TAKS Objective 2 TEKS 6C (Mutations)

TAKS Objective 2 TEKS 6C (Mutations)

Presented by:

Alexander FedorovComposite Science Teacher

Lesson Title:Applicable Text: Handouts

TAKS Objective 2 TEKS 6C (Mutations)

6C 6C The student knows the structures The student knows the structures and functions of nucleic acids in the and functions of nucleic acids in the mechanisms of genetics.mechanisms of genetics. Students Students should be able to identify and should be able to identify and illustrate how changes in DNA illustrate how changes in DNA cause mutations and evaluate cause mutations and evaluate the significance of these the significance of these changes.changes.

Wild Type Head Mutant Head (Antennapedia)

Proteins and Mutations:Proteins and Mutations: Some proteins carry out Some proteins carry out

functions within the cells of an functions within the cells of an organism.organism.

Other proteins are exportedOther proteins are exported

out of the cell for other out of the cell for other purposes.purposes.

Still other proteins are used as Still other proteins are used as activators or repressors, turning activators or repressors, turning genes on or off.genes on or off.

Therefore, a change in a cell’s Therefore, a change in a cell’s

proteins could have dramatic effects proteins could have dramatic effects on the cell’s structure or function.on the cell’s structure or function.

Changes in the DNA can change the Changes in the DNA can change the proteins made by the cell.proteins made by the cell.

A random change in the sequence of A random change in the sequence of nucleotides in DNA is called a mutation.nucleotides in DNA is called a mutation.

Some mutations have little or noSome mutations have little or noeffect on the organism, others effect on the organism, others are harmful and very few are are harmful and very few are beneficial.beneficial.

Harmful mutations, Ahhhhh!!!

There are two types of mutations:There are two types of mutations:

1. Chromosomal mutations1. Chromosomal mutations

2. Gene mutations2. Gene mutations

Chromosomal mutations are changes Chromosomal mutations are changes in the structure of a chromosome. in the structure of a chromosome.

Gene mutations are errors that occur Gene mutations are errors that occur within individual genes in a within individual genes in a chromosome.chromosome.

Gene mutations can involve a single Gene mutations can involve a single nucleotide or they can affect sections nucleotide or they can affect sections of DNA that include many of DNA that include many nucleotides.nucleotides.

The deletion or The deletion or addition of addition of nucleotides that nucleotides that disrupts codons is disrupts codons is called a called a frameshift frameshift mutation.mutation.

Because mRNA is read in codons Because mRNA is read in codons (three-base sections) during (three-base sections) during translation, an addition or deletion of translation, an addition or deletion of nucleotides can alter the sequence of nucleotides can alter the sequence of bases, or reading frame, of the bases, or reading frame, of the genetic message.genetic message.

What are the codons in the original reading frame?

What are the codons in the shifted reading frame?

Recall what happens when a strand Recall what happens when a strand of mRNA is transcribed from DNA.of mRNA is transcribed from DNA.

What might happen if one base is What might happen if one base is deleted from the DNA?deleted from the DNA?

The transcribed mRNA would also be The transcribed mRNA would also be affected.affected.

Because each mRNA codon Because each mRNA codon corresponds to an amino acid, corresponds to an amino acid, altering the codons may alter the altering the codons may alter the amino acid sequence.amino acid sequence.

The end result may be an entirely The end result may be an entirely different protein product. Frameshift different protein product. Frameshift mutations can have an enormous mutations can have an enormous impact on an organism’s structure impact on an organism’s structure and function.and function.

A change in only one A change in only one nucleotide is a nucleotide is a

point mutationpoint mutation. .

Because a point Because a point

mutation affects a mutation affects a single codon, it tends single codon, it tends to be far less to be far less disruptive than a disruptive than a frameshift mutationframeshift mutation

Some amino acids are coded for by more Some amino acids are coded for by more than one codon, and substitution may than one codon, and substitution may simply change one codon to another simply change one codon to another codon for the same amino acid.codon for the same amino acid.

For example:For example: CUU = LeucineCUU = Leucine Any change in the third base: CUC, CUA, Any change in the third base: CUC, CUA,

CUGCUG still codes for the amino acid Leucine.still codes for the amino acid Leucine.

Th

ird L

ette

r

About 30% of all substitution About 30% of all substitution mutations produce no changes in mutations produce no changes in proteins.proteins.

In the remaining 70% of point In the remaining 70% of point mutations, changed nucleotides mutations, changed nucleotides cause a different amino acid to be cause a different amino acid to be incorporated into a protein.incorporated into a protein.

The resulting protein may function The resulting protein may function normally or may be defectivenormally or may be defective

The diagram shows The diagram shows a point mutation a point mutation and how it changes and how it changes the gene from the gene from normal hemoglobin normal hemoglobin production to the production to the production of production of sickle-cell sickle-cell hemoglobin, which hemoglobin, which in turn causes in turn causes sickle-cell disease.sickle-cell disease.

A third and very common point mutation A third and very common point mutation occurs when a codon in the middle of a occurs when a codon in the middle of a gene is changed to a stop codon. gene is changed to a stop codon.

For example: UGC = Cysteine but UGA = For example: UGC = Cysteine but UGA = StopStop

When genes with this mutation go through When genes with this mutation go through protein synthesis, translation is halted protein synthesis, translation is halted before the amino acid chain is completed.before the amino acid chain is completed.

Here is a sampling of Here is a sampling of the more than 200 the more than 200 different mutations different mutations that have been found that have been found in patients with in patients with cystic cystic fibrosisfibrosis

Unlike sickle-cell disease, Unlike sickle-cell disease, then, no single mutation is then, no single mutation is responsible for all cases of responsible for all cases of cystic fibrosis. People with cystic fibrosis. People with cystic fibrosis inherit two cystic fibrosis inherit two mutant genes, but the mutant genes, but the mutations need not be the mutations need not be the same.same.

1 1 Ultraviolet radiation can cause mutations Ultraviolet radiation can cause mutations in the DNA of skin cells that have been in the DNA of skin cells that have been overexposed to the sun. This mutated DNA overexposed to the sun. This mutated DNA has no effect on future offspring because has no effect on future offspring because ——

A A changes in skin cell DNA are changes in skin cell DNA are homozygous recessivehomozygous recessive

B B mutations must occur within the RNA mutations must occur within the RNA codonscodons

C C offspring reject parental skin cellsoffspring reject parental skin cells

DD only changes to gamete DNA can be only changes to gamete DNA can be inheritedinherited

2 2 Mutations in DNA molecules can Mutations in DNA molecules can occur when —occur when —

A A replication of DNA is exactreplication of DNA is exact

B B a DNA enzyme attaches to an RNA a DNA enzyme attaches to an RNA codoncodon

C C RNA codons are replaced by DNA RNA codons are replaced by DNA nucleotidesnucleotides

DD a change occurs in DNA nucleotide a change occurs in DNA nucleotide basesbases

AGAUCGAGUACAUCGAGU3 The chain above represents three codons. Which of the following changes would be expected in the amino acid chain if the mutation shown above occurred?A The amino acid sequence would be shorter than expected.B The identity of one amino acid would change.C The amino acid sequence would remain unchanged.D The identities of more than one amino acid would change.

4 The diagram represents the chromosomes of a person with a genetic disorder caused by nondisjunction, in which the chromosomes fail to separate properly. Which chromosome set displays nondisjunction?A 2B 8C 21D 23

5 The assembly of a messenger RNA strand that normally begins with UAC has been changed so that the newly assembled messenger RNA strand begins with UAG. Which of the following will most likely occur?A The protein will be missing the first amino acid.B The amino acids that make up the protein will all be different.C The mRNA will become attached to a ribosome.D The production of the protein will be stopped.

The EndThe End

TAKS Objective 2 TEKS 6C (Mutations)

Documents

Transcript of TAKS Objective 2 TEKS 6C (Mutations)