Biology Class 4 Flashcards
Virus
Obligate intracellular parasite
Components of a virus
Head, Tail fibers, genome (nucleic acid)
Capsid (protein shell containing genetic information)
Basic steps of Virus
- Attachment (adsorption)
- specific
- host not yet infected - Injection (Penetration)
- host is infected
Following this, one of 3 life cycles take place
3 different life cycles
Lytic, lysogenic & productive life cycle
Lytic Cycle
- Transcribe & translate the viral genome
Early genes: hydrolase, capsid proteins - Replicate the viral genome
- Lysis of host & release of new viral particles
Late genes: lysozyme
Lysogenic Cycle
- Integrate viral genome with hos genome
- Normal host activity, including reproduction
- Excision & lytic cycle
Advantages to productive cycle
- Protection from immune system
- Easy infection (envelope can fuse with another membrane)
- Get more virus (long life)
Why does virus want to kill the hose genome in lytic cycle?
- All cellular energy used to work with the viral genome
2. Create a pool of free dNTPs to use in viral genome replication
Why does virus want to kill the hose genome in lytic cycle?
- All cellular energy used to work with the viral genome
2. Create a pool of free dNTPs to use in viral genome replication
While transcribing & translating host genome, how does the virus make sure its genome is not expressed in the lysogenic cycle?
Viral genome codes for repressors to make sure it’s not expressed
Lysogen
When virus incorporated in the host genome, host is referred to as lysogen
Provirus/Prophage
Host genome and viral genome are incorporated together
Animal virus
Virus with an envelope (productive cycle)
Subviral particles: Prions
Proteins (both good ones and mutant ones) Characteristics: - no DNA or RNA - non membranes - no organelles - very small - extremely stable
How do mutant (bad) prions come?
- Spontaneous mutation
- mutation in gene coding for mutant prion and then prions accumulate & lead to cell death - Be genetically transmitted
- can have bad prion & pass off to offspring - Ingested through diseased tissue
- Healthy cell transcribing & translating normal “good” prion
- Consumption of mutant “bad” prion from diseased tissue
- Mutant “bad” prion changed normal “good” prions to bad ones
- Cell death
Subviral particles: Viroids
- virus-like Characteristics: - circular RNA - no capsid - must be coinfected - don't code for proteins - act as miRNAs or siRNAs to block translation
Mechanism of viroid
Mechanism 1
- +RNA circular form as template to make -RNA
- -RNA linear form
- Ligase to make a circular -RNA
- Use -RNA as template to make +RNA
- RNA makes more circular +RNA viroids
Mechanism 2
- +RNA circular form as template to make -RNA
- -RNA is template to make +RNA linear form
- Multiple +RNA linear form
- Circularized to form more viroids
Both mechanisms equally preferred
How viral genome (+RNA or -RNA) is made
Mechanism 1
- +RNA (same as mRNA) can either be translated using host ribosomes to form viral proteins OR complementary form using RNA dependent RNA polymerase to make -RNA
- Use RNA dependent RNA polymerase to make more +RNA
* In this situation, the virus will code for the enzyme on its +RNA genome
Mechanism 2
- -RNA available and you use RNA dependent RNA polymerase to make +RNA
- +RNA is now available to translate using host ribosomes to make viral proteins OR to make complementary -RNA using RNA dependent RNA polymerase
* In this situation, the virus will have to carry then code for the enzyme
Mechanism 3 (+RNA lysogenic)
- +RNA that will create ssDNA using RNA dependent DNA polymerase
- ssDNA will replicate using host DNA polymerase to make dsDNA
- dsDNA can be inserted into host cell genome which can then be transcribed and translated using host enzymes to make viral proteins OR transcribed using only hosr RNA polyermases to make +RNA
Problems with +RNA lysogenic
- Very rapid mutation
- Will permanently be in host genome
Ex. HIV
Bacteria: Structure
Shape
- Round - coccus
- Elongated - bacillus
- Spiral - spirochetes
Bacterial: Structure
Flagella
____“trichous”
- mono (1 flagella)
- amphi (2 flagella)
- peri (multiple flagella)
Have basal unit connected to cell membrane
- hook is connected to basal unit
- flagella is connected to hook
As hook rotates, the cell moves
Chemotaxis
Moving towards favourable chemicals & away from unfavourable chemicals
Bacteria: Structure
Cell wall/ cell membrane
Gram positive - stains purple
- has cell membrane surrounded by thick cell wall
Gram negative - stains pink
- has thin inner cell membrane, then cell wall, then outer cell membrane
Is gram + or gram - harder to kill with antibiotics?
Gram - because it has antibody degrading enzymes in periplasmic space (inbetween OM and IM)
Mesophiles
Bacteria that live in medium temperature
Psychrophiles
Bacteria that live in cold temperature
Thermophiles
Bacteria that live in hot temperatures
Faculative Anaerobe
Oxygen Present - use it to survive
Oxygen Absent - ferment & survive
Obligate Aerobe
Oxygen Present - use it to survive
Oxygen Absent - Die
Obligate Anaerobe
Oxygen Present - Die
Oxygen Absent - ferment & survive
Tolerant Anaerobe
Oxygen Present: doesn’t use it, but tolerates it to survive
Oxygen Absent: Ferment & survive
Energy Sources
Photo vs Chemo
Photo - energy from Sun
Chemo - energy from ATP
Where Carbon chains come from
Auto vs Hetero
Auto - CO2 (will build own sugar but needs carbon source)
Hetero - eats other critics
Example of photoautotroph
Plants
Example of chemoautotroph
Deep sea vent bacteria
Example of photoheterotroph
Carnivorous plants
Example of chemoheterotroph
Humans
Carrying capacity
Maximum amount of bacteria an environment can sustain
Phases of Reproduction
- Lag Phase - little population growth, nothing happening except bacteria getting ready to split
- Exponential/log phase - bacteria are happily dividing and growing
- Stationary phase - reach carrying capacity, bacteria is unable to divide because nutrients are depleted and will be over crowded
- Death - Cells die
Binary Fission vs Conjugation
Will grow in population size, but no genetic diversity (phases of reproduction)
Produce sexually
- will have genetic diversity but no growth in population size
Conjugation Process
F+ bacterium (male) that has genome & F plasm
- F plasmid is for fertility
- F plasmid has everything needed to create conjugation bridge /sex pilus to copy F plasmid into F- (female)
- F- now becomes F+
Transduction
Transfer genomic DNA from one cell to another by viral infection
HFr Cell
- When F plasmid is incorporated into host genome
- now called High Frequency of recombinant cell
- will be copied over throughout genome and cross over resulting in recombination (increase in genetic diversity)
