Viruses Flashcards
Virome
Types of viruses you have in you, affected by breast feeding, genetics, travel, where you live, who you live with etc
Virus size
20-230nm, 100 to 1000 times smaller than human cells
5 Virus characteristics
- Intracellular parasites
- A cellular, lack cellular structure, no organelles, no cytoplasm, no nucleus
- Cannot replicate or metabolism
- Interact with specific cell receptors
- Tissue/host tropism
What do viruses lack?
ATP generation, lack enzymes for protein synthesis, can only reproduce using cellular machinery of other organism
Explain the virus host range
range refers to what organisms (hosts) that a virus can infect and it is basedon a virus’s capsid structure. Viruses have a very narrow host range
Define tropism
Affinity of viruses to certain tissues or cells
HIV host range and tropism
Host range (human)
Tropism (macrophages and T helper cells)
Rabies host range and tropism
Host range (human/warm blooded animals)
Tropism (nervous system)
What are viruses made of?
Nucleocapsid
Capsid (capsomer)
Nucleic acid
Nucleocapsid
The combination of capsid + nucleic acid
What is the capsid and what is it made of?
Protein coat around the nucleic acid made up of capsomers
Nucleic Acid
– Contains the viral genome- only one type of nucleic acid - DNA or RNA nucleic acid of a virus can be single ordouble stranded
– the nucleic acid can be linear or circular
DNA vs RNA virus
(genome size, replication rate, mutations)
DNA has:
- Large genome, less dependent on host
- Slower replication due to size
- Lower mutation due to decreased transcription error (double strand = more stability)
RNA has:
- Small genome and highly dependent on host
- Rapid replication due to small size
- High mutation due to high errors in transcription
Explain the viral envelope and it’s 3 components
Derived from the host cell membranes, made up of either lipid or glycoprotein, consists of three main proteins (enveloped protein, spike protein, membrane)
Examples of enveloped viruses
COVID, influenza, HIV and RSV
Examples of NON-enveloped viruses
Norovirus, adenovirus, rhinovirus
Give an overview of enveloped viruses
- Cause less serious infection
- Low resistance to extreme pH, heat, dryness and disinfectants
- Easily destroyed outside of body
- Not easily recognized
Non-enveloped virus
- When leaving host cell causes lysis of host cell = sicker and more harm
- Resistant to extreme conditions (most GI viruses)
- Easily recognized by immune system
How are viruses classified? (5)
1.Genome composition (RNA vs DNA)
2.Capsid structure
3.Presence of envelope
4.Type of host; plants, animals or human
5.Mode of action/how they replicate
Viral life cycle : 8 Steps
- Binding and Attachment
- Fusion
- Uncoating
- Reverse transcriptase
- Integration
- Transcription
- Translation
- Budding
Explain: Binding and Attachment
Virus has attachment sites that attach to complementary receptor sites on the host cell’s
surface
Explain: Fusion
The virus envelope fuses with the host cell membrane, and the virus’s RNA and enzymes enter the cytoplasm.
Explain: Uncoating during viral replication
After penetration the virus uncoats the protective capsid and releases the viral genetic information + the ezymes integrase and protease into the host cytoplasm.
Explain the Reverse Transcriptase step of viral replication
The enzyme reverse transcriptase now copies the virus’s single stranded RNA, and then in reverse makes another mirror-like copy to create a double-stranded DNA (sDNA) – this is
an error prone process
Explain the Integration step of viral replication
New DNA enters the host cell nucleus and integrase facilities the integration of viral DNA into host chromosome. Viral DNA is now called a PROVIRUS - it remains latent or is transcribed into RNA
Explain the Transcription step of viral replication
Since provial DNA cannot leave the nucleus, gets transcribed into mRNA and transported to ribosomes
Explain the translation step of viral replication
mRNA gets turned into viral proteins by the host cell’s ribosomes. The protease enzyme then helps process the new polypeptides into proteins which then get turned into viral particles
Virion may choose to live as latent and not go out of the cell
Budding
Virus buds out the cell. Viral particles released from the host cell enveloped in plasma membrane from the surface of the infected cell, new viruses go and infect other cells
Chain of infection (6 steps)
6 steps of disease course
- Exposure to pathogen
- Incubation stage
- Prodromal stage
- Acute stage (disability or DEATH)
- Convalescent stage
- Resolution stage
Explain the exposure stage in the disease course
Virus enters system
Explain the incubation stage of the disease course
- Virus invades host cell and replicates
- Each virus produces a million copies
** * Asymtomatic phase
Factors that affect duration of the incubation period
- Health of host
- Size of innocuous
- Virulence of virus
Explain the prodromal stage of disease course
INFECTIOUS
- Typically contagious 24h before symptoms occcur
- Contagious for a period of 3-5 days following onset of symptoms
Acute stage
(influenza)
Resp Symptoms
Systemic Systems
Respiratory symptoms – runny nose, cough, sore throat
Constitutional symptoms – fever, fatigue, malaise, chills
Complications of influenza
Secondary infections, pneumonia, sinus infection, ear infection, DEATH
Explain the convalescent/resolution stage of the disease course
- Convalescent: immune system has contained the infection, progressive elimination of virus, repair tissue damage, symptoms dissipate, few days to a week longer depending on person’s health
- Resolution: total elimination of virus and no s/s
