Download 13.3 Mutations File

13.3 Mutations
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
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 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
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...
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 transcribed into mRNA
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)
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
WB CHECK:
What is a point mutation?
When do point mutations usually occur?
POINT > Define and describe genetic mutations
Three types of point mutations:
1. Substitution
2. Deletion
3. Insertion
POINT > Demonstrate how point mutations can
affect zero, one or many amino acids
Imagine the following as ‘codons’:
TH E FAT CAT ATE THE RAT
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)
POINT > Demonstrate how point mutations can
affect zero, one or many amino acids
Substitution
TH ET FAT CAT ATE THE RAT
POINT > Demonstrate how point mutations can
affect zero, one or many amino acids
DNA
Template C
T
C
A
T
C
G
G
A
C
T
G
C
mRNA
G
A
U
A
G
C
C
U
G
A
C
G
Amino Acids
mRNA with
Mutation
G
G
U
A
G
C
C
U
G
A
C
G
Amino Acids
with Mutation
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…
POINT > Demonstrate how point mutations can
affect zero, one or many amino acids
 Frameshift
Mutation:
TH E FAT CAT ATE THE RAT
POINT > Demonstrate how point mutations can
affect zero, one or many amino acids
DNA
Template C
T
A
G
T
C
G
G
A
C
T
G
C
mRNA
G
A
U
A
G
C
C
U
G
A
C
G
Amino Acids
mRNA with
Mutation G
A
U
C
A
G
C
C
U
G
A
C
G
Amino Acids
with Mutation
POINT > Demonstrate how point mutations can
affect zero, one or many amino acids
DNA
Template C
T
A
T
C
G
G
A
C
T
G
C
G
mRNA
G
A
U
A
G
C
C
U
G
A
C
G
Amino Acids
mRNA with
Mutation
Amino Acids
with Mutation
G
A
U
G
C
C
U
G
A
C
G
C
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)
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
POINT > Distinguish between gene and chromosomal
mutations
(Original)
 Deletion
 Duplication
 Inversion
 Translocation
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
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)
WB CHECK:
Give an example of a physical mutagen.
What are three examples of chemical mutagens?
What causes most mutations?
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
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
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
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!
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?
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.
Read pages 372-376
Assess p. 376
Workbook pages 230-233, 239