BIOL 107 606 Fundamentals of Microbiology

Correct answer B: mRNA

Detailed Explanation:

B. mRNA (messenger RNA) is the correct answer because mRNA's primary function is to carry genetic information from the nucleus (where DNA is located) to the ribosomes in the cytoplasm. This process is crucial for protein synthesis. In eukaryotic cells, the process begins with transcription, where an mRNA molecule is synthesized as a complementary copy of the DNA code. This mRNA molecule then exits the nucleus and enters the cytoplasm, where it acts as a template for the ribosome to produce proteins during translation. The ribosome reads the codons (three-nucleotide sequences) on the mRNA to assemble amino acids into the correct order, creating proteins.

Explanation of Incorrect Options:

A. tRNA (transfer RNA):

While tRNA plays a crucial role in protein synthesis, it is not the correct answer. tRNA's primary function is not to carry genetic information from the nucleus to the ribosome. Instead, tRNA works in the cytoplasm and assists in the translation of the mRNA sequence. Specifically, tRNA molecules bring the correct amino acids to the ribosome by matching their anticodons with the corresponding codons on the mRNA strand. In summary, tRNA helps decode the mRNA, but it does not carry genetic information from the nucleus.

C. DNA (deoxyribonucleic acid):

DNA is the molecule that stores genetic information in the cell, but it does not leave the nucleus in eukaryotic cells. DNA is used as a template to create mRNA during the process of transcription, but DNA itself does not directly transport genetic coding information to the ribosome. Therefore, it does not fit the question, as it remains confined within the nucleus for cellular processes like replication and transcription.

D. TRNA:

This is simply a typo of option A (tRNA), and as mentioned earlier, tRNA does not carry genetic information from the nucleus to the ribosome. It assists in protein synthesis by translating the mRNA into an amino acid sequence. So, this option is incorrect for the same reasons as A.

Summary:

The correct molecule that carries genetic coding information from the nucleus to the ribosome in the cytoplasm is mRNA (Option B). It is transcribed from DNA in the nucleus and transported to the cytoplasm, where it serves as a template for protein synthesis during translation.

Correct Answer B: Hydrolysis

Explanation:

Hydrolysis is a chemical reaction in which water is added to break the bonds between monomers in a polymer. This process splits large molecules into smaller subunits, and it’s essential in digestion and cellular metabolism.

Why the other options are incorrect:

A) Dehydration synthesis:

This is the opposite of hydrolysis. It joins monomers by removing water to form polymers.

C) Oxygenation:

This involves adding oxygen to a molecule, commonly in metabolic or combustion processes, not polymer breakdown.

D) Hydrogenation:

This involves the addition of hydrogen, typically to unsaturated fats, and is not related to breaking polymers.

Correct Answer B: Life needs to arise from pre-existing life

Explanation:

The theory of biogenesis states that all living organisms come from other living organisms, not from non-living material. This concept was solidified by Louis Pasteur’s experiments, which disproved the idea of spontaneous generation (the belief that life could emerge from non-living matter).

Why the other options are incorrect:

A) Bacteria can reproduce using the process of binary fission:

This describes a method of reproduction, not the core principle of biogenesis.

C) Life can arise from non-living matter:

This reflects spontaneous generation, which is the opposite of the theory of biogenesis.

D) A specific bacteria can be identified as the cause of a specific disease:

This refers to Koch’s postulates, which relate to germ theory, not biogenesis.

Correct Answer B: It is covered with ribosomes

Explanation:

The rough endoplasmic reticulum (RER) appears "rough" under a microscope because its outer surface is studded with ribosomes. These ribosomes are the sites of protein synthesis, giving the RER its characteristic bumpy texture.

Why the other options are incorrect:

A) It has a high density of receptor proteins on its membrane:

While membranes can have receptors, this is not what gives the RER its rough appearance.

C) Its surface is highly folded to increase surface area:

This describes many cellular membranes, but folding alone does not make the RER rough.

D) It is covered with cilia:

Cilia are hair-like structures found on the surface of some cells, not on internal organelles like the RER.

Correct Answer B: To demonstrate that a disease is caused by a specific organism

Explanation:

Koch's postulates are a set of criteria developed by Robert Koch in the 19th century to establish a cause-and-effect relationship between a specific microbe and a specific disease. They provide a scientific framework to prove that a particular microorganism is the causative agent of an infectious disease.

The four postulates involve:

The microorganism must be found in all organisms suffering from the disease but not in healthy ones.

It must be isolated and grown in pure culture.

The cultured microbe must cause disease when introduced into a healthy organism.

It must then be re-isolated from the newly infected host and shown to be the same organism.

Why the other options are incorrect:

A) To identify and completely characterize a microorganism:

This may happen during the process, but it is not the primary goal of Koch’s postulates.

C) To isolate and grow microorganisms:

Isolation is one step in the postulates, but not the main purpose.

D) To develop a vaccine against a microorganism:

Vaccine development is not related to Koch’s postulates and comes much later after the organism has been identified as a disease cause.

Correct Answer D: 0%

Explanation:

Let’s assign alleles:

A = normal (healthy) allele

a = sickle cell allele (recessive)

Mother’s genotype: Aa (heterozygous — carrier)

Father’s genotype: AA (homozygous dominant — healthy)

Results:

50% chance the child will be AA (healthy, not a carrier)

50% chance the child will be Aa (carrier, but healthy)

0% chance the child will be aa (have the disease)

Since two copies of the sickle cell allele (aa) are required for the disease, and the father contributes only A alleles, no child can inherit two "a" alleles.

So, the probability the child will have sickle cell anemia is 0%.

Correct Answer C: Metaphase

Detailed Explanation of the Correct Answer:

C. Metaphase is the correct answer because during this phase of mitosis, the chromosomes fully attach to the spindle fibers at their centromeres and are aligned along the metaphase plate, which is the center line (equator) of the cell. This alignment ensures that when the chromosomes are later pulled apart, each new daughter cell will receive an identical set of chromosomes.

This precise organization is crucial for equal and accurate genetic distribution.

Explanation of Why the Other Options Are Incorrect:

A. Interphase – This is the preparation phase before mitosis. DNA is replicated, but chromosomes are not visible, and no spindle fibers are formed yet.

B. Telophase – In this phase, chromosomes reach the poles of the cell, the nuclear membrane reforms, and chromosomes begin to uncoil. There is no alignment or migration to the center.

D. Anaphase – This phase comes after metaphase. It is when the sister chromatids separate and move to opposite poles of the cell, not when they align at the center.

E. Prophase – In this early phase of mitosis, chromosomes condense and become visible, and spindle fibers start to form, but chromosomes have not yet aligned at the center.

Summary:

During metaphase, chromosomes attach to spindle fibers and line up at the center of the cell, ensuring accurate division. Therefore, the correct answer is C. Metaphase.

Correct Answer B: Lowercase letter

Detailed Explanation of the Correct Answer:

B. Lowercase letter is the correct answer because, by genetic convention, recessive alleles are represented using lowercase letters (e.g., a). This indicates that two copies of the recessive allele (homozygous recessive, aa) are needed for the trait to be expressed in the organism. In contrast, dominant alleles are written with uppercase letters (e.g., A) and require only one copy to be expressed.

Explanation of Why the Other Option Is Incorrect:

A. Uppercase letter – This format is used to represent dominant alleles, not recessive ones. Dominant alleles mask the effect of recessive alleles when present.

Summary:

Recessive alleles are always written using lowercase letters to distinguish them from dominant alleles. Therefore, the correct answer is B. Lowercase letter.

Correct answer A: Ribosomes

Detailed Explanation:

A. Ribosomes

Ribosomes are not involved in the process of transcription. Ribosomes are primarily involved in translation, the process in which mRNA is read to build proteins. Translation occurs in the cytoplasm, where ribosomes use the mRNA transcript produced by transcription to assemble amino acids into a polypeptide chain (protein). In transcription, the focus is on creating an mRNA copy of a DNA sequence, not on protein synthesis. Therefore, ribosomes are not a part of the transcription process.

Explanation of Correct Involvement:

B. RNA polymerase

RNA polymerase is essential for transcription. This enzyme binds to the DNA at the promoter region and synthesizes a complementary strand of RNA based on the DNA template. It is the core enzyme responsible for transcribing genetic information from DNA to mRNA in both prokaryotic and eukaryotic cells.

C. DNA

DNA is absolutely involved in the process of transcription. It serves as the template for mRNA synthesis. The sequence of nucleotides in the DNA is transcribed into an RNA molecule, which will later be translated into a protein. Without DNA, there would be no genetic information to transcribe.

D. Transcription factors

Transcription factors are proteins that help initiate and regulate the transcription process. They bind to specific regions of the DNA (such as the promoter) and assist RNA polymerase in beginning the transcription process. They are crucial for ensuring the gene is expressed at the right time and in the right cells.

Summary:

Ribosomes are not involved in transcription; they are involved in translation. Transcription focuses on creating RNA from DNA, a process driven by RNA polymerase, DNA, and transcription factors. The correct answer is A. Ribosomes.