In: Biology
BACKGROUND:Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2)is an enveloped, (+)-sense, single-strandRNA virus that causes coronavirus disease 2019(COVID-19). The coronavirus family is named for the crown-like spikes on the outer surface of the virus and includes viruses that infect many species of animals, including camels, cattle, bats, and cats. The SARS-CoV-2 virus appears to have “spilled”out ofbats,its primaryanimal host,and into humansin December of 2019 in Wuhan, China. COVID-19 symptoms appear 2-14 days after exposure and include fever, dry cough, shortness of breath, chills, muscle pain, headache, diarrhea, and loss of taste or smell.The virus spreads from person-to-person, primarily through droplets that are released when a person coughs or sneezes, but also through indirect contact with secretions. It is highly contagious and spread primarily by symptomatic individuals but also by individuals who are asymptomatic. Researchers are working at a frantic pace to design an effective vaccine and determine whether people who recover from COVID-19 can be re-infected. Coronaviruses have remarkably low mutation rates for RNA viruses. Their replicative enzyme has low fidelity (accuracy) but they have acquired the gene for a 3’-to-5’ exonuclease (ExoN) that removes mismatches during and after RNA synthesis
QUESTIONS TO ANSWER:
1.(5pts) Fill in the missing terms in the replication cycleof SARS-CoV,a virus that is very similar toSARS-CoV-2with respect to its replication.
A.During attachment, the SARS-CoV___________________[name specific viral ligand] binds receptor molecules on the ___________________[name specific structure] of the host cell.
B.During penetration and uncoating, the virion enters the cell by___________________ and then releases its genome into the cytoplasm of the cell through ___________________[name process].
C.During biosynthesis, the ___________________[positive-and/ornegative] –sense genome is replicated using the viral ______________________[name specific enzyme]to produce ___________________[positive-and/or negative] –sense strands. This activity will also produce ___________________[name specific macromolecule] that will be translated to produce viral structural proteins.
D.As a precursor to assembly, viral surface proteins are translatedin the ___________________[name host cell compartment]. These surface proteins will then assemblewith other viral proteins and a copy of the genome.
E.During release, infectiousvirions leave the host cell by the
process of ___________________[name cell process].
Question 1A) During attachment, the SARS-CoV spike protein binds receptor molecules on the cell membrane of the host cell.
Explanation:
The receptor binding domain of the viral spike protein binds with the ACE2 receptor molecule on the host cell membrane. This binding facilitate the entry of the virus into the host cell.
Question 1B) During penetration and uncoating, the virion enters the cell by receptor-mediated endocytosis and then releases its genome into the cytoplasm of the cell through nuclear import.
Explanation:
Once the virus establish the binding of viral spike protein with the host cell receptor protein ACE2, the virus enter into the host cell via receptor mediated endocytosis. Inside the cell, the virion releases its genetic material into the cytoplasm of the host cell.
Question 1C) During biosynthesis, a positive-sense genome is replicated genome is replicated using the viral RNA-dependent RNA polymerase produce negative –sense strands. This activity will also produce subgenomic mRNA that will be translated to produce viral structural proteins.
Explanation:
Corona virus is a positive-sense strand RNA virus. Thus it use positive sense RNA as the genetic material.
Question 1D) As a precursor to assembly, viral surface proteins are translated in the cytoplasm. These surface proteins will then assemble with other viral proteins and a copy of the genome.
Explanation:
The replication and translation of the viral genome occur in the nucleus of the host cell. After transcription the mRNA is transported into the cytoplasm and the translation occur in the ribosomes.
Question 1E) During release, infectious virions leave the host cell by the process of exocytosis.
Explanation:
After the assembly of the viral genetic material and the associated proteins, the newly formed virion are transported towards the cell membrane. From there, the virions are released from the cell by the process called exocytosis.