MBLG2972 Lecture Notes - Lecture 13: Dna Replication, Covalent Bond, Amine

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5 Jul 2018

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MBLG2072

Genetics and Genomics

Monica Zanuttini !

460381099

Lecture 13 "Mutation and repair

•Mutations (eﬀect) and polymorphisms (no eﬀect) can occur in every generation. Humans acquire

one to four new mutations each generation and have the probability of being passed on. !

•Bacteria has a high rate of mutation, while humans have a relatively high rate of mutation. !

Mutations: !

1. Substitution!

•Base pair substation mutation: the replacement of one nucleotide base pair by another. !

•Transition mutations: one purine (A, G) replaces another, or one pyrimidine (C, T) replaces

another. !

•Transversion mutations: a pyrimidine is replaced by a purine, or vice versa. !

2. Addition !

3. Deletion (one or more base pairs)!

4. Localised mutations or point mutations !

5. Varied consequences (e.g. type of sequencing change or location in the gene) !

Silent mutation:

A base-pair change, no amino acid sequence change.

Missense mutation:

A base-pair change, amino acid change.

Nonsense mutation:

A base-pair change, early stop codon.

Frameshift mutation:

Through the insertion of one or more base pairs, addition or deletion of

mRNA nucleotides, alters the reading frame, wrong amino acid sequence

and premature stop codons downstream.

Can occur outside coding region (i.e. within the regulatory region). Can

alter the amount of protein product or expression of gene through:

•Interference with promoters or introns.

•Production of new splice sites (cryptic splice sites).

Forward mutation:

Converts a wild-type allele to a mutant allele.

Reverse mutation:

Convert mutant alleles to wild-type or near wild-type.

True reversion:

Wild-type DNA sequence is restored by a second mutation within the

same codon (i.e. leu to Phe back to Leu).

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Document Summary

Lecture 13 mutation and repair: mutations (e ect) and polymorphisms (no e ect) can occur in every generation. Humans acquire one to four new mutations each generation and have the probability of being passed on: bacteria has a high rate of mutation, while humans have a relatively high rate of mutation. A base-pair change, no amino acid sequence change. Through the insertion of one or more base pairs, addition or deletion of mrna nucleotides, alters the reading frame, wrong amino acid sequence and premature stop codons downstream. Can occur outside coding region (i. e. within the regulatory region). Converts a wild-type allele to a mutant allele. Convert mutant alleles to wild-type or near wild-type. Wild-type dna sequence is restored by a second mutation within the same codon (i. e. leu to phe back to leu). Second-site reversion: mutation in a different gene and together the two mutations restore the organism to wild-type.

Related Questions

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.

mauvetrout554

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

The amino-acid sequence shown in the following table was obtained from the central region of a particular polypeptide chain in the wild-type and several mutant bacterial strains: Codon 1 2 3 4 5 6 7 8 9

a. Wild-type: Phe Leu Pro Thr Val Thr Thr Arg Trp

b. Mutant 1: Phe Leu His His Gly Asp Asp Thr Val

c. Mutant 2: Phe Leu Pro Thr Met Thr Thr Arg Trp

d. Mutant 3: Phe Leu Pro Thr Val Thr Thr Arg

e. Mutant 4: Phe Pro Pro Arg

f. Mutant 5: Phe Leu Pro Ser Val Thr Thr Arg Trp

Each mutant represents a single nucleotide change from the original wild-type gene. For each mutant, explain what SINGLE nucleotide mutation at the DNA level accounts for the change(s) in amino acid sequence. Also, state in which codon and which position the mutation took place and then fully characterize the mutation as a base-pair substitution mutation (transversion or transition; and missense, nonsense, etc.) or a frameshift mutation. Finally, recreate as much of the original wild-type mRNA sequence as possible.

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MBLG2972 Lecture Notes - Lecture 13: Dna Replication, Covalent Bond, Amine

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