ch 20 Flashcards
Viruses are what
particles that consist of segments of a nucleic acid contained in a protein sheath. Because viruses require living cells for reproduction, biologists do not consider them to be living organisms.
Viruses reproduce where
inside living cells. They can enter a cell by injecting their genetic material into the cell, slipping through tears in the cell wall, or binding to molecules on the cell surface and triggering endocytosis.
Viruses are able to reproduce by doing what
taking over a host cell’s machinery. Retroviruses, such as HIV, are equipped with reverse transcriptase, a unique enzyme that can transcribe DNA from an RNA template.
Bacteria can be classified into two groups according to what
cell wall structure.
what can be used to identify bacteria because it distinguishes between two different kinds of bacterial cell walls.
Gram staining
Bacteria and eukaryotes differ in their whats
cellular organization, cell structures, and in metabolic activities.
Bacteria can be classified according to what
the ways in which they get energy.
Photosynthetic bacteria are autotrophs.
Chemoautotrophic bacteria use inorganic molecules as a source of energy.
Heterotrophic bacteria obtain energy by feeding on organic matter.
Pathogenic bacteria are harmful because what
they attack cell or secrete toxins. Antibiotics are used to fight pathogenic microorganisms and work by interfering with the microbe’s cellular processes.
Viruses do what
damage cells and cause illness.
Viruses discovered when investigating cause of Tobacco Mosaic disease:
FIRST DISCOVERY
- Disease tobacco plant is pureed into a liquid.
- Resulting liquid is run through a filter designed to catch bacteria (has holes too small for bacteria to pass through).
- liquid passed through is still able to cause disease (when applied to healthy plants)
THEREFORE - scientists conclude that whatever is the agent of disease, it is smaller than known bacteria.
SECOND DISCOVERY
- When Wendell Stanley purifies extract of virus (liquid that comes through a filter) the solutions crystallizes.
- Since only inorganic chemicals crystallize….
- scientists conclude that whatever is the agent of disease, it is not living.
Virus
strand of DNA or RNA encased in a protein coat.
Capsid
protein sheath.
Viruses are not considered to be living because
they cannot reproduce on their own and they have no mechanisms for reproduction, cellular respiration or protein synthesis. The only thing viruses do is to have their DNA or RNA to take over host cells’ machinery to make more copies of the virus.
Many plant and some animal viruses have ___ but most viruses have
RNA
DNA.
Many viruses have a ___ look (rod-like) or
helical
polyhedral structures. Most polyhedrals are icosahedrons (20 triangles faces and 12 corners).
Bacteriophages
(bacteria viruses) have polyhedral head attached to helical tail through which the DNA is injected into cell.
Many animal viruses
also have a membranous envelope made of proteins, phospholipids and glycoproteins made of the same or similar phospholipids and proteins as the host cells that it infects. The phospholipids disguise it and help it avoid detection by the hosts immune system. Some of it’s marker proteins bind to a host cells receptor proteins and trick the host cell into taking it in through endocytosis.
Three methods of entrance:
· Injection by punching hole in cell’s wall (bacteriophages).
· Pass through tear in damaged cell wall (plant viruses).
· Animal viruses have specific glycoproteins embedded in phospholipid bilayer that bind to specific receptors on specific cells and trigger endocytosis (engulfing).
Pathogens
agents of disease.
Animals immune systems
respond to pathogen marker proteins and eventually begin to have specialized cells that are able to create massive quantities of antibodies - proteins that will attach themselves to marker proteins of the virus of bacteria (or viral infected cells) and mark them for destruction by other immune system “warrior” cells. Some of these cells will remain in the animal’s body to give the animal lifelong immunity to the pathogen.
Mutations in viral or bacterial DNA that codes for marker proteins can enable the pathogen to now evade immune system cells that can no longer recognize it’s new marker protein.
Mutations in gene encoding for glycoproteins (marker proteins) may cause
some viruses to be able to bind to and infect a different type of cell. This might be the way a virus can move from one species to another like HIV that may originally have been a virus in monkeys.
Because:
- Retroviruses have two nucleic acid copying (or transcribing) events and….
- mutations most commonly happen when copying (or transcribing) nucleic acid
- their marker proteins change more often than viruses with DNA….
- therefore long term immunity is difficult.
HIV
transmitted by exchanging of body fluids (semen or vaginal secretions) during unprotected sex or mixing of contaminated blood by sharing needles.
The reason why these fluids pose a danger of infection is that they have many macrophages that have many viral particles inside.
Retrovirus
virus that uses reverse transcriptase to translate RNA into DNA
why they are species specific and as diverse.
Viruses considered to be escaped fragments of host species genome (DNA)
Bacteria are what
oldest and simplest life on earth. Small single celled prokaryotes.
Three basic shapes of bacteria
Bacillus – rod shaped.
Coccus – spherical shaped.
Spirillum - spiral shaped.
Eubacteria have a cell wall made of
peptidoglycan (network of polysaccharide molecules linked with amino acids). Some membrane made of a lipopolysaccharides. Many bacteria have a gelatinous layer outside cell wall or membrane called a capsule.
Eubacteria generally classified by differences in
cell wall. Bacteria with thick wall containing large amount of peptidoglycan are gram-positive because they hold the stain when subjected to staining procedure. Bacteria with thin wall of peptidoglycan are gram-negative because they do not hold the stain.
Medical implications of stain test:
Gram-positive –
Gram-negative –
tend to be killed by Penicillin which prevents proper cell wall formation.
susceptible to Tetracycline
Some bacteria form
thick-walled endospores around their chromosomes when exposed to harsh conditions which protect against the conditions until germination later in better conditions.
caparison between bacteria and eukaryotes
COMPARTMENTS -no --yes SIZE -small: almost 1 um --Large: most >100 um MULTICELLULAR CELL DIVISION -Single curricular --linear strands CHROMOSOMES -Binary fission --mitosis FLAGELLA -Single corkscrew; Some with Pili used to attach --Complex structures made of microtubules that whip back & forth METABOLIC DIVERSITY -Very diverse: some aerobic some anaerobic, some oxidize inorganic compounds --Only aerobic
Pili
are short projection that help bacteria adhere to surfaces or to each other in order the exchange plasmids in the process of Bacterial Conjugation
Energy classifications:
-Photosynthetic bacteria – much of world’s photosynthesis carried on by bacteria. Types of photosynthetic: Cynobacteria (original oxygen producers, many fix nitrogen from atmosphere), green & purple sulfur bacteria (live in anaerobic environments and use hydrogen sulfide instead of H2O in for electrons), purple non-sulfur
-Chemoautotrophic bacteria – get energy by removing electrons from inorganic molecules such as ammonia, methane or hydrogen sulfide.
Many perform nitrification role in soil.
-Heterotrophic bacteria – decomposers and bacteria that eat other live organisms.
Helpful bacteria:
Rhizobium – live within plant nodules and converts atmospheric nitrogen into ammonia.
Nitrobacter and Nitrosomonas convert ammonia into a more usable nitrate molecules.
E. coli and other bacteria in animal intestines help with
food digestion.
Bacteria also help create
food products (cheese and yogurt) and some create antibiotics.
In times of stress some bacteria can form
endospores
endospores
harden structures that can lie dormant until better times.
Pathogenic bacteria harmful because
they attack cells or secrete toxins.
Tuberculosis
disease of respiratory tract, bacteria usually inhaled.
Alexander Fleming notices
mold Penicillum secreted substance (penicillin) that killed some bacteria.
Antibiotic
substance obtained from fungi or bacteria (later - produced chemically) that is used as a drug to treat bacterial disease, works by interfering with cell processes , won’t work on viruses (no cell processes).
Antibody
is a protein secreted by cells in the mammalian immune system in response to a foreign substance in the body – used to mark substances for destruction.
Viruses also damage
body cells and cause illness.
More than 200 viruses can cause colds.
Influenza,
one of most devastating diseases of all times, is a viral illness that also affects respiratory tract. 1918 strain killed 20 million.
Bacteriological drug resistance:
3 causes:
Not taking prescribed medicines the entire period - those bacteria remaining after a shortened exposure ARE more resistant (because they were able to survive) and WILL pass on their more resistance to the next generation
Feeding livestock antibiotics to make them grow fatter - exposes our bad bacteria to selective pressure, selecting for more resistance.
Taking antibiotics for viral illnesses, inadvertently exposes bad bacteria to selective pressure.
4 methods of bacterial resistance to antibiotic:
Developing pumps to remove antibiotics
Altering cell wall to keep it out
Making enzymes to attack antibiotics
Making new proteins resistant to antibiotics.
Human resistance to pathogens:
Exposure to pathogen or marker protein in a vaccine and subsequent development of antibodies.
Mutation or genetic variation resistance (sickle cell).
Isolated communities are at greater risk for epidemics because
the entire population has not been exposed to outside illnesses and had chance to develop resistance
antibodies
proteins used to identify foreign bodies or infected cells so that other cells can recognize and destroy them
Antibiotic Resistance
Many bacteria can develop resistance to our antibiotics because we do something inappropriately like:
Not taking the antibiotic for the prescribed time (regimen). If we stop after we feel better and do not finish the regimen, the only bacteria that will have been killed off are the less-resistant. The more resistant will survive to reproduce.
We take an antibiotic for an pathogen that it will not work on (like a virus). Any bacteria that may be in our body towards the end of the regimen will be exposed to the antibiotic (selective pressure) but not long enough to kill off the more resistant.
Putting antibiotics in livestock feed. Any bacteria that may be in our body when we eat that meat will be exposed to the antibiotic (selective pressure) but not long enough to kill off the more resistant.
Viruses that have RNA for genetic material are called
retroviruses and must have the enzyme, reverse transcriptase translate their RNA into DNA before they can take over a host cell.
