Genetic Mutation and mRNA Modifications

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Questions and Answers

What is a codon composed of?

Three nucleotides (correct)

A single nucleotide

Four nucleotides

Two nucleotides

What is the primary role of the 3' poly-A tail added to mRNA?

Protecting mRNA from degradation (correct)

Facilitating RNA transcription

Promoting splicing of introns

Enhancing translation efficiency

What are the sequences called that interrupt the coding sequences of genes?

Codons

Promoters

Exons

Introns (correct)

What is mutation primarily a source of in biological evolution?

Genetic variation Signup and view all the answers

What is the process called that modifies the primary mRNA transcript before it is exported to the cytoplasm?

Pre-mRNA splicing Signup and view all the answers

What can point mutations result in?

Altering a single base pair Signup and view all the answers

Which of the following statements about mutations is true?

Many mutations can lead to diseases and disorders. Signup and view all the answers

What is the primary mechanism by which intercalating agents produce mutations?

They sandwich themselves between adjacent bases in DNA. Signup and view all the answers

What type of mutations do intercalating agents frequently produce?

Frameshift mutations. Signup and view all the answers

How does ultraviolet (UV) light primarily damage DNA?

By forming chemical bonds between adjacent pyrimidine bases. Signup and view all the answers

Which type of radiation is considered ionizing and capable of dislodging electrons from atoms?

X-rays. Signup and view all the answers

What happens to most pyrimidine dimers formed due to UV light exposure?

They usually get immediately repaired. Signup and view all the answers

What is the primary method used to understand the effects of mutations in biological systems?

Genetic dissection Signup and view all the answers

What distinguishes somatic mutations from germ-line mutations?

Only somatic mutations can lead to clones of genetically identical cells. Signup and view all the answers

How often do mutations typically arise in somatic cells?

Once in every million cell divisions Signup and view all the answers

Which type of mutation can directly affect an organism's phenotype and be identified by observing phenotypic effects?

Gene mutations Signup and view all the answers

What can large-scale genetic alterations that affect chromosome structure or number be termed?

Chromosome mutations Signup and view all the answers

What is a potential outcome of a somatic mutation that stimulates cell division?

Formation of a cancerous growth Signup and view all the answers

Which type of mutation arises in cells that produce gametes and can be inherited by the next generation?

Germ-line mutations Signup and view all the answers

Which of the following best describes a somatic mutation?

It affects only somatic tissues and not gametes. Signup and view all the answers

How can chromosome mutations be detected?

By visually inspecting chromosomes under a microscope. Signup and view all the answers

What type of mutation is primarily caused by 5-bromouracil mispairing with guanine?

Transition mutations Signup and view all the answers

What specific mutation does ethylmethylsulfonate (EMS) produce when it adds an ethyl group to guanine?

C · G→T · A transition Signup and view all the answers

What happens during depurination in DNA?

A purine base is lost, creating an apurinic site. Signup and view all the answers

How does nitrous acid contribute to transition mutations?

It deaminates nucleotide bases, altering their pairing properties. Signup and view all the answers

What is a direct consequence of an apurinic site during DNA replication?

An incorrect nucleotide is often incorporated into the new DNA strand. Signup and view all the answers

What effect does hydroxylamine have on cytosine in DNA?

It adds a hydroxyl group to cytosine, changing its pairing behavior. Signup and view all the answers

Which of the following statements about alkylating agents is true?

They introduce alkyl groups that can alter base pairing. Signup and view all the answers

What type of mutation does deamination of cytosine produce?

Transition mutation Signup and view all the answers

How does the presence of uracil affect DNA replication?

It causes a transition mutation by pairing with adenine. Signup and view all the answers

What type of mutations does nitrous acid produce exclusively?

Transition mutations Signup and view all the answers

What is a mutagen?

An agent that elevates the spontaneous mutation rate. Signup and view all the answers

What happens when deamination occurs in cytosine induced by nitrous acid?

Cytosine is converted into uracil, pairing with adenine. Signup and view all the answers

Which of the following pairs correctly identifies a transition mutation caused by hydroxylamine?

C · G→T · A Signup and view all the answers

What is the role of base analogs in mutagenesis?

They can be mistakenly incorporated during nucleic acid synthesis. Signup and view all the answers

Which of the following best describes the effect of deamination on cytosine?

It transforms into uracil, altering its pairing properties. Signup and view all the answers

What is a characteristic of mustard gas as an alkylating agent?

It adds alkyl groups to nucleotide bases like other alkylating agents. Signup and view all the answers

What distinguishes hydroxylamine from other mutagens in its effect on DNA?

It exclusively affects cytosine without changing thymine. Signup and view all the answers

What leads to an error being retained through DNA replication?

The absence of a complementary base. Signup and view all the answers

Which of the following correctly describes the process of spontaneous mutation?

It can occur due to chemical changes in DNA. Signup and view all the answers

What happens after an incorrect nucleotide is incorporated into a DNA strand due to an apurinic site?

It causes a replication error in the next round of synthesis. Signup and view all the answers

Study Notes

Mutation

Genetic code is a series of codons, each coding for an amino acid in a protein.
Codons are sequences of three nucleotides.
Addition or deletion of nucleotides alters the entire protein sequence.
Modifications occur to initial mRNA transcripts before export to the cytoplasm.

mRNA Modifications

5' cap: An adenine (A) or guanine (G) base is added to the 5' end of mRNA, which is further modified by the addition of GTP.
3' poly-A tail: A series of adenine (A) residues (100-200) are added to the 3' end. This tail protects mRNA from degradation.

Eukaryotic Genes

Many eukaryotic genes contain non-coding sequences (introns) that are not present in the final mRNA.
Coding sequences (exons) are expressed.
Pre-mRNA splicing: Introns are removed, and exons are joined to create mature mRNA. This process occurs in the nucleus.

Mutation Types

Point mutations: Changes in a single base pair of DNA.
Mutations: can be the cause of great suffering and also the source of life's evolution.
Mutations are the raw material of evolution.
Somatic mutations: Occur in somatic cells (non-sex cells).
Germ-line mutations: Occur in germ cells (sex cells).

Types of Gene Mutations

Base substitution
- Transition: purine to purine, or pyrimidine to pyrimidine
- Transversion: purine to pyrimidine, or pyrimidine to purine
Insertion or deletion (indel) mutation:
- Addition or removal of one or more base pairs. This can lead to frameshift mutations.

Spontaneous Mutations

Occur naturally during DNA replication.
Tautomeric shifts: Purines and pyrimidines exist in different chemical forms (tautomers).
Errors in DNA replication.
Spontaneous lesions: Such as depurination (loss of a purine base), where the purine is removed from the DNA. Deamination: spontaneous loss of an amino group (NH2).

Induced Mutations

Occur due to exposure to mutagens.
Chemical mutagens: Base analogs (similar structure to bases but different pairing properties like 5BU); alkylating agents (add alkyl groups to bases like EMS) and nitrous acid(can deaminate bases).
Physical mutagens: Ionizing radiation (X-rays, gamma rays), Ultraviolet (UV) light (creates pyrimidine dimers).

Molecular Consequences of Gene Mutations

Point mutations in non-coding regions.
Point mutation in coding regions
- Silent mutation
- Missense mutation
- Nonsense mutation.
- Frameshift mutations from indels
Forward mutation alters the wild-type phenotype.
Reverse mutation reverses a forward mutation from mutant to wild-type.
Neutral mutations have no change in function.
Loss-of-function mutations: reduced or absent protein function.
Gain-of-function mutations: new or altered protein function.
**

Ames Test

Bacteria (Salmonella) used in a model to assess mutagenicity.
Compounds are tested for the ability to cause mutations, often as a first step to evaluating their carcinogenicity.
Liver enzymes needed to activate some compounds to mutagenic forms are included in the assay.

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Description

Explore the intricate processes of genetic mutations and mRNA modifications in this quiz. Learn how codons, introns, and exons play crucial roles in protein synthesis and gene expression. Test your understanding of point mutations and the significance of mRNA processing in eukaryotic cells.