MCB 100- Chapter 13: Characterizing and Classifying Viruses, Viroids, and Prions

What is the term used to describe viral nucleic acid surrounded by a protein "shell"? a. Nucleocapsid b. Icosahedron c. Capsomere d. Capsid

a. Nucleocapsid - A nucleocapsid is the term used to describe the viral nucleic acid in association with its capsid, the protein shell surrounding its genome.

How can viruses be distinguished from eukaryotic and prokaryotic organisms? a. Viruses are acellular. b. Viruses may only be observed with a light microscope. c. Viruses contain more genetic material than eukaryotic and prokaryotic organisms. d. Unlike eukaryotes and prokaryotes, all viruses have RNA genomes.

a. Viruses are acellular. -Viruses are small, acellular, obligate intracellular parasites that consist of a small amount of genetic material enclosed in a protein shell.

How is latency of animal viruses different from lysogeny of phages? a. Animal viruses are not induced or excised from the host's DNA. b. Latent viruses emerge from the cell by lysis; lysogenic viruses bud from the cell. c. Latency involves enveloped viruses, while lysogeny does not. d. Latency involves RNA viruses; lysogeny involves DNA viruses.

a. Animal viruses are not induced or excised from the host's DNA. - Latency is permanent; lysogeny is reversible.

List the steps of lytic phage replication in order. a. Attachment, entry, synthesis, assembly, and release b. Synthesis, assembly, entry, attachment, and release c. Entry, attachment, synthesis, assembly, and release d. Attachment, synthesis, entry, assembly, and release

a. Attachment, entry, synthesis, assembly, and release - The virus attaches to the bacterium, the viral genome enters the cell, cellular machinery synthesizes viral proteins and nucleic acid, the cell breaks open, and complete viral particles are released from the cell.

Which part of animal viruses is involved in membrane fusion with a host cell? a. Envelope b. Glycoprotein spikes c. The capsid d. Viral nucleic acid

a. Envelope - A viral envelope, which was derived from a membrane of a host cell that replicated the virus, can fuse with the cytoplasmic membrane of a cell to infect it.

What is transduction? a. Host DNA is packaged into a viral capsid by chance and is transferred to a new host cell. b. DNA from the virus is introduced into a new host cell when the tail of the virus punctures the host nucleus. c. Viral DNA enters a new host. d. During viral release from a cell, some of the host DNA sticks to the outside of the virion and is transmitted into the next cell.

a. Host DNA is packaged into a viral capsid by chance and is transferred to a new host cell. - Pieces of host DNA floating in the cytoplasm may be packaged in nearby assembling virions and be transferred to another cell infected by that transducing virion.

What type of organisms do phages infect? a. Plants b. Bacteria c. Animals d. Protozoa

b. Bacteria - Phages (or bacteriophages) infect bacteria. Press enter after select an option to check the answer Animals

Where does an enveloped virus get its envelope? a. From the bacterial cell wall b. From a membrane of its host cell c. From the host immune system d. From host proteins

b. From a membrane of its host cell

How can prions be destroyed? a. Soaking in detergent solution for four hours b. Heating to 482°C for four hours c. Rinsing with a 10% bleach solution d. Boiling for 2 hours

b. Heating to 482°C for four hours - Heating to 482°C for four hours or autoclaving at 132°C in concentrated sodium hydroxide for one hour deactivates prions.

What are viroids? a. Virus-like particles that cause disease in bacteria b. Short, naked stretches of RNA that do not code for proteins but cause disease in plants c. Short, naked stretches of RNA that infect fungi d. Virus-like particles that cause disease in humans

b. Short, naked stretches of RNA that do not code for proteins but cause disease in plants - Viroids lack capsids (and so are not viruses), do not code for proteins, but do cause disease in plants.

How are lysogenic phages different from lytic phages? a. Lysogenic phages have dsDNA genomes, while lytic phages have ssRNA genomes. b. The genome of a lysogenic phage is integrated into its host genome. c. Lytic phages prevent reinfection of their host bacterium by the same type of phage, while lysogenic phages do not. d. Lytic phages can change the phenotype of a bacterium, while lysogenic phages do not.

b. The genome of a lysogenic phage is integrated into its host genome. - The genome of a lysogenic phage becomes a physical part of its host's DNA

What effect does lysozyme have on bacteria? a. Lysozyme punctures holes in bacterial cytoplasmic membranes. b. Lysozyme oxidizes bacterial cytoplasmic proteins. c. Lysozyme digests peptidoglycan, weakening their cell walls. d. Lysozyme inhibits bacterial DNA replication.

c. Lysozyme digests peptidoglycan, weakening their cell walls. - Lysozyme breaks down peptidoglycan, a component of bacterial cell walls, thereby weakening the cell walls. Gram-positive bacteria, which rely on their peptidoglycan layers for structural support, are especially sensitive to the action of lysozyme.

How do negative-sense single-stranded RNA (−ssRNA) viruses generate mRNA? a. Ribosomes facilitate transcription of −ssRNA. b. They first reverse transcribe their −ssRNA into DNA, then the DNA is transcribed into mRNA. c. They have an enzyme packaged in their capsids that transcribes −ssRNA into +ssRNA, which is used as mRNA and as a template for RNA replication. d. They use host cell enzymes to generate mRNA from their −ssRNA genome.

c. They have an enzyme packaged in their capsids that transcribes −ssRNA into +ssRNA, which is used as mRNA and as a template for RNA replication - RNA-dependent RNA transcriptase synthesizes mRNA from −ssRNA.

What is a continuous cell culture? a. A culture derived from normal diploid cells b. A culture of viruses maintained in a laboratory indefinitely. c. A culture derived from normal haploid cells. d. A cell culture derived from tumor cells

d. A cell culture derived from tumor cells - Tumor cells do not stop dividing, and viruses grown in tumor cells are called continuous cultures.

Name a structural difference between animal viruses and bacteriophages. a. Bacteriophages have glycoprotein spikes, while animal viruses do not. b. Animal viruses may have tails or tail fibers, while bacteriophages do not. c. The capsid of animal viruses enters the host cell, while those of bacteriophages stay outside the host cell. d. Animal viruses may be enveloped; bacteriophages are always naked.

d. Animal viruses may be enveloped; bacteriophages are always naked.

What type of genome do viruses have? a. A virus always has a single-stranded DNA (ssDNA) genome. b. Most cellular organisms have a genome consisting of double-stranded DNA (dsDNA), while viruses have a genome consisting of single-stranded RNA (ssRNA). c. Viruses have a double-stranded RNA (dsRNA) genome. d. Depending on the virus, viral genomes can be either DNA or RNA, either of which can be single stranded or double stranded.

d. Depending on the virus, viral genomes can be either DNA or RNA, either of which can be single stranded or double stranded.

Where does transcription occur in eukaryotic cells? a. In the cytosol b. In the rough endoplasmic reticulum (rough ER) c. In the lysosomes d. In the nucleus

d. In the nucleus - Transcription is the synthesis of RNA from a DNA template. In eukaryotic cells this occurs in the nucleus. After transcription RNA is transported to the cytoplasm where translation (protein synthesis) occurs.

What are the template and end-product of the enzyme reverse transcriptase? a. Protein is the template and RNA is the end-product. b. RNA is the template and protein is the end-product. c. cDNA is the template and RNA is the end-product. d. RNA is the template and cDNA is the end-product.

d. RNA is the template and cDNA is the end-product. - Reverse transcription is the synthesis of DNA from an RNA template. This DNA is then called cDNA (for complementary DNA). The enzyme, reverse transcriptase, that catalyzes this reaction is a commonly used tool in recombinant DNA technology.

What are the differences between DNA and RNA? a. Pyrimidines found in RNA are thymine and cytosine. b. DNA always functions as genetic material, whereas RNA is only used for protein synthesis. c. RNA is usually a double helix, while DNA is usually single stranded. d. The RNA backbone is made up of ribose sugars and phosphate, while the DNA backbone is made up of deoxyribose sugars and phosphate; further, RNA uses uracil nucleotide whereas DNA uses thymine nucleotide.

d. The RNA backbone is made up of ribose sugars and phosphate, while the DNA backbone is made up of deoxyribose sugars and phosphate; further, RNA uses uracil nucleotide whereas DNA uses thymine nucleotide. -RNA is usually a single-stranded nucleic acid. It has a backbone of ribose sugars and phosphate, the purine bases adenine and guanine, and the pyrimidine bases uracil and cytosine. In cellular organisms, the genetic material is DNA, while in viruses the genetic material can be either DNA or RNA

How does the replication of animal RNA viruses differ from that of animal DNA viruses? a. Whether the virus is enveloped or not b. The mode of entry c. The type of capsid the virus has d. The method of RNA synthesis and the nucleic acid that serves as template for viral replication

d. The method of RNA synthesis and the nucleic acid that serves as template for viral replication

Which characteristics are used to classify viruses? a. Shape, size, and staining characteristics b. Presence or absence of an envelope, shape, and size c. Type of nucleic acid alone d. Type of nucleic acid, presence or absence of an envelope, shape, and size

d. Type of nucleic acid, presence or absence of an envelope, shape, and size