Download File - Mr. Swords` Classes

Chapter 18
Viruses and Bacteria
Viruses
 Non-living particles composed of nucleic acids
enclosed in a protein coat
 Smaller than the smallest bacterium
 In fact, they can even infect a bacterium
 T4 bacteriophage
Why aren’t viruses considered
alive?
 They don’t exhibit all of the criteria for life
 Don’t carry out respiration
 They don’t grow
 They don’t develop
 They only make copies of themselves
 This cannot be done without the help of living cells (host)
T4 Bacteriophage
Attaching to a host cell
 Viruses must enter a host cell before replicating
 They recognize and attach to a receptor site on a cell’s
plasma membrane
 Specific
 T4 Bacteriophage can only infect certain types of E. coli
 Poliovirus
Retroviruses
 RNA viruses with the most complex replication cycle
 RNA is their only nucleic acid
 Incorporate their RNA into the host cell chromosome
which is DNA
 Example: HIV
 An enzyme that it carries inside its capsid, called reverse
transcriptase, helps produce dsDNA from the viral RNA
 Then the dsDNA is integrated into the host cell’s
chromosome and becomes a provirus
HIV
 HIV infects WBCs when it enters its host cell
 Exocytosis releases the newly made viruses into the
bloodstream where they are able to infect other WBCs
 Host cells continue to function normally
 WBCs are an integral part of our body’s immune
system
Cancer and Viruses
 Some viruses disrupt normal cell growth and division of
host cells which may cause abnormal growth, leading
to tumors
 Hepatitis B is a virus that has been shown to play a role
in causing liver cancer
 Prions – composed of proteins but have no nucleic
acids to carry genetic info.
 Mad Cow Disease and Creutzfeld-Jakob disease
Prions
Plant Viruses
 Viroids – composed of a single circular strand of RNA
with no protein coat that cause infectious disease in
plants
 Can cause stunted growth and yield losses in their host
plants
 Not all are harmful/fatal
Where did viruses come
from?
 They’re very simple so one might think they might be
an ancestral form of life. However, they require a host
cell, so we think that they may have originated from
their host cells
Prokaryotes
 Prokaryotes – unicellular organisms that don’t have a
nucleus or membrane-bound organelles
 2 Kingdoms: archaebacteria and eubacteria
 Differences: lipids of plasma membranes and their cell
walls
 Structure/function of archaebacteria is closer to
eukaryotes than to eubacteria
 They probably arose from a common ancestor several
billion years ago
Archaebacteria
 Live in extreme habitats where there is
usually no oxygen
 Live in water with high salt concentrations such as
Utah’s Great Salt Lake and the Middle East’s Dead Sea
 Methane-producing archaebacteria live in marshes,
lake sediments, and the digestive tracts of some
mammals, sewage disposal plants
 Live in hot acidic waters of sulfur springs or near cracks
deep in the ocean floor where it is the autotrophic
producer for a unique animal community’s food chain
Eubacteria
 Heterotrophs
 Live in places more hospitable than archaebacteria and
vary in nutritional needs
 Live almost anywhere and use organic molecules as food
source
 Some are parasites – obtain nutrients from living
organisms
 Some are saprophytes – feed on dead organisms or
organic wastes; they break down/recycle the nutrients
locked in the body tissues of dead organisms
 Photosynthetic autotrophs
 Live in places with sunlight because they make their own
food
 Cyanobacteria – have chlorophyll and use photosynthesis
 Most are blue-green, some are red or yellow
 Streams, ponds, moist areas of land
 Chemosynthetic autotrophs
 Break down and release energy of inorganic compounds
containing sulfur and nitrogen using chemosynthesis
 Can convert atmospheric nitrogen into the N-containing
compounds that plants need
Bacteria
 Bacterium – consists of a very small cell with all the
structures necessary to carry out its life functions
 Structure: smaller ribosomes than eukaryotes’, single
circular chromosome, cell wall
 Most live in a hypotonic environment (higher conc. of
H2O outside that is always trying to move into the cell)
 Cell wall = protection
Penicillin
 1928 – Fleming discovered penicillin when an airborne
mold (penicillium notatum) contaminated his bacterial
culture plates
 Penicillin interferes with bacteria’s ability to make cell
walls
 Holes develop in the cell walls and water enters the cells
so that they rupture and die
Identifying Bacteria
 Gram staining reflects a basic difference in the
composition of bacterial cell walls
 G+ is purple, G – is pink
Arrangements of Bacteria
 Diploe – growing in pairs
 Staphylo – resembling grapes
 Strepto – chains
Reproduction of Bacteria
 Binary Fission
 Bacteria lack a nucleus, so they can’t do meiosis or
mitosis
 Some bacteria can reproduce every 20 minutes
 Conjugation – one bacterium transfers all or part of its
chromosome to another cell using a bridgelike structure
called a pilus that connects the 2 cells
Bacteria and Oxygen
 Anaerobic bacteria were probably among the first
photosynthetic organisms
 Obligate anaerobes – killed by oxygen
 Treponema pallidum – causes syphilis
 Botulism
Bacteria and Oxygen
 Obligate aerobes – require O2 for respiration
 Mycobacterium Tuberculosis – causes lung disease
 Other bacteria exist with or without oxygen, releasing
energy in food aerobically by cellular respiration or
anaerobically by fermentation
Survival Mechanisms
 Endospore – tiny structure that contains a bacterium’s
DNA and a small amount of cytoplasm, encased by a
tough outer covering that resists drying out, temp
extremes, and harsh chemicals
 Can survive temp of 100C (boiling point of H2O)
 To kill endospores, items must be sterilized
 Canned foods must be sterilized/acidified because C.
botulinum can easily get into foods being canned if
improperly sterilized
The Clostridia Group
 Obligate anaerobes that form endospores
 Bacteria grow in the anaerobic environment of the can
and produce toxin as they grow
 Causes botulism if eaten – rare but often fatal
Bacteria is important!
 Some bacteria have enzymes that convert N2 into ammonia
NH3
 Other bacteria then convert NH3 into nitrite and nitrate for
plants to use
 Some of these bacteria live symbiotically within roots as
nodules
 Most of the N on earth is in the gaseous form N2
 All organisms need N because it is a component of their
proteins, DNA, RNA, and ATP, but few organisms can
directly use it from air
 Decomposing bacteria break down organic molecules
in dead organisms and wastes, returning nutrients to
the environment
 Autotrophic bacteria and plants/algae use the nutrients
in the food they make
 Food and medicine:
 Cheese, vinegar, sauerkraut
 Antibiotics
 Intestines: bacteria produce vitamins and enzymes that
help us digest food