Question 1: General structures of a virus
A virus is made up of at least two parts. The first part is the nucleic acid in its core and its outer is surrounded by a protective layer. Generally, all viruses comprise at the least two parts which include the following; the core is called nucleic acid and some biologists term it as “genome”. The nucleic acid core can either be a deoxyribonucleic acid (DNA) or ribonucleic acid (RNA) but cannot be both. It is usually either just 1 or 2 molecules (LO3, slide 29). The structure of the DNA and the RNA can only be in these two states; linear or circular, or it can also be one strand or two strands. DNA and RNA are the genetic material or code of the virus. Nonetheless, the genomes in certain RNA are segmented, which refers that the virus segment having numerous varying RNA molecules.
The second part is the protein layer which is termed the capsid. This is the part/layer that beset the nucleic acid core and serves to safeguard it. It comprises 1 or more proteins replicated numerously. The capsid is literally composed of recurrent structural subunits. Just to recap, these subunits are made up of one polypeptide. In essence, in many instances, these structural subunits are referred to as protomers conjured by numerous polypeptides. This layer generally takes either a helical or icosahedral shape. Other viruses exhibit a complex shape which is a binal symmetry which cannot be described purely as either icosahedral or helical. An example of this is the T-even bacteriophages. Some other viruses also have two other parts; envelope and viral-specific enzyme. The envelope besets the protein layer and is composed of lipids, proteins, and glycolipids. It is obtained from the membrane of the cell of the host but it also has proteins with the genetics of the virus (LO3, slide 29). The viral-specific enzymes are the enzymes that are needed by the virus which the host cell cannot supply. It carries the genome of the virus and is stored in the protein layer.
Viruses are inert chemicals which cannot execute any life processes. They have a small and simple structure, possess some characteristics of living things, and have contained genetic information thus are not considered living cells since they are parasites which enter a host cell, lie passively and then depend on the host cell in order to reproduce (LO3, slide 28).
Question 2: Steps of Viral replication
1. Attachment. This is the first step where the superficial protein layer of the virus gets attached to certain receptors on the host cell’s surface (LO3, slide 31).
2. Penetration. Once the virus has attached itself, the enveloped HIV then enters cells by fusing its envelope and the cell membrane of the attacked cell (LO3, slide 31).
3. Uncoating. At this step, the contents of the HIV virus are released (LO3, slide 31).
4. Biosynthesis. At this step, the HIV RNA enters the nucleus a point at which the RNA polymerase will replicate it (LO3, slide 31).
5. Assembly. The new phage elements are combined or assembled together.
6. Release. This is the final step where the newly formed elements of the HIV virus are created and released to intracellular fluid. This process does not kill the cell and hence the process of making the new viruses continues (LO3, slide 31).
Question 3: HIV basics
Human immunodeficiency virus (HIV) is especially harmful as it targets T-helper cells which are lymphocytes that can be differentiated by having the CD4 protein on their cell membrane (LO1, slide 22). When these specific cells are activated by an antigen they release cytokines to help other B-cells, which are responsible for cellular immunity, and cytotoxic T-cells, which are responsible for humoral immunity, to produce an immune response (LO1, slide 32).
A person infected with HIV is classified as having acquired immunodeficiency syndrome (AIDS) when the person’s immune system has become very weak that it cannot defend the body against some types of infections and diseases including cancer (LO1, slide 31). This is indicated by the reduction of the CD4 cells that is less than 200 (AIDS, 2018).
Question 4: How viral proteins are synthesized by the host cell
Once the viral DNA has been incorporated into the host cell, an “uncoating” process occurs which is a disassembly of DNA and the process presents the nucleic acid for transcription into the messenger RNA and this is utilized in directing the synthesis of proteins. This takes place by the genomic RNA binding itself onto the ribosomes and is then decoded into a polyprotein which is then cleaved. The RNA virus commonly utilizes the RNA core as a base for synthetization of viral RNA contained in the genome and messenger RNA. The viral messenger RNA then commands the cell of the host to synthesize enzymes with the virus and capsid proteins in order to create other viruses. For HIV however, an RNA genome must be changed back into the DNA before being incorporated into the genome of its host cell (LO1, slide 22). For these viruses which are called retroviruses to change RNA into DNA, they must have genes that command the enzymes specific to them to reverse the process. The enzymes required for transcription are derived from the viral genes that are within the host cells and this reverse transcription does not affect the uninfected cells (LO1, slide 07).
Question 5: Vaccination and antigen variation
Vaccination makes individuals develop immunity against a viral infection which helps avert the spread of communicable disease among a group of people who may have contact and hence preventing a general epidemic (“Vaccines,” 2018).
Antigenic drift is a sudden/abrupt alteration in the nucleic acid core of the genome of a virus, and its occurrence is ascribed to a combination of a number of the strains of the virus leading to a new type an example is an H1N1 flu (LO3, slide 33). On the other hand, the antigenic shift is a gradual change in the genes of the virus and is ascribable to errors in its reproduction and unsystematic mutations (LO3, slide 32). In antigenic drift, the new type cannot be recognized by the host’s immune system while in an antigenic shift, a few allow an immune response from the host’s system.
Antigenic variation poses a challenge to vaccine development for viruses since once the antigens have modified themselves, the immune system of the host no longer responds to them and therefore they will not be able to produce antibodies requisite for the fight against the virus. Usually, vaccine development leads to antigens that are specific to a certain antigen of a virus and there once they are injected into the body of the host, they serve to only fight the particular type of the antigen. Variation of the antigen will lead to a different type of antigen which the vaccine does not recognize and hence it will direly affect the host (LO3, slide 34). Therefore, the development of vaccines needs to take into consideration this variation, an aspect which is not easily solved since the variation is dynamic and is not predictable.