12.1-12.3 - Viruses, prokaryotes, conjugation Flashcards
virus genetics
genes may overlap with each other, utilizing more than 1 ORF
why injection into bacteria
bacteria have cell walls
animal cells don’t have cell walls
virus is defined as a…
…obligate intracellular parasite – they must produce in cells
viruses are not cells, do not produce ATP
virus genetics
DNA or RNA, single or double stranded, linear or circular
protein shell
a virus can have only one type of NA, and mature viruses do not contain nucleic acids outside of its genome
genes may overlap with each other (multiple reading frames), and host-encoded proteins are used for transcription/translation/replication
capsid and envelope
protein coat surrounding the viral nucleic acid genome
the “capsid head” holds to genome
surrounded by an ENVELOPE - derived from the membrane of the host cell, made of phospholipids, proteins, and carbohydrates - acquired through BUDDING through the host cell membrane
enter a host through fusing envelope with the host’s plasma membrane = OPPOSITE OF BUDDING
The envelope is essential for entering a host.
no envelope = NAKED; all phages and plant viruses are naked (plants and bacteria have cell walls, which means the host membrane is ruptured during a lytic explosion)
viral infection is extremely…
…specific
virus binds to a specific receptor on the cell surface, then internalized by fusion with plasma membrane or receptor-mediated endocytosis
the viral surface is important for recognition by immune system
the EPITOPE is capsid surface, which may be blocked by the envelope
attachment and… before cycle
= adsorption (binding to exterior of bacterial cell)
penetration (eclipse) = removes infectious virus from the media
enters LYTIC or LYSOGENIC cycle
lytic cycle
- hydrolase is expressed, degrading the entire host genome
- multiple copies of phage genome produced (using dNTPs) and capsid proteins
- lysozyme (late gene) destroys the bacterial cell wall
cell wall found in…
most bacteria/prokaryotes
algae, plants, fungi (but rarely other eukaryotes)
bacteriophage and plant viruses -> they don’t bud
lysogenic cycle (define: lysogen, prophage)
phage genome incorporated into the bacterial genome, referred to as a PROPHAGE
the host is now a LYSOGEN
dormancy: phage-encoded repressor protein binds to specific DNA elements in phage promoter (operators)
the prophage may activate, removing itself from the host genome (EXCISION) and entering the lytic cycle
transduction
when a virus excises with host DNA, and that new DNA becomes evident in the new host (e.g. the ability to metabolize galactose)
the dormancy, phage-encoded repressor protein may not repress the transduced genes
detergent removes envelope
- some of the protein released were encoded by the genome of the infected cell
- Impacts infectivity (fusion with plasma membrane)
viruses enter animal cells via…
…endocytosis
viral genome is uncoated - released from capsid
animal virus life cycles
lytic (same as phages)
productive cycle - enveloped viruses exist the host cell by BUDDING and coating itself - the animal cell does not die
lysogenic cycle - provirus (like prophage)
the role of RNA polymerase
the host cannot produce RNA from RNA, it must have DNA. but an RNA polymerase can produce RNA from RNA
(+) RNA viruses
single-stranded RNA, immediately translated
one of its proteins must be RNA-dependent RNA polymerase (to replicate itself)
common cold, polio, rubella
(-) RNA virus
the negative strand is a template for the (+) strand, which is the mRNA
the viral RNA-dependent RNA pol is brought in with the virus, which does the job of transcription and replication simultaneously without host enzymes
retroviruses
a (+) viruses whose viral genome encodes for reverse transcriptase, which makes DNA from an RNA template
dsDNA viruses
large genomes that encode enzymes require for dNTP synthesis and DNA replication
they carry genes for enzymes that synthesize dNTP (so that they don’t have to wait for the host to generate dNTP)
RNA viruses don’t have genes for enzymes that produce NTPs because transcription is always occurring in all cells
prion diseases
prior is an abnormally folded protein that acts as a template and becomes infectious
viroids
circulator single-stranded RNA (200-400 bps) with self-complementarity
non-coding
lack capsids
catalytic ribozymes
produce siRNA that can silence normal gene expression
usually infect plants
ex. Hep D - needs to co-infect with Hepatitis B
prokaryotes
lack membrane-bounded organelles
bacteria, archea, blue-green algae
proteins are made… C-N?
N->C
three bacterial shapes
- coccus (round)
- bacillus (rod shaped)
- spirillum (spiral-shaped)
