Transcript virus

Bacterial transformation can be a natural or a manipulated
(artificial) process that provides a mechanism for the
recombination of genetic information in some bacteria. Small
pieces of extracellular DNA are taken up by living bacteria,
ultimately leading to a stable genetic change in the recipient
cell.
You can take the DNA
• A Plasmid is a small circular
from two different
piece of DNA that is
organisms and recombine
contained in the bacteria.
them together in a new
How to do it:
DNA molecule, and then
• Use restriction enzymes (which “restrict” the transform another
specific segment of DNA to be cut, and lyse it
organism giving it the
out)
desired trait.
• These restriction enzymes recognize certain
DNA sequences by their “recognition
sequences”.
• The “sticky ends” of the cleved DNA
fragment join up readily with new DNA
Hundreds of restriction
enzymes have been isolated:
• EcoRI; BamHI; HindIII
The human gene for
insulin production has
been successfully
inserted into E. coli,
where it produces
insulin which is then
isolated and used to
treat the disease.
Gel electrophoresis is a method used to
separate restriction fragments of
different lengths, as they diffuse
through the gel.
A virus is a parasitic particle that can live only inside another
cell. The cell that it “infects” (as they are pathogens) is
tricked into producing the proteins that the virus needs to
make more viruses. It does this through hijacking the
pathway to protein synthesis.
The basic structure of the
virus is a DNA or an RNA
enclosed by a protein coat
called a capsid.
Viruses are cell-specific,
and can only infect certain
kinds of cells.
This is because the virus gains entrance into a cell by binding
to specific receptors on the cell surface. The AIDs virus
(HIV) can only bind to the surface of Helper “T” cells.
Lysogenic (DORMANT)
• Some viruses initiate an infection into cells, and then may remain
dormant inside host cells for long periods, causing no obvious change in
their host cells (a stage known as the lysogenic phase).
In this cycle, viruses replicate without destroying the host cell. The
phage (virus) becomes incorporated into a specific site in the host’s
DNA. It remains dormant within the host genome and is called a
prophage. As the host cell divides, the phage is replicated along with
it, and a single infected cell gives rise to a population of infected
cells. At some point, the environment triggers the prophage to switch
to the lytic phase.
Lytic (ACTIVE)
• When a dormant virus is stimulated, it enters the lytic phase: new viruses
are formed, and burst out of the host cell, killing the cell and going on to
infect other cells.
The phage enters the host cell, takes control of the cell machinery and
forces the cell to replicate viral particles. The cell replicates more
viral particles to be manufactured, which are assembled into viruses.
This will cause the host cell to lyse (rupture) killing the host, and the
viruses are spread then to new host cells.
A virus that contains RNA instead of
DNA is a retrovirus. These viruses
replicate in an unusual way.
• Virus injects genome into host cell
• Their RNA serves as a template to
build a cDNA (complementary DNA)
• This reverse
transcription occurs with
the help of the enzyme
reverse transcriptase.
Examples of retroviruses are:
HIV, and polio
Levels of Ecological Organization:
A group of individuals all of the same
•Population species in a defined geographical region.
A group of species in a
• Community defined geographic region.
Relationships between
• Ecosystem organisms and environment.
• Biosphere All regions of the Earth
that contain living things.
• Habitat The place where an organism lives.
The role an organism plays in its environment, such as producer;
• Niche consumer; decomposer; diurnal; nocturnal; ground dweller; mates
for life; egg layer…etc.
The size of a population is represented symbolically with the
letter N, which is the total number of individuals.
Populations can be dense…that is many individuals in a given
area, or diffuse, only a few in a given area.
Individuals may be dispersed
in a population uniformly,
randomly, or in clumps.
Through an age structure diagram, the age structure of a
population can be studied, showing the abundance of
individuals of each age.
By analyzing the
graphic
structure, you
can determine
whether the
population is
growing rapidly,
slowly, or not at
all.
The biotic potential is the maximum growth rate of a
population under ideal conditions, with unlimited resources and
without any growth restrictions.
Some bacteria have the potential to produce over a trillion
offspring within ten hours! The following factors contribute
to the biotic potential of a population:
• Age at reproductive maturity
• Clutch size
• Frequency of reproduction
• Reproductive lifetime
• Survivorship of offspring to reproductive maturity
The carrying capacity is the maximum number of individuals
of a population that can be sustained by a particular habitat.
It is often evident on a graph of population growth.
“S” or “J” type
shapes on a
population graph
are typical of
exponential growth
patterns.
• Log phase
• Carrying Capacity
If the environment has
not been irreparably
damaged, the
population may rebound
Once the population reaches carrying capacity, if you add more individuals,
you are inviting catastrophe! The population plunges.
A limiting factor is any element that prevents a population
from attaining its biotic potential. Limiting factors are
categorized into:
Density-dependent
Those agents whose limiting effect becomes
more intense as the population density
increases. Examples include parasitic
infections, disease, competition for resources,
and the toxic effect of waste products.
Predation is also density-dependent!
• Density-independent
Factors which occur independently of the
density of the population, such as natural
disasters, and extremes of climate.
Species have different reproductive patterns that can help enhance their
survival.
• High reproductive rate (r) : r-selected species
These species usually have many small offspring, and give them little or no
parental care.
They overcome potential offspring
loss by producing so many.
r-selected species do relatively
well in unstable or unpredictable
environments.
Other r-selected Traits Include:
• early maturity onset
• short generation time
Organisms whose life history is subject to r-selection are often referred
to as r-strategists or r-selected.
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•
•
•
•
•
bacteria and diatoms,
insects
weeds
semelparous cephalopods
mammals
reptiles
What exception to the
rule do mammals exhibit,
that none of the other
groups do?
They nurture and care for
their young for an
extended period of time.
In stable or predictable environments, K-selection predominates as the
reproductive strategy.
Unlike r-selected populations, where population size can change
dramatically overnight, K-selection populations are typically close to the
maximum that the environment can bear (carrying capacity) at most times.
The ability to compete successfully for limited resources is crucial for
that reason.
K-Selected Traits Include:
• Large body size
• Longer life expectancy
• Fewer offspring
• Extensive parental care
Although some organisms are identified
as primarily r- or K-strategists, the
majority of organisms do not follow
this pattern.
• Trees have traits such as longevity
and strong competitiveness that
characterize them as K-strategists.
• In reproduction, however, trees
typically produce thousands of
offspring and disperse them widely,
traits characteristic of r-strategists.
• Sea turtles display both r- and Ktraits: although large organisms with
long lifespans (should they reach
adulthood), they produce large numbers
of un-nurtured offspring.
If you suddenly stopped cutting the grass in your
yard, what would it look like in a year?
You don’t have to be an ecologist to know that your
grass would grow longer, and that weeds would take
over your yard if you let them.
In 10 years?
Your yard would resemble
a meadow, with small
bushes and shrubs, but
still mostly grasses
What about in 50
years?
The bushes and
trees change the
environment. Less
light reaches the
ground as they grow
taller, and grasses
eventually die out.
Succession occurs in stages, and can often take
decades or even centuries to occur. There are two
types of succession:
Primary and Secondary
These organisms of primary succession are known as
“pioneer species”.
This occurs when
the land is new,
and has never
been colonized by
organisms before.
Primary
succession occurs
in previously
uninhabited areas
with no soil.
Primary succession occurs on barren land, where
there are and have been no living organisms in the
past.
When a natural disaster such as a forest fire
destroys a community of living organisms, and nature
takes over to replace these organisms, then
secondary succession begins. Severe disruption of an
existing community is the key factor in this type of
succession.
Mirror Lake, Yosemite
Mirror Meadow, Yosemite
Secondary succession occurs where there is
developed soil on the ground. It is much faster than
primary succession.
After time passes, succession slows down, and the
community becomes fairly stable. A stable mature
community that undergoes little or no change in
species is known as a climax community.
The nutrient cycles you should be thoroughly familiar with are:
You may also see the phosphorus cycle show up on
• Carbon,
• Hydrologic, and the AP test. This is the simplest cycle. Most of the
phosphorus found in the phosphorus cycle originates in
• Nitrogen.
the rocks beneath your feet. (if a cycle has an origin).
The hydrologic cycle helps the
phosphorus cycle out, by
eroding the rocks, and
releasing the phosphorus into
the soil, and water.
It is taken up by plants and
animals, and then when they
die, it is added back to the
soil, where it has the potential
to be made into rocks again!
The carbon and hydrologic cycles are also quite
easy. Remember the following:
Hydrologic cycle Processes:
• Evaporation: liquid to a gas
• Condensation: gas to a liquid (clouds)
• Precipitation: liquid or solid to the ground
• Runoff: over the ground
• Infiltration: Into the ground
• Transpiration: Plants participating in the cycle as
water vapor moves through the stomata of a plant.
Carbon cycle Processes:
• Photosynthesis: Plants manufacture glucose, and
take CO2 in, Oxygen out
• Respiration: Both cellular, and breathing…it is the
exchange of gases O2 for CO2. (opposite of
photosynthesis) Process breaks down glucose to
produce ATP
• Decomposition releases CO2 back to atmosphere Carbon is also found in our fossil fuels, and
when we burn them (combustion), we add the
• Largest Carbon sink: Ocean (dissolved CO2) and
original carbon from the organisms that
shelled organisms (CaCO3)
fossilized, back into the atmosphere.
Of all the nutrient cycles, the Nitrogen Cycle is the most difficult to
understand, because of all the different stages.
Stages of the Nitrogen Cycle to Remember:
Nitrogen Fixation: Soil bacteria convert N2
(atmospheric nitrogen) into ammonia (NH3)
• Nitrification: Nitrifying bacteria convert
the ammonia into nitrate.
• Assimilation: Nitrate is assimilated and
absorbed by plants (which are consumed by
animals to pass the nitrogen on in the food
web) This nitrogen in plants is used to help
make amino acids, the building blocks of
proteins.
• Ammonification: After death,
ammonifying bacteria break nitrogen
compounds in the body down, and return
them back to the soil in the form of
ammonia.
• Denitrification: Denitrifying bacteria can
take nitrates and convert them into
atmospheric nitrogen again, completing the
cycle.
Polar Tundra; Taiga (Boreal Forest); Temperate Deciduous
Forest; Grasslands; Desert; Rainforest; Marine and
Freshwater
• Camouflage
• Hibernation
• Migration
• Thick coats and extra fat
• Dry and warm
• Cold winters, hot
• Wet…large leaves with drip tips
summers
• Hot and dry…small surface area, extensive roots close to
surface
• Cold…low growers