2.1 Viruses and Prokaryotes Flashcards
The Discovery of Viruses
-Discovered in 1892
-Russian biologist, Dmitri Iwanowski
-Noticed Tobacco Mosaic Disease would spread if
infected leaves rubbed on uninfected leaves
-Assumed it was bacterial
-Designed a technique to “filter” out the bacteria…
BUT Leaves still got infected
-Therefore, it couldn’t be bacteria, but something else, much smaller that couldn’t be filtered out
what was the term ‘virus’ used to describe?
The term ‘virus’ was used to describe the organisms that were isolated
Give three reasons why viruses seem to be living
They seem to be living because:
They have genetic material and protein.
They can adapt to different environments
Their genes can mutate and evolve.
Give 5 reasons why viruses aren’t living
Viruses are not living, however, because:
-they have no cellular organelles
-they cannot produce their own energy or proteins
-they must rely on their host cell for all cellular
functions.
-they cannot grow.
-they also do not respire.
structure and function of viruses
-Viruses are very small.
-They contain genetic material (DNA or RNA) surrounded by a protein coat called a capsid.
-The capsid gives the virus its shape, which is usually geometric.
What is a capsid?
protein shell of a virus, enclosing its genetic material
True or false: Viruses can live independently
Viruses CANNOT live independently; they need to live inside living cells
True or false: Viruses can only infect a specific type of organism.
true
which category of viruses are known as “bacteria eaters?
bacteriophages
structure of bacteriophages
they have a distinct head shape and tail region
genetic information of a DNA virus
double stranded DNA
examples of a DNA virus
Chicken pox; smallpox; papillomavirus; herpes simplex; hepatitis B
genetic information of an RNA virus
Single stranded RNA
examples of an RNA virus
Polio; mumps; measles; flu; hepatitis A and C; SARS; Ebola; yellow fever; rabies
genetic information of a retrovirus
Single stranded RNA; used to copy host DNA
retrovirus examples
HIV; feline leukemia virus
Which type of virus is used to copy host DNA
retrovirus
Replication
Viruses DO NOT reproduce – b/c they are not living!
There are 2 ways for viruses to replicate:
1) Lytic Cycle
2) Lysogenic Cycle
Lytic Cycle- attachment
Attachment: phage (virus) chemically recognizes a host cell and attaches to the cell membrane.
Lytic Cycle- Penetration/Injection
viral nucleic acid (DNA/RNA) is injected into the host cell
Lytic Cycle- Synthesis
Viral nucleic acid takes over by inserting itself into host. Normal cell functioning stops. Host cell functioning is essentially ‘hijacked’; it is now directed to make copies of viral nucleic acid and proteins instead of its own
Lytic Cycle- Assembly
viral nucleic acid and protein coat are assembled into new viruses.
Lytic Cycle- Lysis/Release
host cell is now programmed to make enzymes that digest itself from the inside out. Cell lyses, or bursts open, releasing hundreds of new viruses that can now infect other cells.
-cell dies
steps in the lysogenic cycle
Attachment
Penetration/Injection
Latent/Dormant Phase
Stimuli
Synthesis
Assembly
Lysis/Release
in the lysogenic cycle, what are two options that can happen?
cell and viral DNA keep on reproducing in a continuous cycle
viral DNA separates from bacterial chromosome, initiating a lytic cycle
What occurs in the Latent/Dormant Phase
phage is hidden and inactive
What occurs in the Stimuli phase?
stressors like temperature change, chemicals, shock, etc. trigger Lytic Cycle
In which cycle does the cell die and in what phase does it die?
Lytic cycle; lysis/release phase
Example of a lysogenic cycle in real life
If you’ve ever had a cold sore, you may notice it can remain dormant for long periods of time, but flare up when you are stressed
Another example of a lysogenic cycle
Some people can have HIV but experience no symptoms for years
Prokaryotes and Eukaryotes
-Two basic types of cells
-Characterized by size and type of organelles
-Bacteria are types of PROKARYOTES
-All other organisms are classified as EUKARYOTES
-Prokaryotes are thought to be the first forms of life on Earth
bacteria are types of ___________
prokaryotes
prokaryotes
-NO nuclear membrane
-NO membrane-bound organelles
-Small amounts of DNA
-Single chromosome without protein
-Mostly Asexual Reproduction by binary fission
eukaryotes
-Defined nuclear membrane
-Diverse number and type of membrane-bound
organelles
-Large amounts of DNA
-Numerous chromosomes with associated proteins
-Reproduction by mitosis and meiosis
Kingdom Archaebacteria
-Closest living relatives of first cells on Earth
-Members of this kingdom called Extremophiles live
in extremely harsh environments
-e.g. Dead Sea, Great Salt Lake, acidic hot springs,
animal gut
what are the members of kingdom archaea called?
extremophiles
Eubacteria
-Exist almost everywhere
-Can be either autotrophic or heterotrophic
-Cell walls contain peptidoglycan (sugar)
What is the classification of Eubacteria based on?
-Ability of cell wall to take up stain
e.g. Gram Stain
-Cell shape
-Movement
-Nutrition
Cell Wall Responses to Gram Stain
If Eubacteria contains THICK walls, it stains purple called “Gram-Positive”
If Eubacteria contains THIN walls, it stains pink called “Gram-Negative”
Cell Shape
Three types:
Spherical
(Coccus, plural = cocci)
Rod-shaped
(Bacillus, plural = bacilli)
Spiral-shaped
(Spirillum)
Diplo
pairs
Strepto
linear chains
Staphlo
grape-like clusters
Spirillum are usually found as
singles
common name of Treponema pallidum
syphillis
Movement of prokaryotes
-About ½ of all prokaryotes have a long, whip-like protein tail attached to them called a flagellum (p. flagella)
-used to propel bacteria toward food, light or oxygen
Heterotrophic bacteria consume ________
Heterotrophic bacteria consume other organisms
how do autotrophic bacteria get nutrition
Autotrophic bacteria can feed themselves.
how do photoautotrophs get nutrients
Photoautotrophs can photosynthesize to acquire nutrients
how do photoheterotrophs get nutrients?
Photoheterotrophs are a combination of the rest and can eat other organisms, feed themselves and photsynthesize.
Extremophiles
live in extreme, harsh environments
(e.g. boiling hot springs, salty waters, deep sea volcano vents, mud and digestive tracts of animals.
Chemoautotrophs
Chemoautotrophs are extremophiles that use chemicals such as hydrogen sulphide to metabolize and create energy.
Asexual Reproduction
-Most bacteria reproduce asexually through binary fission
-The genetic material (DNA/RNA), is duplicated and split between the two daughter cells
-Each of the daughter cells is a clone;
they are genetically identical to each other
Bacterial Growth via Binary Fission
Bacteria reproduce exponentially, (and quickly – once every 20 minutes or so!)
-however, they cannot increase in number indefinitely due to limiting factors like food availability and space
Sometimes, bacteria can acquire different genetic material via ____________________; 3 ways
Sexual Reproduction
3 ways of sexual reproduction in bacteria
transformation, conjugation and transduction
Describe transformation
bacteria pick up free floating DNA and incorporate it into their own genome
Describe conjugation
bacteria create a cytoplasmic ‘mating bridge’ or pilus between them and exchange plasmids
small circular pieces of DNA
Describe transduction
occurs when DNA is transferred from one bacterium to another via bacteriophages [virus].
Advantage of sexual reproduction
Can allow for mutations so that bacteria can better adapt to their environment — to EVOLVE
Disadvantage of sexual reproduction
Can lead to antibiotic resistance in harmful bacteria (e.g. MRSA)
Endospores
-When conditions are unfavourable, bacteria form endospores for protection
-protective layer that covers the DNA and some cytoplasm during times of stress
-Can persist through heat, cold, water and nutrient deprivation and even poisons for many years
give an example of an endospore
Bacillus anthracis can survive for years in the soil because of its ability to form an endospore.
Describe how viruses can be classified
Viruses come in many shapes and sizes and
are usually classified based on the type of cell
they infect
Explain how a virus reproduces itself
can’t reproduce, but can replicate itself in 2 ways:
-lytic cycle
-lysogenic cycle
-When a virus infiltrates a cell, it unloads its genetic material, takes control of the cell’s processes, and replicates.
-Replication may happen immediately, or the viral genes may lie dormant for a period of time before
any changes occur to the cell.
Identify three differences between archaea
and bacteria
-Archaea are more complex than bacteria
-Archaea DON’T have peptidoglycan and bacteria do
-Archaea DON’T form endospores and bacteria do
Summarize three mechanisms of genetic
recombination in prokaryotes
Transformation
-some bacteria take up pieces of DNA from the environment. Such pieces of DNA might come from nearby bacteria that have died
Conjugation
-two bacterial cells temporarily join and directly exchange genetic material; involves plasmids (separate rings of DNA apart from the cell’s main chromosome)
Transduction
-viruses that infect bacteria (bacteriophages) carry genes from one cell and inject them into another
When resources are too limited for bacteria to
survive, many transform into a dormant stage, called
an endospore
Explain the role prokaryotes play in nitrogen
recycling.
Bacteria play a key role in the cycling of nutrients throughout the biosphere.
They decompose organic matter, releasing nutrients back into ecosystems.
Some species convert nitrogen gas from the atmosphere into nitrogen compounds that plants can absorb from the soil
Describe how prokaryotes are able to move
through the environment
-half of all prokaryotes lack movement.
-others use long whiplike structures called flagella
to propel themselves toward food, light, or oxygen. -spiral-shaped bacteria use a corkscrew motion to move.
-other bacteria glide on slimy mucous that they secrete
What is structural diversity? Use a specific
example to explain your answer
Differences in structure are known as structural diversity
-e.g. Bacteria have cell walls of peptidoglycan, this differs from those of archaea, which have no peptidoglycan
True or false: Bacteria have one type of cell wall that contains peptidoglycan
False
Bacteria have one of two types of cell walls.
One type is composed mostly of peptidoglycan, a thick coat of sugars.
The other
has less peptidoglycan and an additional outer membrane.
How do the two cell walls in bacteria differ?
One type is composed mostly of peptidoglycan, a thick coat of sugars.
The other has less peptidoglycan and an additional outer membrane.
What are the three major types of morphology
found in bacteria?
spherical (coccus)
rod-shaped (bacilli)
spiral shaped (spirochetes)
The largest spiral-shaped bacteria are called
spirochetes
The bacteria that cause Lyme disease
and those that cause syphilis are
spirochetes
There is disagreement in the scientific world
about whether viruses are actually living
organisms. Why is there confusion?
It is easy to mistake viruses for living organisms.
-Viruses use nucleic acids, such as deoxyribonucleic acid (DNA) and ribonucleic acid (RNA) to store genetic information
-adapt to changing conditions like living
things by genetically mutating, which can allow
them to avoid destruction by medicines.
-unlike living things, viruses are not made of cells
and cannot reproduce on their own.
-made of proteins and nucleic acids
-need to use the cells of a host organism to make
copies of themselves
How is the viral structure well-suited to its
function?
The structure of a virus is well-suited to its
function: entering a host cell and reproducing.
-A virus is composed of a relatively short piece
of nucleic acid, DNA or RNA, surrounded by
a protein coat
-Some viruses also have outer membranes that merge with a host cell’s membrane, making it easier for the virus to infect the cell.
-Viruses come in many shapes and sizes and
are usually classified based on the type of cell
they infect.
-The protein coat that surrounds a virus is like a key to a door.
-Patterns on the viral coat unlock an entryway into a host cell
The rabies virus infects cells of the central
nervous system.
(a) Explain why the virus does not infect the
muscle cells in your leg
These patterns on viruses are very specific, and normally a particular virus will open only
one type of cell, so if it affects your nervous system, it can’t affect your leg muscles
The rabies virus infects cells of the central
nervous system.
(b) Explain why you need a rabies shot if you
are bitten by a rabid dog
because the virus can infiltrate the cells in your body
-it unloads its genetic material, takes control of the cell’s processes, and replicates.
-can happen immediately, or the viral genes may lie dormant for a period of time before any changes occur to the cell
Both bacteria and viruses can infect humans.
How then is it possible for viruses to infect
bacteria cells?
Viruses called bacteriophages attack and infect specific bacterial cells
-they infect bacteria cells through the lytic and lysogenic cycles
Suppose a bacterium has exhausted all the
resources in an area and is not able to travel to
another area. Describe a process where it may
survive to reproduce at a future point in time
-When resources are too limited for bacteria to
survive, many transform into a dormant stage, called an endospore
-A thick internal wall circles the DNA and a small amount of cytoplasm.
-The outer cell disintegrates, leaving the highly resistant endospore.
-Some endospores can survive lack of water and nutrients, heat, cold, and most poisons for many years.
-When the environment becomes more favourable, endospores can absorb water and grow again
Bacteria consuming energy from
human tissue is an example of which type of nutritional classification?
heterotroph
Bacteria receiving all their energy
from sunlight is an example of which type of nutritional classification?
photoautotroph
Bacteria using energy from the sun during
the day and then consuming other bacteria
at night is an example of which type of nutritional classification?
photoheterotroph
Bacteria receiving energy from chemical
reactions around a deep sea vent is an example of which type of nutritional classification?
chemoheterotroph
What type of bacterial reproduction that
you read about in this chapter would
account for this type of rapid growth?
binary fission
Describe one way that climate change has
affected the diversity of prokaryotes.
-Rising sea levels and vigorous storm surges associated with climate change are destroying peat wetlands
-The peat soils contain large pop. of methane-producing bacteria that play a critical role in maintaining the ecosystems.
-peat is also home to smaller pop. of sulphate-metabolizing bacteria and archaea, which release toxic compounds that kill off surface vegetation
and destroy peat.
-When these bacteria are exposed to salt water, they outcompete and replace the populations of methane-producing bacteria, virtually eliminating the peat and destroying the wetland habitat
-Species that live there either die or move to another habitat
