Transcript Viruses and Bacteria - Klahowya Secondary School

Viruses and Bacteria
Chapter 18
Viruses–small ½-1/100 size of bacterium 20 nm Considered non–living because:
1. They are not cells with cell structures
2. They do not carry out functions of respiration,
growth or development
3. Must have host cell to replicate
4. Do not metabolize, no energy
5. They are parasitic
Named after the disease they caused
Bacteriaphage – virus that infects a bacterium like
E.coli
Viral structure:
1. Inner core of genetic material either
RNA or DNA
2. Capsid – or outer coat of protein
Attachment specific to receptor proteins
2 types of Viral Replication:
1. Lytic Cycle – virus reproduces with host
cell than bursts from it killing it
1. Attachment: Virus attaches itself to the cell.
2. Entry: Enzymes weaken the cell wall and
nucleic acid is injected into the cell, leaving
the empty capsid outside the cell. Many
viruses actually enter the host cell intact.
3. Replication: Viral DNA takes control of cell
activity.
4. Assembly: All metabolic activity of the cell is
directed to assemble new viruses.
5. Release: Enzymes disintegrate the cell in a
process called lysis, releasing the new
viruses
2. Lysogenic Cycle – replication cycle that
integrates virus’s nucleic acid into chromosome of host
The virus attaches itself and injects its DNA into the
cell.
The viral DNA attaches itself to the host DNA,
becoming a new set of cell genes called a prophage.
When the host cell divides, this new gene is replicated
and passed to new cells. This causes no harm to the
cell, but may alter its traits.
Now there are two possibilities:
The prophage survives as a permanent part of the
DNA of the host organism.
Some external stimuli can cause the prophage to
become active, using the cell to produce new viruses
Viruses
Provirus – the viral DNA is integrated into the host’s
genetic material, continues to replicate and may
become active at any time
Cold sores, Hepatitis B, chicken pox, shingles
Retrovirus – RNA virus that through reverse
transcriptase produces DNA
HIV, cancers, tumor viruses ,papilloma virus
What fights them:
1.White Blood Cells-engulf virus and ingests them
2.Interferons – protein that interferes with ability of
the virus to penetrate host cell
Origination of viruses from host cells newer form of
life
Prokaryotes – unicellular organisms without
membrane bound organelles
2 Kingdoms:
1. Arachaebacteria – extreme habitats, no O2
Anaerobic environment that produces methane gas
they live in marshes, lakes, sediments and digestive
tracts of cows, sewage disposal plants
High salt water concentrations like the Great Salt
lake and Dead Sea
Hot acidic water of sulfur
springs, cracks deep in
the Pacific Ocean, autotrophic
producer for food chain
www.physics.uc.edu
2. Eubacteria – heterotrophs, most
commonly known as germs, live almost
everywhere and use organic molecules as
a food source
Phyla:
Cyanobacteria: these bacteria are photosynthetic,
carrying on the same chemical processes as green
plants.
Spirochetes: gram-negative, spiral-shaped,
heterotrophic bacteria that move with a corkscrew-like
rotation. These bacteria live freely in the environment
or have a symbiotic or parasitic relationship with other
organisms.
Phyla (cont)
Proteobacteria: this group of gram-negative
bacteria includes the human intestinal bacteria
Escherichia coli, bacteria
that extract energy from
minerals, and nitrogen-fixing
bacteria that convert
atmospheric
nitrogen into nitrates
in the soil.
Gram-positive
bacteria
this large group of bacteria
includes the streptococci
Bacteria in Yogurt
bacteria that cause strep
throat, the lactic acid
producing bacteria that turn
milk into yogurt, the
lactobacilli that cause tooth
decay, and soil bacteria that
produce many antibiotics.
Staphylococci
www.carnegieinstitution.org
Infection
Structure of Bacteria
Cell wall - some rigid and others flexible.
Cell membrane - same as other cells.
Cytoplasm - same as other cells.
DNA - a single, circular chromosome located in the
cytoplasm. Remember, bacteria cells do not have a
nucleus.
Capsule - a thick, gel-like, protective coating on some
bacteria cells.
Pili - short, hair like protein
structures on the surface of
some bacteria that help them
stick to host cells.
Flagella - long protein structures
that turn to propel some bacteria
cells.
Identifying Bacteria
1. Shape:
Cocci - round bacterial cells.
Bacilli - rod-shaped bacterial cells.
Spirilli - spiral-shaped bacterial cells.
2. Clustering
staphylo - a prefix used with the shape
name to indicate clusters.
strepto - a prefix used with the shape
name to indicate filaments
Respiration:
Obligate anaerobes - cannot survive in the
presence of atmospheric oxygen. Ex: TB
Facultative anaerobes - can live with or without
atmospheric oxygen. Use fermentation
Obligate aerobes - cannot survive without
atmospheric oxygen. Ex: syphilis
Two types of cell walls in Eubacteria: hypotonic
environment – higher concentration outside cell
1. Gram-positive bacteria - have a thick peptide
layer, retain the crystal violet, and appear purple
when viewed under a microscope.
2. Gram-negative bacteria - have a thin peptide
layer, take up the pink stain, and appear pink
when viewed under a microscope.
Sir Alexander Flemming 1928 – discovered
penicillin because it destroyed the cell walls in
the bacteria – bacteria bursts due to pressure
Reproduction:
Asexual, by binary fission - the
DNA replicates and then the
cell pinches inward and splits in
two
Conjugation - two cells exchange a portion of their DNA
material replaces old material in the cell. While this
increases the genetic variability in the organisms, it is
not true sexual reproduction.
Endospores - during adverse
conditions, the DNA is encased
in a protective envelope. This
endospore can lie dormant for
years or until favorable conditions
return. Tetanus, botulism
Importance of Bacteria
Nitrogen fixation – conversion of nitrogen gas
N2 into ammonia NH3 which other bacteria
then convert to nitrite and nitrate which
plants than use and we can utilize the
nitrogen into DNA, RNA and ATP