BIOL10221 Molecular Biology

Hepatitis B Virus

This is a virus that attacks the hepatic cells and it can cause both acute and chronic liver disease and liver cancer called hepatocellar carcinoma (Venkatakrishnan et al., 2017). This virus is small DNA and enveloped virus belonging to the hepednaviridae family (Liang, 2009).

The possible virus transmission is body contact with infected body fluids. Vertical transmission can also take place and this mostly causes chronic hepatitis disease in children as suggested by Chisari et al. (2010).

Symptoms mostly do not occur during the acute viral infection. However, some individuals may have acute symptoms such as jaundice, dark urine, vomiting and abdominal pain. In chronic liver disease, an infection can develop into liver cirrhosis.


Poliovirus is non-enveloped RNA virus that invades the nervous system and causes total paralysis and it causes poliomyelitis (Francki et al., 2012; Kumthip et al., 2017). The virus is transmitted through faecal-oral route by a common vehicle such as contaminated water and food.

The initial symptoms include fever, fatigue, vomiting, painful limbs and headache. Eventually, the virus causes paralysis. Among the individuals who are paralyzed 5% to 10% die having trouble breathing because of immobilized breathing muscles (Strauss et al., 2017).  

Hepatitis B virus is an enveloped virus and it contains its genetic material in form of DNA while Poliovirus is a non-enveloped virus and contains its genetic materials in form of RNA. Hepatitis B virus uses the lipid-protein layer that is the envelope to attach and enter the host cell during viral replication whereas the virulence of poliovirus can be attained due to lack of envelope, this enables the virus to penetrate the intestinal cells without being degraded by the gastric acid.

The knowledge of virus structures will help the doctors to understand the mode of action of the drugs used to treat different viral diseases. The doctor will have a full understanding on which structural parts of the virus will the drug target. the virus will be enveloped or non-enveloped at the same time viruses will be classified as RNA or DNA viruses depending on their genetic material.

Importance Of Gram Staining

The gram staining is the first step in the initial characterization and classification of the bacteria. The bacterial morphology in terms of shape, arrangements, and color can then be determined and microscope after gram staining. For example, when examining urine for urinary tract infections (UTI), the urine sample can be stained using gram staining method, therefore urine being non-sterile sample some non-pathogenic gram-positive bacteria such as Staphylococcus saprophyticus can be visualized and differentiated from pathogenic gram-negative bacteria such as E coli. 

Catalase Test

It is a test used to differentiate Staphylococcus producing catalase enzyme bacteria from non-catalase producing bacteria such as Streptococcus. The principle of this test is such that catalase produced by the bacteria acts as a catalyst in the breakdown of hydrogen peroxide to produce oxygen and water (Murray et al., 2015).


2-3 ml of hydrogen peroxide to be poured into a clean test tube.

Pick several colonies using sterile glass rod, and drop the colonies into hydrogen peroxide solution.

Observe for immediate bubbling.

Results: Active bubbling – Catalase positive; No bubbles – catalase negative.

Adapted from Murray et al. (2015).

The principle of the Gram stain is such that, the primary stain gets into the peptidoglycans layer found in the cell wall and stains it. Due to some rapid physiological changes that take place within the bacteria. It is advisable to perform the gram staining using bacterial colony not older than 48 hours. To prevent false results.  

The microscopic examination of the bacteria under the microscope should not take more time especially for unfixed samples this is because the bacteria may change its morphological characteristics in the harsh environment. For example, sporulation can take place.

It is important to use bacterial culture that is not more than 24 hours sold when carrying out catalase test. This is because the older colonies tend to lose the catalase production activity. Therefore, leading to the false negative result. 

Reference List For Virology

Chisari, F.V., Isogawa, M. and Wieland, S.F., 2010. Pathogenesis of hepatitis B virus infection. Pathologies Biology, 58(4), pp.258-266.

Francki, R.I., Fauquet, C.M., Knudson, D.L. and Brown, F. eds., 2012. Classification and Nomenclature of Viruses: Fifth Report of the International Committee on Taxonomy of Viruses. Virology Division of the International Union of Microbiological Societies (Vol. 2). Springer Science & Business Media.

Liang, T.J., 2009. Hepatitis B: the virus and disease. Hepatology, 49(S5).

Strauss, M., Schotte, L., Karunatilaka, K.S., Filman, D.J. and Hogle, J.M., 2017. Cryo-electron Microscopy Structures of Expanded Poliovirus with VHHs Sample the Conformational Repertoire of the Expanded State. Journal of Virology, 91(3), pp.e 01443-16.

Strauss, M., Schotte, L., Karunatilaka, K.S., Filman, D.J. and Hogle, J.M., 2017. Cryo-electron Microscopy Structures of Expanded Poliovirus with VHHs Sample the Conformational Repertoire of the Expanded State. Journal of Virology, 91(3), pp.e01443-16.

Kumthip, K., Khamrin, P. and Maneekarn, N., 2017. Detection of poliovirus infection in children with acute gastroenteritis in Chiang Mai, Thailand. Journal of medical virology, 89(5), pp.775-781.

Murray, P.R., Rosenthal, K.S. and Pfaller, M.A., 2015. Medical microbiology. Elsevier Health

Venkatakrishnan, B., Katen, S.P., Francis, S., Chirapu, S., Finn, M.G. and Zlotnick, A., 2016. Hepatitis B virus capsids have diverse structural responses to small-molecule ligands bound to the heteroaryldihydropyrimidine pocket. Journal of virology, 90(8), pp.3994-4004.

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