Viruses and Vaccines Flashcards
What is a Virus
→ Very small submicroscopic particles that can only be seen with an electron microscope. (10-400nm)
→ Non-living
→ Not a cell because they do not have cellular structures
→ They are dependent on a host cell to provide organelles that can synthesize proteins and replicate DNA.
→ Identified in 1934 with the invention of the electron microscope.
Why are Viruses considered non-living?
→ Does not maintain Homeostasis ( no cellular structure so nothing to maintain )
→ Does not grow like living things
→ Don’t respond to stimuli (tho this is kinda iffy)
→ Does not metabolize
→ Cannot reproduce on it’s own
↪ Requires a host cell
→ No cellular structure
↪ No cytoplasm, organelles or cell membrane
However there are things that indicate that it is living like…
→ Made of smaller biological subunits
→ The adapt to their environment
→ Technically they have metabolisms and replication abilities but need a host cell (is that living, idk)
→ Viruses can get infected by other viruses, if they can get sick they should be living?
How are Viruses Classified
1) Shape
2) Reproduction
3) Type of Disease they cause
Virus Morphology
Viruses are extremely diverse, there are over 70 different families of them.
→ Viral nucleic acid and proteins may be surrounded by…
↪ A lipid bilayer membrane envelope with viral proteins (spikes) that enable it to bind to its host. Or it can have a protective protein coat shell called a capsid.
↪ They acquire the envelope when they bud out of a host cell
↪ Viruses that lack an envelope are considered naked viruses
→ Capsid
↪ The capsid can be rod-shaped, helical, polyhedral, spherical, icosahedral, filaments, complex, etc
↪ Made of different protein subunits called capsomeres that associate with the viral genome to protect it from digestion by the host cell
→ Genetic material of viruses can be DNA or RNA
↪ If they contain RNA that can be immediately translated, they are called positive strand RNA virus. If they have a complementary strand they are called negative Strand RNA virus
→ Tails and Fibers
↪ Some viruses like bacteriophages have fibers attached to a tail made of additional fibers
↪ Have pin-like proteins that help penetrate cell membrane
→ Most viruses are RNA viruses
↪ Dangerous because RNA replication causes more errors (i.e. mutations). More mutations means more variants = more viruses that can invade more host cells
Virus Reproduction
Because Viruses don’t have organs they have to use a host cell to replicate.
There are two cycles for this: Lytic cycle and Lysogenic Cycle
Lytic Cycle
1) Attachment and Entry: The proteins on the virus surface interact with the receptors on it’s host cells. Either can inject DNA (bacteriophage) or go through phagocytosis
2) DNA copying and Protein Synthesis: The viral genetic material is released from the virus and enters the nucleus of the host cell where it is copied and genes are expressed to make proteins like capsomeres (proteins that make capsids)
3) Assembly of units: Viral protein components and a copy of the genetic material self-assemble into a complete viral particle
4) Lysis: Late in the lytic cycle, the virus expresses genes for proteins that poke holes in the plasma membrane and cell wall. The holes let water flow in, making the cell expand and burst like an overfilled water balloon.
Lysogenic Cycle
→ Specific to bacteriophages
→ Seen in viruses that do not outright kill the cell
→ Coexist with cell and carried through many generations without harm to host
1) Attachment and Entrance
2) The phage DNA is not immediately replicated or expressed, instead it combines with a particular region of the bacterial chromosome. Sometimes it forms it’s own little rejoin of DNA that lives in the nucleus, this gets replicated as well.
↪ Integrated DNA is called a Prophage
3) Viral DNA is replicated along with the host DNA and passed on to daughters cells
4) The cell is in a Dormant state called lysogeny.
→ Cycle continues until UV radiation, chemical or environmental triggers lytic cycle - When the time is right, virus can become active and enter the lytic cycle. (DNA copying, protein synthesis, phage assembly and lysis)
Viruses and Human Health
→ Destruction of Host cell by viral replication causes symptoms
→ Infections are difficult to treat and antibiotics don’t work on viruses, only on micro-organisms.
Viral technology
→ Vaccines: reduce the virulence (Severity of the virus) of the virus
→ Gene therapy - To replace a defective gene with a normal gene, viruses can be used as a vehicle to deliver good gene to the target cell.
Vaccines
A vaccine is a biological preparation that improves immunity to a particular disease.
→ A vaccine typically contains an agent that resembles a disease causing microorganism and is often made from weakened or killed forms of the microbe
→ The agent stimulates the body’s immune system to recognize the agent as foreign, destroy it and keep a record of it
↪ This way, the immune system can more easily recognize and destroy any of these microorganisms that it later encounters
Types of Vaccines
Live Attenuated: Weakened version of virus used. (Small pox, Chicken pox, Yellow fever)
↪ Strong long-lasting immune response
↪ Week immune systems are vulnerable
↪ Need to be kept cold to logistics is interesting
Inactivated/Killed: Use a killed or inactive version of the virus (Hepatitis A, Polio)
↪ No harm but needs booster shots as the inactivated viruses provide a week immune response
Subunit: Subunit vaccines contain purified pieces of the virus that have been selected to stimulate the immune system (HPV, Hepatitis B, Shingles). Recombinant vaccines are a type of this but use protein spikes.
↪ Very strong immune-response
↪ Need for Booster to Stay resistant’
Toxoid: Uses a weakened toxin made by a bacteria that causes the disease. (Tetanus and Diphtheria)
↪ Need a booster to keep ongoing boosters
mRNA: Uses messenger RNA to produce proteins that induce a immune response. Newest type (Used for COVID-19)
↪ Shorter manufacturing times
↪ no risk of causing disease
Provirus
every time the host cell divides it replicates the provirus along with its own DNA
this can continue for years without any impact to the host
Retrovirus
use reverse transcriptase to copy their RNA genome into DNA
