Lecture 31 Flashcards
What are viruses ?
Acellular microorganisms (biological) that cannot survive without a host: no metabolic abilities of their own “a borrowed life”
They reply completely on biosynthetic machinery of infected cell to multiply
Parasitic entities that hijack the molecular resources of the host
What type of cells do viruses infect
- infect all types of cells (animal, plant, bacterial) - obligate intracellular parasites (must enter the cell to replicate)
Most abundant biological entities on earth:
Viruses
Composition of a virus
Viruses consists of two parts:
- GENETIC MATERIAL - made from either DNA or RNA
- CAPSID - a protein coat that surrounds and protects the genetic material
(And in some cases a third part)
- ENVOLOPE OF LIPIDS that surrounds the protein coat when they are outside a cell
What are capsids made of
- multiple units of the same protein building black known as capsomers
What are capsomers
Subunit of the capsid arranged in a precise and highly repetitive pattern around the nucleic acid
Capsid/ capsomers can be arranged in three types of symmetry…
- Helical (e.g TMV)
- Icosahedral (e.g Adenovirus - like common cold)
- Complex (e.g bacteriophage)
Helical structure
Lots of capsomers that have a slight rotation in them forming a helix - encapsulates globular proteins in a helix
- rod shaped viruses
Icosahedral
- 20 faces polyhedron - each face is a equilateral triangle - icosahedron
- many axis of symmetry
- efficient way of packing lots of globular proteins into the capsid
Another example of helical lol
Complex
- the head has Icosahedral symmetry and tail is helical
Viral genome could be made up of:
RNA
DNA
Viral genome could be structured as:
- linear (e.g poxvirus)
- circular (e.g hepatitis B)
- segmented (e.g influenza virus)
Viral genome size variation
Size can vary form 4,000 to > 1 million nucleotides (3 genes to 100-1000)
All four possible forms of RNA and DNA are found in viruses
Single stranded and double stranded DNA and RNA
In 1940….
The first electron micrograph of a bacteriophage was published
- this silenced sceptics who had argued that bacteriophages were relatively simple enzymes and not viruses
Lytic (virulent) cycle of bacteriophage infection (TALKING)
- Attach to host cell - through some Dort of receptor
- Penetrate host cell to get into cell, bacteriophage T4 penetrates by punching a hole into the cell membrane and at the same time..
3… uncoats - exposes its genetic material and releases its genetic material (DNA) into host cell - Genome replication and gene replication - makes copies of itself, uses the polymerase to replicate the virus genome and makes many copies of itself, these genes that its making then get expressed into proteins (3D structures get to a concentration where they must assemble)
- Assembly - assemble into virus particles and are then released from the host cell
- Release - may break out of host cell leaving it dead or they could be released from host cell leaving it intact
Viruses that infect eukaryotic cells
- virus attaches to cell using receptor
- penetrates cell membrane and gains entry
- uncoats to expose genetic material
- undergoes gene expression and gene replication where it builds proteins
- assembles into virus particles and is then released from the cell
SARS - CoV - 2
Enveloped + ssRNA, Linear, Non-segmented
- includes RNA polymerase to copy the genome
- limited prof reading so makes some errors: generated variants - makes genetic variation
- allows tracking
- leads to new strains
Genome = 30,000 nucuelotides in length
- first 20,000 nucleotides encode the replication module (16 proteins involved in replication)
- spike encodes proteins that look like a spike, within replication modules (16 proteins) in the RNA polymerase
- RNA genomes need an RNA polymerase to make copies of themselves
700m cases
7m deaths
(Just look at the slide attached)
The spike protein
- critical for attachment and cell entry
- a major target for neutralising immunity
- viruses must bind to a receptor protein to infect a cell
- vaccines target the spike to prevent infection
SARS - CoV - 2 replication cycle
- Attaches - spike binds to ACE2 receptor
2+3. Entry + Uncoats to release its genetic material into host cell - Genetic material undergoes replication and gene expression and makes all the different proteins neede to make the virus particle
- Assembles and then hijacks our own cellular processes such as exocytosis in the golgi to exit (through normal cellular processes
Replication of RNA enveloped virus (HIV): (TALKING JUST LEARN THING AT END)
retrovirus that clauses aids
- fuses with cells and wants to infect T cells using
- has to bind to T cells using CD4
- when it attaches it binds to the membrane and releases virus particles into the cell then uncaots genetic material and the enzymes
- retro virus means reverse - it has a viral RNA genome but then it makes DNA from that RNA (making a RNA-DNA hybrid in between) using reverse transcriptase
- DNA then enters the nucleus and uses viral intergrase
- viral intergrase chops up our genome (host genome) and inserts the virus into out host genome
- thus when your cells divide and replicate, so does the virus
- some RNA gets made into the progeny virus and makes things like viral proteins, envolope glycoprotiens and transports it out of the cell - buds off from cell membrane and forms a brand new virus (ALL FROM TALKING)
