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Who discovered viruses?
Dmitri Iwanowski : Found that juice in tobacco leaves caused infections in other plants
- Martinus Beijerinck : Realized tiny particles in juice that caused infection
- -named particle "virus" which means infection
What is the definition of Virus?
-Non-cellular particle made of genetic material and protein that can invade living cells.
Structure: components of a virus
- 1. Core of nucleic acids (DNA, RNA)
- 2. protein coat (capsid) that surrounds nucleic acid
- *some have more complex structures.
What is a bacteriophage?
-Virus that infects bacteria
Diversity in structure: what are the shapes of viruses?
Average size of virus?
- between 10-300 nm. (nano-metres)
- * must use scanning electron microscope or transmission electron microscope
Why are viruses specific?
-Can only infect a specific host
ex: HIV specific to humans
Are viruses living?
Viruses are obligate intercellular parasites.
(must feed off of host cell)
Living Characteristics of viruses?
- -genetic material
- -replicate (reproduce)
- -evolve (mutate)
Non-living characteristics of viruses?
- -requires host
- -doesn't use energy
What are viral infections?
-Causes infections by injecting DNA into host
What are the 4 general phases of viral infection?
- 1. infection
- 2. growth
- 3. replication
- 4. Lysis
What are the two different ways viruses can infect cells?
- 1. Lytic infection
- 2. Lysogenic infection
What is the main difference between Lytic and Lysogenic infection?
- - Growth phase of Lysogenic infection:
- *Viral DNA is incorporated into host DNA (prophage)
- -remains dormant for a long period of time
- -cell replicates viral DNA by binary fission
What happens during infection phase ?
- -virus attaches to host cell using tail fibres
- -inserts DNA into cell
What happens during the growth phase of Lytic infection?
- -Host's RNA polymerase (enzyme) make MRNA from viral DNA
- -MRNA takes over host cell
What happens during the replication phase?
-virus uses host's machinery (ribosomes, golgi apparatus etc) to construct :
- 1) DNA
- 2) Capsids (protein)
What happens during the lysis phase?
- -Host cell becomes filled with new viruses....then bursts (lyse)
- - Spreads viruses to neighbouring cells.
How long can a Lytic infection occur in?
What is the origin of viruses?
- -evolved after first living cell (because must live inside host)
- - evolved from genetic material of living cells, mutated and evolved
What are the advantages of viruses?
- - genetic research (cancer)
- - Gene therapy
- - genetic engineering (injecting specific DNA)
What are the disadvantages of viruses?
1. Disease (HIV, Influenza) viruses are pathogens
- 2. Cancer
- - during infection when DNA is inserted, gene may become an oncogene causing cancer
- -cell undergoes uncontrolled divisions forming tumor (benign or malignant)
How can you prevent viral infections?
- 1. good hygiene
- 2. Healthy lifestyle (diet, exercise)
What are the two lines of defence against viruses?
1. Non-specific defences
2. Specific defenses
What are the non specific defences and what do they do?
- - skin (oil and sweat provide acidic environment)
- -cilia/mucus (traps virus)
- -secretions (destroys virus)
- -phagocytes (engulf bact/viruses -> leads to fever)
- -interferon (infected cell produces protein that interferes with virus & slows it)
What are the specific defences against viral infection?
- 1. Antibodies/immune response
- 2. Immunity
- 3. Cell mediated immunity
How do antibodies/immune response defend against viral infection?
Pathogen specific antibodies are produced that bind to and inactivate virus (antigen)
How does immunity defend against viral infection?
- i) active : injection of vaccine that causes body to produce antibodies
- ii) passive: injection of antibodies produced in another animal
How does cell mediated immunity defend against viral infection?
Killer T-cells attack antigen-bearing cells and destroy them
What are the main differences between prokaryotic and eukaryotic cells?
Prokaryotic cells do not have a nucleus, or membrane.
How are monerans classified?
- -all monerans are prokaryotic
- - All called bacteria
- - Divided into 4 phyla
What are the 4 phyla that monerans are divided into?
- - archaebacteria
What are the characteristics of Eubacteria?
- - surrounded by cell wall composed of complex carbs
- - within cell wall is membrane
- -some have flagella
- - photosynthetic
what are the characteristics of Cyanobacteria?
- -contain chlorophyll
- -found on water+land
- -first to recolonize after nat. disaster
characteristics of archaebacteria?
-live in extremely harsh environments
characteristics of prochlorobacteria?
- -contain chlorophyll A and B as principal pigments
- - similar to chloroplasts of plants
- -only 2 species discovered
What are the three cell shapes of monerans?
What are the characteristics of Bacilli?
- -produce endospores (dormant, waiting for ideal conditions)
- -gram positive
what are the characteristics of Cocci?
- -grow in colonies of two cells
- -long chains
- - clumps or clusters
what are the characteristics of spirilla?
- - possess bipolar tufts of flagella
What are the different types of bacterial movement?
- - propelled by flagella
- - lash, snake, spiral forward
- - glide on slimelike material
- - sessile (no movement)
What are the two major ways bacteria obtain energy?
How do Autotrophic bacteria obtain energy?
a) Phototrophic autotrophs : obtain energy from sunlight
b) chemotrophic autotrophs: live in harsh environments, obtain energy from inorganic molecules
How do heterotrophic bacteria obtain energy?
a) chemotrophic heterotrophs: Break down organic molecules, most bacteria and animals
b) phototrophic heterotrophs : Photosynthetic but also need organic compounds
How can we look at the composition of the cell wall?
using gram staining
what 2 chemicals are used for gram staining?
crystal violet (purple)
What does it mean when bacteria takes up the crystal violet chemical?
- -gram positive
- eg. clostridium tetanus
what happens when bacteria take up the safranine chemical?
- -gram-negative bacteria
- *more toxic, more resistant to antibiotics
eg: e coli.