Quiz week 6-

 

	Attempt	Time	Score
LATEST	Attempt 1	15 minutes	10.5 out of 11

 Correct answers are hidden.

Submitted May 18 at 6:27pm

 

Question 1

1 / 1 pts

Which of the following is a property of a virus? (Select all that apply)

  

A. It is an infectious cellular pathogen

 

  

B. It is an obligate intracellular pathogen

 

  

C. Its genome consists of DNA or RNA

 

  

D. Its genome is surrounded by a protein capsid

 

 

Question 2

1 / 1 pts

A bacteriophage infects a host cell and the genome integrates itself into the host chromosome. Sometime later, the phage is excised along with a short piece of DNA adjacent to the insertion point. Both the phage DNA and the host DNA are packaged into the same capsid. The bacteriophage then infects a new cell, delivering both phage and bacterial DNA.

 

Which process is being described in this scenario above?

 

  

The lysogenic cycle, reactivating as the lytic cycle, followed by transduction

 

  

The lytic cycle, reactivating as the lysogenic cycle, followed by transduction

 

 

PartialQuestion 3

0.5 / 1 pts

Which of the following is a novel enzyme found in retroviruses?

 

  

DNA polymerase

 

  

retrotranscriptase

 

  

reverse transcriptase

 

  

integrase

 

 

Question 4

1 / 1 pts

(-)ssRNA can be directly used in translation at the ribosome.

 

  

True

 

  

False

 

 

Question 5

1 / 1 pts

Put the steps of HIV infection in order by matching the correct events with each step:

Step 1

 

               iii.   HIV RNA and other viral proteins enter the cell.             

Step 2

 

               v.     Viral DNA is synthesized.             

Step 3

 

               ii.    Provirus appears.             

Step 4

 

               iv.   Viral DNA is transcribed into viral RNA.             

Step 5

 

               i.      New virus particles are released.             

 

Question 6

1 / 1 pts

________ are molecules, receptors, or surface structures necessary for attachment to a host cell.

 

Question 7

5 / 5 pts

Take your time on this one. I recommend writing out the table by hand in front of you & filling it out before submitting your final answer.

Once you have the completed, accurate table, please use it to study for Midterm 2!

Enzyme	Host or viral?	Template molecule (what does the enzyme "read?")	Product of the reaction (What does the enzyme "make?")	Typical location of reaction?
DNA polymerase	host	DNA	DNA	nucleus
RNA polymerase (DNA-dependent)	host	DNA	RNA	nucleus
RNA-dependent RNA polymerase	viral	+ ssRNA or -ssRNA	RNA	cytoplasm
Reverse Transcriptase	viral	+ ssRNA or -ssRNA	DNA	cytoplasm
Ribosome	host	+ ssRNA	protein	cytoplasm

Answer 1:

host

 

Answer 2:

DNA

 

Answer 3:

DNA

 

Answer 4:

nucleus

 

Answer 5:

host

 

Answer 6:

DNA

 

Answer 7:

RNA

 

Answer 8:

nucleus

 

Answer 9:

viral

 

Answer 10:

+ ssRNA or -ssRNA

 

Answer 11:

RNA

 

Answer 12:

cytoplasm

 

Answer 13:

viral

 

Answer 14:

+ ssRNA or -ssRNA

 

Answer 15:

DNA

 

Answer 16:

cytoplasm

 

Answer 17:

host

 

Answer 18:

+ ssRNA

 

Answer 19:

protein

 

Answer 20:

cytoplasm

 

Previous

Next

(-)ssRNA can be directly used in translation at the ribosome. 

True or False 

 ❌ False

---

Explanation:

• (-)ssRNA (negative-sense single-stranded RNA) cannot be directly used for translation by ribosomes.

• It must first be converted into complementary (+)ssRNA (positive-sense RNA), which can be used as mRNA for translation.

Viruses with (-)ssRNA genomes must carry their own RNA-dependent RNA polymerase to make the +ssRNA needed for protein synthesis.

Group of answer choices

True

False

Which of the following is a novel enzyme found in retroviruses?

Group of answer choices

• DNA polymerase
• 
  
• retrotranscriptase
• 
  
• reverse transcriptase
• 
  
• integrase

The correct answer is: ✅ reverse transcriptase

---

Explanation:

• Reverse transcriptase is a novel enzyme found in retroviruses.

  • It converts RNA → DNA, which is the reverse of normal transcription (DNA → RNA).

  • This allows the viral RNA genome to be converted into DNA and integrated into the host genome.

---

Why not the others?

• DNA polymerase: Common in many organisms, not unique to retroviruses.

• Retrotranscriptase: Not an actual enzyme name — this is a misleading term; the correct name is reverse transcriptase.

• Integrase: Retroviruses do use integrase to insert viral DNA into the host genome, but it's not unique to retroviruses and not as central as reverse transcriptase.

A bacteriophage infects a host cell and the genome integrates itself into the host chromosome. Sometime later, the phage is excised along with a short piece of DNA adjacent to the insertion point. Both the phage DNA and the host DNA are packaged into the same capsid. The bacteriophage then infects a new cell, delivering both phage and bacterial DNA.

Which process is being described in this scenario above?

• Group of answer choices
• The lysogenic cycle, reactivating as the lytic cycle, followed by transduction
• The lytic cycle, reactivating as the lysogenic cycle, followed by transduction

✅ The lysogenic cycle, reactivating as the lytic cycle, followed by transduction

---

Explanation:

1. Lysogenic cycle:

   • The phage genome integrates into the host chromosome (called a prophage).

2. Reactivation:

   • Later, the prophage is excised from the host DNA. In rare cases, it accidentally takes some nearby host DNA with it.

3. Lytic cycle:

   • The phage enters the lytic cycle, making new viruses and packaging the combined phage + host DNA into capsids.

4. Transduction:

   • When a new cell is infected, it receives both phage DNA and host DNA — a process known as specialized transduction.

Which of the following is a property of a virus? (Select all that apply)

Group of answer choices

A. It is an infectious cellular pathogen

B. It is an obligate intracellular pathogen

C. Its genome consists of DNA or RNA

D. Its genome is surrounded by a protein capsid

The correct answers are:

✅ B. It is an obligate intracellular pathogen
✅ C. Its genome consists of DNA or RNA
✅ D. Its genome is surrounded by a protein capsid

---

Explanation:

• ❌ A. It is an infectious cellular pathogen → Incorrect
  Viruses are not cellular. They are acellular (not made of cells) and therefore not considered cellular pathogens.

• ✅ B. It is an obligate intracellular pathogen → Correct
  Viruses must infect a host cell to replicate; they cannot reproduce on their own.

• ✅ C. Its genome consists of DNA or RNA → Correct
  A virus has either DNA or RNA, but never both.

• ✅ D. Its genome is surrounded by a protein capsid → Correct
  The capsid is the protein shell that protects the viral genome.

Which of the following is true regarding capsids? Select ALL that apply.

Group of answer choices

Capsids are made up of lipids

Capsids aid in protection of viral genomes

Capsids aid transfer from one host to another

Capsids are sometimes surrounded by a lipid membrane

• ❌ Capsids are made up of lipids → Incorrect
  Capsids are made of proteins, not lipids.

• ✅ Capsids aid in protection of viral genomes → Correct
  The capsid encloses and shields the viral genetic material from damage.

• ✅ Capsids aid transfer from one host to another → Correct
  Capsids help the virus attach to and enter new host cells.

• ✅ Capsids are sometimes surrounded by a lipid membrane → Correct
  Some viruses have an envelope (a lipid membrane) that surrounds the capsid. This is derived from the host cell’s membrane.

✔️ So, the correct choices are:
– Capsids aid in protection of viral genomes
– Capsids aid transfer from one host to another
– Capsids are sometimes surrounded by a lipid membrane4

Viral RNA polymerases make more errors than DNA polymerases, explaining the higher mutation rate in RNA viruses over DNA viruses. (True or False ) 

Explanation:

Viral RNA polymerases lack the proofreading ability that DNA polymerases have. This means:

• RNA viruses make more copying errors during replication.

• These errors lead to a higher mutation rate in RNA viruses compared to DNA viruses.

This is one reason why RNA viruses (like influenza and HIV) evolve so quickly.

Group of answer choices

True

False

What is the name for the transfer of genetic information from one bacterium to another bacterium by a phage? (hint we covered this in lecture 9; also phage = bacterial virus)

• Which of the following are ways we can categorize the types of viruses by their genetic content?
  Group of answer choices

  Linear or circular nucleic acids

  RNA or DNA

  Single Stranded or Double Stranded

  Icosohedral or Complex

• The correct answers are:

  ✅ Linear or circular nucleic acids
  ✅ RNA or DNA
  ✅ Single Stranded or Double Stranded

  Explanation:

  These three options refer specifically to the genetic content of viruses:

  • RNA or DNA: Viruses can have either RNA or DNA genomes (but never both).

  • Single Stranded or Double Stranded: Viral genomes can be either single-stranded (ss) or double-stranded (ds), whether it's RNA or DNA.

  • Linear or Circular Nucleic Acids: Some viral genomes are linear (like most viruses), while others are circular.

  ❌ Incorrect:

  • Icosohedral or Complex: This refers to the shape/structure (capsid symmetry) of the virus, not the genetic content.

  ✔️ So, the first three options are correct ways to categorize viruses by genetic content.

• 
  

Group of answer choice

The envelope of a virus is derived from the host’s...

Group of answer choices

1. nucleic acids
2. membrane structures
3. cytoplasm
4. genome 

The correct answer is: ✅ membrane structures

Explanation:

The envelope of a virus is typically derived from the host cell’s membrane, such as the plasma membrane or sometimes the nuclear or endoplasmic reticulum membranes.

This occurs when the virus buds out of the host cell, taking a portion of the host's membrane along with viral proteins embedded in it.

Other options:

Nucleic acids: These make up the viral genome, not the envelope.

Cytoplasm: Not directly used to form the envelope.

Genome: Refers to genetic material, not structural components like the envelope.

✔️ So the envelope comes from the host’s membrane structures.

What is the name for the transfer of genetic information from one bacterium to another bacterium by a phage? (hint we covered this in lecture 9; also phage = bacterial virus)

Group of answer choices

• transduction
• penetration
• excision
• translation

The correct answer is: ✅ transduction

Explanation:

• Transduction is the process by which a bacteriophage (phage) transfers genetic material from one bacterium to another.

• It’s a form of horizontal gene transfer in bacteria.

Other options:

• Penetration: Step where a virus injects its genetic material into a host cell.

• Excision: Removal of viral DNA from the host genome (like in the lysogenic cycle).

• Translation: Process of making proteins from mRNA, not related to gene transfer by phages.

Which of the following does a virus lack? Select all that apply.

The correct answers are:

✅ metabolic processes
✅ ribosomes

Explanation:

• Viruses lack metabolic processes: They cannot carry out metabolism on their own and must rely on a host cell for energy and resources.

• Viruses lack ribosomes: They cannot synthesize proteins independently and must use the host cell’s ribosomes to translate viral proteins.

• Glycoprotein: Many viruses have glycoproteins on their surface (e.g., spike proteins on coronaviruses), so they do not lack these.

• Nucleic acid: All viruses contain either DNA or RNA, so they do not lack nucleic acid.

Group of answer choices

metabolic processes

glycoprotein

nucleic acid

ribosomes