Complete and in-depth Term Test 1 Notes for CSB351 for EXAM prep. Kevin has combined notes from his peers and his own work to provide the most complete and comprehensive study guide for all types of students. He has achieved an overall cumulative GPA of 3.95 during his undergrad at the University o...
Lecture 1 – Discovery and Nature of Viruses
So what’s a virus?
o Lwof
Strictly intracellular
Potentially pathogenic
Infectious
Only one type of nucleic acid
Multiply only in that one type of nucleic acid
Cannot grow or perform binary fssion
No Lipmann system
Cannot produce ATP/ribosomes
No energy, prety much
o Someone else
Tiny submicroscopic particle
Can multiply in living cells, inducing illness
Can atack everything
o Goodheart
Genetic material in a protective coating
No metabolism, no mobility, no response, no growth
Can be considered “alive” solely due to ability to transmit genetic code
With possibility of mutation
o Regardless…
During reproduction, virus inserts itself into host cell’s machinery
Genes of virus cause cell to either produce more virus or to adapt to
further serve the virus
When ready, virus leaves either through budding or through splitng
cell open
Viral properties
o Smaller than life
o Simpler than life
Only a few genes worth of nucleic acid plus a shell of protein, in general
o Cannot multiply in vitro
Requires life in order to reproduce
Hijacks host’s nucleus, mitochondria, ribosome, etc.
Life cycle
o Virus enters cell
Receptor recognizes virus and lets it in
Virus ataches to cell membrane and gets involuted
Vesicle opens up, then viral capsid
o Viral replication
, Viral nucleic acids converted, somehow, to mRNA
mRNA translated, viral proteins made
Capsid made afer viral nucleic acids, since capsid is marker to stop
replication
o Exit
Lysis
Enough viral nucleic acids packaged into capsids provides signal to get
show on the road
Cell bursts open and new virus particles pop out
Budding
Same signal, except it’s to go to the plasma membrane and bud of
Glycoproteins added as necessary to lipid membrane
New virus particles bud of
Lecture 2 – Composition of Viruses
Nucleic acids
o RNA or DNA, but not both
Ribose vs deoxyribose
Phosphate backbone is very charged (negativee
Glycosidic (covalente bonds between NH group of acid (pos. 9 of purine/1 of
pyrimidinee to 1’ of sugar
Phosphates link to sugars at 3’ and 5’
3’ and 5’ ends of DNA
o Covered with protein
o Some viruses contain lipids and carbohydrates
Enveloped, for example
o Nucleic acids and proteins are not covalently linked, but rather maintained by non-
covalent interactions
Hydrogen bonds, charge, hydrophobicity, etc.
Allows for easy uncoating
o Modifed nucleic acids
Some viruses have modifed nucleic acids
m7G
Guanine, but with methylated cap
o 5’-5’ link, which is unusual
Methylated cap marks RNA to be translated
o Cap-binding enzyme fnds it and brings it over to ribosome
Most tRNA have caps, some don’t
o Poliovirus, for one
Prevents degradation by exonucleases, promotes translation of mRNA
and +ssRNA
o Nucleic acid synthesis
, RNA polymerase binds to double stranded DNA
Helicase splits open double strands
RNA polymerase continues along one strand, adding complementary
nucleotides
o Synthesis enzymes
Polymerases
Add nucleotides to 3’ end of a strand of DNA/RNA
Sequence determined by following template strand
o Add complementary to template strand
Some RNA polymerases do not require primer
o Primers are small segments of DNA/RNA that are hybridized to
the template strand
o Polymerase latches onto primer to fnd out where it’s going
DNA polymerases require primers
Most viruses code for their own polymerases
Classes of polymerase
DNA-dependent RNA polymerase (DdRpe
o Take DNA template, write mRNA
Nuclear, mostly
o Only pox viruses and other huge viruses code for this
Most cells use cellular DNA-dependent RNA polymerase
Those go to nucleus
Pox doesn’t need to go to nucleus, it has its own DNA
and its own DdRp
RNA-dependent RNA polymerase (RdRpe
o Take RNA template, make RNA
Cytoplasmic
o Encoded by RNA viruses so they can replicate
+ssRNA make their own in cytoplasm
-ssRNA, dsRNA bring their own in capsid
RNA-dependent DNA polymerase (RdDp/RTe
o Take RNA template, make DNA
o Retroviruses
This is reverse transcriptase
o Modifcation enzymes
Methylase
Adds methyl groups to bases
Most mRNA, many +ssRNA viruses have methylated 5’ caps
Nuclease
Cleave the individual nucleotides in a stretch of acids
Endonuclease
o From the middle
, Exonuclease
o From the end
Ribonuclease
o RNA
Deoxynuclease
o DNA
Ligase
Join two stretches of nucleic acids together through covalent bonding
o Hydrolysis
RNA and DNA ligases
Shapes
o Helical
Rod-shaped capsid with nucleic acid embedded inside wall of rod
Hollow
o Icosahedral
20-sided ball of repeated subunits
“Spherical”
o Enveloped
Lipid envelope surrounding viral nucleic acids
o Bacteriophage
Round ball on top of helical rod, plus “legs”
Lecture 3 – Composition: Proteins, Lipids, Glycoproteins
Proteins
o Function
Structure
Capsid, for protection of viral innards
Enzyme
Facilitate reactions
Polymerase, integrase, etc.
Signaling
Receptors and receptor binding molecules
Movement
Plant viruses require movement protein
Antigenic
Viruses (viral proteinse induce production of antibodies
Pathology
Capsid protein itself can be what induces viral symptoms in plants
Virus takes structural with it when it leaves cell, leaves behind enzymes
(sometimese
-ssRNA, dsRNA package RdRp into daughters
o Structure
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