Mutations

Georgia Standard:•Describe the relationships between mutations in DNA and potential appearance of new traits.•Identify the types of mutations that can alter DNA. •Explain the role of DNA in storing and transmitting cellular information.

Essential Question: •What is the role of mutation in producing variation?•How does a cell make protein?

Warm-up:1. Copy the following information about Protein X: Methionine—

Phenylalanine—Tryptophan—Asparagine—Isoleucine—STOP.

2. Use the genetic code in your textbook to determine one possible sequence of RNA to code for this information. Write this code below the description of Protein X. Below this, write the DNA code that would produce this RNA sequence.

3. Now, cause a mutation in the gene sequence that you just determined by deleting the fourth base in the DNA sequence. Write this new sequence.

4. Write the new RNA sequence that would be produced. Below that, write the amino acid sequence that would result from this mutation in your gene. Call this Protein Y.

5. Did this single deletion cause much change in your protein? Explain your answer.

Mutations:

• Changes in the DNA sequence that affect genetic information.

• Gene mutations result from changes in a single gene.

• Chromosomal mutations involve changes in whole chromosomes.

Molecular Genetics

Mutations

A permanent change that occurs in a cell’s DNA is called a mutation.

Types of mutations

Point mutation InsertionDeletion

12.4 Gene Regulation and Mutation

Chapter 12

Molecular GeneticsChapter 12

Gene Mutations:

– Point mutation = affects one nucleotide• Insertion• Deletion• Substitution

• Cause frameshift mutations: they shift the reading frame of a genetic message.

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Substitution InsertionDeletion

Gene Mutations:

Substitution, Insertion, and Deletion

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Chromosomal Mutations:

– Changes in the number or structure of chromosomes

• Result: Change the locations of genes on chromosomes or the number of copies of some genes.

• Ex: Down Syndrome

Types of Chromosomal Mutations:

• Deletion = loss of all or part of a chromosome

• Duplication = a segment of chromosome is repeated

• Inversion = chromosome is inverted in reverse of its usual direction

• Translocation = part of a chromosome breaks off and attaches to another, nonhomologous, chromosome

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Deletion

Duplication

Inversion

Translocation

Chromosomal MutationsSection 12-4

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Molecular Genetics

Protein Folding and Stability

Substitutions also can lead to genetic disorders.

Can change both the folding and stability of the protein

12.4 Gene Regulation and Mutation

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Molecular Genetics

Body-cell v. Sex-cell Mutation

Somatic cell mutations are not passed on to the next generation.

Mutations that occur in sex cells are passed on to the organism’s offspring and will be present in every cell of the offspring.

12.4 Gene Regulation and Mutation

Chapter 12

Molecular Genetics

12.4 Gene Regulation and Mutation

What Causes These Mutations?

• High energy radiation: x-rays, ultraviolet light, gamma rays

• Chemicals

• Environmental Factors

• Can occur spontaneously

Good Mutations:

• Mutations cause diversity of genes in the living world

– This diversity makes evolution and natural selection possible.

– Mutations create the different alleles needed for genetic research

Checkpoint Questions:

1. What is a gene mutation? What is a chromosomal mutation?

2. What is a point mutation? 3. What are two kinds of frameshift mutations? 4. What are four types of chromosomal

mutations?5. The effects of a mutation are not always

visible. How might a biologist determine whether a mutation has occurred and, if so, what type of mutation it is?

Gene Regulation:

Essential Question:•How does a cell know when to stop making a protein? •How does the cell determine which genes will be expressed and which will remain “silent”?

Georgia Performance Standards•Compare and contrast gene regulation in eukaryotes and prokaryotes.

Gene Regulation:

• Only a fraction of the genes in a cell are expressed at any given time.

• An expressed gene is a gene that is transcribed into RNA.

Warm-up:1. Do you think that cells produce all the proteins

for which the DNA (genes) code? Why or why not? How do the proteins made affect the type and function of cells?

2. Consider what you now know about genes and protein synthesis. What might be some ways that a cell has control over the proteins it produces?

3. What type(s) of organic compounds are most likely the ones that help to regulate protein synthesis? Justify your answer.

Gene Regulation:

• In fact, cells are filled with DNA-binding proteins that attach to specific DNA sequences and help to regulate gene expression. – Promoters– Start and stop sequences

Regulatory sites

Promoter(RNA polymerase binding site)

Start transcription

DNA strand

Stop transcription

Typical Gene StructureSection 12-5

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12.4 Gene Regulation and Mutation

Molecular Genetics

Prokaryote Gene Regulation Ability of an organism to control which genes are

transcribed in response to the environment

An operon is a section of DNA that contains the genes for the proteins needed for a specific metabolic pathway.

Operator Promoter Regulatory gene Genes coding for proteins

Chapter 12

Molecular Genetics

The Trp Operon

12.4 Gene Regulation and Mutation

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Prokaryotic Gene Regulation Ex:

• E.Coli bateria:• Operons operate together to make a needed

protein for a certain metabolic pathway.

• Because these genes must be expressed in order for the bacterium to be able to use the sugar lactose as a food, they are called the lac operon.

• The lac genes are turned off by repressors and turned on by the presence of lactose.

Molecular Genetics

The Lac Operon

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Chapter 12

• The lac genes in E. coli are turned off by repressors and turned on by the presence of lactose.

• When lactose is not present, the repressor binds to the operator region, preventing RNA polymerase from beginning transcription.

• Lactose causes the repressor to be released from the operator region.

Function of the Lac Repressor

Molecular GeneticsChapter 12

Molecular Genetics

Eukaryote Gene Regulation

Controlling transcription

Transcription factors ensure that a gene is used at the right time and that proteins are made in the right amounts

The complex structure of eukaryotic DNA also regulates transcription.

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Chapter 12

Eukaryotic Gene Regulation:

• Genes are regulated in a variety of ways by enhancer sequences located before the beginning of transcription.

• An enormous number of proteins can bind to different enhancer sequences, which is why eukaryotic gene regulation is so complex.

• Some of these DNA-binding proteins enhance transcription by opening up tightly packed chromatin. Others help to attract RNA polymerase.

Molecular Genetics

RNA Interference

RNA interference can stop the mRNA from translating its message.

12.4 Gene Regulation and Mutation

Chapter 12

Eukaryotic Gene Regulation:• Operons are generally not

found in eukaryotes.    

• Most eukaryotic genes are controlled individually and have regulatory sequences that are much more complex

• One of the most interesting is a short region of DNA about 30 base pairs long, with a sequence of TATATA or TATAAA, before the start of transcription.

– The “TATA” box seems to help position RNA polymerase by marking the promotor (a point just before the point at which transcription begins).

• Eukaryotic promoters are usually found just before the TATA box, and they consist of a series of short DNA sequences.

Introns & Exons:

Eukaryotic genes are more complex than prokaryotic genes. Many eukaryotic genes include a sequence called the TATA box that may help position RNA polymerase.

Eukaryotic Gene Regulation

Molecular Genetics

Hox Genes

Hox genes are responsible for the general body pattern of most animals.

12.4 Gene Regulation and Mutation

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• A mutation in one of these “master control genes” can completely change the organs that develop in specific parts of the body.

• Genes descended from common ancestors.

In fruit flies, a series of hox genes along a chromosome determines the basic structure of the fly’s body. Mice have very similar genes on four different chromosomes.

Hox Genes

Why is gene regulation in eukaryotes

more complex than in prokaryotes? • Cell specialization requires genetic

specialization– multicellular organism = eukaryotes– Unicellular organism = prokaryotes (no cell

specialization)

• Only a tiny fraction of the available genes needs to be expressed in cells of different tissues throughout the body.

• The complexity of gene regulation in eukaryotes makes this specificity possible.

Checkpoint Questions:

1. How is the lac operon regulated? 2. Describe how most eukaryotic genes are

controlled. 3. What is a promoter? 4. Why are only a limited number of genes

expressed in each cell of a multicellular eukaryote?

5. How is the way hox genes are expressed in mice similar to the way they are expressed in fruit flies? How is it different?

Announcements:

• Chapter 12 Quiz Friday

• ICA/HW: Mutations WS

• ICA/HW: Compare and contrast gene regulation in prokaryotes and eukaryotes. (Venn Diagram)