Question 1

A bacterial cell has replicated its plasmid, and when this cell divides into 2 daughter cells, each cell receives one copy of the plasmid.This is an example of horizontal gene transfer.

Accepted Answer

This is an example of vertical gene transfer, where genetic material is passed from parent to offspring during cell division, not horizontal gene transfer, which involves the transfer of genetic material between different organisms.

Question 2

A mutation has occurred during DNA replication while the cell was preparing to divide.As a result of this, the codon ACU of mRNA has now become ACC.Interestingly, there is no change to the protein being made.Why not?

Accepted Answer

This is a silent mutation because the change from ACU to ACC still codes for the same amino acid, which is threonine. Therefore, there is no change to the protein being made, as the same amino acid is still incorporated into the protein.

Question 3

All mutations are not beneficial to the cell.

Accepted Answer

The answer of All mutations are not beneficial to the...

Question 4

Induced mutations are initiated by errors in DNA replication.

Accepted Answer

Induced mutations are caused by exposure to mutagens, such as chemicals or radiation, and not by errors in DNA replication.

Question 5

Excised introns form structures called lariats.

Accepted Answer

Excised introns are formed into lariat structures through a covalent linkage between the 5' and 2' positions of the intron.

Question 6

Lactose is a corepressor in the lac operon.

Accepted Answer

Lactose acts as an inducer in the lac operon, not a corepressor. It binds to the repressor, causing it to change shape and release from the operator, allowing transcription of the operon.

Question 7

Looking at your results of the Ames test using bacteriological agar medium plates lacking the amino acid histidine, you find that there are many colonies growing on the agar.How do you interpret this result?

Accepted Answer

Based on the information provided, the Ames test is being used to determine if a chemical is mutagenic or not. If there are many colonies growing on the agar medium plates lacking histidine, it suggests that the chemical being tested caused mutations in the bacteria, allowing them to grow on the medium despite the lack of histidine. Therefore, choice B is the most appropriate interpretation of the result. Choices A, C, and D are not relevant to the Ames test or the result described.

Question 8

The fields of genomics and proteomics differ in that

Accepted Answer

Genomics is the study of an organism's entire genome, while proteomics is the study of expressed proteins. Genomics focuses on analyzing genetic information, including DNA sequence, gene expression, and gene structure. In contrast, proteomics focuses on the study of proteins, including their structure, function, and interactions. The main difference between the two fields is their focus on genetic versus expressed information.

Question 9

Repressible operons are normally turned on in the cell.

Accepted Answer

Repressible operons are normally turned on in the cell, but can be turned off when the end product of the pathway they control accumulates and acts as a co-repressor.

Question 10

DNA polymerase can catalyze a dehydration synthesis reaction only at the 3'carbon of the daughter strand of DNA. This means that

Accepted Answer

Since DNA polymerase can only catalyze a dehydration synthesis reaction at the 3'carbon of the daughter strand, one strand will have to grow towards the fork as it opens, and the other strand will grow in fragments away from the fork due to the antiparallel nature of the strands. This is known as the leading and lagging strand synthesis. The leading strand extends towards the replication fork as the nucleotide bases are exposed, while the lagging strand is synthesized in fragments called Okazaki fragments, which extend away from the fork.

Question 11

In order for protein synthesis to begin, which of the following statements reflects the correct sequence of events?

Accepted Answer

Protein synthesis begins with the binding of the small ribosomal subunit to the 5' end of the mRNA. The large subunit then joins, creating the P and A sites where reactions between codons on the mRNA and anticodons on tRNA are stabilized. The initiation codon AUG on the mRNA then base pairs with the anticodon UAC on the initiator tRNA, allowing the large subunit to attach and start protein synthesis. Choice A is incorrect because it reverses the roles of the AUG codon and UAC anticodon. Choice B is incorrect because it describes a step that occurs during elongation, not initiation. Choice D is incorrect because it reverses the roles of the mRNA and tRNA in base pairing.

Question 12

Introns have no detectable functions.

Accepted Answer

Introns have various functions such as regulating gene expression, alternative splicing, and influencing genomic evolution.

Question 13

You have taken E. coli strain A which has its own plasmids, and mixed it with E. coli B strain without plasmids. E. coli B cells now have plasmids but, in addition, they also carry some genes from E. coli A strain. What has happened is

Accepted Answer

Hfr (High frequency of recombination) cells can transfer chromosomal genes to a recipient cell during conjugation, which explains why E. coli B now has plasmids and genes from E. coli A.

Question 14

Proteomics is the study of all proteins that are expressed by an organism, whereas genomics refers to the study of the organism's entire genome, not simply the protein-coding regions.

Accepted Answer

Proteomics specifically focuses on the study of proteins, while genomics is a broader field that encompasses the study of an organism's entire genetic makeup, including non-coding regions.

Question 15

An unidentified cell was found to contain introns and exons.It also expresses DNA polymerase and RNA polymerase.Although it exhibits a promoter region, it has no operons.You conclude that this cell

Accepted Answer

The presence of introns and exons, along with DNA and RNA polymerase and a promoter region, suggest that this cell is eukaryotic. Prokaryotes generally do not have introns and exons or a complex transcriptional machinery. The absence of operons is not a definitive characteristic of either prokaryotes or eukaryotes. The option of it being a virus is unlikely because viruses do not have introns and exons within their genome.

Question 16

The antibiotic rifamycin is selectively toxic in blocking protein synthesis in Mycobacterium tuberculosis because

Accepted Answer

Rifamycin binds preferentially to bacterial RNA polymerase rather than the eukaryotic protein, effectively halting transcription in the pathogen but not the host. This selectively targets the bacterial cells while leaving the host cells relatively unharmed.

Question 17

DNA photolyase, in the presence of visible light, can repair DNA damage due to ultraviolet radiation.

Accepted Answer

DNA photolyase is a type of enzyme that repairs DNA damage such as thymine dimers caused by UV radiation. It uses visible light in the blue or green spectrum to break the chemical bonds between the damaged DNA strands, restoring the DNA to its original state.

Question 18

The mechanism of DNA synthesis differs between the two new daughter strands during replication.This is due to the fact that

Accepted Answer

The DNA strands run antiparallel to each other, with one strand being 5' to 3' and the other strand being 3' to 5'. Therefore, the DNA polymerase can only add nucleotides to the 3' end of the growing strand, resulting in the leading and lagging strands being synthesized differently.

Question 19

The fundamental difference between an organism's genotype and its phenotype is that

Accepted Answer

The genotype refers to all of the genetic material in the organism including both expressed and non-expressed genes, while the phenotype represents only the observable traits that result from the expression of the genes. Thus, the genotype can include non-coding segments of DNA or genes that are not currently being expressed.

Question 20

The field of genomics refers to

Accepted Answer

The field of genomics refers to the study of an organism's complete genome, including plasmid, mitochondrial, and chloroplast DNA.

Option B is not correct because genomics is not limited to just chromosomal DNA. Option C is too limiting because genomics is not just focused on plasmids. Option D excludes the study of viral genomes, which is also a part of genomics.

Quiz 9: Microbial Genetics