in the same amino acid (unaltered protein)

10 Missense Mutation

11 Silent Mutation

12 The Importance of Mutations Most gene mutations are. neutral They have little or no effect. Some mutations cause such dramatic changes that normal cell functions are disrupted and may result in a genetic disorder. Some mutations may actually be beneficial. The mutation may cause a change in the organism that makes it better suited for its environment. Those organisms that are better suited are more likely to survive, reproduce, and pass these favorable traits on to their offspring. This is the mechanism of Natural Selection.

13 Mutate a Sentence! We can think about DNA gene sequence as a sentence made up entirely of three-letter words. In the DNA sequence, each threeletter word is a "codon," specifying a single amino acid in a protein.

14 Mutate a Sentence! Have a look at this "sentence": thesunwashotbuttheoldmandidnotgethishat If we were to split this sentence into individual three-letter words, we would read it like this: The sun was hot but the old man did not get his hat

15 Mutate a Sentence! The sun was hot but the old man did not get his hat The sentence represents a gene. Each letter corresponds to a nucleotide, and each word represents a codon. Only one of the three possible "reading frames" translates into an understandable sentence. In the same way, only one three-letter "reading frame" within a gene codes for the correct protein.

16 Mutate a Sentence! The sun was hot but the old man did not get his hat What if you shifted the three-letter "reading frame? On the left side of your notes, show how you can change the "reading frame" of the above sentence by inserting or deleting letters within the sentence. The result should be a "nonsense" sentence.

17 X The sun was hot but the old man did not get his hat hes unw ash otb utt heo ldm and idn otg eth ish at

18 Mutate a sentence! The sun was hot but the old man did not get his hat Now make a mutation that maintains or changes the meaning of the sentence without creating such nonsense. The sun was hot but the old man did not get his hat The sun was hot not hot but but the the old man old man did not get did get his eat hat his hat

19 Mutations Can Alter Phenotypes Mutations in genes can result in changes to the phenotype by altering the shape (and therefore the function) of the resulting protein.

20 What causes mutations? Mutations often happen when mistakes occur during replication. Also caused by mutagens like UV light, radiation, and certain chemical toxins. However, mutations are rare 1 in a million

21 Are mutations always harmful? Most mutations produce no observable effect they are neutral. Of those that have significant effect, most are harmful or lethal. Some mutations are beneficial. It all depends on the environment in which the mutation occurs. Examples: General & Humans

22 Question Explain why a base substitution is often less harmful than a base deletion or insertion. Answer: a base substitution potentially affects only one amino acid of the polypeptide, but a base deletion or insertion affects all the amino acids downstream from where it occurs.

23 Question Describe how a mutation could be helpful rather than harmful. Answer: A mutation could be considered helpful if it alters a protein in a way that benefits an organism in its environment.

24 Question Give an example of a mutagen. Answer: X-rays, UV light, cigarette smoke, radiation, chemicals.

Mutations. Lecture 15

Mutations. Lecture 15 Mutations Lecture 15 Objectives 1: Mutation Define mutation. Describe the types of mutations and their effects on the protein that is produced Distinguishing between spontaneous and induced mutations.