1. 13.3 Mutations

2. POINT > Define a gene in simple terms
POINT > Define and describe genetic mutations
POINT > Distinguish between gene and chromosomal mutations
POINT > Demonstrate how point mutations can affect zero, one or many amino acids
POINT > Identify causes of mutations
POINT > Describe how mutations can be harmful, beneficial or have no effect on the cell/organism

3. POINT > Define a gene in simple terms
A gene is a segment of DNA that contains the information to construct one protein
A gene includes the exons and introns
One DNA molecule (chromosome) has many genes
ex. 22,000 human genes (x2) on 46 chromosomes in each cell =
~ 950 genes per chromosome (average)

4. POINT > Define a gene in simple terms
Each gene codes for one protein that has an important role to play in the cell
Recall that the DNA sequence specifies the amino acid sequence in the protein
Recall that the order of amino acids in the protein determines how the protein folds up into its functional conformation
In order to fulfill its function in the cell, the amino acid sequence of the protein has to be correct! If not...

10. WB CHECK: find all that are correct
A gene
a) is a DNA sequence
b) is an RNA sequence
c) has the information to build one protein
d) has the information to build different proteins
e) would be found on a chromosome
f) is used to make an mRNA during transcription

11. POINT > Define and describe genetic mutations
A mutation is a heritable change to the DNA of an organism
A mutation can affect:
A single gene (gene mutation)
Large portion of a chromosome (chromosomal mutation)

12. POINT > Define and describe genetic mutations
Most gene mutations are point mutations:
a change of one nucleotide at a single point in a DNA sequence
This can occur during DNA replication (DNA polymerase makes a mistake during proof-reading)
The mutation gets passed to every cell that develops from that parental cell

13. WB CHECK:
What is a point mutation?
When do point mutations usually occur?

14. POINT > Define and describe genetic mutations
Three types of point mutations:
1. Substitution
2. Deletion
3. Insertion

15. Imagine the following as ‘codons’:
POINT > Demonstrate how point mutations can affect zero, one or many amino acids
Imagine the following as ‘codons’: T H E F A T C A T A T E T H E R A T

16. One base gets changed to another base
POINT > Demonstrate how point mutations can affect zero, one or many amino acids
1. Substitution
One base gets changed to another base
Usually corrected by DNA polymerase, but can be missed (~ 1 per 1,000,000,000)

17. POINT > Demonstrate how point mutations can affect zero, one or many amino acids
Substitution T H E T F A T C A T A T E T H E R A T

18. POINT > Demonstrate how point mutations can affect zero, one or many amino acids
mRNA with
Mutation
Amino Acids
with Mutation
DNA
Template
mRNA
Amino Acids C G G
Asp
Gly T C A G A U U T A A
Ser
Ser C G G G C C G C C
Leu
Leu A U U C G G T A A
Thr
Thr G C C C G G

19. POINT > Demonstrate how point mutations can affect zero, one or many amino acids
Insertion or deletion: a base is either inserted or deleted from the DNA sequence This results in a frameshift mutation: the entire reading frame following that point is thrown off This is much more severe than a substitution, because many amino acids will be altered…

20. POINT > Demonstrate how point mutations can affect zero, one or many amino acids
Frameshift Mutation: T H E F A T C A T A T E T H E R A T

21. POINT > Demonstrate how point mutations can affect zero, one or many amino acids
mRNA with
Mutation
Amino Acids
with Mutation G
DNA
Template
mRNA
Amino Acids C G A
Asp
Asp T A U G A U C T A A
Gln
Ser C G G G C C G C C
Pro
Leu A U U C G G T A A
Asp
Thr G C C C G G

22. POINT > Demonstrate how point mutations can affect zero, one or many amino acids
mRNA with
Mutation
Amino Acids
with Mutation
DNA
Template
mRNA
Amino Acids C G G
Asp
Asp T A A A U U T A G
Ser
Ala C G C G C C G C U
Leu
STOP A U G C G A T A C
Thr G C G C G G C

23. WB CHECK:
What are three types of point mutation?
Why is an insertion mutation worse than a substitution mutation?
Which type of mutation is shown here?
ATCCCGGCTA (original sequence)
ATCCCGCTA (mutated sequence)

24. POINT > Distinguish between gene and chromosomal mutations
Sometimes entire sections of a chromosome are involved in mutation
Chromosomal mutations result in changes to the number or structure of chromosomes
May alter location of genes or change how many copies of a gene are present

25. POINT > Distinguish between gene and chromosomal mutations
(Original)
Deletion
Duplication
Inversion
Translocation

26. POINT > Identify causes of mutations
1. DNA Replication
DNA Polymerase is not perfect, balances speed and accuracy. Most mutations arise here
2. Mutagens: Environmental factors that damage DNA
There are two broad categories of mutagens: chemical and physical

27. POINT > Identify causes of mutations
2. Mutagens, con’t
A. Chemical mutagens: pesticides, tobacco smoke, industrial toxins
B. Physical mutagens: radiation, X-rays, UV cause of skin cancers due to sun exposure
3. Biological factors (viruses, bacteria)

28. WB CHECK:
Give an example of a physical mutagen.
What are three examples of chemical mutagens?
What causes most mutations?

29. If it occurs in a gamete, changes are passed to offspring
POINT > Describe how mutations can be harmful, beneficial or have no effect
Once the DNA sequence is altered, the change is passed to every daughter cell
If it occurs in a gamete, changes are passed to offspring

30. POINT > Describe how mutations can be harmful, beneficial or have no effect
Most mutations have little or no effect. Why? Mutations may occur in stretches of DNA that are not genes (this includes most DNA!) If a mutation does occurs in a gene, the amino acid change might not be catastrophic to the protein function

31. Some mutations are harmful
POINT > Describe how mutations can be harmful, beneficial or have no effect
Some mutations are harmful
Ex. Mutations to cell cycle control proteins (cyclins) may lead to uncontrolled cell division, i.e. cancer
Ex. Altered protein structure: sickle cell disease –
A single substitution mutation causes a red blood cell protein to fold up irregularly. This leads to sickle cell

32. POINT > Describe how mutations can be harmful, beneficial or have no effect
Some mutations are beneficial
Ex. Chemical resistance to pesticides and antibiotics (plants, insects, bacteria)
Ex. Polyploidy (extra copies of chromosomes) in plants often results in larger, stronger organisms
This is a key biological mechanism of evolution!

33. WB CHECK:
Why are most mutations harmless?
Give an example of a mutation that is helpful to the organism.
What are two diseases caused by mutations?

34. Summary:
Gene & chromosomal mutations get passed to every daughter cell
Mutations can happen during DNA replication or from mutagens in the environment
Some mutations are harmful, while some may be beneficial. Most are neutral.

35. Homework
Read pages Assess p. 376 Workbook pages , 239