BSC 310 Lecture Notes - Lecture 20: Meiosis, Nonsense Mutation, Microbial Genetics

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silvercicada472

28 Jun 2018

School

University of Alabama

Department

BSC

Course

BSC 310

Professor

Julie Olson

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Mutation

A mutation is a permanent alteration in the sequence of nitrogenous bases of a DNA

molecule. The result of a mutation is generally a change in the end‐product specified by that

gene. In some cases, a mutation can be beneficial if a new metabolic activity arises in a

microorganism, or it can be detrimental if a metabolic activity is lost.

Types of mutations. The most common type of mutation involves a single base pair in the

DNA molecule and is known as a point mutation. In this case, a different base is substituted

for the normal base, thus altering the genetic code. Should a new amino acid be substituted

in the final protein, the mutation is known as missense mutation.Certain mutations change

the genetic code and destroy the information it contains. Such a mutation is referred to as

a nonsense mutation.

In another type of cell mutation, a frameshift mutation, pairs of nucleotides are either added

to or deleted from the DNA molecule, with the result that the “reading frame” is shifted. The

amino acid sequence in the resulting protein changes as a result of this frameshift. If a

mutation occurs without laboratory intervention, it is a spontaneous mutation; if it occurs as

a result of laboratory intervention, it is an induced mutation.

Mutagens. Physical and chemical agents capable of bringing about mutations are

calledmutagens. Chemical mutagens include nitrous acid. This substance converts adenine to

hypoxanthine, a molecule that will not pair with thymine, and thus interrupts the genetic

code. A base analog is a chemical mutagen that resembles a nitrogenous base and is

incorporated by error into a DNA molecule. Such a DNA molecule cannot function in protein

synthesis. Certain dyes and fungal toxins (for example, aflatoxin) are known to be

mutagens.

Physical mutagens include X rays, gamma rays, and ultraviolet light. X rays and gamma rays

break the covalent bonds in DNA molecules, thereby producing fragments. Ultraviolet light

binds together adjacent thymine bases, forming dimers. These dimers cannot function in

protein synthesis, and the genetic code is thereby interrupted. Radiation damage can be

repaired by certain bacterial enzymes, a process known asphotoreactivation.

The probability of a mutation occurring during cellular division is known as the mutation

rate. In bacteria, the spontaneous mutation rate is about one in a billion reproductions. This

factor implies that in every population of a billion cells, there is at least one mutant. This

mutant organism may never express its mutation. However, for example, if the mutation

renders antibiotic resistance, then the mutants will survive when an antibiotic is applied to

the population, and a new colony of antibiotic-resistant bacteria will emerge.

Introduction to Microbial Genetics

Microorganisms have the ability to acquire genes and thereby undergo the process

of recombination. In recombination, a new chromosome with a genotype different from that

of the parent results from the combination of genetic material from two organisms. This new

arrangement of genes is usually accompanied by new chemical or physical properties.

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Related Questions

1. An occurrence of a gene made larger by trinucleotide repeats is:

Allelic expansion

Nucleotide expansion

Translocation mutation

Transformation

2. a chemical that can damage and/or change DNA is called a/an:

Allele

Endonuclease

Vector

Mutagen

3. An occurrence when a section of a chromosome relocates itself to an entirely different (non-homologous) chromosome is called a/an:

Inversion mutation

Translocation mutation

Transformation mutation

Duplication mutation

4. The tandem repeat in the sequence GGGAAGGGAAGGGAAGGGAAGGGAAG is:

GGA

GGGAA

GGAAG

GGAAGGG

A disease characterized by abnormally shaped hemoglobin is called:

Cystic Fibrosis

Sickle Cell Anemia

Marfan Syndrome

Leukemia

5. A point mutation that causes a substitution of a stop codon with an amino acid and leads to the formation of a longer protein is a:

Nonsense mutation

Missense mutation

Sense mutation

Frameshift mutation

6. Addition or deletion of nucleotides in a DNA sequence is known as a:

Nonsense mutation

Missense mutation

Sense mutation

Frameshift mutation

7. The least severe type of chromosomal mutation is:

Point

Frameshift

Inversion

Translocation

8. Chemicals inserting themselves into DNA can cause a:

Missense mutation

Nonsense mutation

Sense mutation

Frameshift mutation

9. A genetic condition caused by allelic expansion is:

Familial hypercholesterolemia

Fragile X syndrome

Alkaptonuria

Galactosemia

10. Which of the following is most likely the original DNA strand if the mutated DNA strand is ATAGUUGATGUA ?

ATAGAAGATGAA

ATAGCCGATGCA

ATAGGGGATGGA

ATAGTTGATGTA

11. An unbalanced chromosomal mutation would include a/an:

duplication (insertion)

inversion

translocation

denaturation

12. Many translocation mutations are found to be involved with:

cancers

sickle cell anemia

Huntington disease

cystic fibrosis

13. A common repeat throughout the human genome that is approximately 300 bases in length is called a/an:

EcoRI repeat

Hind repeat

Exo repeat

Alu repeat

14. A balanced chromosomal mutation includes:

imprintation

denaturation

inversion

deletion

salmondinosaur263

5). The table shows five different mutations of a small section of a gene.

Use the base-pairing rules to complete the second column. For each mutation, write the sequence for any mRNA codons that will be changed as a result of the mutation in bold. Write any codons that wonât be changed in regular font.

Using the genetic code chart from question #3, identify any stop codons in the mRNA molecules â write these codons in red

For each mutation, write any amino acids that will be changed in the last column in bold font. Use red XXXs to indicate any amino acids that will be missing as a result of stop codons and use use regular font indicate any amino acids that will not be changed.

DNA (Template Strand)	mRNA codon	Polypeptide
Original DNA = GCAAGTACCTGA	CGU UCA UGG ACU	arg â ser â trp â thr
Mutation = GCCAGTACCTGA (nucleotide change underlined)	____ ____ ____ ____	___ ___ ___ ___
Mutation = GCACGTACCTGA (nucleotide change underlined)	____ ____ ____ ____	___ ___ ___ ___
Mutation = GCAAGTACTTGA (nucleotide change underlined)	____ ____ ____ ____	___ ___ ___ ___
Mutation = GAAGTACCTGA (first C deleted)	____ ____ ____ ____	___ ___ ___ ___
Mutation = GCAAGTACTGA (second C deleted)	____ ____ ____ ____	___ ___ ___ ___

ambergnu488

Part B

Think about the DNA coding sequence of a gene. If an A were swapped for a T, what kind of mutation could it cause and why?

a) It could cause a frameshift nonsense or frameshift missense mutation because it would change the reading frame of the codon triplet.

b) It could cause a silent, missense, or nonsense mutation because those are the types that can be caused by a nucleotide-pair substitution like this one.

c) It could cause a nonsense mutation because the sequence would no longer be the same, so the protein would be shorter and non-functional.

d) It could cause a silent mutation because A and T are complementary to each other so it is not really a substitution mutation.

Part C

Why is a frameshift missense mutation more likely to have a severe effect on phenotype than a nucleotide-pair substitution missense mutation in the same protein?

a) A substitution missense mutation causes the protein to be shorter and thus non-functional.

b) A frameshift missense will cause the codons to be out of order, but a substitution missense does not change the order of the codons.

c) A frameshift missense mutation will cause an early Stop codon, but a substitution missense might be silent.

d) A substitution missense affects only one codon, but a frameshift missense affects all codons downstream of the frameshift.

Part D

Which of the following sequences shows a frameshift mutation compared to the wild-type mRNA sequence?

a) wild-type	5â-AUGCAUACAUUGGAGUGA-3â
mutant	5â-AUGCAUACAGAGUGA-3â

b) wild-type	5â-AUGCAUACAUUGGAGUGA-3â
mutant	5â-AUGCAUACGUUGGAGUGA-3â

c) wild-type	5â-AUGCAUACAUUGGAGUGA-3â
mutant	5â-AUGCAUACAUCUGGAGUGA-3â

d) wild-type	5â-AUGCAUACAUUGGAGUGA-3â
mutant	5â-AUGCAUGUGACAUUGGAGUGA-3â

Part F

Suppose that the triplet of nucleotides indicated in bold (AGC) spans two codons, that is, CTA and GCC. If the triplet AGC were deleted from this DNA coding sequence, what effect would it have on the resulting protein?

5â-ATGCTAGCCTATCGTAAC-3â

a) The two flanking codons would be altered, but the rest of the amino acid sequence would be the same because there would be no frameshift.

b) The entire amino acid sequence would be altered due to the frameshift.

c) All of the amino acids after the deletion would be altered due to the frameshift.

d) All of the amino acids up to the deletion would be altered due to the frameshift.

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BSC 310 Lecture Notes - Lecture 20: Meiosis, Nonsense Mutation, Microbial Genetics

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