Free USABO Genetics and Cell Biology Questions and Answers — Questions and Answers
Question 1: In the extracellular matrix of an animal cell, you would like to test the binding partner of integrins in vitro. Integrins would most likely require a firm attachment to which of these options?
- Actin (Correct answer)
- Myosin
- Dynein
- Kinesin
- Cyclin
Correct answer: Actin
Explanation: <br> Integrins are transmembrane proteins that serve as receptors for extracellular matrix components, such as fibronectin, collagen, and laminin. They play a crucial role in cell adhesion, migration, and signaling. Integrins typically bind to actin filaments inside the cell, forming focal adhesions that anchor the cell to the extracellular matrix. This interaction provides a firm attachment for cell adhesion and movement. Myosin, dynein, and kinesin are motor proteins involved in intracellular transport and movement along cytoskeletal filaments, while cyclin is a regulatory protein involved in cell cycle control and not directly associated with integrin binding in the extracellular matrix.
Question 2: You are working with Dr. Lee at the University of Wisconsin-Madison to investigate cytokinesis in a newly discovered marine worm. You generated antibodies to conserved proteins involved in cell division in another organism to look for proteins that localize to important structures during cell division. What molecular motor protein should you look for in the contractile ring?
- Actin
- Myosin (Correct answer)
- Dynein
- Kinesin
- Cyclin
Correct answer: Myosin
Explanation: <br> The contractile ring, which forms during cytokinesis, is primarily composed of actin and myosin filaments. Myosin II, a molecular motor protein, interacts with actin filaments and plays a central role in generating contractile force during cytokinesis. As the contractile ring contracts, myosin motors slide actin filaments inward, leading to the division of the cell into two daughter cells. Therefore, when investigating proteins that localize to the contractile ring during cytokinesis, one should look for myosin, which is essential for its function.
Question 3: An unnamed acid has a pKa value of 4.76. Which of the following is closest to the ratio of the concentration of its protonated to deprotonated forms in a pH environment of 6.8?
- 100:1
- 10:1
- 1:1
- 1:10
- 1:100 (Correct answer)
Correct answer: 1:100
Explanation: <br> The pH of the environment is higher than the pKa of the acid, so it's mostly deprotonated. When comparing the deprotonated form (A-) to the protonated form (HA), the ratio is approximately 1:100.
Question 4: Which scientist(s) is incorrectly matched with his/her/their discoveries?
- Frederick Griffith – discovery of transformation through bacteriophages. (Correct answer)
- Hershey and Chase – discovery of DNA as the hereditary material of cells.
- Chargaff – discovery that relative amounts of nucleotide bases varies among organisms.
- Watson and Crick – discovery of the double-helix structure of DNA.
- Meselson and Stahl – discovery of the semi-conservative replication of DNA.
Correct answer: Frederick Griffith – discovery of transformation through bacteriophages.
Explanation: <br> Frederick Griffith is incorrectly matched with his discovery. He is not associated with the discovery of transformation through bacteriophages. Instead, Frederick Griffith is known for his experiments with Streptococcus pneumoniae bacteria, which demonstrated the phenomenon of bacterial transformation, where harmless bacteria could become virulent through the uptake of genetic material from other bacteria.
Question 5: Which of the following amino-acid substitutions is LEAST likely to be disruptive to protein function?
- Lysine to glycine
- Cysteine to leucine
- Alanine to proline
- Aspartate to valine
- Alanine to valine (Correct answer)
Correct answer: Alanine to valine
Explanation: <br> Both alanine and valine are similar in size and hydrophobicity, so the change is less likely to cause significant disruption to the protein's structure or function compared to the other options.
Question 6: Which of the following is incorrect about operons?
- Operons can be switched off with a repressor.
- The lac operon is an inducible operon.
- In the presence of lactose and glucose, the lac operon will not be repressed.
- CAP is an activator of transcription when not bound to cAMP. (Correct answer)
- A mutation in the operator of the trp operon can lead to the overproduction of tryptophan.
Correct answer: CAP is an activator of transcription when not bound to cAMP.
Explanation: <br> CAP (catabolite activator protein) requires binding to cyclic AMP (cAMP) to become active as a transcription activator. When bound to cAMP, CAP activates transcription by binding to the CAP site in the DNA, enhancing the recruitment of RNA polymerase. Without cAMP binding, CAP cannot activate transcription.
Question 7: After Pete was infected with Chikungunya virus, his immune system developed immunoglobulins against the virus’s epitope with a peptide sequence VPRNAELGD. Which of the following mutated sequences will most likely lead to immune evasion? (Assume that the mutated virus retains function)
- APRNAELGD
- VPRQAELGD
- VPRNAELAD
- VPRNYELAD (Correct answer)
- VPRNAEIGD
Correct answer: VPRNYELAD
Explanation: <br> The mutation in option VPRNYELAD involves changing the amino acid at the fifth position from Glycine to Tyrosine. This alteration is more likely to lead to immune evasion as it significantly changes the peptide sequence within the epitope. Changing a small amino acid like Glycine to a larger one like Tyrosine can greatly affect the structure of the peptide and its recognition by the immune system. Thus, this mutation is most likely to result in immune evasion.
Question 8: Which process likely explains why exons of the tissue plasminogen activator (TPA) are also found in other proteins?
- Exon shuffling (Correct answer)
- Clonal selection
- Translocation
- Heterochrony
- Transposition
Correct answer: Exon shuffling
Explanation: <br> Exon shuffling is a process where exons from different genes are brought together, either through recombination events or transposition, to form new genes with novel functions. This process can result in the sharing of exons among different proteins, leading to the presence of common exons across multiple genes. Therefore, exon shuffling is the most likely explanation for why exons of TPA are also found in other proteins.
Question 9: Eye color in fruit flies shows an X-linked recessive mode of inheritance with red being the dominant phenotype and white being the recessive phenotype. Which of the following mating experiments best proves this observation?
- Mate is a heterozygous red-eye female fly with a red-eye male fly.
- Mate is a homozygous red-eye female fly with a white-eye male fly.
- Mate is a white-eye female fly with a red-eye male fly. (Correct answer)
- Mate is a white-eye female fly with a white-eye male fly.
- Mate is a heterozygous red-eye female fly with a white-eye male fly.
Correct answer: Mate is a white-eye female fly with a red-eye male fly.
Explanation: <br> This mating shows that white-eyed females result from inheriting the recessive allele from both parents, while red-eyed males demonstrate that eye color is inherited from the mother.
Question 10: A 30-year-old woman (is planning to have a child and visits a genetic counselor. The only observed genetic disorder in her immediate family is that her brother was afflicted by Hurler syndrome (also known as mucopolysaccharidosis type I), a monogenic, autosomal recessive metabolic disorder caused by a loss of function of a lysosomal enzyme named alpha-L iduronidase. Hurler syndrome manifests itself early in childhood and is often fatal. What is the probability that the woman is a carrier for a disease-causing allele of alpha-L iduronidase?
- ¼
- ½
- 9/16
- 2/3 (Correct answer)
- ¾
Correct answer: 2/3
Explanation: <br> If both parents are carriers (Aa), there are four possible combinations of alleles for their children: AA, Aa, Aa, and aa. <br><br> Out of these possibilities: <br> *Only one results in the woman being homozygous for the normal allele (AA). <br> *Two result in her being a carrier (Aa). <br> *One results in her being homozygous for the disease-causing allele (aa). <br><br> So, the probability that the woman is a carrier for a disease-causing allele is 2 out of 3.
Question 11: The ratio of synonymous to nonsynonymous mutations that a protein-coding gene experiences in a given period of time is frequently used to infer the evolutionary pressures acting upon that gene. In particular, let ω = dN / dS, where dN is the number of nonsynonymous mutations per nonsynonymous site, and dS is the number of synonymous mutations per synonymous site. Which of the following statements about ω and protein evolution is NOT correct?
- A viral protein that experiences strong selection from the host immune system is likely to have ω > 1.
- In the absence of selection, nonsynonymous changes are more likely to occur than synonymous changes at any given codon site.
- A gene paralog that is no longer expressed is likely to have ω = 1.
- For most genes, ω = 1. (Correct answer)
- A highly conserved housekeeping gene is likely to have ω < 1.
Correct answer: For most genes, ω = 1.
Explanation: <br> The statement that is NOT correct is: For most genes, ω = 1. <br> In reality, most genes don't evolve neutrally, so their ω values vary depending on the evolutionary pressures they face.
Free USABO Genetics and Cell Biology Questions and Answers
In the extracellular matrix of an animal cell, you would like to test the binding partner of integrins in vitro.
Integrins would most likely require a firm attachment to which of these options?