Viruses Flashcards
Most abundant microbes on earth
Virus
What does it mean that a virus is an “obligate intracellular parasite”
Must exist within a cell
What kinds of cells do viruses infect
Infect all kinds of cells (prokaryotes and eukaryotes)
Specific, eukaryote virus vs prokaryote virus
What kind of cells do viruses have
Acellular (not all the characteristics of the cell) or subcellular (missing stuff that constitutes thecell entities
Why are viruses not considered living
Acellular and cannot reproduce independantly
Size of virus
Extremely small: 30nm (poliovirus) to 300nm (vaccinia virus) in diameter
Structure of virus
Outside: protein coat (capsid)
Some have lipd envolope (envolope virus
No evnolpe = naked virus
Small genomes, very few genes (3-100s)
DNA or RNA (NEVER BOTH)
Few proteins, NO ribosomes or ATP-generating mechanism
Compare viruses and bacteria
Viruses do not contain both RNA and DNA
Bacteria does
Viruses are not sensitive to antibiotics while bacteria are
Viruses are sensitive to interferons
Capsid
protein coat that enclose and protect genetic material
Some of have external lipid covering, some do not
Capsid made from identical subunits called capsomers
Viruses classified into several morphological types
Helical
Polyhedral
Complex
Envoloped
Helical viruses
Long rods, cylindrical capsid; rigid OR flexible
DNA/RNA within a hollow, cylindrical capsid (Helical structure_
Ex. Ebola or rabies
Polyhedral viruses
Many anim, plant and bacteria viruses tend to be this type
Icosahedron shape: 20 trianglualr aces and 12 corners
Each face forms and equilateral triangle
Ex. Adenovirus, poliovirus
Complex viruses
Complicated structures (i.e. bacteriophage)
Capsid head is polyhedral and the tail sheath is helical
Other structures such as tail fibers (proteins) and pin (for injecting DNA)
Ghost virus: Have already injected DNA into bacterial cell
Are Helical, polyhedral, and complex viruses normally naked or enveloped?
Most are naked
Envoloped virus
Envolope: composed of lipids, proteins and carbohydrates
Derived from host
May be covered with spikes
Glycoproteins fro attachment
Ex.
SARS Coronavirus
Influenza virus
Herpesvirus
How do viruses avoid recognition
Viruses change spike composition to avoid antibody recognition
Naked viruses (plus examples)
No lipid coat outside the capsid
Ex. Rhinovirus
Polivirus
Norwalk
Where do viruses gr ow
Grow in living cells
Bacteriophages from plaques on a lawn of uninfected bacteria
Animal viruses are grown in living animals, embryonic eggs, cell cultures etc.
What is the viruses growth cycle called
One-step growth curve
Eclipse period:
The initial period following the virus entering a host, where the viruses enter the host cells, and so none are detected in circulation
After the eclipse, virions are released from the host cell
Known as the one-step growth curve
Two major cycles of viral replication
Lytic cycle (Reproduction of more viruses) Transcription and translation.
Lysogenic cycle (incorporation of DNA into cell DNA)
Viral DNA incorporated into cell genome
6 steps of viral reproduction
Attatchement
Penetration
Transcription (DNA is transcribed into RNA and used to make proteins from ribosomes)
Biosynthesis (Viral components (proteins) are assembled)
Maturation
Lysis
How do regular bacterial cells produce sickness
Only cells that have picked up extra genes can produce sickness
Lytic cycle
Attatchment and penetration
Biosynthesis, beginning with replication or transcription and translation
Synthesising proteins and assembly into viral particles
Cell lyses and releases viruses
Lysogeny cycle
Cell can continue it’s life indefinitely
Incorpration of phage DNA into bacteria genome = phage conversion, therefore, host acquirees new properties
Some pathogenic E. coli have picked up extra genes from viruses
Diphtheria toxin corynebacterium diphtheria
Many pathogenic bacteria are innocent, but they have been hijacked by viruses to make them pathogenic
Multiplication of animal viruses
Attatchment: Attachment to cell membrane
Penetration: endocytosis (Eukaryote grabs whole viral particle and internalizes it) or fusion
Uncoating: Require viral or host enzymes to break up coat on outside to expose genome
Biosynthesis: The Genome of virus can be used by animal cells to make mRNA, proteins etc. using nucleic acid and oriteinb synthesis
Maturation: Mucleic acid and capsid asembly
Release: Budding (envoloped viruses) or rupture(non-envoloped viruses)
Multiplication of animal viruses
ways a virus can enter a host cell
Endocytosis or fusion for animal viruses
DNA injection by bacteriophages
What is the purpose of encoating the virus once within the cell?
To release genetic material in the case of animal cells
Unneccessary in bacteria cells
What is a part of the biosynthesis stage
Proteins are made based on the mRNA code
What occurs in the maturation stage
Involves the assembly of new viral particles (packaging the DNA/RNA into protein coat)
Two ways that the “release phase” can occur
Budding (if it is an envolope virus) or lysis for naked viruses
Host cell is always lysed in bacteria
Where do the steps of replication occur in bacteria and animal cells
Replication, and transcription takes place in nucleus and translation (mRNA) occurs in the cytoplasm
ALL of these 3 occur in cytoplasm in the bacteria cells
Storage form of genetic info is always
DNA
How are transcription, translation and protein synthesis connected
Viral DNA (Genetic code) transcribed to mRNA (same language, but placed in different form) (Code in transit) Translated to protein by ribosomes (performs functions nd activities and structural support for the cell.\
Is replication connected to transcription/translation
An independent event, not needed for transcription
What is the virus objective in invading a host cell
Multiplication
What enzyme is involved in DNA replication?
DNA dependent DNA polymerase
What is transcription, and what enzyme is involved?
Transcription is the copying of one DNA strand into mRNA, done my DNA dependent RNA Polymerase
What is translation, and which organelle is involved?
mRNA moved to nucleus, ribosomes read info on mRNA, translate to the language of proteins, and then make the proteins (protein synthesis)
When does translation begin in bacteria cells?
Even before mRNA has been completely formed, Ribosomes can begin transcription bc there is no nucleus separation
What is the DNA template strand?
Aka the negative strand or Anti-sense strand
The unzipped strand of DNA from which the mRNA is made from (mirrored from)
RNA vs DNA
RNA: Ribose: One extra oxygen, single stranded, U instead of T
Deoxyribose: missing one oxygen, Double helix, no U but T
What is the mRNA strand that is transcribed from the template DNA strand called?
The Sense mRNA or Positive strand
What is the non-template strand of DNA called?
AKA sense strand OR positive strand of DNA
How many strands of DNA are being used at once in viral replication (assuming there is DNA present)
one, since it will coordinate with specific proteins, and the non template strand is the template for completely different proteins
What is negative mRNA?
AKA Antisense mRNA (-)
Made from the sense mRNA (+)
Exact copy (besides U instead o T) of antisense DNA
How many DNA/RNA do viruses caryy
Single, double, RNA or DNA
What must viruses with a single strand of DNA do to start replication process within a host cell?
The virus must have info/genes that call for the enzyme polymerase to use single-stranded DNA to make double-stranded DNA
Which type of virus carry strand(S) if genetic material that can be used immediately for protein synthesis
mRNA(+)
What happens if a virus carries a double stranded RNA
the host cell must separate the two strands and use the sense strand for protein synthesis
What is multiplied in viral replication?
The viral genome
What enzyme do the host cells not have that single stranded (-)mRNA require?
RNA dependent RNA polymerase
What are the three things a virus needs to do to successfully multiply
Make genome available to the host
Multiply the genome
Multiply the protein components
What does DNA polymerase do
Use DNA templates to make DNA
DNA-dependent DNA polymerase
What does transcriptase do
RNA polymerase (transcriptase)
Use DNA templates to make RNA (mRNA,tRNA, rRNA)
What do DNA viruses do to get the enzymes they need?
Can use host cell polymerase OR can code for their own DNA polymerases and transcriptase
How do RN viruses get the enzymes they need?
Can use host cell polymerase OR code for their own polymerases OR carry own viral polymerases
What type of enzymes can RNA viurses have
“RNA-dependent RNA polymerases”
What type of enzymes do retroviruses have?
Retroviruses (RNA viruses) have reverse transcriptase OR RNA dependent DNA polymerase
Two types of host polymerase
DNA-dependent DNA polymerase
DNA-dependent RNA polymerase
dsDNA double-stranded DNA examples
Herpes viruses (Envoloped; common human infection)
Herpes simplex virus (HSV) or human herpes virus (HHV)
HHV-1 & HHV-2 (Cold sores & genetital herpes)
HHV 3 (chickenpox and shingles) - Varicella-zoster virus
HHV-4 (Mononucleosis and cancer)
HPV (Common cause of warts)
HPV-16and 18 (Genetical warts and cervical cancer
ssRNA(-) examples
Genome: Single-stranded antisense or -ssRNA
Measles virus (evoloped, influenza virus (multiple strands, enveloped), rabies virus (encoloped), ebola virus
ssRNA(+)
Covid19, rhinovirus, hepatovirus, poliovirus
Can carry RNA dependent RNA polymerase
Some do not carry their own enzyme, but it is coded in their genome to make the enzyme RNA dependent RNA polymerase
example of dsRNA
Rotavirus
What is a retrovirus
A unique ssRNA(+) virus that uses reverse transcripase to be converted into DNA and inserted into the host cells genome
this reverse transcriptase is carried by the virus and converts RNA to DNA
What are enzymes made of
Proteins
Where is RNA assembled in the cell
Cytoplasm
Where is DNA assembled in the cell
Nucleus if present, cytoplasm if not
Most of the viruses that cause cancer are
double stranded ones nad the retroviruses bc the genetic material of the viruses become integrated into the host genome
How do cancer causing viruses work
Viruses activate parts of cellular genomes called oncogenes
Oncogenic viruses or oncoviruses
Viruses activate these parts of our genes
Activated oncogenese transform normal cells into cancerous cells
Transformed cells have increased growth, loss of contact inhibition, have virus specific antigens on surface called tumor specific transplantation antigens TSTA or T antigens in nucleus
Examples of retrovirus
HIV-1: AIDS
Examples of Oncogenic DNA virus
Human herpesvirus
Pappillomavirus cause almost all cervical cancers
Hepatitis B virus
Oncogenic RNA viruses
Retroviruses
Human T-cell Leukemia viruses
Types of viral infections
Acute: Sudden onset, e.g. Influenza virus
Latent infections
Virus remains in asymptomatic host cell for long periods
Cold sores, shingles, HIV/AIDS/Leukemia
Recurrent: e.g. shingles
Persistent or chronic infections
Occur over long periods, often fatal
Cervical cancer, Burkitt’s lumphoma, liver cnacer, AIDS
Viruses share similar mechanisms to each other, what process may vary?
the biosynthetic processes to replicate their nucleic acid and transcribe their mRNA vary.
Some viruses use host cell enzymes (DNA polymerase and RNA polymerase) to replicate their nucleic acid and transcribe their genes, whereas other viruses make use of viral-encoded enzymes. In all cases, it is the host cell ribosomes, tRNAs, and ATP that enable translation of viral proteins.
What is the function of the structural elements of a virus?
To package and protect the viral genome
In which stage does formation of mature viruses occur?
Assembly
In which stage is the viral DNA introduced into the cell?
Penetration
The host DNA is usually degraded during which stage?
Biosynthesis
What would be the fate of a lytic bacteriophage if the host cell died prior to the assembly stage?
The virus would not be able to infect new hosts.
When the phenotype of a bacterium is changed via ________________
, harmless bacteria can become pathogenic and are able to produce deadly toxins and proteins.
Lysogenic conversion
Are capsids aquired from the host upon release?
No
An inactive bacteriophage is a ________
Prophage
When a bacteriophage infects hosts’ cells and allows them to grow and replicate normally for many generations before lysis, this is considered
Lysogeny
Temperate phages
another name for lysogenic phages that have a lysogenic replication cycle.
a phage is excised from the host chromosome via physical or chemical agents that damage the genetic material of the host.
Induction
What can bring on shingles
Stress and old age
Major way viruses differ from bacteria?
Acellular
A feature that may be found in viruses but never in bacteria is
May contain an RNA genome
Are virus enzymes catobloitic
No
Why aren’t viruses living
Not composed of cells
What common bacterial test is NOT used for virus
Biochemical tests
Are Glycoprotein spikes are found on the capsids of all viruses?
No
Bacteriophages and animal viruses do not differ significantly in which one of the infection processes?
Biosynthesis
Lysogeny is the process of:
Phage DNA is incorporated into host cell DNA.
A viral envelope is acquired during ________.
release
A virus’s ability to infect an animal cell depends primarily upon the ________.
presence of the corresponding binding receptors on the cell membrane
What enzyme porudced by the host cell is not used by viruses
DNA polymerase
Most RNA viruses carry which enzyme?
RNA-dependent RNA polymerase
RNA viral multiplication process
