Lecture 2: After The Midterm Flashcards
Viruses
- Acellular infectious particles
* Obligate intracellular pathogens
What does, “Acellular infectious particles” mean?
non-living, goes into a cell & creates a +/- = parasitic relationship (virus benefits & host cell doesn’t), v. small but it’s there
What does, “Obligate intracellular pathogens” mean?
Reproduce ONLY INSIDE of living cells
• LACK independent metabolism
–>NOT free-living
has an obligation to be in the boundaries of the cell, in order to actually execute viral replication, within the cell, that it has an obligation to be within the boundaries of the cell, in order to execute viral replication, & is disease causing
Are viruses free-living?
O - lack independent metabolism
think: on desk you put sugar, lipids, iron, sodium, water, potassium - anything that’s needed for a living cell to thrive, & then you put virus on top (cough SARS-COV 2 on top of that pile of nutrient for ex), you would NOT get SARS-COV 2 replication (not able to), b/c it doesn’t have the machinery & enzymes for glycolysis & TCA cycle or for fermentation, it doesn’t have ribosomes to protein assembly –> therefore lacking independent metabolism & are therefore NOT free-living
- they’re only able to make more of themselves, if they’re inside of a living cell that provides them with machinery in order to be able to do so
- the virus itself couldn’t infect you, but on the pile on its own don’t expect increase in #
- to contrast, if you put bacteria that were free-living on that pile of nutrients & provided the temp & the pH was within the range for growth, you would def. expect that the # of bacterial cells that fell on that pile of nutrients would now start to increase as a result of growth b/c they do have enzymes for growth, ribosomes for protein syn & can replicate their own nucleic acid, so you can see the diff b/t a virus & a living cell
What are viruses composed of?
- Nucleic acid GENOME (DNA or RNA) and protein coat (CAPSID)
- Together=NUCLEOCAPSID (bare min)
capsid= like a 3d dome, made out of proteins called capsiomeres
nucleic acid= provides recipe for whatever the virus knows it needs to make on its own, bc host cells provide everything else “only pack what they need
Give ex of DNA and RNA virus
(DNA or RNA are the recipes to allow for assembly of viral material)
DNA: hepatitis b, HPV, EBV (casues mono) ALWAYS a DNA virus & will NEVER change
RNA: HIV, Covid, Influenza ALWAYS a RNA virus & will NEVER change
Naked virus
has genome
capsid- made out of capsiomeres
; collectively nucleocapsid
spike proteins; embedded on outer surface of capsid for the naked virus
* UNIQUE VIRAL CHARACTERISTIC AS IS CAPSOMERES
Will they find info in YOUR cell to build their capsid protein or to build their spike protein? If not, where is the recipe to make spike protein & capsid protein
NO - it will be on their DNA or RNA
Envelope virus
Some viruses have an envelope – layer of lipid surrounding the nucleocapsid
takes time to build an envelope on the outside of the structure & that’s where the spike protein will get embedded or inserted b/c that’s now the outermost layer
nucleocapsid + envelope
*ENVELOPE IS AQUIRED FROM THE PM WHEN THE VIRUS LEAVES YOUR CELL
Comparison of naked & enveloped virus particles
Naked:
- Nucleocapsid: nucleic acid & capsid (composed of capsomeres)
Enveloped:
- Nucleocapsid: nucleic acid & capsid
- Envelope
what will this envelope be structurally v. similar to?
- it would look exactly like a PM b/c that’s where it came from - BUT it is NOT a PM
- b/c a PM surrounds a living cell creating the boundaries of that cell
- the PM is also gonna provide selective permeability & this envelope does none of that - it’s just an outer layer that it picked up in the process that it uses to leave your cell
- needs it for infectivity b/c that’s where its spike proteins are & spike proteins are critical for infectivity
Anything that disturbs this envelope, disturbs ____
INFECTIVITY
- Covid, HIV, influenza are ENVELOPE VIRUSES
- so any chemical disinfectant that you use that would disrupt a lipid bilayer like a PM will disrupt this envelope, & when it does you lose it, which took the spike protein that were needed for infectivity
Which type of virus do you think is more hardy, & which type of virus is more challenging to get rid of when you use chemical disinfectants & things like it?
NAKED VIRUS are HARDER to get rid of - b/c they don’t have an envelope to disturb
- LAST LONGER when you use chemical disinfectant & not all disinfectants will work against them
ENVELOPED virus is EASIER to get rid of by comparison
Viral Genome
• DNA or RNA- NEVER both
- a virus that’s an RNA virus today, is a RNA virus always (doesn’t change)
- living cells always have DNA as a component of the cell material
• Single stranded OR double stranded
- we only have ds nucleic acid, but viruses get an option
- HIV, covid, influenza are ssRNA
- HPV is DNA virus
• Circular OR linear (ss or ds)
- if circular & ds - comparable to bacterial chromosome
- if linear & ds - comparable to us
• Can be in several pieces – SEGMENTED
- min. amount of waste virus will have on the cell
- Genome size (complexity varies)
- Smallest ~ 3.6 kb for some ssRNA viruses (3 genes)
- Largest > 150 kbp for some dsDNA viruses (> 100 genes)
DNA viruses have the capacity to…
cause cancer (some of them) - b/c their going into the nucleus, interferring with normal cellular activity, they can upset cellular respiration & these processes to make the cell become a danger inside the body
The type of their _____ can play a role in what that virus’ capabilities will be
nucleic acid
Non-segmented viral genome
everything in a line
- b/c it’s all together - you need to make 1000 of all
INCREDIABLY wasteful - using our cell to do this
- more parasitic to the cell if you’re being excessively wasteful beyond your need
Segmented viral genome
influenza has 8 pieces of RNA that constitutes its genome
- each gene gets its own segment
- so you can make what’s needed - NOT being excessively wasteful
BUT you have to package virus into a new viral particle, so it can exit the cell
How will a segmented genome might have more problems than a non-segmented genome?
have to take ALL the pieces with you
think: backpack with everything - grab & go (NON-segmented)
wallet, keys, sunglasses, book etc - SEGMENTED –> increase chance you’ll leave something behind by mistake & then don’t have that to help me for whatever you needed it to do can be detrimental
Capsid
PROTEIN COAT that SURROUNDS the GENOME
- structure that’s part of the nucleocapsid, therefore EVERY SINGLE virus is going to get 1
- compartment where you can pack genetic material into, so you can transfer the viral genome from 1 host cell to another
Made of identical polypeptides – protomers