Question 1

Excised introns form structures called lariats.

Accepted Answer

This is true. Lariats are formed when the intron is looped and spliced to form a circular structure.

Question 2

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 3

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, as well as the expression of DNA polymerase and RNA polymerase, are characteristic features of eukaryotic cells. Additionally, the presence of a promoter region and the absence of operons are also more commonly observed in eukaryotes. Therefore, it is most likely that the unidentified cell is eukaryotic.

Question 4

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 (threonine).

Question 5

The field of genomics refers to

Accepted Answer

Genomics refers to the study of an organism's complete genome, which includes all types of DNA, such as chromosomal, plasmid, mitochondrial, and chloroplast DNA. Therefore, option A is the best choice as it includes all these types of DNA in its definition.

Question 6

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

The answer of You have taken E.coli strain A which...

Question 7

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, one strand of the double-stranded DNA molecule must grow continuously toward the replication fork as it opens, while the other strand must grow in fragments, away from the fork. This is due to the antiparallel nature of the two parent strands, which run in opposite directions. This process is known as semi-conservative replication.

Question 8

All mutations are not beneficial to the cell.

Accepted Answer

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

Question 9

The fields of genomics and proteomics differ in that

Accepted Answer

Genomics deals with the study of the entire genome, including DNA sequencing, mapping, and analysis, while proteomics is the study of expressed proteins in cells and tissues. Therefore, option B is the correct answer. Option A and D are incorrect as they do not provide accurate descriptions of the two fields. Option C is incorrect as the resulting proteins from an organism's chromosomes are studied in proteomics, not in the field of genomics.

Question 10

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

Accepted Answer

The correct sequence of events for protein synthesis to begin is that the 5' end of the mRNA binds to the small ribosomal subunit, and the large subunit joins, creating the P and A sites where reactions between codons on the mRNA and anticodons on tRNA are stabilized. This is the first step in translation and precedes the formation of the peptide bond between amino acids. The other choices are incorrect because they either have incorrect base pairing information or describe events that occur later in translation.

Question 11

Introns have no detectable functions.

Accepted Answer

While introns were originally thought to have no function, it is now known that they play important roles in gene regulation and alternative splicing.

Question 12

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

Accepted Answer

Rifamycin selectively inhibits M. tuberculosis by binding to bacterial RNA polymerase, and thus halting transcription, without affecting the host's eukaryotic protein synthesis machinery. This is because bacterial RNA polymerase has a slightly different structure compared to eukaryotic polymerase, making it a good target for selective toxicity.

Question 13

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 focuses on proteins, while genomics focuses on the entire genome.

Question 14

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

Accepted Answer

The genotype refers to the entire genetic makeup of an organism, including both expressed and non-expressed genes. The phenotype, on the other hand, refers to the observable traits and characteristics of an organism that result from the interaction between its genotype and the environment. Only a portion of an organism's genotype is expressed into its phenotype, as not all genes are active or functional at all times. Therefore, option D correctly states that the genotype represents all of the genetic material in an organism, while the phenotype represents only the expression of that genetic material into observable traits.

Question 15

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 16

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 17

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

Accepted Answer

The mechanism of DNA synthesis differs between the two new daughter strands during replication because DNA polymerase can only add nucleotides to the 3' end of the growing strand, and the DNA strands are antiparallel to each other. Therefore, one daughter strand, the leading strand, can be synthesized continuously in the 5' to 3' direction, while the other daughter strand, the lagging strand, must be synthesized in short fragments called Okazaki fragments in the opposite direction as the replication fork moves forward.

Question 18

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

The Ames test is used to determine whether a chemical is mutagenic by exposing bacteria to the chemical and observing whether it causes a mutation that allows the bacteria to grow on agar lacking the amino acid histidine. If there are many colonies growing on the agar, it suggests that the chemical being tested is mutagenic and has caused mutations in the bacteria that allow them to produce histidine on their own.

Question 19

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

Accepted Answer

DNA photolyase is an enzyme that uses visible light to repair UV-induced DNA damage by breaking the cyclobutane pyrimidine dimers.

Question 20

Repressible operons are normally turned on in the cell.

Accepted Answer

Repressible operons are typically turned on in the cell unless a specific molecule, called a corepressor, binds to the repressor protein and causes it to bind to the operator, blocking transcription.

Quiz 9: Microbial Genetics