Viruses Flashcards
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What are some infectious limitations of viruses?
-Obligate intracellular parasite meaning they can reproduce only within host cell
-Virus can infect only a limited number of host cell types
What are the potential types of nucleic acid found in genomes?
Double- or single-stranded DNA or RNA
What is a capsid?
A protein shell that encloses the viral genome
What is a capsomere?
Built from protein subunits
What is the structure of a tobacco mosaic virus?
cylindrical, made up of capsomeres and has coiled RNA inside
What is the structure of adenovirus
hexagonal made up of capsomeres, with glycoproteins extending from the corners. Contains DNA
What is the structure of Influenza virus?
Membranous envelope with glycoproteins extending from around the sphere. Has Capsids inside with RNA coiled within.
what is the structure of bacteriophage T4?
Has a head containing DNA, has a tail sheath (like a body) and tail fibres (like legs)
What are bacteriophages
Viruses that infect bacteria, have the most complex viral capsids.
elongated capsid head that encloses their DNA/RNA.
Protein tailpiece to attach to host and inject phage DNA.
Can have an envelope.
Reproduces through lytic and lysogenic cycles
Describe the lytic cycle
Phage reproductive cycle that results in host cell death:
1) attachment
2) entry of phage DNA and degradation of host DNA
3) Synthesis of viral genomes and proteins
4) assembly
5) release
Virulent phages reproduce only by lytic cycle
Bacteria have defences against phages
Describe the lysogenic cycle
Replicates phage genome without destroying host
Viral DNA incorporated into host cell chromosome
Integrated viral DNA = prophage
Host cell replicates invaded DNA and passes on to daughter cells
temperate phages use both lytic and lysogenic cycles
Environmental signals such as UV exposure, mutagenic chemicals and desiccation can trigger viral genome and switch to lytic mode
What is the animal virus reproductive cycle?
-Viral genome entry and uncoating of cell
-Cell manufactures viral proteins via replication and transcription
-Viral DNA/RNA and capsomeres self-assemble, producing new viruses
What are viral envelopes?
A membranous envelope
Some envelopes formed from host cell plasma membrane as capsids exit
help virus evade host immune system
Viral glycoproteins on envelope bind to receptor molecules on host cell surface (they do not enter the cell, attach on cell membrane at exit)
Discuss RNA as viral genetic material
-Broadest variety in found in animal viruses
-Retroviruses use reverse transcriptase (RT) to copy their RNA genome into viral DNA
-Functions as both mRNA for synthesis of viral proteins and genome for new virus particles
What is a provirus?
Viral DNA integrated into host genome
Does Provirus remain permanently in the host cell
yes
What does host RNA polymerase transcribe?
proviral DNA -> RNA
What are the 2 major surface antigens of influenza virus
-hemagglutinin (HA)
-neuraminidase (NA)
What usually causes ‘new’ outbreaks of human viral diseases?
Usually caused by existing viruses that expand their host territory
Viral strains that jump species can exchange genetic information with other viruses to which humans have no immunity
What are viroids?
-Simple infectious agents
-Single circular RNA molecule
-A few 100s of nucleobases
-Does not encode any proteins
-Mostly infects plants and disrupt growth
Where is Hep D thought to have originated from?
A viroid
Infection caused by a sub-viral satellite
-ve sense, single-stranded RNA virus
Can propagate only in presence of HBV
What are prions?
slow-acting, virtually indestructible infectious proteins cause brain diseases in mammals. Spread by converting normal form of protein to prion version
Causes mad cow disease
What are the 2 domains of prokaryotes and where do they live?
bacteria and archaea
Thrive almost everywhere in all conditions
Discuss prokaryotic metabolism, (an)aerobes..
-Obligate aerobes require O2 for cellular respiration
-Obligate anaerobes poisoned by O2
-Facultative anaerobes can survive +- O2
Discuss chemical cycling by prokaryotes
Chemoheterotrophs - decompose corpses, dead vegetation and waste products
They are N-fixers, Fix N2 from air to usable NH3 (ammonia) – a fertilizer, e.g.
bacterial genus Rhizobium
Increase availability of N, P, & K for plant growth
Can also immobilise / decrease nutrient availability
What are the typical structures of eukaryotic cells
-nuclear membrane
-cytoplasmic membrane
-ribosomes
-mitochondria
-nuclear membrane
-several chromosomes per cell
membrane-bound organelles
What are Anammoxosomes
-Membrane-bound organelle produces energy for bacteria that perform anaerobic ammonia oxidation
What are Acidocalcisomes?
membrane-bound acidic calcium storage compartments
What are the typical structures of bacterial cells?
-DNA which can be double- or single-stranded. Bacterial chromosome. Can have circular plasmids
-ribosomes
-cytoplasm
-cell wall
-flagellum
-cytoplasmic membrane
-Generally lacks membrane-bound organelles
What are Gram stains and what does it mean if they are negative?
Gram stains test for in bacterialinfections. Coloured pink if ve = negative.
Bacteria cell wall structures?
-Give bacteria shape
-Protect them from
osmotic lysis
t-oxic substances
Contain a unique polymer.. peptidoglycan
-Bacteria classified into 2 groups based on
composition of this polymer in cell wall
-Differentiated by stain developed by Hans Christian Gram in 1884
An additional polysaccharide or protein layer called a capsule
covers many prokaryotes
Bacteria can be one of 3 shapes… what are these?
Coccus, Rod, Spirochete
Bacillus anthracis is an example of what?
Gram-positive that causes anthracis
What is the density of organisms in the stomach
10^3-10^5/g
What is the density of organisms in the large bowel and anus?
> 10^10/g
What is the role of normal microbiota?
Protect surfaces from physical colonisation and by pathogenic bacteria from others..
Define microbiome
microbes, their genomes + environmental interactions in a defined environment
Discuss the (mostly) symbiotic relationship between gut microbiome and host
Human host provides food, warmth etc.
Microbes prevents colonisation by pathogenic bacteria, ferment unused energy substrates, regulate gut development etc.
What are the principles of pathogenesis
1) Attach to / invade host
2) Evade innate local defences & spread in the body
3) Multiply
4) Evade adaptive defences long enough to complete life cycle
5) Leave body and spread to fresh hosts
What is an example of bacterial micro-colonies growing on tooth surface?
Streptococcus mutans which ferment sugar to lactic acid causing decalcification of enamel, leading to tooth decay
How does penicillin work?
Prevents peptidoglycan cross-linking (which is necessary for proper cell wall assembly) and bacteria lyse under osmotic pressure
How do anti-viral agents work?
Must inhibit multiplication of virus but not infected host cell
