Test: Genetic Mutations - 1 - MCAT MCQ

In sickle-cell disease, the substitution of glutamate with valine in the hemoglobin protein results in the formation of abnormal hemoglobin molecules called HbS. These HbS molecules have a tendency to aggregate and form long fibers when deoxygenated. This aggregation causes the red blood cells to assume a sickle shape, leading to various complications. The abnormal aggregation interferes with the normal function of hemoglobin, reducing its ability to adequately carry oxygen, resulting in oxygen deprivation in tissues and organs. Therefore, option A is the correct answer.

Sickle-cell disease is caused by a specific point mutation in the hemoglobin gene, resulting in a non-conservative missense mutation. The mutation involves a substitution of a single nucleotide, leading to a change in the amino acid sequence of the hemoglobin protein. In sickle-cell disease, a glutamate amino acid is replaced by a valine amino acid at a specific position in the hemoglobin protein. This change in amino acid alters the structure and function of the hemoglobin molecule, leading to the characteristic sickle-shaped red blood cells and the associated symptoms of the disease. Therefore, option A is the correct answer.

A nonsense mutation is a type of genetic mutation that introduces a premature stop codon in the DNA or mRNA sequence. A stop codon is a specific sequence of three nucleotides (UAA, UAG, or UGA) that signals the termination of protein synthesis during translation. When a nonsense mutation occurs, it results in the substitution of a normal codon (which codes for an amino acid) with a premature stop codon. This premature stop codon prematurely terminates the translation process, leading to the production of a truncated or non-functional protein. Therefore, option D is the correct answer.

A silent mutation is a type of genetic mutation that occurs in the DNA sequence but does not result in a change in the amino acid sequence of the protein. This is because the genetic code is redundant, meaning that multiple codons can code for the same amino acid. For example, there are multiple codons that code for the amino acid alanine (e.g., GCU, GCC, GCA, GCG). If a silent mutation occurs and changes one of these codons to another codon that still codes for alanine, there will be no change in the resulting protein. Since the same amino acid is incorporated into the protein, its structure and function are unaffected. Therefore, option D is the correct answer.

Explanation: A non-conservative mutation is a type of genetic mutation that results in the substitution of one amino acid with a different amino acid during protein synthesis. In this type of mutation, the new amino acid has different biochemical properties, such as size, charge, hydrophobicity, or reactivity, compared to the original amino acid. This can have significant effects on the structure and function of the protein. In contrast, conservative mutations involve the substitution of an amino acid with another amino acid that has similar biochemical properties. Options B, C, and D are not accurate descriptions of a non-conservative mutation. Therefore, option A is the correct answer.

A transition is a type of point mutation where a purine base (adenine or guanine) is replaced by another purine base, or a pyrimidine base (thymine or cytosine) is replaced by another pyrimidine base, within a DNA molecule.

In option B, the substitution of guanine (G) with adenine (A) represents a transition because both bases are purines. The substitution does not change the category of the base.

Option A represents a transversion, as it involves the substitution of a purine (adenine) with a pyrimidine (thymine). Option C also represents a transversion, as it involves the substitution of a purine (guanine) with another purine (cytosine). Option D represents a transversion, as it involves the substitution of a pyrimidine (thymine) with a purine (adenine).

Therefore, the correct answer is B. G → A, which represents a transition.

Large-scale deletions can involve not only the removal of DNA sequences but also alterations in the surrounding chromatin structure and epigenetic modifications. These changes can affect the regulation of nearby genes and alter the overall chromatin landscape. Therefore, option C is the accurate statement regarding large-scale deletions.

Endogenous mutagens are substances or factors that naturally occur within an organism and have the potential to cause mutations in DNA. Nitric oxide (NO) is produced endogenously in the body and can act as a mutagen, leading to DNA mutations in both bacteria and human cells. While DNA mutations can be associated with cancer formation, in this case, the statement mentions that the mutations caused by NO are not always linked to cancer. Therefore, NO would be considered an endogenous mutagen, as it is a naturally occurring molecule that can induce genetic changes.

Antioxidant compounds play a crucial role in counteracting the actions of damaging reactive oxygen species (ROS) in the body. Reactive oxygen species are highly reactive molecules that can cause oxidative damage to cells, DNA, proteins, and lipids. They are produced as byproducts of normal cellular metabolism and can also be generated due to external factors such as exposure to pollutants, radiation, or certain chemicals.

Antioxidants work by neutralizing or scavenging reactive oxygen species, reducing their harmful effects on cells. They donate electrons or hydrogen atoms to reactive oxygen species, effectively stabilizing them and preventing them from causing damage to cellular components. By doing so, antioxidants help protect cells from oxidative stress and maintain their normal function.

Intercalation of ethidium bromide into DNA refers to the insertion of ethidium bromide molecules between the base pairs of DNA. This intercalation causes the DNA molecule to deform or undergo structural changes. Ethidium bromide is a fluorescent dye commonly used in molecular biology laboratories to visualize DNA in gel electrophoresis.

It is important to note that intercalation of ethidium bromide into DNA does not directly lead to constitutive expression of oncogenes, displacement of RNA polymerase, or missense mutations. Its primary effect is the distortion of the DNA helix, which can affect various processes involving DNA, such as DNA replication, transcription, and DNA-protein interactions.