Question

Choose the true statement about housekeeping genes in Escherichia coli.

Housekeeping genes are constitutively expressed.

A housekeeping gene's expression should stop when the cell is placed in a different environment.

Most of E. coli's genome encodes housekeeping genes.

Examples of housekeeping genes in E. coli include antibiotic resistance genes and lactose catabolism genes.

Choose the frameshift mutation that is the riskiest for a prokaryotic cell.

A deletion of three DNA nucleotides from the DNA template strand

A deletion of one codon on the mRNA strand

A substitution of an A for a T on the DNA template strand

An insertion of one DNA nucleotide in the DNA template strand

The table below shows the results for a theoretical Ames test to determine if various artificial sweeteners are mutagens. Based on the data, which chemical compound(s) is/are likely to be mutagens? To be marked correct, you'll need to select all mutagens, as there may be more than one correct answer.

Table 1. Number of Salmonella typhimurium colonies that grew following the Ames Test

Chemical tested	Number of Colonies on Minimal Media Lacking Histidine
Aspartame	32
Sucralose	20
Acesulfame-K	4
Dulcin	5
None (Control)	5

The table below shows the results for a theoretical Ames test to determine if various artificial sweeteners are mutagens. Based on the data, which chemical compound(s) is/are likely to be mutagens? To be marked correct, you'll need to select all mutagens, as there may be more than one correct answer.

Table 1. Number of Salmonella typhimurium colonies that grew following the Ames Test

Chemical tested	Number of Colonies on Minimal Media Lacking Histidine
Aspartame	32
Sucralose	20
Acesulfame-K	4
Dulcin	5
None (Control)	5

Dulcin

Sucralose

Aspartame

Acesulfame-K

How do retrotransposons differ from DNA transposons?

Retrotransposons exist as RNA in the host cell's genome, while DNA transposons exist as DNA in the host cell's genome.

Retrotransposons excise themselves from the genome and insert themselves into another part of the genome, while DNA transposons do not have this capability.

Retrotransposons rely on reverse transcriptase for transposition, while DNA transposons do not.

Retrotransposons insert into the host cell genome as DNA-RNA hybrid molecules, while DNA transposons insert into DNA as double-stranded DNA molecules.

Chlamydia trachomatis is an obligate intracellular bacterium that causes the sexually transmitted disease chlamydia. When this bacterium was first discovered, it was classified as a virus. However, it was later re-classified as a bacterium. Which of the following is the most likely reason why C. trachomatis was reclassified as a living bacterial cell as opposed to a nonliving viral particle?

Chlamydia trachomatis has a genome consisting of double-stranded DNA.

Chlamydia trachomatis is capable of performing metabolic processes.

Chlamydia trachomatis lacks membrane-bound organelles, such as a nucleus.

Chlamydia trachomatis is visible with a compound light microscope.

PLEASE HELP!

Answer 1

1. Option A is correct.
House-keeping genes are constitutively expressed. They are required for basal metabolism.

2. Option D is correct.
Insertion of a single nucleotide in the DNA would cause a greater effect on the phenotype due to a frameshift mutation.

3. Option A is correct.
Aspartame treatment caused a greater number of revertants. So, it could be a potential mutagen.

4. Option A is correct.
Aspartame treatment caused a greater number of revertants. So, it could be a potential mutagen.

5. Option A is correct.
Retro-transposons utilize a DNA intermediate produced by reverse transcription in their life cycle.