Lesson 8 Flashcards
Variations and Mutations
It occurs when a DNA gene is damaged or changed in such way as to alter the genetic message carried by that gene
Mutation
Refers to the process of altering a DNA sequence
Mutate
Mutation range in magnitude from substitution of a single DNA base to ____
deletion/ duplication of bases and to/of entire chromosomes
Does mutation affect any part of the genome?
Yes, the sequences that encode proteins or control transcription, introns, repeats, and sites critical to intron removal and exon splicing
Refers to the phenotype and also describes an allele
Mutant
Are all DNA sequences likely to mutate?
NO
A Mutant’s nature depends upon _____
how the mutation affects the gene’s product/activity, and usually connotes an abnormal/ unusual characteristic
Can a mutant phenotype be normal?
Yes, it may also be a rare variant that is nevertheless “normal” (such as red hair)
Two kinds of Mutations
Germline and Somatic
What mutation is when the change occurs during the DNA replication that PRECEDES MEIOSIS?
Germline
The resulting gamete and all cells that descend after a Germline Mutation are (transmitted/not)
Transmitted to the next generation
What mutation happens during DNA replication BEFORE MITOSIS?
Somatic
How is a Somatic Mutation passed to the next generation?
All cells that descend from the original changed cell are altered but they might only compromise a small part of the body.
Effects of mutation
Vary
Mutations may ___
Impair function
Have no effect
Beneficial
Can stop or slow production of a protein, overproduce it, or impair the protein’s function (altering its secretion, location, or interaction w/ another protein)
Deleterious (harmful) mutation
When the gene’s product is reduced or absent
“loss-of-function”
When the gene’s activity changes
“gain-of-function”
What most mutations are
Recessive and cause a loss of function
When mutations tend to be dominant
“toxic”
An agent of substance that can bring about a permanent alteration to the physical composition of a DNA gene such that the genetic message is changed
Mutagen
Causes of Mutation
Chemical and Physical Mutagens
Mutagen that changes the sequence of bases in a DNA gene in a number of ways
Chemical
Chemical mutagenic agents
- Base analogs
- Alkylating agents
- Intercalating agents
- Metal ions
- Other chemical mutagens
Chemicals like the bases of DNA or structurally resemble them
(bromouracil and aminopurine)
base analogs
They add alkyl radical to the DNA and damages it (poison gas, vinyl chloride)
alkylating agents
The molecules intercalate between the bases of DNA and disrupt its structure; can cause frameshift mutation; blocks transcription
(proflavine, acridine orange)
intercalating agents
Work by producing reactive oxygen species, hindering the DNA repair pathway, causing DNA hypermethylation, or may directly damage the DNA
(nickel, iron, cobalt)
metal ions
Can be sunlight or radiation
Physical mutagen
It is high energy radiation from a radioactive material or from X-rays is absorbed by the atoms in water molecules surrounding the DNA
Radiation
How does Radiation alter DNA?
High energy radiation from a radioactive material is transferred to the electrons leaving behind a free radical, which is highly dangerous and highly reactive molecule that attacks DNA molecule and alters it in many ways; it also cause double strand breaks (unrepairable)
It contains ultraviolet radiation which, when absorbed by the DNA causes a cross link to form between certain adjacent bases
Sunlight
Is Sunlight mutagen repairable?
In normal cases, yes. But unrepaired dimers of this sort can cause the replicating system to skip over (leaving a gap)
This mutation occurs without exposure to any obvious mutagenic agent when DNA nucleotides shift without warning
Spontaneous mutation
Three types of Mutations
- Point (least harmful)
- Frameshift (more serious/deadly)
- Expanding repeats (add stretches)
A change in a single nitrogen base in a DNA sequence
Point Mutation
When a base in a codon is changed, the amino acid won’t be affected, and mutation does not change the organism
Wobble effect
What does a point mutation cause?
A change in a single amino acid of a protein that may alter the protein’s folding pattern
Example of Point Mutation
Sickle cell anemia
Types of Point Mutations
- transition
- transversion
- missense
- nonsense
- silent
Point mutation that replaces a purine with a purine or a pyrimidine with a pyrimidine
transition
Point mutation that replaces purine with a pyrimidine and vice versa
transversion
Point mutation that the change in a codon normally specifies a PARTICULAR amino acid into one that codes for a DIFFERENT amino acid
missense
Point mutation that the change in a codon specifies an amino acid into a STOP (AUG, UAA, UGA)
nonsense
Point mutation that a change in the sequence of nucleotide bases WITHOUT a subsequent change in the amino acid/ function of the overall protein
silent
Only a single nitrogen base is affected (completely DELETED or an EXTRA one is inserted into the middle of the DNA sequence)
Frameshift Mutation
How does a frameshift mutation alter the sequence?
The deletion or insertion causes the reading frame to shift, changing the three-letter codon sequence for mRNA to transcribe and translate
Types of Frameshift Mutation
- Insertion (added in the middle)
- Deletion (nitrogen base is taken out)
This mutation when a DNA repeats expand because they attract each other
Expanding repeats (trinucleotide repeat) Mutation
