Three "typical" viruses

- Capsid: Protects viral DNA/RNA
- DNA/RNA: Single nucleic acid. Holds the genetic material necessary for new viral particle productions.
- Enzymes: Help viruses enter and/or take over cells in host
- Glycoprotein:Spikes protruding out of envelope that help virus to attach to host cells
- Envelope: Protects virus from host cell's enzymes.

  • All intercellular parasites
  • Contain a core of nucleic acid (single type; DNA or RNA)
  • Can only reproduce by infecting host cells
  • Contain capsid (outer protein coat)
  • Contain enzymes that help the viral genetic material to enter the host cell or take it over

- Differences:
  • Different sizes
  • Different shapes
  • Each targets different specific types of host cells
  • Which type of life cycle it follows (lytic or lysogenic)
  • Naked or enveloped capsids (can be either)
  • Which type of genetic material they each contain (DNA or RNA)

Well, viruses can be considered as non-living because they have no standard structures associated with cells, which means they have no cytoplasm, no cell membranes, no organelles, etc. Not only that, they are known to have the ability to crystallize, which living things do not do. They do not obtain, use, or consume energy.

However, one could also argue that viruses are living organisms because they have DNA/RNA, enzymes (proteins), protein-covered coat, and reproduce along with the ability to change over time (otherwise, all diseases known to mankind would have been cured already).

It is significant to note why viruses can be considered to be non-living or living so that it will help us fight them by understanding them. When we know what we are up against, it is a whole lot easier to prepare to combat later on.


A lytic and lysogenic cycle

- Attachment: The phage first attaches itself to the cell surface. Proteins on the tail fibers of the virus has a shape that fits together with molecules on the cell's surface, allowing it to attach.
- Penetration: The phage tail releases an enzyme that breaks down the cell surface. Outer portion of the tail contracts and the viral nucleic acid is injected into the cell. Sometimes, the capsid is left outside and in other the whole virus enters the cell and the capsid is destroyed.
- Biosynthesis: Inside the cell, the viral nucleic acid takes over. The host cell's DNA is made inactive. Normal cellular metabolism stops. The host cell is directed to make copies of viral nucleic acid and proteins.
- Maturation: The viral protein and nucleic acids assemble into new viruses.
- Lysis: The host cell then makes an enzyme that digests the cell membrane from inside. The cell bursts open, releasing hundreds of new viruses.

- Why are they similar?
  • Because they both go through the same stages of: Attachment, penetration, biosynthesis, maturation, and the lysis of cells that happens after maturation stage.

- Why are they different?
- Lytic:
  • After penetration, the viral DNA is separate from the host's DNA.
  • The viral DNA takes action immediately and takes over host's DNA's functions, which means the viral DNA has the control over the whole cell's mechanisms (organelles).
  • This will complete the biosynthesis where new viral particles will be made.
  • Because of this, the subject (infected) will feel the disease symptoms rather quickly.
  • There is no lag between penetration and biosynthesis.

- Lysogenic:
  • After penetration, the viral DNA is incorporated / has become part of the host DNA.
  • When this occurs, the DNA is called a "prophage"
  • It is obvious to see that the prophage will not be causing any disease symptoms until a stress triggers it, but, in any case, the disease symptoms will be delayed until activation.
  • There is a time lag between penetration and biosynthesis.

Viral specificity is when viruses can select what organism they want to infect.
Some examples of viral specificity are:
  • Rabies infects nervous tissue
  • Poliovirus , destroys cells in the nervous system ,producing paralysis
  • Mumps virus attacks salivary glands
  • Hepatitis virus attacks liver cells

This is significant because if you know what the virus you have is, it can be treated by targeting certain kinds of cells, making the job of eliminating them easier.

Three ways a virus can alter the functioning of a cell:
  • Lytic Infection - A virus enters a bacterial cell, makes copies of itself, and causes the cell to burst. Under the control of viral genes, the host cell's metabolic system now makes thousands of copies of viral nucleic acid and capsid proteins. The viral DNA is assembled into new virus particles. Before long, the infected cell lyses, releasing hundreds of virus particles that may go on to infect other cells.
  • Lysogenic Infection - The host cell is not immediately take over. Instead, the viral nucleic acid is inserted into the host cell's DNA, where it is copied along with the host DNA without damaging the host. Viral DNA multiplies as the host cells multiply. In this way, each generation of of daughter cells derived from the original host cell is infected.
  • Retroviral Infections - The genetic information of a retrovirus is copied from RNA to DNA instead of from DNA RNA. When a retrovirus infects a cell, it makes a DNA copy of its RNA, which inserts into the DNA of the host cell. The viral DNA may remain inactive for many cell cycles before making new virus particles and damaging the cells of the host's immune system.

It is significant to know how a virus can alter the functioning of a cell, so that if we ever get infected, our body will be able to tell what the virus plans to do and try to intercept its plans before it takes over one's body.

There are many ways in which viruses are able to spread, some modes of transmission are:
  • Coughing, Sneezing, and Physical Contact (Coughing and sneezing release tiny droplets that are inhaled by other people, or land on surfaces which someone touches, then touches their mouth spreading the virus to that person. Viruses that cause skin infections can be transferred by skin contact, of if someone uses a towel an infected person uses.)
  • Exchange of Body Fluids (Many viruses are spread by sexual contact or sexual fluids, during any kind of sexual activity. Other diseases are transmitted by people using syringes for injected drugs whom share with other people.)
  • Contaminated Water or Food (Water supplies contaminated with feces from infected people or animals spread viruses to people whom consume the water, or consume products sprayed by this water.)
  • Zoonoses (Animals carrying viruses bite humans, which infects the human. Humans can also get infected by animals if they eat an infected animal, or come in close contact to an infected animal's feces.)
Bats are one of the most notorious carriers of disease in the animal world
Bats are one of the most notorious carriers of disease in the animal world

It is significant to know how diseases are spread, as today diseases are quite common due to antibiotic resistant strains. With that in mind, being able to stay away from areas prone to disease, you are saving yourself from potential hardship, and diseases will be spread less likely than often.

The body is able to fight many various viral attacks through its lines of defence:
  • The skin, mucous membranes, and tears make up the body's first line of defence. These are commonly referred to as nonspecific defences. Our skin is a large physical barrier, with a surface primarily composed of dead cells in which very few viruses can penetrate. The mucous membrane secretes a sticky, thick fluid known as mucus. Mucus in your nose and throat traps pathogens; mucus contains lysozyme, an enzyme that breaks down bacterial cell walls. Tears contain lysozyme as well, protecting your eyes from viral infections.
  • Interferons, and phagocytic white blood cells make up the body's second life of defence. As well as the first line of defence, they are nonspecific defences. Interferons are proteins that inhibit synthesis of viral proteins (they interfere with viral growth). Interferons' main job is to buy time until specific immune defenses respond and and fight an infection. Phagocytic white blood cells are specialized white blood cells that move from blood vessels into infected tissues. What makes them special is that they have the ability to engulf and destroy bacteria they come in contact with.
  • Production of antibodies by B-lymphocytes is essential for targeting and destroying specific infections. B-lymphocytes are only capable of recognizing one specific antigen. B-lymphocytes are embedded with antibodies, which tag antigens for destruction. By producing these antibodies, B-lymphocytes are able to take care of over 10 billion antigens. The combination of the antibodies and B-lymphocytes make up the specific defences.
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It is significant to know how our body deals with pathogens trying to enter it. Without these defenses, pathogens would be able to enter our body with ease. Our specific lines of defence help us with many various diseases, aiding the body in resisting specific pathogens.

There are two types of vaccination:

- First Vaccination:
It activates the primary immune response and will cause memory cells to form and help produce rapid, long-lasting increase in antibodies the second time to the same antigen (should the same one come again) and will prevent disease symptoms.

- Primary Immune response:
  • This is where a first time pathogen invades the body and binds its antigens to B-cells, which will cause the B-cells to produces clones of itself (divide) rapidly.

  • B-cells produce plasma cells, which release antibodies for that specific virus and deactivate it by binding onto them (B's will bind) and will signal the macrophages to engulf and digest the deactivated viruses.

  • B-cells also produce memory cells, which will remain in the system and memorize that antigen, while the plasma cells die out.

- Booster Shot Function:
An injection for a specific antigen that will start the secondary immune response.

- Secondary immune Response:
  • This is where the memory cells activate and divide immediately and shut down the same viruses (should they come again) by producing massive numbers of antibodies for binding and deactivation of virus before it causes disease symptoms.

It is significant to note how vaccines work and how the two types of vaccines work as to not only inform the client exactly what they are getting, but so that it increases our knowledge of our body. Intentionally infecting ourselves with a disease is an unspeakable thing. However, if used correctly with the right dosage and the right strength, it can be insurmountably beneficial for us as it will and has proved to be a great asset.\


Active Immunity is a type of immunity developed in an organisms by its own production of antibodies from an exposure to an antigen, pathogen or to a vaccine.
Passive Immunity is a type of immunity acquired by the transfer of antibodies from one organism to another.
  • Active immunity develops antibodies and Passive immunity acquires antibodies
  • Passive immunity can be acquired by a vaccine or through birth
  • Active immunity takes more energy than Passive immunity
  • Active immunity takes more time than Passive immunity
These are significant

Terms to Know
Virulence- The capability of a microorganism to cause a disease.
Parasite- An organism that lives in or on another organism (its host) and benefits by deriving nutrients at the host's expense.
Interferon- One of a group of proteins that help cells resist viral infection.
Phagocyte- A type of cell within the body capable of engulfing and absorbing bacteria and other small cells and particles.
Macrophage- A large phagocytic cell found in stationary form in the tissues or as a mobile white blood cell.
Antibody- A protein that either attacks antigens directly or produces antigen-binding proteins.
Benign- Tumors that are benign are noncancerous. A benign tumor doesn’t not spread to surrounding healthy tissues.
Malignant- the tendency of a medical condition, especially tumors, to become progressively worse and to potentially result in death.
Prophage- Bacteriophage DNA that is embedded in the bacterial hosts DNA
Latent- Undeveloped but capable of normal growth under the proper conditions
Bacteriophage- Kind of virus that infects bacteria
Vaccine- Preparation of weakened or killed pathogens used to produce immunity to a disease.
Immunity- ability of an organism to resist disease by identifying and destroying foreign substances or organisms
Active Immunity- The immunity that results from the production of antibodies in response to an antigen.
Passive immunity- The short-term immunity that results from the introduction of antibodies from another person or animal.
Lymphocyte- A form of small leukocyte (white blood cell) with a single round nucleus.