Summary CSB351 Term Test 1 Review

CSB351

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