virus Flashcards
virus
- small infectious particle that has DNA or RNA in a protein capsule
- very small: hundreds of thousands can fit into one human cell
virus structure
- DNA or RNA, not both
- capsid-protein coating around the DNA/RNA
- no cytoplasm
naked vs. enveloped virus
enveloped viruses have an envelope surrounding the nucleocapsid: nucleic acid + capsid
DNA and RNA
carry information that provides instructions for synthesizing protein molecules
host cells
the cell that a virus enters
host range
viruses infect specific cells or tissues of specific hosts
- HIV: certain immune cells (white blood cells)
- common cold: upper respiratory tract
- rabies virus: all species of mammals+birds
what causes symptoms of a virus infection + examples
- when a virus replicates inside our cells, it destroys host cells
- our immune system responds to the infection
- e.g. fever, sore throat, most coughs
are viruses living?
no: they can’t reproduce on their own (need host cell) and can only evolve/mutate
what criteria are viruses classified based on?
- size
- shape
- type of genetic material (DNA/RNA)
viral shapes
- polyhedral
- spherical (e.g. coronavirus)
- helical
- complex
bacteriophage
- complex shape (capsid, collar, phage tail)
- infect & destroy bacterial cells
surface proteins
- lock and key mechanism
- outside of viral particles have proteins that are involved in attachment to host cells
- binding of viral surface proteins and host cell receptors is very specific
infectious cycles
- viruses enter host cells and then replicate
- lytic cycles and lysogenic cycle
lytic cycle steps
- binding
- synthesis of viral proteins and nucleic acids
- assembly of the unit
- lysis
lytic cycle: binding
binding: proteins on virus surface interact with host cell receptors and virus binds to surface of host cell
lytic cycle: synthesis
synthesis of viral proteins and nucleic acids: viral genetic materials are released from the virus and enter nucleus of the host cell to be replicated
lytic cycle: assembly
assembly of the units: viral DNA/RNA instructs cell to make and assemble new viral DNA and capsids
lytic cycle: lysis
lysis: host cell bursts, new viruses leave to find new infection site (go on to infect other cells)
lysogenic cycle
- seen in viruses that do not kill the cell right away (e.g. Cancer-causing viruses HPV, Hepatitis C)
- viral DNA is dormant in cell and carried through many generations without harm to host
lysogenic cycle steps
- binding & attachment - virus attaches to host cell
- integration - DNA/RNA integrated into cell’s DNA
- replication - viral DNA/RNA is replicated with host DNA and passed to daughter cells
- cycle continues until a trigger activates the lytic cycle (e.g. UV radiation, stress, chemical or environmental factors)
lysogeny and induction
lysogeny: dormant state during lysogenic cycle
induction: activation of lytic cycle
dormant infection examples
shingles (reactivation of virus that causes chickenpox) and cold sores (herpes simplex)
vaccines
- contain weakened forms or parts of a dangerous virus
- trigger an immune response without actually making us sick
- produces chemicals that will stay in our body for a long time, so if we are exposed to the virus again, our body can quickly respond before we even feel symptoms
gene therapy
- when a genetically modified virus (vector) carries genetic information that will enter the cells of a patient who lacks the gene for a protein
