biol 204 Flashcards
midterm
components of the cell theory
1) All organisms are composed of one or more cells (some organisms like prokaryotes are composed of a single cell)
2) The cell is the smallest unit that has the properties of life. If cells are broken open, the property of life is lost. They are unable to grow, reproduce, or respond to stimuli in a coordinated, potentially independent fashion
3) Cells arise only from growth and division of pre-existing cells. Although DNA and RNA contain the information required to manufacture an array of biological molecules, they cannot orchestrate the formation of the entire cell, new cells can only arise from pre-existing cells
components of primordial earth
h2s, co2, methane and ammonia
DNA
a large double stranded helix molecule that contains a unique alphabet that provides the instructions for assembling many of the important components of a cell organism from simpler molecules
RNA
single strand of nucleotides which is used for protein synthesis and carries genetic information for many viruses.
Protein
Molecules that carry out most of the activities of life, including the synthesis of all other biological molecules.
Difference between prokaryotic and eukaryotic cells
Eukaryote cells are 10x bigger, have nucleus, and are multicellular. They are characterized by an endomembrane system, which consists of the nuclear envelope, the endoplasmic reticulum, and the Golgi complex. They also have specialized motor (contractile) proteins that move cells and internal parts. Prokaryotes are more complex, have no organelles and lack a true membrane bound nucleus, instead their DNA floats freely as a nucleoid, much less internal membrane organization, are biochemically more versatile.
cyanobacteria
The earliest form of photosynthesis relied on compounds such as h2s and ferrous iron (Fe2+), which could be easily oxidized b energy trapped from sunlight (which would reduce CO2 into sugars). However, aprox 3 billion years ago, a group of prokaryotes called cyanobacteria appeared and could be used for something more common than h2s or Fe2+ as an electron donor for photosynthesis. Cyanobacteria were able to harness electrons from water and could thrive virtually anywhere there was sunlight.
endoplasmic reticulum
extensive interconnected network of membranous channels and vesicles. Each vesicle is formed by a single membrane that surrounds an enclosed space called the lumen of the ER. The ER occurs in two forms…
rough&smooth
Golgi complex
consists of a stack of flattened membranous sacs, usually located between rough er&plasma membrane
- receives proteins made in the ER and transports to the complex in vesicles
- more chemical modifications of proteins occur, those proteins are then sorted into other vesicles, then regulated movement of several types of proteins
- proteins secreted from the cell are transported to the plasma membrane by secretory vesicles (release contents to the exterior by exocytosis). Vesicles may also form by the reverse process, calledendocytosis, which brings molecules into the cell from exterior
theory of endosymbiosis
prokaryotic ancestors of modern mitochondria and chloroplasts were engulfed by larger prokaryotic cells, forming a mutually advantageous relationship called a symbiosis and over time, the host cell and the endosymbionts became inseparable parts of the same organism.
factors in endosymbiosis
rise in atmospheric O2 is thought to be a key factor in endosymbiosis
Morphology – the form or shape of the mitochondria and chloroplasts is similar to a prokaryotic cell. Mitochondria resemble aerobic prokaryotes, chloroplasts resemble cyanobacteria
Reproduction – a cell cannot make a mitochondrion from a chloroplast, they are derived only from pre-existing mitochondria or chloroplasts. Both divide by binary fission, which is how prokaryotic cells divide
Genetic Information- mitochondria and chloroplasts contain DNA (as they should if they were free living cells). Where free-living bacterium contain a few thousand protein-coding genes, DNA in energy-transducing organelles contain less than 100 (because many of the genes have been relocated to the nucleus).
Transcription and Translation –chloroplasts and mitochondria contain a complete transcription and translational machinery, including the enzymes and ribosomes necessary to synthesize the proteins encoded by their DNA. Ribosomes of mitochondria and chloroplasts are similar to the type found in prokaryotes.
Electron Transport – Similar to free-living prokaryotes, mitochondria and chloroplasts can generate energy in the form of ATP through the presence of their own electron transport chain
exocytosis
in eukaryotes, the process by which a secretory vesicle fuses with the plasma membrane and releases the vesicle contents to the exterior
9+2 structure
A bundle of microtubules extends from the base to the tip of a eukaryotic flagellum or cilium. In the bundle, a circle of nine double microtubules surrounds a central pair of single micro- tubules, forming what is known as the 9 2 complex. Dynein motor proteins slide the microtubules of the 9 2 complex over each other to produce the flagellar or ciliar movements
endocytosis
brings molecules into the cell from the exterior
ribosomes
the organelle in contemporary organisms required for protein synthesis. It is interesting to note that the modern ribosome, which plays a key role as an intermediate between RNA and protein, is composed of about two-thirds RNA and one-third protein. Interestingly, it has recently been shown that the RNA of the ribosome, not the protein, actually catalyzes the incorporation of amino acids onto a growing peptide chain. Thus, the ribosome may be considered a type of ribozyme
protobionts
term given to a group of abiotically produced organic molecules that are surrounded by a membrane or membrane like structure. Development of protobionts was important because it allowed for an internal environment to develop that was distinctly different from the external environment: the concentration of key molecule could be higher and attain more order in a closed space. May have formed spontaneously. Ex- liposomes.
ribozymes
Group of RNA molecules that themselves could act as catalysts. They catalyze reactions on the precursor RNA molecules that lead to their own synthesis, as well on unrelated RNA molecules. Discovery of ribozymes revolutionized thinking about the origin of life, instead of the contemporary system that requires all 3 molecules (DNA, RNA, protein) early life may have existed in an RNA world – where a single type of molecule could serve as both a carrier of information and a catalyst.
panspermia hypothesis
life on earth could have had an extraterrestrial origin:
1) Although life seems very complex, it arose relatively quickly after the formation of Earth. The Earth formed 4.6 billion years ago, and we have clear fossil evidence of life dated to about 3.5 billion years ago and chemical evidence to about 3.9 billion years ago. Given that primordial Earth had to cool after being formed, many scientists argue that this window for the development of life is very narrow.
2) Research in the past decade has shown that life is far more resilient than previously thought and could possibly survive for years in space. Extremophiles, which are mostly prokaryotes, can thrive under very harsh conditions of temperature, pressure, and nutrients and might be able to survive in a dormant state in interstellar space. Prolonged dormancy is a property of the spores of a range of organisms, including a number of prokaryotes and simple eukaryotes. Spores are highly resistant to changes in the external environment and can be restored to active growth after exposure to high levels of radiation, water deficiency, and/or exposure to extreme temperatures. Given this, one cannot discount the possibility that simple life forms came to Earth about 4 billion years ago and initiated the evolution of life as we know it
autotroph
self nourishment, mostly plants, synthesize organic carbon molecules from using inorganic co2
heterotrophs
mostly animals, obtain carbon from organic molecules (either living hosts or from organic molecules in products, wastes, remains of dead organisms)
chemoautotroph
obtain energy by oxidizing inorganic or organic substances
phototrophs
obtain energy from light
photoautotroph
energy from sunlight, carbon from environmental co2
*some photosynthetic bacteria, some proteins, some plants
photoheterotroph
every from sunlight, carbon from organic substances
*some photosynthetic bacteria
chemoautotroph
energy from inorganic chemicals, carbon from environmental co2
*some bacteria and archness, not found in eukaryotes
chemoheterotroph
energy from inorganic chemicals, carbon from organic sources
*some bacteria and archaens, proteins, fungi, animals, plants
natural selection
changes in environment favour particular genotypes that survive
evolution
- Evolution is a gradual change in the characteristics of a population of organisms over time, and can be the result of selection
- evolution is a central key to understanding the diversity of life on earth
- theory of evolutionexplains both the unity and diversity of all life; tells us all organisms alive today descended from a common ancestor, which explains why all organisms share features such as the use for ATP as an energy source, DNA as genetic material, and plasma membranes composed of lipid bilayers
- evolution also tells us species change over time as a result of natural selection
adaptive radiation
adaptive radiations, therefore, occur when an evolutionary breakthrough allows diversification of life. Adaptive radiations are a recurring theme in the development of biodiversity. At one level, we can see it in the evolution of the fauna and flora of the Hawaiian Islands, arguably the most isolated landmasses in the world. Adaptive radiation on islands reminds us that species can be adapting to new ways of life at the same time in different parts of the world. The result is a mosaic of life, with many examples of parallel and convergent evolution
challenges from organisms moving from water to land
matters of support, conservation of water, reproduction, and disposal of wastes. Other facts of life are also different for organisms living on land as opposed to in water. Some of the differences between water and air include density and viscosity, which, in turn, affect rates of diffusion and availability of oxygen.
opportunities from organisms moving to land
easy access and less energy expended to get oxygen. terrestrial plants had developed specialized sexual organs, stems with mechanisms for fluid transport, structural elements such as wood to provide mechanical support, roots for anchorage, leaves as sites of photosynthesis, stomata in the leaves to allow passage of CO2 and O2, and seed transport. Terrestrial animals of this period had skeletons for support and anchoring muscles (allowing locomotion), organs for gaseous exchange (breathing atmospheric oxygen), and systems for circulating materials within the body. Terrestrial animals and plants also had waterproof coverings to minimize the chances of desiccation. Terrestrial animals used nontoxic excretory products (urea and uric acid), whereas aquatic ones still relied heavily on ammonia
seasonal variation -northern hemisphere
receives its maximum illumination, and the Southern Hemisphere its minimum, on the June solstice (around June 21), when the sun shines directly over the Tropic of Cancer. The reverse is true on the December solstice (around December 21), when the sun shines directly over the Tropic of Capricorn (23.5 S latitude). Twice each year, on the vernal and autumnal equinoxes (around March 21 and September 21, respectively), the sun shines directly over the equator
topography
In the Northern Hemisphere, south-facing slopes are warmer and drier than north-facing slopes because they receive more solar radiation. In addition, adiabatic cooling causes air temperature to decline also establish regional and local rainfall patterns.
parasitism
a symbiotic relationship in which one organism benefits at the expense of another
forms of energy
heat, chemical, electrical and mechanical energy
first law of thermodynamics
Energy can be transformed from one form into another or transferred from one to another, but it cannot be created or destroyed. Example is Niagara falls – water at the top of the falls has high potential energy because of its location within earths gravitational field. As water moves over the waterfall, its potential energy is converted into kinetic energy. When it reaches the bottom of the waterfall, the kinetic energy of the water is dissipated into various forms of potential and kinetic energy. At Niagara falls, the kinetic energy of the moving water is converted into electricity through hydroelectric turbines. A living example is – 40% of glucose is harnessed in cellular respiration
second law of thermodynamics
the total disorder (entropy) of a system and its surroundings always increases. The physical disintegration of an organized system is the second law in action. Life does not apply as it is highly organized.
entropy
the unusable energy that is produced during energy transformations results in an increase in the disorder or randomness of the universe. In thermodynamics, this randomness or disorder is a quantity called entropy. Ex: cup of coffee gets cold, new car doesn’t stay new and loses its ‘‘new car smell’’, etc
what determines a spontaneous reaction
- Reactions tend to be spontaneous if the products have less potential energy than the reactants. The reaction is exothermic (process that releases energy), producing a large amount of heat, as the products have less potential energy than the reactants. Alternatively, reactions that absorb energy are endothermic, if the products have more potential energy than the reactants.
- Reactions tend to be spontaneous when the products are less ordered than the reactants. Reactions tend to occur spontaneously if the entropy of the products is greater than the entropy of the reactants, that is, if the products are more random than the reactants. (ex- melting of ice)
equilibrium
maximum stability. It is represented by ΔG=0, a state in which the reaction does not stop but rather a state in which the rate of the forward reaction equals the rate of the backward reaction. As a system moves toward equilibrium, the free energy of the system becomes progressively lower and reaches its lowest point and maximum stability when the system is at equilibrium.
Enzymes
protein based catalysts which speed up a spontaneous reaction by lowering the activation energy of spontaneous (exergonic) reactions. They are crucial since you cannot use heat due to the fact that heat would cause more problems (like destroying cell structure) and it could speed up all other reactions that should not be going faster than needed.
how enzymes catalyze reactions
1: bring reactants close together
2: exposing reactants to an electrical charge
3: changing conformation of the substrate.
conditions that affect enzyme activity
changes in the concentration of substrate and other molecules that bind to enzymes. In addition, a number of control mechanisms modify enzyme activity, thereby adjusting reaction rates to meet a cell’s requirements for chemical products. As well, changes in temperature and pH can have a significant impact on enzyme activity.
competitive inhibition
where there is an inhibitor molecule that competes with the substrate (same shape) for the active site and can slow down the reaction or stop altogether if there is too many competitive inhibitors.
non competitive inhibition
inhibitor binds elsewhere on the enzyme which distort the activation site (allosteric inhibition) (sometimes the inhibitor in any inhibition case may for covalent bonds and completely disable the enzyme)
feed back inhibition
occurs in regulations where the product of a reaction also acts as its regulator. It acts in a similar fashion to allosteric inhibition by minimizing wastage of cellular energy and resources during molecular synthesis in the pathway. Both processes are similar in controlling enzyme activity
allosteric inhibition
a reversible way of regulating enzyme activity. It uses the binding of regulatory molecule and the allosteric site, causing an increase or decrease in enzyme activity. An allosteric inhibitor binds to an allosteric site on the enzyme in order to release the substrate, and the enzyme will go from high-affinity state to low-affinity state because it is catalyzing too many molecules. Allosteric inhibitors are often a product of their metabolic pathway. If accumulates in excess, the inhibitor will slows or stops the reaction producing it. If product is scarce, it will increase production and decrease inhibition. The product of the pathway regulates the reaction by acting on the primary enzyme.
fluid mosaic model
Membranes are fluid and the membrane proteins move across the membrane (not rigid). Experiment was conducted with rat cell and human cell (each got membrane proteins dyed a different color) when they fused together the proteins moved from the original starting position and moved across the cell. Lots of different protein that scatter the membrane and different membranes have different proteins
factors in simple diffusion
size and charge, determines the ease with which a molecule can move across a membrane. Very small nonpolar molecules such as O2 and CO2 are readily soluble in the hydrophobic interior of a membrane and move rapidly from one side to the other. In contrast, the membrane is practically impermeable to charged molecules, including ions such as C1-, Na+, and phosphate (PO4-). The presence of a charge and a hydration shell of water surrounding the ion contribute to ions being prevented from entering the hydrophobic core of the membrane.
how cells move different materials across a cell membrane
Facilitated diffusion allows transport to be helped or facilitated by protein complexes that span the membrane (although facilitated diffusion uses specific transporters, the movement of molecules is still initiated by diffusion based on a concentration gradient against the membrane).
Channel proteins form hydrophilic pathways in the membrane through which water and ions can pas, which aids the diffusion of molecules through the membrane (gives them an avenue where they don’t have to interact with the hydrophobic portions of the membrane). Carrier proteins also form passageways through the lipid bilayer, binging a specific single solute (such as sugar molecule or amino acid) and transports it across the lipid bilayer (uniport transport). The carrier protein undergoes conformational changes which progressively move the solute binding site from one side of the membrane to the other, transporting the solute.
how ATP is synthesized by chemiosmosis
ATP is formed by hydrogen protons being pumped into the mitochondrial intermembrane from complex 1,3 and 4. More hydrogen in intermembrane makes a proton-motive force which the hydrogen protons want to return into the matrix and can do so through the ATP synthase which pump the protons back into the matrix and in turn changes the conformation of ATP synthase which makes a turning motion that synthesized ADP +P into ATP.
how cellular respiration is regulated in the cell
Most metabolic pathways are regulated by supply and demand through the process of feedback inhibition: the end products of the pathway inhibit an enzyme early in the pathway
Not surprisingly, the rate of cellular respiration is controlled by key metabolic intermediates. The rate of sugar oxidation by glycolysis is closely regulated by several mechanisms to match the cell’s need for ATP. For example, if excess ATP is present in the cytosol, it binds to phosphofructokinase, inhibiting its action. The resulting decrease in the concentration of fructose- 1,6-bisphosphate slows or stops the subsequent reactions of glycolysis and, as a consequence, the remainder of cellular respiration. Thus, glycolysis does not oxidize fuel substances needlessly when ATP is in adequate supply.
describe how chlorophyll in photosystems traps light, and explain how this results in an electron transport chain.
1) Absorption of photons by antenna complex and funneling of energy to the reaction centre results in an electron with P680 being raised from ground to excited state (P680)
2) P680 can be easily oxidized to P680+ by the primary electron acceptor of photosystem II, a molecule called pheophytin, which initiates electron transport by donation to plastoquinone (PQ) which is analogous to ubiquinone of respiratory electron transport
explain how pigment molecules absorb light energy.
The absorption of a photon by a pigment molecule excites a single electron, moving it from the ground state to an excited state. The difference in energy level between the ground state and the excited state is equivalent to the energy of the photon of light that was absorbed. Can either return to ground state, returns to ground state, or donated to electron accepting molecule
main pigments in photosynthetic apparatus
P680 → p680* in PSII and p700 → p700* in PSI and they are arranged at the reaction centre where the photon in funnelled to get to that excited state and electron transport chain
phases of the Calvin cycle
1 carbon fixation
2 reduction
3regeneration
rubisco
Rubisco is slow and inefficient enzyme. As an oxygenase, rubisco catalyzes the combination of RuBP with O2 rather than with CO2, forming toxic products that cannot be used in photosynthesis. The toxic products are eliminated by reactions that release carbon in inorganic form as CO2, greatly reducing the efficiency of photosynthesis. The entire process is called photorespiration because it uses oxygen and releases CO2
CAM plants
CAM plants typically live in regions that are hot and dry during the day and cool at night. Their fleshy leaves or stems have a low surface-to-volume ratio, and their stomata are reduced in number. Further, the stomata open only at night, when they release O2 that accumulates from photosynthesis during the day and allow CO2 to enter the leaves. The entering CO2 is fixed by the C4 pathway into malate, which accumulates throughout the night and is stored in large cell vacuoles.
Daylight initiates the second phase of the strategy. As the sun comes up and the temperature rises, the stomata close, reducing water loss and cutting off the exchange of gases with the atmosphere. Malate diffuses from cell vacuoles into the cytosol, where it is oxidized to pyruvate, and CO2 is released in high concentration. The high CO2 concentration favours the carboxylase activity of rubisco, allowing the Calvin cycle to proceed at maximum efficiency with little loss of organic carbon from photorespiration. The pyruvate produced by malate breakdown accumulates during the day; as night falls, it enters the C4 reactions, con- verting it back to malate. During the night, oxygen is released by the plants, and more CO2 enters.
c4 plants
In c4 plants, the C4 cycle occurs in mesophyll cells, which lie lose to the surface of leaves and stems, where O2 is abundant. The malate intermediate of the C4 cycle diffuses from the mesophyll cells to bundle sheath cells, located in deeper tissues, where O2 is less abundant. In these cells, in which the Calvin cycle operates, the malate enters chloroplasts and is converted to pyruvate and CO2. Because O2 concentration is low and CO2 concentration is high because of its release by malate breakdown, the oxygenase activity of rubisco is inhibited, and the carboxylation reaction runs highly efficiently. The pyruvate produced by malate oxidation returns to the mesophyll cells to enter another turn of the C4 cycle.
importance of the thylakoid membrane
It houses the molecules that carry out the light reactions of photosynthesis, including the pigments, electron transfer carriers, and ATP synthase enzymes for ATP production.
The enzymes that catalyze the reactions of the Calvin Cycle are found in the chloroplast.
-But cells lacking a chloroplast can still be photosynthetic. Many photosynthetic prokaryotes also have thylakoid membranes tthat are formed from infoldings of the plasma membrane.
what is CO2 converted to in the Calvin cycle
Three carbon sugars, which can be readily combined to form six-carbon monosaccharides, including glucose.
function of a photosystem
The function of a photosystem is to trap photons of light and use the energy to oxidize a reaction centre chlorophyll, with the electron being transferred to the primary electron acceptor.
if eukaryotes require their daughter cells to be exact genetic copies of the parental cell - which process is used?
mitosis
when cells are needed that are different from the parent cells - which process is used?
meiosis
diploid
2 copies of each chromosome, also referred to as 2n
haploid
1 copy of each chromosome, also referred to as n
number of chromosome sets in a cell is called a ___
ploidy of the cell or species
replication of the DNA of each individual chromosome creates ___
two identical molecules called sister chromatids
held together until mitosis separates them
equal distribution of daughter chromosomes to each of the two cells the result from cell division is called___
chromosome segregation
The precision of chromosome replication and segregation in the mitotic cell cycle creates a group of cells called a__
clone
true or false: all cells of a clone are genetically identical
yes except in the case of genetic mutation
interphase
-cell grows and replicates DNA in preparation for mitosis (M phase) and cytokinesis
-g1 phase: cell makes various RNAs, proteins, other types of cellular molecules, but NOT nuclear DNA (period of cell growth before DNA replicates)
-if the cell is going to divide, DNA replication begins, initiating the S (synthesis) phase
-S phase is the period when DNA replicates and chromosomal proteins are duplicated, cell enters G2 phase when complete
-The g2 phase: cell continues to synthesize RNAs, proteins, continues to grow. Period after DNA replicates, cell prepares for division
During these steps chromosomes are loose, but organized in nucleas. After this, mitosis begins
which phase of the cell cycle varies in length between species?
G1 phase
thus, whether cells divide rapidly or slowly depends on length of g1
what is the g0 phase?
g1 is the stage in which many cells stop dividing. this state of division arrest is designated as the g- phase.
ex: in humans, cells in nervous system reach g0 phase when fully mature
what are the stages of mitosis? (list the names)
prophase, metaphase, anaphase telophase
prophase
- greatly extended chromosomes that were replaced in interphase condense and compact into rod like structures
- while condensation is in progress, nucleus becomes smaller and eventually disappears in most species: reflects a shut down of all types of RNA synthesis
- in the cytoplasm, mitotic spindle begins to form between the 2 centrosomes as they migrate to opposite ends to form spindle poles
- spindle developer as bundles of microtubules that radiate from the spindle poles
- nuclear envelope breaks down, heralding the beginning of pro metaphase
prometaphase
- bundles of spindle microtubules grow from centrosomes at the opposing spindle poles toward the centre of the cell
- some of the developing spindle enters the former nuclear area and attaches to the chromosomes
- remember* each chromosome is made up of 2 identical sister chromatids held together only at their centromeres
- complex of several proteins, kintechore, has formed on each chromatid at centromere
- kintechore microtubules bind to kintechores, which determine the outcome of mitosis (bc they attach the sister chromatids of each chromosome to microtubules leading to the opposite spindle poles) , microtubules that do not attach to kintechores overlap those from the opposite spindle pole
metaphase
- spindle reaches its final form and spindle microtubules move chromosomes into alignment at spindle midpoint (metaphase plate)
- chromosomes complete condensation and assume characteristic shape as determined by location of the centromere and length and thickness of chromatid arms
- once chromosomes are assembled at spindle midpoint with 2 sister chromatids of each one attached to microtubules leading to opposite spindle poles, can metaphase give way to actual separation of chromatids
- complete collection of metaphase chromosomes arranged according to size and shape, forms the KARYOTYPE of given species
anaphase
- sister chromatids separate and move to opposite spindle poles
- first signs of chromosome movement can be seen at the centromeres as the kintechores are the first sections to move toward opposite poles
- movement continues until separated chromatids, now called daughter chromosomes, have reached the 2 poles, and chromosome segregation has now completed
telophase
- spindle disassembles and chromosomes at each spindle pole decondense and return to the extended state typical of interphase
- nucleolus disappears, RNA transcription resumes, new nuclear envelope forms around the chromosomes at each pole, producing 2 daughter nuclei.
- nuclear division is completely, cell has 2 nuclei
cytokinesis
division of the cytoplasm
usually follows nuclear division stage of mitosis and produces 2 daughter cells, each one containing 2 daughter nuclei
-in most cells, cytokinesis begins during telophase or late anaphase
-when cytokinesis is completed, daughter nuclei have progressed the interphase state and entered the g1 phase of the next cell cycle
proceeds….
in animals: the furrow girdles the cell and gradually deepens until it cuts the cytoplasm in 2
in plants: cell plate forms between daughter nuclei and grows laterally until it divides the cytoplasm
furrowing
- the layer of microtubules that remains at the former spindle midpoint expands laterally until it stretches entirely across the dividing cell
- as layer develops, band of microfilaments forms just inside plasma membrane, forming a belt that follows the inside boundary of the cell plane in the microtubule layer
- powered by motor proteins, microfilaments slide together, tightening the band and constricting the cell - forming a groove or furrow in plasma membrane that gradually deepens until daughter cells are separated
- cytoplasmic division isolates the daughter nuclei in the 2 cells at distributes organelles/ other structures approximately equally
cell plate formation
- layer of microtubules that persists at the former spindle midpoint serves as organizing site for vesicles produced by the ER and Golgi complex
- as vesicles collect, layer expands until it spreads entirely across the dividing cell, during this, vesicles fuse together and contents assemble into new cell wall- the cell plate- stretching completely across the former spindle midpoint
- this separates cytoplasm and its organelles into 2 parts and isolates the daughter nuclei in separate cells
- plasma membrane that lines the two surfaces of the cell plate are derived from vesicle membranes
centrosome
site near the nucleus from which microtubules radiate outward in all directions
- centrosome is the main MTOC (microtubule organizing centre) of the cell, anchoring the microtubule cytoskeleton during interphase and positioning many of the cytoplasmic organelles
- contains a pair of controls, arranged at right angles to each other
- as prophase begins in the M phase, centrosome separates into 2 parts (step3)
- duplicated centrosomes, with centrioles inside, continue to separate until they reach opposite ends of the nucleas
- as centrosomes move apart, microtubules between them lengthen and increase in number
cytoplasmic division in prokaryotes
- occurs through an inward growth of the plasma membrane, along which new cell wall material is assembled to cut the cell into two parts
- new wall divides the two replicated DNA molecules and cytoplasmic structures and molecules equally between the daughter cells
discuss binary fission(3 steps) of prokaryotes in a little more detail
Replication of the bacterial chromosome begins at a site called the “origin” through reactions catalyzed by enzymes located in the middle of the cell. Once the origin of replication is duplicated, the two origins migrate to the two ends of the cells. Division of the cytoplasm then occurs through a partition of cell wall material that grows inward until the cell is separated into two parts
- describe how the genetic material of eukaryotes is organized (i.e., in chromosomes)
• Human DNA is organized into chromosomes which are diploid (is when there are 2 copies which is shown as n). Human chromosomes contain 23 diploid chromosome pairs, since human chromosomes are 2n humans have 2*23 = 46 chromosomes. Sometimes it is organized into haploids (1n which would mostly be microorganisms). Also, they can be organized as ploidy (mostly plants and have multiple chromosomes). When DNA is separated (chromosome segregation) it would be split into 2 sister chromatids
- describe the function of mitosis as equal distribution of chromosomes and DNA from the dividing parent cell to two daughter cells.
• Chromosomes consist of 2 genetically identical pairs of chromatids which are bound together at the centromere. When they are pulled to each spindle pole the identical pairs are separated and each spindle pole contains 23 chromatids from the 46 that were aligned in metaphase. Replication of the DNA of each individual chromosome creates two identical molecules called sister chromatids. Newly formed sister chromatids are held together until mitosis separates them, placing one in each of the two daughter nuclei. As a result of this precise division, each daughter nucleus receives exactly the same number and types of chromosomes, and contains the same genetic information, as the parent cell entering the division. The equal distribution of daughter chromosomes to each of the two cells that result from cell division is called chromosome segregation.
- contrast how binary fission (the cell division in prokaryotes) differs from that in eukaryotes.
• Most prokaryotes have a single circular DNA (bacterial Chromosome) vs the multiple chromatids in eukaryotes. DNA is not separated by microtubuli but rather from the origin of replication (ori) in a zipper like fashion where DNA is separated actively on opposite ends of the cell. When replication is complete the cell division begins as the plasma membrane grows inward, and a new cell wall is synthesized. Prokaryotic cells only have one circular DNA and if each daughter cell gets one copy the genetic information was separated evenly where eukaryotic cells have much more DNA to split and more chance of error.
what is genetic recombination
Since mutations are relatively rare, diversity is amplified through various mechanisms that shuffle existing mutations into dif- ferent combinations.
- This process, of literally cutting and pasting DNA backbones into new combinations, is called genetic recombination and is very widespread in nature.
- Genetic recombination allows “jumping genes” to move, inserts some viruses into the chro- mosome of their hosts, underlies the spread of anti- biotic resistance among bacteria, and is at the heart of meiosis in eukaryotes. Genetic recombination puts the “sexual” in sexual reproduction; without genetic recombination, reproduction is “asexual,” and off- spring are simply identical clones of their parent
what things does genetic recombination require?
two DNA molecules that differ from one another in at least two places, a mechanism for bringing the DNA molecules into close proximity, and a collection of enzymes to “cut,” “exchange,” and “paste” the DNA back together.
what holds DNA together?
The sugar–phosphate backbone is held together by strong covalent bonds, whereas the bases pair with their partners through relatively weak hydrogen bonds
What would happen if two circular DNA molecules were involved in a single recombination event?
TWO CIRCULAR MOLECULES ‘FUSE’ TOGETHER AS A RESULT OF A SINGLE RECOMBINATION EVENT
____ allows DNA on different molecules to line up and recombine precisely.
homology
phototroph
Strains that are able to synthesize the necessary amino acids for protein synthesis
auxotrophs
mutant strains that are unable to synthesize amino acids
a strain that cannot manufacture its own arginine is represented by
arg-
normal form is arg+
conjugation
The basis of a kind of sexual reproduction in bacteria
- Instead of fusing, bacterial cells conjugate
-Contact each other by a long tubular
structure called a sex pilus and then form a
cytoplasmic bridge
-Part or all of the DNA of one cell moves into
the other through the bridge. The donated DNA can then recombine with homologous sequences of the recipient cell’s DNA
-Conjugation is initiated by the bacterial cell that has the fertility plasmid, or the ‘F Factor’ (It carries about 20 or so genes, several encoding proteins for the sex pilus). One strand of the F factor breaks at a specific point and begins to move from F+ to F- cell as the F factor replicates. No genetic recombination occurs between the DNA of two different cells in such a mating
• Hfr Cells and Recombination- Occasionally F factor can integrate into the chromosome in a single crossover event. Due to this phenomenon, some of the actual chromosome is transferred into F- cell, which results in recombination of the two cell’s DNA
transformation
Living cells of some species absorb pieces of DNA released from cells that have disintegrated. The entering DNA fragments can recombine with the recipient cell’s DNA.
(Griffith and pneumonia in mice -> . In 1928 Dr Griffith was studying how pneumonia was cause Griffith found that a mixture of heat-killed virulent cells plus living nonvirulent cells still caused pneumonia. The living nonvirulent cells had been transformed to virulence by something released from the dead cells. The substance derived from the killed virulent cells, the substance capable of transforming nonvirulent bacteria to the virulent form, was DNA. virulent cells recombine with the chromosomal DNA of the nonvirulent cells in much the same way as genetic recombination takes place in conjugation. Only some bacteria can use this form of genetic recombination.)
transduction
DNA is transferred from one cell to another by mistake inside the head of an infecting virus.
-During infection, the host bacterial chromosome is degraded to provide raw material for synthesis of new bacteriophage chromosomes. Sometimes, a fragment of host chromosome avoids degradation and is packed into the head of a new phage by mistake
In general, transduction begins when new phages assemble in an infected bacterial cell; they sometimes incorporate fragments of the host cell DNA along with, or instead of, the viral DNA. After the host cell is killed, the new phages that are released may then attach to another cell and inject the bacterial DNA (and the viral DNA if it is present) into that recipient cell. The recipient cell becomes partial diploid.
Generalized transduction: in which all donor genes are equally likely to be transferred, is associated with some virulent bacteriophages, which kill their host cells during each cycle of infection (the lytic cycle). the host bacterial chromosome is degraded to provide raw material for synthesis of new phage chromosomes. However, sometimes a fragment of host chromosome avoids degradation and is packed into the head of a new phage by mistake. This particular phage now contains a small random sample of bacterial genes instead of phage genes.
Specialized transduction: Lambda is a temperate bacteriophage. That is, when it first infects a new host, it determines whether the host is likely to be a good one. Is it starving? Is it suffering from DNA damage? If the host cell passes this molecular health checkup, then the lambda chromosome lines up with a small region of homology on the bacterial chromosome and a phage-coded enzyme catalyzes a single recombination event. The phage is thus integrated into the host chromosomal DNA and, in this state, is called a prophage. The prophage is then replicated to daughter cells as long as conditions are favorable (it stays in the lysogenic cycle). If, however, the host cell becomes inhospitable (perhaps as a result of ultraviolet-induced DNA damage), the prophage activates several genes, releases itself from the chromosome by a recombination event, and proceeds to manufacture new phage, which are released as the cell bursts as a result of lytic growth. the “mistake” occurs when the prophage is excised from the chromosome. Sometimes this recombination event is imprecise; bacterial DNA is removed from the host chromosome, and some prophage DNA is left behind. As a result, this bacterial DNA is packaged into new phage and carried to recipient cells. Since the transducing phage is defective, having left some of its genes behind in the host, it does not kill its new host
CONTRAST THE CHARACTERISTICS OF F-, F+, AND Hfr CELLS
F- IS THE RECIPIENT CELL WHILE F+ IS THE DONOR CELL. BETWEEN THESE TWO CELLS, NO GENETIC RECOMBINATION OCCURS. THE Hfr CELL IS A SPECIAL DONOR CELL THAT CAN TRANSFER GENES ON A BACTERIAL CHROMOSOME TO A RECIPIENT BACTERIUM (BECAUSE THE F FACTOR IS INCORPORATED INTO THE SINGLE BACTERIAL CHROMOSOME)
Q-EXPLAIN WHY ALL GENES HAVE AN EQUAL LIKELIHOOD OF TRANSFER BY GENERALIZED TRANSDUCTION BUT NOT BY SPECIALIZED TRANSDUCTION
SINCE GENERALIZED TRANSDUCTION TRANSFERS RANDOM FRAGMENTS OF THE HOST CHROMOSOME, ALL HOST GENES ARE TRANSFERRED AT EQUAL FREQUENCY. SPECIALIZED TRANSDUCTION ONLY TRANSFERS GENES LYING CLOSE TO THE POINT OF INSERTION OF THE PROPHAGE
T/F meiosis makes gametes in plants
F- only in animals
In house plants/fungi - the haploid products are spores
Outline the life cycle in animals
Follow the pattern in which the diploid phase dominates the life cycle , the haploid phase is reduced, and meiosis is followed directly by gamete formation. In male animals, each of the four nuclei produced by meiosis is enclosed in a separate cell by cytoplasmic divisions, and each of the four cells differentiates into a functional sperm cell. In female animals, only one of the four nuclei becomes functional as an egg cell nucleus. Fertilization restores the diploid phase of the life cycle. Thus, animals are haploids only as sperm or eggs, and no mitotic divisions occur during the haploid phase of the life cycle.
outline the life cycle in most plants/fungi
In all plants (except bryophytes), the diploid sporophyte generation is the most visible part of the plant. The gametophyte haploid generation is reduced to an almost microscopic stage that develops in the reproductive parts of the sporophytes—in flowering plants, in the structures of the flower. The female gametophyte remains in the flower; the male gametophyte is released from flowers as microscopic pollen grains. When pollen contacts a flower of the same species, it releases a haploid nucleus that fertilizes a haploid egg cell of a female gametophyte in the flower. The resulting cell reproduces by mitosis to form a sporophyte. Sphagnum moss (commonly known as “peat moss”) is a good example of a plant in which the gametophyte is the most visible and familiar stage of the life cycle. In this case, the sporophyte is reduced and develops from a zygote within the body of the gametophyte. Vast peatlands of Sphagnum gametophytes are industrially harvested in many parts of the world for fuel and horticultural use.
outline the life cycle specifically in some fungi
During fertilization, two haploid gametes, usually designated simply as positive (+) or negative (-) because they are similar in structure, fuse to form a diploid nucleus. This nucleus immediately enters meiosis, producing four haploid cells. These cells develop directly or after one or more mitotic divisions into haploid spores. These spores germinate to produce haploid individuals, the gametophytes, which grow or increase in number by mitotic divisions. Eventually, positive and negative gametes are formed in these individuals by differentiation of some of the cells produced by the mitotic divisions. Because the gametes are produced by mitosis, all the gametes of an individual are genetically identical.
explain why meiosis results in a reduction of genetic material.
Genetic material is cut in half through the process of meiosis since once the male gamete meets with the female gamete they can form a diploid cell and share each half of the chromosome.
essence of ‘‘difference’’ in meiosis
two kinds of difference: halved chromosome number and recombined chro- mosomal DNA sequence.
essence of ‘‘sameness’’ in meiosis
chromosomes are replicated and partitioned to ensure that cells produced by the process have the same number of chromosomes, with the same DNA sequence, as the cell that began the process. In this way, somatic cells are produced for most of the requirements of multicellular bodies
paternal chromosome
derived from the male parent of the organism
maternal chromosome
derived from the female parent of the organism
in dogs (for example), what gives each individual offspring a unique Como of traits, such as size, coat, colour, susceptibility to certain diseases and disorders, aspects of behaviour/intelligence?
alleles
