Proterozoic Eon Keywords
9+2 organization refers to the structure / configuration of the flagellar set up involved in
protist locomotion. Flagellum in protists differ from that of bacterium. Flagella are set up
with microtubules (where tubulin is the major protein) and these microtubules are
polymerized into a 9+2 structure. In this configuration, there are 9 paired clusters around
a central core pair with dyenin arms connecting the pairs. The dyenin motor / arm acts
like a myosin motor, where it crawls around the microtubule tract (the central core of the
structure) for movement. The dyenin motors are located in the flagella.
Alternation of Generations
Alternations of generations deals with the life cycle of organisms such as brown algae
and other plant-like protists. In an alternation of generations life cycle, both the haplontic
and diplontic cycles have equal contribution. The first stage involves a sporophyte (2n)
which creates spores (n) by meiosis. The spores, instead of immediately combining as in
the haplontic and diplontic lifecycles, settle on the ground and undergo mitotic divisions
which build into a cluster of cells (a gametophyte) that resemble a small sporophyte (this
marks the beginnings of the 2nd stage). The gametophytes make gametes and the
gametophytes undergo meiosis to create eggs and sperm (female spores = female
gametophytes = eggs, male spores = male gametophytes = sperm). The sperm fertilize the
egg and create a zygote which then undergoes mitotic divisions to create the sporophyte
Amoeboid movement involves the cytoplasm in the amoeba switching between a slight
solid ectoplasm to a slight liquid endoplasm. This conversion of ectoplasm to endoplasm
is associated with changes in the cytoskeleton within the cell, where the actin
cytoskeleton and skeletal mesh changes its fluid properties. The cytoplasm streams
toward the front of the amoeba. Endoplasm moves forward and hits the hyaline cap
(modified cytoplasm) and causes it to curl back on itself (change in actin cytoskeleton)
and thus, becoming more rigid and allowing the protist to move forward. At the back, the
actin cytoskeleton is dissolved and liquid is pulled forward to cap (conversion from stiff
to soft at the back). This process is known as cytoplasmic streaming.
An antibody is an immunoglobin which is released from B lymphocytes after activation
by an antigen which binds to the antigen and aids its elimination of foreign objects by
other components of the immune system.
An antigen is a foreign molecule that when introduced to the body causes an immune
response and the production of antibodies in order to neutralize the antigen. It is a
substance that is also capable of binding specifically to an antibody or T-cell receptor. Asexual reproduction
Asexual reproduction is a mode of reproduction by which offspring arise from a single
parent, and inherit the genes of that parent only
Bovine spongiform encephalopathy
Bovine spongiform encephalopathy is also known as mad cow disease and it involves
aberrant prions. Prions are small protein particles that can be folded into 1 of 2
configurations. Its aberrant configuration causes other prions to change into the aberrant
configuration. This results in explosive exponential growth in the number of misfolded
prions. When they are misfolded they can form fibres and add more of the altered prions
at the tip, growing the fibre. The fibres often break and the number of growing points
increases and as the fibres enlarge they create aggregates that appear as spongy holes in
Capsid protein make up the protein casing on viruses. Capsid protein surround a strand of
genetic information. This viral genetic information contains the genes required to
duplicate the viral genome, manufacture the capsid proteins, and assemble the capsid
around the copies of the genome. Both enveloped and non-enveloped have the capsid
casing surrounding the genome but an enveloped virus has an additional lipid bilayer
membrane surrounding the capsid and the genome inside.
The chloroplast (or a plastid) in plants arose by endosymbiosis and internalization of an
autotrophic phototroph bacteria, most likely a cyanobacterium. There is a double plasma
membrane around the plastid which also has it's own circular DNA resembling bacterial
DNA and bacteria-type ribosomes. Some plastid in the algae have traces of the
peptidoglycan cell wall that is typical of bacteria. Chloroplasts replicate via binary fission
from the egg of the mother.
Cilia represent many short flagella and are modifications of flagella. Cilia are involved in
protist locomotion. Ciliated organisms have many flagella-like structures on their surface
and these cilia have the same 9+2 structure as dyenin motors, except there are thousands
located on the surface of the organism that are constantly beating in a wave-like motion.
A metachronal wave ensures continuous motion, where there are a certain proportion of
cells in the power stroke phase, a certain proportion in the recovery phase, and a certain
proportion in between. Ciliates can hover and manoeuvre and have flexibility in
movement. The recovery beat of the cilia occur at right angles to the original beat and
this allows for co-ordination of the whole set of cilia.
As protists move to freshwater environments, water begins to move in since the inside of
the body is salty (due to its evolutionary origins in salt water / the oceans). The
contractile vacuole in protists deal with this inundation (flooding) through the use of a
contractile vacuole which pumps out excess water that is flowing in. The organism uses ATP to pump water into this vacuole which swells and releases water. This is the early
forms of osmoregulation and ion balance.
Creutz-feldt-Jakob disease is a spongiform encephalopathy caused by aberrant prion
(misfolded proteins). When one misfolded prion comes into contact with a normal prion,
the normal prion is converted into the aberrant form. This results in an exponential
growth in the number of misfolded prions. They end up forming fibres which grow as
they come into contact with other prions and they create aggregates that appear as spongy
holes in brain tissue. In animals, this disease is called mad cow disease and in humans, it
is called Creutzfeldt-Jakob disease.
The diploid state or the 2n state is the state where chromosomes have been duplicated and
contains the maternal and paternal set. The haploid number is doubled. Somatic cells are
in the diploid state.
Diplontic refers to the diplontic lifecycle, which is dominant in the kingdom animalia and
animal-like protists. In the diplontic lifecycle, the diploid stage is dominant. For example,
in diatom algae, mitotic division occurs in the diploid (2n) state in order to exploit the
good environment. When conditions are poor, the diatoms undergo meiosis to create 4
new cells which emerge from their pill box. One product is immotile and the other
product can swim. They form a zygote (2n), which creates its own pill box and undergo
mitotic divisions. These meiotic divisions allow for variability which may help when
conditions are poor.
Ectoplasm is involved in the cytoplasmic streaming used for amoeboid movement.
Ectoplasm is the slightly solid form of cytoplasm.
The endomembrane system are a set of elaborate internal membranes. In order to increase
the surface area of a cell to keep up with the demands of life processes, the plasma
membrane was folded inwards. In eukaryotes, genetic material of the cell was the first
material to be wrapped inside the endomembrane system. This results in the formation of
the nucleus, nuclear membrane, nuclear pores, endoplasmic reticulum, golgi complex,
vesicles, and lysosomes.
Endoplasm involved in the cytoplasmic streaming used for amoeboid movement.
Endoplasm is the slightly liquid form of cytoplasm.
Endosymbiosis refers to any organism that lives within the body or cells of another
organism. The origins of mitochondria and chloroplasts have its beginnings as bacteria which were incorporated into simple eukaryote cells with a nuclear membrane and
endomembrane system. It is believed that mitochondria appeared before the plastid. At
some point in time, a large bacterial cell engulfed a bacterium that had the electron
transport chain in it and when it engulfed it, it kept some plasma membrane around the
bacterium. The bacterium created ATP as the cell fed pyruvate to the bacterium. A
partitioning of the energy system has occurred and the engulfed bacterium is doing the
majority of the work. This was a tremendously successful event and organisms that took
advantage of this system thrived. Proof that mitochondria have bacterial origins include
its double bilipid membrane (the inner membrane is the original bacterial membrane and
the outer mitochondrial membrane was produced by the cell as it surrounded the
bacterium), mitochondria have their own circular DNA and resembles the bacterial
genome, mitochondria contain its own transcription and translation system using
ribosomes that are bacterial in size, and mitochondria use binary fission as a means of
replication. The same story can be applied to chloroplasts. Endosymbiosis of eukaryote
cells involves certain algal groups. In this case, a small eukaryotic green algae was
engulfed and surrounded by a larger eukaryote and was set up in a symbiotic relationship.
Since this symbiont was a eukaryote, it is known was a secondary endosymbiotic event.
As a consequence of this process, there is a 4 bilipid membrane surrounding plastids that
have arisen from secondary endosymbiosis. Secondary endosymbiosis has occurred twice
with one algal group using the red algal plastids and the other plastids from green algae.
Enveloped viruses have an additional lipid bilayer membrane surrounding the capsid and
genome. The lipid bilayer membrane is formed from the plasma membrane of the host
and includes host membrane proteins and additional plasma membrane proteins added by
the virus. These additional viral proteins are used to identify the virus via H and N
antigen proteins. The H-antigens are important in recognizing a host cell and attaching
the virus so that the genome can move into the host cell. The N-antigens are involved in
the escape from the host cell when the virus has completed replication. Enveloped viruses
tend to escape from cells slowly via budding and don't kill the host cell. When new
enveloped virus particles are being produced, the capsid remains and the genetic
information is contained in it. When the virus escapes from the host cell, it wraps itself in
the host's plasma membrane and embeds antigen proteins into the host and this new virus
contains the virus antigens for recognition.
An epidemic occurs when new cases of a certain disease, in a given human population,
and during a given period, substantially exceed what is expected based on recent
experience. It is an outbreak of a disease in a large number of individuals over a
considerable geographic area (i.e.: the Spanish flu virus in 1918 after WWI).
Eukarya are one of the three domains of life (the others being Archaea and Monera /
Bacteria). The word comes from the Latin 'eu' meaning true and 'karyote' meaning seed,
referring to the nucleus. The eukaryote contains complex structures within its membrane. Flagellum
Flagellum in amoeba differ from flagellum in bacteria. Flagellum in amoeba are set up
with microtubules, where tubulin is the major protein that is polymerized in a 9+2
configuration. This configurations is set up with 9 paired clusters around a central core
pair with dyenin arms connecting the pairs. The dyenin arm acts like a myosin motor,
where it crawls around microtubule tract (central core of structure) for movement. The
motors are located in the flagella.
A gametophyte is the haploid (n), multicellular phase of plants and algae that undergo
alternation of generations, with each of its cells containing only a single set of
chromosomes. The gametophyte produces male or female gametes (or both), by a process
of cell division called mitosis. The fusion of male and female gametes produces a diploid
zygote, which develops by repeated mitotic cell divisions into a multicellular sporophyte.
The haploid (n) state is the state where the chromosome set divides through meiosis
which allows for recombination and variability. Sperm and egg cells are haploid.
Haplontic refers to the haplontic lifecycle, which is dominant in the kingdom fungi and
fungal-like protists and deals with the rearrangement of chromosomes. In the haplontic
lifecycle, the haploid stage is dominant where almost the entire life is spent in the
haplontic state (i.e.: dinoflagellate). Dinoflagellate (n) multiply by binary fission (asexual
reproduction) to increase in numbers when conditions are right in order to exploit the
environment. Under sever conditions, sexual reproduction and recombination occurs to
create variation in order to survive. 2 dinoflagellate fuse and now there are 2 nuclei inside
which forms the diploid zygote (2n). A meiotic event creates 4 products which are
genetically different from the 2 dinoflagellate cells that originally fused.
Histone proteins are a mechanism for wrapping DNA and providing protection to the
genetic material. Eukarya and archea use the same type of proteins to package and
stabilize DNA within the cell. Histones are highly alkaline proteins found in eukaryotic
cell nuclei that package and order the DNA into structural units called nucleosomes.They
are the chief protein components of chromatin, acting as spools around which DNA
winds, and play a role in gene regulation
A host is an organism that harbours a parasite, or a mutual or symbiont, typically
providing nourishment and shelter. For example, bacteria are hosts to bacteriophage,
larger bacterial cells were host to bacterium which become the mitochondria and
chloroplasts in modern-day organisms, and larger eukaryote cells were hosts to smaller
eukaryotic green algae. Latent viral phase
Latent viral phase refers to a phase in the lysogenic replication cycle where the viral
DNA is incorporated in the circular genome of the bacterial cell and lies dormant as the
bacterial cell replicates.
The lysogenic cycle is a cycle for replication in viruses. Viral DNA gets incorpora