Viruses Flashcards
Do viruses have ribosomes?
- no
If viruses don’t have ribosomes, how do they form viral proteins?
- they use ribosomes of their host cells to translate viral messenger RNA into viral proteins
Where do viruses get energy?
- they derive their energy and all other metabolic functions from host cells
Do viruses contain DNA?
- all of them contain nucleic acid: either DNA or RNA but not both
- they also have a protein coat which encases a nucleic acid
What are some viruses enclosed by?
- an envelope of fat and protein molecules
What is a virion?
- a virus particle in its infective form outside the cell
- each virion contains at least one unique protein synthesized by specific genes
What are virioids?
- disease-causing organisms that contain only nucleic acid and have no structural proteins
- virus-like
What are prions?
- virus-like particle
- composed primarily of a protein tightly integrated with a small nucleic acid molecule
How are plant viruses transmitted?
- they can’t penetrate plant cell walls
- transmitted by insects or other organisms that feed on plants
How are bacterial viruses like T4 bacteriophage transmitted?
- they have a tail which attaches to bacterium surface by means of proteinaceous pins
- tail contracts and tail plug penetrates cell wall: inject viral nucleic acids
How are viruses classified into families and genera?
- the type and size of their nucleic acid
- size and shape of the capsid
- whether they have a lipid envelope surrounding the nucleocapsid (the capsid enclosing nucleic acid)
Two main types of virus shape
- rods or filaments:: linear array of nucleic acid and protein subunits making up capsid
- sphere: 20-sided polygon
What is the capsid?
- protein shell enclosing nucleic acid
Protein shell enclosing nucleic acid
- capsid
- nucleocapsid
What is capsid composed of?
- proteins organized in subunits known as capsomers
3 functions of capsid
- protect nucleic acid from digestion by enzymes
- contain sites on surface that allow virion to attach to host cell
- provide proteins that enable the virion to penetrate host cell membrane // to inject infectious nucleic acid into cell cytoplasm
What is envelope?
- glycoprotein envelope surrounding the nucleocapsid
What is the envelope composed of?
- 2 lipid layers interspersed with protein molecules (lipoprotein bilayer)
- material from the membrane of the host cell
How does virus obtain lipid molecule for envelope?
- from cell membrane during viral budding process
- replaces the proteins in cell membrane with its own proteins creating a hybrid structure of cell-derived lipids and virus-derived proteins
2 types of RNA based viruses
- with + strand: acts as messenger RNA for direct synthesis of viral protein
- with - strand: virion has an enzyme called RNA-dependent RNA polymerase (transcriptase)
Virus with - RNA strand
- has an enzyme called RNA-dependent RNA polymerase (transcriptase)
- have to catalyze production of complementary messenger RNA from virion genomic RNA before viral protein synthesis occurs
6 steps in viral replication cycle
- attachment
- penetration
- uncoating
- replication
- modification/assembly
- release
What is a lysogenic cycle?
- viral genome is incorporated by genetic combination into a specific place in host’s chromosome
- viral genome here is known as provirus or prophage
What is viral replication?
- formation of biological viruses during infection process in target host cells
Where do DNA viruses develop?
- on the nucleus of host cell
Where do RNA viruses develop?
- in the cytoplasm
Attachment stage in viral life cycle
- binding between viral capsid proteins (or via glycoproteins in viral envelope) and specific receptors on the host cellular surface
Why can HIV infect only a limited range of human leukocytes?
- its surface protein gp120 specifically interact only with CD4 molecule (a chemokine receptor)
How does virion enter the cell in penetration?
- through receptor-mediated endocytosis or membrane fusion
- it’s called viral entry
What is uncoating?
- 3rd stage in viral life cycle
- process in which viral capsid is removed through degradation by viral or host enzymes or by simple dissociation
- end result is release of viral genomic nucleic acid
Replication stage (4) in viral life cycle
- depends on multiplication of genome
Modification: stage 5 in viral life cycle
- sometimes called maturation or assembly
Lysis: stage 6 in viral life cycle
- kills the host cell by bursting its membrane and cell wall if present
How are enveloped viruses like HIV released from the host?
- by budding
What are prions?
- infectious particles that contain no nucleic acids
- transmission is not reliant upon DNA or RNA
What are viroids?
- small plant pathogens that do not encode proteins
- do not have capsid or envelope
- not known to cause human diseases
What causes spongiform encephalopathies?
- infectious structural variant of a normal cellular protein called PrP (prion protein)
Fatal neurodegenerative diseases prions are responsible for
- kuru in humans
- bovine spongiform encephalopathy (BSE) in cattle
Common symptoms of individuals with kuru and BSE
- loss of motor control and unusual behaviors followed by death
Some examples of contagious viral diseases
- flu, common cold, HIV and herpes
Common symptoms of respiratory viral diseases
- runny or stuffy nose
- coughing or sneezing
- fever
- body aches
Examples of respiratory viral diseases
- flu
- common cold
- respiratory syncytial viral infection
- adenovirus infection
- parainfluenza virus infection
- SARS: severe acute respiratory syndrome
- Covid 19
How are respiratory viral diseases transmitted?
- droplets generated through coughing and sneezing
- contaminated objects
Prevention of respiratory viral diseases
- good personal hygiene
- vaccine
Stomach flu
- gastroenteritis
Common symptoms of gastrointestinal viral diseases
- abdominal cramps
- diarrhea
- vomiting
Examples of gastrointestinal viral diseases
- norovirus infection
- rotavirus infection
- some adenovirus infection
- astrovirus infection
Transmission of gastrointestinal viral diseases
- feces
- sharing utensils/personal objects
Exanthematous viral diseases
- cause skin rashes
- measles virus is highly contagious
Examples of exanthematous viral diseases
- measles
- rubella
- chickenpox
- roseola
- smallpox
- chikungunya virus infection
How do chickenpox and smallpox spread?
- by coming into contact with fluid in broken skin lesions
Shingles
- exanthematous disease
- only happens in people who had chickenpox at some point
- reactivation of varicella-zoster virus that’s been dormant
How is chikungunya disease transmitted?
- through mosquito bite and can’t be transmitted from person to person
Treatment of exanthematous diseases
- fever-reducing medications like acetaminnophen
- antiviral drugs like acyclovir can be given for chickenpox and shingles
Hepatic viral diseases
- cause inflammation of liver known as viral hepatitis
- most common types are A,B and C
Transmissions of hepatic viral diseases
- B and C can be transmitted from person to person through body fluids
- B => sexual contact
- A and E through feces contaminated water
- D only if you have B virus
Cutaneous viral diseases
- cause lesions or papules to form on skin
Examples of cutaneous viral disesases
- warts
- oral herpes
- genital herpes
- molluscum contagiosum
Transmission of cutaneous viral diseases
- physical contact
- contaminated object
Treatment of cutaneous viral disesases
- warts and molluscum contagiosum often go away on their own
- can be removed by cryotherapy
- no cure for herpes
Hemorrhagic viral diseases
- damage to circulatory system
Symptoms of hemorrhagic diseases
- high fever
- body aches
- weakness
- bleeding under the skin
- bleeding from mouth or ears
- bleeding in internal organs
Examples of hemorrhagic viral diseases
- Ebola
- Lassa fever
- dengue fever
- yellow fever
- Marburg hemorrhagic fever
- Crimean-Congo hemorrhagic fever
How are dengue fever and yellow fever spreaded?
- bite of an infected insect
How does Ebola spread?
- contact with blood or bodily fluid
How does Lassa fever spread?
- inhaling or consuming dried feces or urine of a rodent with virus
Neurological viral diseases symptoms
- fever
- confusion
- drowsiness
- seizures
- coordination problems
Neurological viral diseases examples
- polio
- viral meningitis
- viral encephalitis
- rabies
