Topic 3 Flashcards
Name some microorganisms that are prokaryotes
Eubacteria, Archaebacteria, cyanobacteria (blue green algae)
Name some microorganisms that are Eukaryotes
Fungi, protozoa, unicellular algae
Are all cellular microbes infectious? expections
Both prokaryotes and eukaryotes have many infetious cellular microbes. Exccept for Archaebacteria
Examples of non-cellular (acellular) agents? Are they all infectious?
Viruses
Viroids
Prions
Plasmids
Transposons
(plasmids and transposons can move cell to cell)
All non-cellular agents are infectious, but in some cases, the exact mechanism of transmissibility is not yet understood
What virus causes measles? How does it spread?
morbillivirus causes measles. It’s an airborne disease, which means it spreads through the air when an infected person breathes, coughs, sneezes or talks.
About viruses: are they self-sustaining, why do they reproduce within a susceptible (host) cell:
- Viruses are not self sustaining
They reproduce within a susceptible (host) cell: are an obligate intracellular parasite because:
- they have no metabolic or energy generating pathways
- they cannot synthesize constituent molecules (nucleic acid or protien outside the host cell)
- they are infectious (transmission between hosts)
- can use the machinery of the susceptible host to produce more viruses at the expense of the host cell
Whats the smallest particle/agent
A ribosome
Whats the largest
Pox virus, approx. bacterium
What criteria is used to group viruses?
- Size and morphology (consider presnence of envelop and organiziation of capsid)
- Host specificity (host range)
- Type of nucleic acid present in the viral genome
- Viral genomes consisting of single stranded DNA are divivided according to the “sense” of the RNA in the virus particle (virion)
- the disease or syndrome caused by the virus
Size and morphology (consider presnence of envelop and organiziation of capsid)
- Enveloped or naked
Do all viruses have capdis
yes
what shapes can virus capsids have
spherical, icosahedral, helidcal or complex (neither purely icosahedral nor helical)
Where are the virus specific spikes
On capsid of naked or evnilop
Where does the lipid come from?
Host membranes
What is harder to kill? enveloped or non-enveloped viruses
naked viruses
What is the capsid made of?
protein
made up of capsomer units
usually 1 protein/many subunits, repeating
What is the structural unit of capsids?
Capsomeres
Is the tobacco Mosaic virus envloped? waht is its capsid structure
its helical. no envelope
What makes bacteriophage T4 complex?
Icosahedral head (capid) + tail (no envelope
What determines specificity in viruses?
Spike proteins
Is corona virus enveloped? what is the shape of the capsid? What does its spike protein target?
Yes. Helical capsid
Targest respiratory system and gastrointestinal system (diareaarrer)
Is influenza enveloped? What is the nucleocapside shape of influenza? How many spike proteins does influenza have?
Pleomorphic?
yes. Helical
Influenza has 2 different type of spike proteins.
Pleomorphic due to having a flexbible nucleocapsid
Examples of viruses with capsids of complex symmetry
Pox viruses and bacteriophages
Elaborate on criteria used to group viruses: 2. Host specificity (host range)
The cell or organism that the particular virus can bind to (absorb), infect, and grow in (reporduce)
Bacterial viruses: (bacteriophage); E.coli virus
Plant virus: tobacco mosaic virus
Animal virus: human virus, avaian virus
- Type of nucleic acid present in the viral genome
RNA or DNA
Linear or circular
Double stranded or single stranded
Continuous or in segments
Classify the classes of genomes in viruses: DNA viruses, RNA viruses, RNA/DNA viruses
DNA viruses: ssDNA, or dsDNA
RNA viruses: ssRNA or dsRNA
RNA <-> DNA viruses
ssRNA (retroviruses)
dsDNA (hepadnaviruses)
Whats the most common form of DNA virus?
Doubel stranded
- Viral genomes consisting of single stranded DNA are divivided according to the “sense” of the RNA in the virus particle (virion)
(+) (sense) sequence of RNA pakcaged the same as that of the viral mRNA, such that the mRNA can be directly TRANSLATED
(-): minus or anitsnese: the sequence of the packaged RNA is complementary to the viral mRNA and cannot be directly TRANSLATED
-> influenza virus
Explain how each of the following reaches mRNA (+)
dsDNA (+) virus
transcription of minus trand -> (+) mRNA
Explain how each of the following reaches mRNA (+)
ssDNA(+) virus
syntheissi of other strand -> ds DNA intermeidate -> transcription of minus strand -> +MRNA
Explain how each of the following reaches mRNA (+)
dsRNA (+) virus
transcription of minus strand -> mRNA (+)
Explain how each of the following reaches mRNA (+)
ssRNA (+)
used as mRNA directly
Explain how each of the following reaches mRNA (+)
ssRNA (-)
transcription of minus strand -> mRNA (+)
Explain how each of the following reaches mRNA (+)
ssRNA (+) retroviurs
reverse transcription -> dsDNA intermeidate -> transcription of minus strand -> mRNA (+)
Whats the difference between viruses and cells
Metabolism
Division/grow
acellular
obligate
DNA/RNA?
ssds?
size?
capsid/envelop
replicate in essmebly manner
Poxviridate?
ds DNA , orthopoxvirus 9small box)
herpesviridae
dsDNA,
Simplex virus ; herpese type 1
Vaericellovirus (chicken pox)
Hepadnaviridate
partial single partial double DNA, example hepatisits B
Paroviridae
single stranded DNA; erthyrovirus (paro infection)
Coronaviridae
ssRNA, +
Retroviridae
single +, segmented
example leukemia virus, lentivirus (ADIS)
Orthomyoxiviridae
ss RNA -, segmented, influenza (flu)
Paramyoxyviridae
ssRNA, (-),
Paramyoxyvirus (common cold, respiratory infections)
pneumonia virus (pneumonia, common cold)
Morbilivirus (measasle)
Rhadoviridae
RNA Ss (-): rabies
lyssavirus
Is the spike protein in coronavirus a glycoprotein?
Yes
What is a virion?
the complete, infective form of a virus outside a host cell, with a core of RNA or DNA and a capsid.
How does the organization of the viral genome within the viral particle vary?
Some viruses are ssRNA or DNA
can be segmented
-> dictates how and where within the host cell the viral genome is replicated
How do viruses reproduce?
- Viruses attach the host cell
- Penentration into the host cell. Nucleocapsid or nucleic acid enters The genetic material enters into the host cell
- the genetic material is replicated
- the virion assembles
- the particle exits via lysing or budding out
What proteins to virions carry
capsid protein
envelop prtien
retroviruses carry out accessory proteiins
What happens if a receptor is removed from the host cell
virus wouldnt attach but would be detrimental to the host cell
Is attachment a random event? What allows viral attachmnet
Receptors on the host cell.
it is the basis of specifificity of how viruses gain entry.
depends on the virus (if a host cell does not have a receptor -> it cannot be a host for that specific virus
receptors play an important role in the host cell
example of receptor: bacteriophage lamda
receptor: lamB protein on SURFACE of E.coli
Part of transport system for the uptake of sugars such as maltose. if lamda receptor was missign, lamda cannot infect. but host would lose ability to take up maltose -> losing viability in enviornments where maltose is the predominant sugar source
Virus: bacteriophage R17.M13, f1,d1
recpetor: specific positions on pili
infects E.COli
Bacteriophage spo receptor
Bacterium B.subtiliss
binds to flagella structures used for motility
Viral receptors in multicellular organisms are usually?
Usually a specific protein or glycoprotien on the surface of specific cell types within certain tissues. The prescence of the receptor determines the host specificiity and the tiusse specificity within a particular host.
Whats the receptor for poliovirus
A specific glycoprotein intracellular adhesion moleule (ICAM) located on the human nasophraynix, gut and spinal cord
Picornavirus DAN
positive-sense, single-stranded RNA (ssRNA)
Rhnovirus (common cold)
Rhinovirus receptors
ICAM found in the nasophraynyx and respiratoryr epithelium
Measles receptor
Protien CD46 found in a number of tissues (less speicfic)
Receptors of HIV
Protein CD4 found in the plasma membrane of CD4+ leukocytes (type of while blood cell)
Rabies virus receptor
Acetylchloine receptors in the neuronal plasma membrnae
SARS receptosrs
ACE 2 (angiotensin converting enzyme): blood pressure regulation (spike protein cause leaky lung tissue (pneumonia)
What is hemagglutinin
Hemagglutinins are homotrimeric glycoproteins present on the protein capsids of viruses in the Paramyxoviridae and Orthomyxoviridae families
What is infleunza receptors
Hemagglutinin contains a receptor bidnign site for sialic residues on glycans of host cell surface
Adsoprtion is the same as
attachment
What is the nucleocapsid?
Nucleocapsid is an unit of vrial structure, consisting of a capsid with the enclosed nucleic acid
What are the steps to virus adsorption (attachment), penetration and uncoating
Several different mechanisms by which different animal viruses gain entry into the host cell. Each step includes:
- Initial contact between host receptor and the virus by random collision
- Following contact, virus binds tightly to its receptor
- Induction of a number of host and viral processes
-> can result in the viral genome only or viral capsid containing the genome or entire enveloped virus entering the host cell.
What are the different entry mechanisms/penetration mechansims?
- Fusion
- Caveolin mediated endocytosis
- Clatherin mediated endocystotis
- Non clatherin non caveolin endocystotis
- Bulk phase endocytosis
- Phagogytosis (lysosome later fusees with the phagosome, decoats the virus)
How does HIV enter the cell
Binds to CD4 receptors. fuses with plasma membrane. Carries its own reverse transcriptase protein -> conducts reverse transcription and merges with the nucleus.
How does Influenza enter the cell
Via silated receptors. Endocystosis. Endosome (low pH -> genetic material is released)
How does the virus replicate, package and exit from the host cell
- the nucleic acid genome is released from the nucleocapsid
- The viral genome is replicated first (exception of plus strand RNA which can immediately be used to make early proteins if needed)
- Viral genome is transcribed
- Copies of viral genome are packaged into new capsids to give nucleocapsids
- Neew viruses leave the cell and infect other cells.
(if virus needs an envelop, it buds with an envelop, ER< nucleomembrane, plasma.
What machinery do viruses use for replication and transcription?
Some viruses either encode or bring into the cell certain enzymes required for replication and on occasion the enzymes needed for transcription.
Other viruses use all host enzymes and accessory proteins
What is common in the process of replciation packaging and export of all viruses
The precursors required for the processes are hijacked from the host cell (nucleotides for nucleic acid syntehsis, ribosomes for amino acids,etc.)
The new copies of viral genome are packaged into the newly synthesized capsids. Where do DNA/RNA viruses replicate and package?
Viruses that have DNA genomes replicate in the nucleus and the viral genome is pakcaged in the nucleus (mRNA moves out of the nculesu -> moves back into the package)
Most RNA viruses replicate and package in the cytolasmi
How do packaged capsids leave the host cell and infect other host cells
Enveloped virurses either bud from the host plasma membrnae, nuclus or from the endoplasmic reticulum or Golgi.
The mature viral particle is than released from the host plasma membrnae by exocytosis
(the membrane from which viruses bud are altered to include viral envelop proteins)
Naked viruses usually lyse the host cell
Difference between lytic and lysogenic cycles
Lytic cycle:
virus enters the cell -> replicates -> assembles and leaves the cell via lysing
Lysogenic cycle:
virus enters the cell -> genome is inserted intot eh host DNA. (as the cell divides more copies of the genome magnify)
But some induction event can cause it to turn to the lytic pathway
Where does Herpes virus bud otu from?
the nuclues
Where does influenza virus bud out from
bud out from plasma membrane
How does the herpes virus replicate? where does it bud out from? What is its DNA?
dsDNA
Herpes virus enters by fusing with the host membrnae
DNA enters nucleus.
mRNA is transcribed in cytoplasm-> proteins attach to membrane of nucleus
after DNA is replicated, buds off from nucleus
How does coronavirus 3 replicate? get in and otu of the virus
SARs-Cov 2 enters via membrane fusion or endocytosis (on interaction with spike protein and ACE-2 receptor)
Releases the genome. -> translation of viral polyprotein
Exits via ER or golgi budding, endocytosis
Whats the structure of HIV?
Enveloped with glycoproteins
Capsid
RNA (two identical strands of ss (+) sense RNA)
Pakcaged 3 different enzymes; integrase, reverse transcriptase and protease
How does HIV replciate?
HIV enters by fusing with the plasma membrane.
Revser transcriptase (not only in genome but also packaged along) makes RNA-DNA hybrid -> DNA-DNA hybrid.
This gene is integrated in othe nucleus. => genetic material is made.
Later -> the RNA genome for the next viral generation with the proteins can be made.
Bud out of the plasma membrane
Elaborate on the mechanism of viral release (for enveloped viruses
Speical matrix protein (m protein encoded by virus) attaches to the PM and aids binding.
Envelop rptoeins such as hemaglutinin and neuraminidase are inserted into the plasma membrnae.
Host membrnae proteins are excluded.
VIrus buds out to form viral envelop and mature virion rleased
Function of neuraminidase
is a silaidase, removes sialic acids from glycoprotein found on the host receptor (thought to aid the escsape from the host cell but aalso may help to alter the mucous covering memrbane for entry and/or altering the host recpetor
Function of Hemagglutinin
Hemaglutinin spike causes host cell membrane to bulge inward to form vesicle for receptor mediated endocytosis
What is Influenza A/B/Cresponsible for?
A: Pandemics, epidemic spreading over large geographical areas
B: cause localized outbreaks /epidemics with no clear subtypes
C: cause only mild symptoms and no clear subties
Antigenic shift. vs. antigenic drift.
Shift (usually specific to influenza)
Called viral shift or re-assortment for other virues
2 different strains of influenza combine to form a new subtype havinf a mixture of surface antigens.
(occurs only in influenza A, since it can infect more than just humans)
antigenic shift: natural mutations that occur overtime of known strains to evade the immune system. (mutation/random point mutation such as change in neuraminidase/hemagglutinin)
(happens in all types of influenza: A,B and C. (B, and C only infect humans which minizmies the chance of mutating drastically)
Example of antigenic shift in fluenza (pandemic)
H1N1.
Antigenic shift occurs when an individual is infected with human type A, annd another viruses
What are the types of viral infections
- Acute
- Persistent
+ Chronic viral infections
+ Latent viral infections
What is acute viral infection?
Rapid onset and lasts relatively short time like influenza
Types of persistent infection:
- Chronic viral infections: symptosm mild or absetn for long periods but virus always detectable (hepatitis or HIV)
What is Latent viral infection? Examples
Virus stops reproducing and remains dormant for long periods of time before coming active again.
During latency, has no symptoms, antibodies or virus detectable.
- Herpes simplex virus: cold sores/ genital herpes
Disease is contagious particularly during an outbreak and is incurable. Usually an infection on the lips. (different from canker sore)
Initial outbreak less severe (flu like symptoms, swollen glands), subsequent outbreaks periodic/espiodic: stress, illness fatigue
- Epstein Barr virus: chronic fatigue syndrome and infectious mononucleosis:
When infected, usually asymptomatic, Epstein-Barr can reoccur any time, especially after illness or stress
- Varicella zoster (shingeles)
Where does chicken pox remain dormant in the body
in the nerve root cells of the boy
What is shingels
also known as herpes zoster.
chicken pox awakens within the nervous systme and causes shingles (causing a blistering rash and severe brunign pain)
Shingles isn’t contagious but coming into contact with a person with shingels could lead to chicken pox
Where at how does Cold sores infect?
Initial infection occurs and symptoms include cold sores or fever blisters, the virus than moves up the trigemial nerve where it becomes latent.
When activated by fever, sunburn, other infection, moves down the nerve
How are viruses transmitted?
Direct transmission via contact with an infected host (secretions)
Indirect transmission via contact with virus on a non-living object or aerosol
Via a vector that may or may not be the host
like insects
Which viruses use mosquitos to transmit disease?
West Nile virus and yellow fever virus
Antiviral targets: viral uncoating. Effective against?
Effective against Influenza A virus.
Amantadine
Rimantadine
Antiviral target: nucleic acid sysntheiss
effective against herpesvirus and HIV
such as nucleoside analogs
Non-nucleoside polymerase inhibitors
Non-nucleoside reverse transcriptase inhibitors
Antiviral target: assembly and release of viral particles
Effective against HIV: protease inhbitors
Effective against influenza viruses: neuraminidase inhibitors:
Tamiflu and Zanamivir
What were the 2 types of COvid vaccines?
mRNA vaccine:
mRNA containing instructions on how to make spike protein dilivered in lipid nanopartciles
Non-replicating viral vector
A viral vector without the ability to replicate carries a gene that encodes for the spike protein -> host uses gene to make spike proteins -> induce immune repsonse
What is virus tropism
the affinity and ablity of the virus to seek out and find specific host cell types
What is gene therapy.
The component of the virus with a desired tropism is altered so that a desired gene replaces certain viral genes.
Natural tropism of a virus is used to deliver the desired gene to the appropriate cell.
Waht is the requirement for gene therapy
new gene must be able to fucntion after delivery to host cell
must not induce massive inflammatory response or significiant immune resposn
Ecample of success gene therapy?
Using tropism of certain viruses for receptors in bone marrow cell. Used to treat severe combined immunodeficiency disease SCID (“bubble baby syndrom”)
What are some common mechanisms for gene therapry DNA entry
- Retroviral entry
Via receptor (endosome)
Single stransded RNA -> RNA/DNA -> dsDNA
which then gets integrated into the host genome during mitosis when the nuclear membrane disoslves
- Adenoviral entry:
double stranded DNA, receptor mediated, endocytosis.
Can enter nuelcus anytime via formation of capsid pore complex. Can be expressed without integration into host cell.
Nonviral vector (not yet understood)
What is a viroid
Smaller and simpler than viruses.
INfectious agents of plants (can be transmitted plant to plant).
Mechanisms of transmission is poorly understdood.
Structure of viroid
Circular, single stranded RNA, exist as a closed circle collapsed into a rod-like structure by instrastrand base pairing.
Viroid RNA is not packaged into protein capsid. Usually found in the nucleolus of infected cells
viroid RNA does not act as mRNA to direct protein syntehsis
Do not replciate in hte cyltoplasms, but replicate in the nucleus or chlropoast
Appear to be replicated by rolling circle type of repication with the RNA mistaken for piece of DNA
Have enzymatic acitivty (ribonuclease that cleaves other RNA molecules -> ribozyme)
How cause disease? Not known, but may cleave specific plant mRNA that cause silencing of certain genes
What are prions?
Proteinaceous infectious particles or plaques of PrP (Prion protein)
Infectious, theres no evidence they are asosicated with any type of nucleic acid
What do prions cause
tranmissible, progressive neurodegenerative diseases called transmissible spongiform encephalopahties (TSEs)
-> results in progressive degeneration of brain tissue, resulting in dementia, dealth -> similar disease seen in humans, sheep and cattle
Exa,ples of disseases related to prions in humans, sheep, cattle, deer
Humans; Creutzfeldt-Jacob disease (CJD) or vCJD (eating tainted meat), kuru
Sheep: scrapie
cattle: bovine spongiform encepalopathy (BSE) or “mad cow disease”
how does prion cause isuses
brain in infected animals contain high lvels of a varient of a normal brain protein called PrPc.
Normal PrPc: role as a chaperone
Infectious form: PrPsc (abnormally folded) or chmeically modified.
PrPsc induces abnormal folding and conformational changes in cell proteins leading to protein tangles.
Is infectious PrP associated with nucleic acid
All studies support the conclusion that prions only consist of protien
Can a prion-associated disease be transmitted from person to person or from animal to animal?
Kuru was transmitted between humans in Paupa new guinea tribes by eating disease brain tissues of other umans
CDJ between humans occured via corneal transplants
Increase in human form of BSE: eating BSE tainted beef
BSE (mad cow), prsence of briain, spinal cord, bone meal in cow feed
