Answer to Question #253610 in Molecular Biology for Assignment

Question

Why positive mRNA is placed at the center?

How to designate positive and negative strands?

What is the basis of Baltimore classification system? Identify each class with proper justification
Compare Virus and bacteria in the basis of Route of transmission, Structure, Immune system protetion and infection Pattern

What is the special feature of Class positive RNA and negative DNA?

Answer 1

a. Bacause all viruses must direct the synthesis of mRNA to produce proteins. All viral proteins synthesis is completely dependent upon translational machinery of the cell.

b.mRNA is regarded as positive (+)strand since it is the template for protein synthesis. A strand of DNA of the equivalent sequence is also regarded a (+) strand. RNA and DNA strands that are complementary to the (+) stands are called (-)strands.

c. Baltimore classification system is a scheme for classifying viruses based on type of genome and its replication strategy. The classification contains seven classes of viruses as follows:

Class I. Double stranded DNA(dsDNA).Enters the host nucleus and uses its polymerase to replicate.

Class II. Single stranded DNA(ssDNA). They contain a circular genome and replicate within the nucleus of the host by rolling circle mechanism.

Class III. Double stranded RNA(dsRNA). Replicate in the capsid in the host cell cytoplasm.

Class IV. Single stranded RNA(ssRNA). They have positive-sense RNA genomes such that they can read ribosomes and translate into proteins.

Class V. Single stranded RNA (ssRNA). They have a negative-sense RNA genome such that they need to be transcribed by a viral polymerase to produce readable strand of mRNA.

Class VI. Positive sense(ssRNA) reverse transcriptase viruses. They replicate through DNA intermediate.

Class VI. Double stranded DNA.(dsDNA) reverse transcriptase viruses. They contain double stranded DNA genome and replicate through ssRNA intermediate.

d. Transmission

Viruses are mostly spread through contact. Bacteria can be transmitted to humans through air, water, food or living vectors.

Structure

All viruses contain nucleic acid surrounded by a protein coat. Bacteria are prokaryotes lacking a well-defined nuclei and membrane-bound organelles.

Immune system protection

Virally infected cells produce and release small proteins called interferons, which play a role of immune protection. The body reacts by producing antibodies to fight bacteria.

Infection pattern

Viral pathogenesis include several stages including transmission and entry to the host, spread into the host, tropism, virulence, patterns of viral infection and disease, host factors and host defence. Bacterial infection form colonies made up of many cells all growing and dividing together.

e.Single stranded RNA viruses can be classified according to the sense or polarity of their RNA into negative-sense and positive-sense,