10X smaller than eukaryotic cells, SA to V ratio high enough to support cell functions without internal membrane structures. no internal membrane bound organelles, except some photosynthetic bacteria. nucleoid region, cell wall, pili, capsule, ribosomes, bacterial flagellum
basic features of prokaryotic cells
made of peptidoglycan layers that surround the plasma membrane. allow cell to tolerate different osmotic conditions. can survive many extracellular conditions.
prokaryotic cell walls
single plasma membrane surrounded by a thick peptidoglycan layer (cell wall). gram positive because gram stain binds to protiens on cell wall. Sometimes surrounded by capsule. R-strep bacteria tested in Griffith's experiment
gram positive bacteria
2 phospholipid bilayers sandwich a thin peptidoglycan layer. Sometimes surrounded by a capsule. 2 membranes give extra protection against immune system. Gram stain doesn't stain these cells because protiens are not detectible directly on surface of capsule/ membrane. Usually more pathogenic because they can survive in more extreme environments. virulent S bacteria tested in Griffith's experiment. live R cells transformed DNA from dead S cells that coded for formation of double membrane/ capsule.
gram negative bacteria
nucleus, rough ER, smooth ER, golgi complex, mitochondria, lysosome, peroxisome, pair of centrioles, free ribosomes, ER associated ribosomes, plasma membranes, microtubules, microfilaments, intermediate filaments.
eukaryotic organelles/ other
double membrane: folds in on itself. nuclear pore complex ribosomes on outer surface of nuclear envelope. nuclear lamins
features of nucleus
special cytoskelaton of nucleus just under inner membrane made of Intermediate filaments. provides structure and protenction of DNA. filaments regulate nuclear envelope during mitosis, directly phosphorylated by CDKs
regulates what goes in and out of nucleus, except for ions, small molecules, and water that can pass through the membrane, and will prevent unprocessed RNA from leaving. directional movement regulated in both directions. Admits: transcription factors, hormones, etc... ensures that unproccessed mRNA cannot pass through.
nuclear pore complex
continuous membrane system with nuclear envelope. membrane encloses interior space where Ca+ is stored, as well as transfers. Functionally divided into rough and smooth ER. Rough has ribosomes docking to it. synthesizes secreted protiens. Smooth synthesizes lipids, detoxifies certain toxic molecules (lots of smooth ER in liver cells), sarcoplasmic reticulum in muscle cells.
ribosome starts translation of mRNA, Signal Recongition Particle binds to first two amino acids created by ribosome, SRP pushes protien into ER and binds to SRP receptor, translation resumes, polypeptide enters lumen or if hydrophobic remains embedded in the ER membrane, signal peptidase cleaves signal peptide from growing peptide.
movement of protiens into ER
further processes protiens (glycosilation), sorts protiens, sends them to cell surface or lysosome.
contents of some endocytic vescicles and golgi-created vescicles (enzymes) go to lysosome. breaks large macromolecules into monomer subunits.
not part of ER/ Golgi/ lysosome network, functions in lipid metabolism, detoxification of toxins, same size as secratory vescicles, Also aids in transportation.
different types of protiens form long polymers that support cell, including: microtubules, microfilaments, intermediate filaments.
come from the mitotic spindle, built of small subunits of globular protiens, each dimer subunit contains 2 proteins: an alpha tubulin and beta protien. come together to form a hollow tube. Not as strong, not flexible. Polar (directional) structure, does not refer to charge. MTs have + and - end. Growth occurs from - to + end of MT. MTs move organelles and other things (chromosomes) around in the cell, and anchoring membrane bound organelles according to function. Important in transportation of neurotransmitter vescicles from Golgi in neurons. Regulate movement of Flagella and Cilia.
associated with microtubules and microfilaments: kinesin for MTs, myosin for MFs. Kinesin domains undergo conformational changes due to the binding of ATP that cause them to "walk" along the microtubules, transporting vescicles, or organelles. Kinesins move from - to + end of microtubule. Dyenins (also associated) move from + to - end.
responsible for cell shape changes, such as ameboid motion of leukocytes, formation of cleavage furrow, and contraction of muscle cells. smallest cytoskeletal protien. monomer: actin subunit that wrap around other actin subunits to form a twisting MF structure. also has + and - ends. myosin motors associated with microfialments to create cell shape changes.
provide structural support: no motor protiens associated. more diverse subunits of long filamentous protiens, such as Keratins (in skin and hair cells), and lamens (inside of nucleus, protect DNA) that coil to form long, cord-like structures. stronger and more flexible than other cytoskeletal protiens. Different cell types have specialized IF protiens that provide varying degrees of support.
membranous structures not found in animal cells, including: chloroplasts (energy production), amyoplasts (starch storage), and chromoplasts (pigmentation).
prevents cell lysis due to osmotic pressure. provides force for turgidity along with water vacuole in hypotonic environment. contains plasmodesmata that allows for cytoplasmic exchange and communication of chemicals between adjacent cells. Can be divided into primary and secondary cell walls. primary secreted into extracellular space, mainly modified cellulose. Secondary cell walls contain lots of lignin (alcohol), and are associated with woody plant cells.
holds adjacent cells together, made of pectin (used to make jams and jellies)
pores that allow cytoplasmic exchange and chemical communication in adjacent cells.
gap junction (desmosomes or hemi-desmosomes), tight junction, anchoring junction.
types of cell junctions
cylindrical arrays of protiens form direct channels allowing small molecules and ions to flow between cytoplasm of adjacent cells. analagous to plasmodesmada. present in cells of similar type that need to work in coordination, eg. cardiac muscle cells (intercalated discs). defective gap junctions cardiac muscle=arrythmia.
connections between intermediate filament cytoskelatons of 2 cells (desmosomes), or Microfilament complexes of two cells (adhering junctions).
anchoring junction that creates a large gap between plasma membranes of cells. Plaque, a mass of protiens on the plasma membrane, is anchored by intermediate filaments to cell. Connects Intermediate filament cytoskelaton of two adjacent cells.
links the cytoskelaton of one cell to the extracellular matrix. connect epithelial cells to the rest of the extracellular matrix, for example.
connect the microfilament cytoskelatons of cells to facilitate the shape changes of a group of cells, such as the invagination of the neural plate during development.
maintain impermeable barrier between two areas. found in epithelial cells of nephron, regulate movement of filtrate and preven leakiness of epithelium. No water/ ions can move through.
varies based on cell type. basically a bunch of fibrous protiens: proteoglycans, collagen, and fibroconnectin secreted into the space outside of the cell. cushions cells
linkage of microfilaments to extracellular matrix. Used in cells that crawl along the ECM, such as leucocytes and metastitized cancer cells.
connects collagen fibers to integral membrane protiens. Often used as a track for mobile cells during development.
synthesized on or in ER, passed to Golgi in cell body, secratory vescicles moved via microtubules, wait for Calcium signal to fuse with plasma membrane.
tubes that run next to the sarcoplasmic reticulum (modified ER), depolarization is continued through T tubules.
modified ER, stores calcium ions and has voltage-gated calcium channels that, upon contact with action potential, open and release calcium ions into the cytoplasm.
Ca2+ released into cytoplasm, binds to troponin, which displaces tropomyosin and uncovers the actin binding site. myosin head bonded to ATP, causes a conformational change, mysoin crossbridge formed. when ATP is hydrolyzed, another conformational change occurs, and myosin head wratchets actin forward. after action potential, Ca2+ taken back into sarcoplasmic reticulum, and troponin and tropomyosin re-cover the actin binding site.
lacks almost all organelles. essentially a moving package of a haploid nucleus. motion usually facilited by flagella (nematode sperm move by ameboid motion) powered by microtubule motors. specific DNA binding protiens pack DNA very tightly. lots of mitochondria to create ATP for movement. Acrosome is a secratory vescicle that contains hydrolytic enzymes that digest zona pellucida (extracellular matrix) of oocytes.
slow: cortical granule reaction involving secratory vescicles just inside plasma meembrane whose contents are released to extracellular matrix after fertilization, and build up a physical barrier to fertilization. Fast: change in membrane potential due to calcium release.
blocks to polyspermy
potential/ stored energy= any energy due to position of two things relative to one another due to gravity, or electrical energy. kinetic=released "energy of movement", energy given off when things change relative position thru movement.
forms of energy
stored in relation of electrons to nucleus. electrons attracted to nucleus. The farther away they are from the nucleus, the more energy they can give off by moving closer to the nucleus. electrons release energy as they decrease in energy level. Also, molecules with two charges that repel each-other have high energy when forced to be together, and release energy when they separate (ATP).
chemical potential energy
transfer of potential to kinetic and back. catabolic: molecules breaking down to release energy, anabolic: molecules built from smaller subunits, takes up energy.
1) energy in any system will always remain constant.
2) entropy of the universe is always increasing with any energy conversion.
laws of thermodynamics
delta G (energy available to do work or free energy)= delta H (total energy of system) - T(Temp) X delta S (heat of reaction or enthalpy, always positive, unusable energy.
Free energy equation
exergonic (spontaneous) reactions: yields a negative delta G, uses free energy. increases entropy of universe. eg. combustion of sun. endergonic reactions: create positive delta G, use energy, will not happen on its own without the input of energy from another source. decreases entropy. Total exergonic reactions increase entropy more than endergonic reactions of life decrease entropy. Both can be facilitated by enzymes.
Free energy changes
coupling of a reaction that decreases entropy with another one that increases entropy. greater increase in entropy than decrease to fulfill the second law of thermodynamics.
free energy from ATP hydrolysis
free energy=0. spontaneous reactions tend towards equillibrium.
available free energy required for a reaction to proceed, or a certain amount of random movement that allows reaction to continue. Thermal energy must be high to get over activation energy hump, body cannot provide that much heat.
reduce the activation energy required for a reaction so that reaction can take place at a lower tempurature/ level of random movement. reduce activation energy by bringing reactants to transition state by: bringing reactants in close proximity, creating a favorable environment through electrostatic interactions with charged amino acids, changing physical state of reactants.
function of enzymes
made of peptides active site= where it binds to substrate. some contain allosteric site. induced fit model generally accepted.
Tempurature: increases random movement and increases chances that substrate will bump into active site of enzyme, but too high tempurature breaks hydrogen bonds causing denaturation. reaction rate sharply declines after it peaks at a certain tempurature. pH: low pH can neutralize negatively charged amino acids, causing shape change. most enzymes have an optimum pH depending on location. Substrate concentration: reaction rate increases until the saturation point. finite number of enzymes each have a maximum rate of reaction.
Things that effect enzyme activity
don't change covalent structure of enzyme. They either: have a similar shape as the substrates, and competatively inhibit enzyme by binding to active site. Allosteric or non competative inhibition/ activation: where molecule binds to another site on enzyme, changing its tertiary structure and shape of active site to render the enzyme active or inactive depending on the situation. Bonding usually reversable depending on concentration of inhibitor.
activators and inhibitors
when a product or intermediate product binds to an enzyme that functions in the pathway as an allosteric or competative inhibitor which inhibits the reaction that produced it, creating a negative feedback loop. eg. change of threonine to isoleucine takes about 5 enzymes. Isoleucine acts as a competative inhibitor of the first enzyme (threonine deaminase), halting the reaction.
kinases covalently add phosphate to enzyme that changes conformation to activate/ inhibit enzyme. other types of modification also occur.
chemical modification of enzymes
RNA-based enzymes: ribosome, spliceosome (SNRNAs). Thought to have evolved first, since early life is said to have been RNA based.
any reaction with movement of electrons relative to atoms including gain/ loss of electrons. Reduction=gain of electrons, oxidadation=loss of electrons. Reduction usually uses free energy to create molecules with more potential energy, oxidation releases free energy, creating molecules with less potential energy (more polar bonds). Reduction and oxidation reactions are always coupled.
O=most electronegative element of life, electrons attracted to oxygen, so oxygens associated with oxygen occupy very low energy levels. electrons moving from other, higher energy molecules to oxygen releases energy.
oxygen as final electron acceptor
C6H12O6 + 6O2 + 32ADP + 32Pi = 6CO2 + 6H2O + 32 ATP. includes the reactions that transfer electrons from organic molecules to oxygen, and the reactions that use the released energy to make ATP. glycolysis in cytoplasm, Substrate Level phosphorylation, Pyruvate oxidation - Acetyl CoA, mitochondrial matrix, the Citric acid cycle, inside mitochondrial matrix, and Electron Transport Chain: across christae membrane that creates most ATP by oxidative phosphorylation.
summary of cellular respiration
oxidative reaction where 6C glucose is broken down into 2 3C pyruvate molecules by 10 enzymes in the cytosol. Uses 2 ATP at the beginning, and synthesizes 4 ATP by substrate-level phosphorylation. 2 H2O molecules produced. 2 NAD+ molecules oxidized into NADH. At 4th step, 6 carbon sugar is split into two 3C molecules, and the reaction proceeds on each of them to form 2 pyruvate molecules. Most of the energy in pyruvate is then contained in the CH3 group.
enzymes that function at key points, such as the 3rd step involving phosphofructokinase, are inhibited by ATP and NADH and activated by ADP, ensuring that glycolysis only occurs when the body is using a lot of energy. NADH inhibits enzymes to slow blycolysis if oxidative phosphorylation has been slowed by limited oxygen supplies. This is an example of a negative feedback pathway.
regulation of glycolysis
a complex of enzymes oxidizes pyruvate generating a CO2 by removing the -COO- from pyruvate, and oxidizing the remaining 2C fragments into an acetyl group. NAD+ reduced to NADH. Takes place in the mitochondrial matrix
Oxidizes acetyl groups completely. Everything doubled because 1 glucose produces 2 pyruvate molecules that each undergo oxidation and the citric acid cycle. Reactants (2X): Acetyl-CoA, 3 NAD+, 1FAD, 1ADP, 1Pi, 2H2O. products (2X): 2CO2, 3NADH, 1FADH2, 1ATP, 3 H+, 1CoA. process is cyclic, and has 8 reactions, each catalyzed by a specific enzyme. The cycle begins and ends with Oxyloacetate, a 4 carbon molecule.
citric acid cycle
transfers an electron from electron carriers of lower electronegativity where it occupies higher energy levels (first=NADH) to molecules whith higher electronegativity (final=Oxygen). intermediate electron acceptors are embedded in the thylakoid membrane. using the energy released to pump hydrogen from the matrix into the intermembrane space, creating stored energy in the low entropy of the proton gradation. Upon recieving an electron, oxygen combines with protons and low energy electrons to produce water.
Electron Transfer system
ATP synthase uses energy released when protons move back across their concentration gradient to synthesize ADP and P into ATP. Unused energy released as heat.
Oxidative phosphorylation (chemiosmosis)
allow the protons to diffuse back into the matrix without going through ATP synthase, so heat is released without production of ATP. Commonly used to retain body heat in hibernating animals. Brown fat contains lots of these protiens.
after the ETC, NADH produces 2.5 ATP and FADH2 produces 1.5. In sum, respiration produces 32 ATP with an energy efficiency of 1/3 (30%)
Energy output of respiration
depending on number of carbons in macromolecules, they start a different points in the cycle. eg. protiens and fats are digested by peroxisomes into small 2C or 3C molecules that are modified to become Pyruvate or Acetyl CoA, and enter into pyruvate oxidation or the citric acid cycle. Protiens must be first deaminated.
Using other molecules for respiration
production of ATP when oxygen is not present in the environment. ATP acquired from Glycolysis. Since NAD+ is oxidized in limited amounts in the electron transport chain, Pyruvate acts as a high energy electron acceptor, oxidizing NADH into NAD+ so it can be reduced during glycolysis. Pyruvate is converted to lactate in human cells, and CO2 and ethyl alcohol in alcoholic fermentation done by yeast. This process is much less efficient than aerobic cellular respiration.
Also have their own DNA. three membranes total: a double membrane envelope with a small space in between them called the intermembrane space. 3rd=Thylakoid membrane in the stroma arranged into stacks. Space inside the thylakoids is the thylakoid lumen. Chlorophyll molecules are embedded in the Thylakoid membrane.
2 different kinds: chlorophyll a and chlorophyll b each have a slightly different absorbtion spectrum, absorbing red and yellow light while reflecting green and blue light. Chlorophyll's hydrophobic fatty acid chain is embedded in the membrane.
properties of chlorophyll molecules
where an excited electron returns to its ground state and the energy released transfers to a neighboring pigment molecule, exciting another electron. This energy transfer doesn't work for all molecules, as some electrons can only be excited by photons.
The arrangement of chlorophyll, accessory pigment molecules, and pigment-binding proteins into light-gathering units in the photosystems of the Thylakoid. They absorb energy from light, and pass it through inductive resonance to the reaction center of the photosystem.
pigment p700, the primary electron acceptor in this photosystem, recieves 2 electrons indirectly from p680 that are excited by a photon into a higher state. They are then passed onto ferredoxin and are put into NADP+ to reduce it to NADPH.
H2O first lysed by a photon of light to create O, and gives up 2 electrons to P680, a strong oxidizing agent in photosystem II. P680 passes these excited electrons to the cytochrome complex, where they are transferred to lower energy levels, giving off energy used to pump protons from the stroma into the thylakoid lumen (opposite of ETS in respiration). at the end of the transfer, plastocyanin passes the electrons to p700 in photosytem I. When protons flow out of the lumen thru ATP synthase, ATP synthesized.
the two electrons gained from the hydrolysis of water, after being passed to P700 and Ferredoxin can be passed to NADPH or they can return to the reaction center of photosystem II. Often return to photosytem II because more ATP than NADPH is needed, and also because NADPH may be toxin in high concentrations due to the high energy electrons' potential to interact with other molecules.
cyclic electron flow
takes CO2 and H2O, using the C and H to make high energy organic molecules. Ribulose-5 phosphate (RuBP) is reduced and carbons are added, using the ATP created during the light reactions to create higher energy Glyceraldehyde-3 phosphate (G3P) used to syntheze sugars and other organic molecules, or to regenerate ribulose 5-phosphate.
Calvin cycle basics
1) RuBP, a 5C molecule, reacts with Co2 producing 2 3C low energy molecules: 3PGA. 2) ATP adds Phosphate to each 3PGA molecule, producing 2 biphosphoglycerate, raising the energy content of products. 3) two biphosphoglycerate reduced by electrons carried by NADPH, and phosphate is removed from each molecule, yielding 2 G3P molecules. 4) G3P either goes on to produce organic molecules, or is converted into ribulose 5-phosphate. 5) ribulose 5-phosphate kinase uses ATP to phosphorylate Rib 5-phosphate, to create RuBP, and cycle can turn again.
Calvin Cycle steps
1X3C G3P that leaves to produce sugars, and 5X3C G3p rearranged to form 3X5C RuBPs.
3 turns of Calvin cycle produce
happens in high levels of oxygen and low CO2 levels. Oxygen fits in active site of RuBP carboxylase and acts as a competitor to CO2. Very inefficient process, since new carbon molecules can't be made. Some plants use PEP carboxylase to fix carbon since it can act in low CO2 and high O2 environments.
Location of C4 cycle and calvin cycle is different in C4 plants. C4 cycle occurs in the mesophyll in the same place as the light reactions, so oxygen levels are high. Malate converted into CO2 in bundle sheath cells in a part of the leaf without much oxygen.
change the timing of CO2 fixation to reduce water loss through stomata. Since stomata can't be opened during the day to acquire CO2 because too much water would be lost in hot environments, carbon fixation occurs at night when stomata can be open. CO2 is converted to malate at night, malate releases CO2 for calvin cycle during the day. both of these reactions occur in the same cell in CAM plants.
C3 (RuBP carboxylase using plants) thought to have evolved first, since all C3 plants have similar enzymes to cAM plants, only minor changes occured in regulation of enzymes. pathways evolved at different times, evolution of CAM pathway in different plants was due to convergent evolution.
evolution of C3, C4, and CAM plants
signalling done over gap junctions or plasmodesmata. Cell's cytoplasm must be in contact for this type of signalling.
cell contact dependant signalling
local signalling events occuring over a few cell diameters via extracellular matrix and fluid.
long range signalling events that occur through the bloodstream. eg. insulin and glucagon regulation of blood glucose.
classical endocrine signalling
ligand binds to cell surface receptor, since it can't pass through the membrane. Usually peptide signals.
signal, such as a steroid hormone, can easily pass through membrane. the receptor can be a cytoplasmic protien or the hormone can act as a transcription factor and go directly into the nucleus to regulate DNA transcription. eg. thyroid hormones.
1) reception: binding of ligand to receptor or effector depending on the nature of signal. 2) Transduction: when binding of signal to receptor causes a conformational change in protien which activates an enzyme that activates multiple protiens activated by other protiens. number of pathways varies. eg. thyroid hormones activate a protien complex that acts as transcription factor. Transduction is its movement into the nucleus.
3) response is the activation of the molecule that brings about the change, such as modification of cytoskelaton, activation of transcription factor, activation of certain enzymes.
events of signalling
Ligand-binding domain is extracellular, kinase domain is intracellular. binding of signal molecules causes autophosphorylation of tyrosines, which causes receptors to assemble in pairs, or to dimerize, which activates intracellular kinase domain. Then, RTK can directly phosphorylate other protiens. adapter protiens recognize phosphorylated RTKs and recruit other protiens to complex to be phosphorylated. Adapters dock to RTKs.
Receptor Tyrosine Kinases (RTKs)
often, binding of receptor and signal induces endocytosis of receptors, and degradation of the receptor. G-protiens then hydrolyze GTP and return to their inactive state, ensuring the short persistence of the cascade reaction. phosphatases also play a role in inactivating phosphorylated molecules.
turning off signalling
Mitogen Activating protien kinase that activates mitogens, which are cellular processes that stimulate mitosis.
surface receptors associated on their intracellular domain with G-protiens, activate this inner membrane protien in response to the binding of a signal. 1000 different G-protien coupled receptors identified in mammals, the most abundant are oderant receptors.
G-protien coupled receptors
1) extracellular signal molecule. 2) nonprotien signal molecules produced by the effector, which is activated by a G-protien. Second messanger then activates protien kinases that regulate the response. Protien kinases all add phosphate groups to serine or threonine
Messangers in GPCR signalling
Effector: adenylyl cyclase converts ATP to cAMP, activating the second messanger. In second pathway, effector phospholipase breaks down a membrane phospholipid to activate second messangers inositol triphosphate (IP3), and diacylglycerol (DAG). IP3 diffuses rapidly through the cytoplasm. DAG is hydrophobic and remains in the plasma membrane. IP3 activates transport protiens which release Ca2+ from sarcoplasmic reticulum. Both pathways regulated by enzymes that eliminate second messangers. eg. phosphodiesterase which degrades cAMP.
two different GPCR pathways
interaction between more than one signaling pathway. eg. second messangers can phosphorylate messangers in other pathways, activating or inhibiting them. It often leads to modifications of cellular responses controlled by pathways.
a trans-membrane G-protien coupled receptor that binds to external oderant molecules. The binding ultimitely causes a neuron to release an action potential. Each substance that an organism can detect has a corresponding oderant receptor. A disporportanitely high percentage of our genome codes for oderant receptors. different oderants trigger different locations in olfactory bulb. The G-protien used, G-olf, is the same for all oderants, however.
olfactory neurons which contain GPCR receptors project into olfactory epithelium. cilia project out of epithelium to increase surface area. receptor binds to oderant, activates G-olf, activates adenyl cyclase which phosphorylates cAMP, which opens gated sodium channels, so sodium ions diffuse into the neuron which starts an action potential.
function of oderant receptor
GPCR linked with molecule Retinol, that changes shape from cys to Trans retinol, which causes a shape change in GPCR rhodopsin. G-protien activates phosphodiesterase, which, in a reversal of the usual process, converts cGMP to GMP, which detaches from the cyclic nucleotide gated sodium channels, halting membrane depolarization. Activation of Rhodopsin stops the sending of an action potential.
don't require cell surface receptors because they can pass thru the plasma membrane and bind to cytoplasmic steroid hormone receptors. all steroid hormone receptors directly act as specific transcription factors. No second messangers needed.
steroid hormone receptors
steroid hormone with many functions, including raising blood pressure. released by adrenal cortex, targets nephron tubule cells, and upon binding to cytoplasmic protien, enters into the nucleus and initiates synthesis of sodium channel protiens. Sodium is reabsorbed into the bloodstream, and water follows, raising blood pressure.
gas that responds to changes in blood pressure: increase activates NO synthase in endothelial cells, which diffuses into smooth muscle cells. binds to and activates GTP, which activates cGMP, which causes relaxation of smooth muscle cells, dilation of arteries, and lower blood pressure. Nitroglycerine was used to treat angina. Most modern drugs inhibit phosphodiesterase, which turns off the pathway. Lead to the discovery of viagra, since relaxation of smooth muscle cells cause increased and prolonged erections in males.
Nitric oxide signalling
much smaller than those in animal cells due to larger molecules' inability to get through the cell wall. Examples: Abscysic Acid, Auxins, Giberillins, Cytokinins, ethylyne. Plants do, however, use many of the same second messangers as animals, such as NO, Ca2+, and Cyclic GMP.
Plant signalling molecules
lots of signalling events. in response to drought stress, roots synthesize ABA, moves thru xylem, gets to leaves, enters guard cells, stimulates potassium ions to move out of guard cells, followed by water, which makes them flaccid causing them to close.
Abscysic acid (ABA) signaling
when undifferentiated cells turn on specific transcription factors that determine the cell type they will become. eg. activation of Myo D causes determination of muscle cells, since it activates other STFs that turn on actin, myosin, and other protiens. Cascade of TFs
turning on of genes that activate differentiating events in cell. such as synthesis of Actin and Myosin in muscle cells.
process of getting 2 cells to be different from one another. Can occur cell-intrinsically or cell-extrinsically.
asymmetric cell division
done by the partitioning of a cytoplasmic determinant differently in cells which determines fate of cells. in C elegans, the partitioning of protien P1 E1 divided asymmetrically, and determines germ cells.
cells initially chemically equivalent recieve different signals that determine their fate. Shown by Hans Spemann and Hilde Mangold's experiment on newts.
cell-extrinsic: induction thru cell signalling pathways
experimentally took the dorsal lip of a newt embryo and placed it on the side of another embryo opposite to the existing dorsal lip, second dorsal axis developed on newt, creating siamese twin newts connected at their ventral end. Discovered induction's role in determination. used 2 species of newt with difft. pigmentation. Cells making new embryo came from cells already on embryo, inducted ventral cells to ecome dorsal cells. Conclusion: dorcal lip acts as inducer to signal other cells to take on a dorsal fate.
Hans Spemann, Hilde Mangold
how animals develop differential anterior-posterior axes with repreating segments and repeating structures (segments, ribs, vertebrae), each with a slightly different function.
Genes, such as bicoid and nanos genes, expressed by mother during oogenesis and control the polarity of the egg. They code for mRNAs that are localized at one end of the cell. Translated upon fertilization, diffusion forms a gradient of protien product (ie. BICOID) that activate/ repress certain genes for other transcription factors along axis of embryo.
maternal effect genes
different homeotic genes that are expressed each determine the identity of one segmant. They code for transcription factors, determine anterior and posterior axis.
An egg polarity gene in Drosophila, concentrated at the anterior pole of the egg and required for subsequent anterior structures. bicoid at mRNA level remains tethered to anterior end mediated by sequences in the 5' and 3' UTR. in stem cells. Translation of RMAs on differential gradations create a gradation of protiens.
mutation in homeotic genes that causes a change in the identify of one segment into identity of another. eg. antenna segment replaced with leg segment creates legs where the antenna should be. different homeotic genes are expressed in different segments in drosophila. in mammalian organisms, since homeotic genes are duplicated on many chromosomes, all of them need to be turned off to create homeotic transformation.
process by which an organism takes on a specific shape. three processes cause it in animals: cell division orientation, cell shape changes, and cell migration
axis of division can change to produce a line of cells, a row of cells, or a mass of cells. astral microtubules orient the mitotic spindle on a certain axis according to desired orientation of cell division.
cell division orientation (morph an)
cells can grow in various ways: either equally in all directions, or they can gro more in one direction, creating longer cells. microtubules lengthen and slide further apart to elongate cells, and slide close together to constrict top of adjacent cells using adherans junctions. differential constriction causes invagination of tissue.
cell shape changes (morph an)
cells can remove themselves from epithelium and crawl along using ameboid motion to another location. Neural crest cells bud off from neural tube and form melanocytes, peripheral neurons, and teeth cells.
similar to posterior and anterior axis in animals:cause differentiation in root and shoot cells. At first cell division of zygote, apical cell gets cytoplasm, basal gets most of vacuole, determination caused by unequal distribution of cytoplasmic determinants. However, cell devision only occurs in small areas of the plant.
apical and basal meristems
radial patterning events in floral development used instead of segmentation. different genes are expressed in each whorl, making them take on different features. Can undergo homeotic transformation like animal cells. Whorl 1: sepal, whorl 2: petal, whorl 3: stamen, Whorl 4: carpels.
use oriented cell divisions, and cell shape changes. NO CELL MIGRATIONS due to cell walls.
morphogenesis in plants
caused by changing the orientation of synthesis of cellulos microfibrils in the cell wall, which causes shape changes in the cell. If fibers are randomly fixed, cells can expand equally in all direcrtions. if microfibrils are in paralell bundles, synthesis in one direction can cause lengthening in one direction. Once cell wall is loosened, cell expands due to the uptake of water and vacuole expansion. Plants still undergo cell shape changes but use a different mechanism than animals.
polarized cell growth in plants
peripheral membrane protiens that regulate the formation of vescicles. ADH affects whether clathrins create vescicles containing aquaporins, regulating the reabsorbtion of water.
different cells produce different myosins (eg. alpha and beta myosins in cardiac muscles) that function differently.
take home message of cardiac article
general inability to smell due to mutations that affect the G-olf gene, preventing proper signal transduction in the GPCRs. inability to smell specific oderants is due to mutations in genes coding for specific GPCRs in nose.
it takes place inside discs of membrane in the inner portion of rod cells instead of on the plasma membrane. Neurons active in the dark. However, activation of rhodopsin leads to change from cGMP to GMP, closing sodium channels, reducing neurotransmitter released when photons are hidding rod cell.
why rhodopsin signalling is wierd
subdivide embryo into 24 regions in drosophila. Activated by maternal affect protiens. Their activation causes a regulatory cascade determining divisions along posterior/ anterior axis.
divide the embryo into units of 2 segments, creating bilateral symmetry
set boundries and axes of each segment
segment polarity genes
specify identity of a segment after metamorphosis.
homeobox containing genes
gene segment corresponding to an amino acid section of a specific transcription factor. Homeodomain is the actual domain of the protien transcribed that binds to the promoter of the regulated gene
adapter protiens bridge G-protien (RAS) and RTK, which phosphorylates GTP to activate G-protien (RAS). G-protien activation causes a protien kinase cascade. last activated MAP (mitogen activated protien kinases) kinase moves into the nucleus to phosphorylate protiens that control expression of genes relating to mitosis.
example of RTK associated with a G-protien
eye-cup of planaria
visual units in insect eyes, good at detecting movement.
receptor-like glycoprotiens that link cells together or bind them to ECM molecules. Binding of CAM to another substance often causes a cellular response.
cell adhesion molecules (CAMs)
citrate synthase is inhibited by ATP to ensure that respiration is not conducted if enough ATP is present in the cell.
regulation of citric acid cycle
inorganic or organic non-protien group necessary for enzyme function. coenzymes are organic cofactors, such as vitamins.
organisms that can undergo either aerobic or anaerobic respiration depending on O2 concentration. eg. E-Coli
boutulism bacteria: organisms that can only undergo anaerobic respiration to produce ATP.
can only undergo aerobic respiration: eg. vertebrate brain cells.
neurosecratory neurons release a neurohormone into the circulatory system. unlike neurotransmitters, neurohormones affect distant cells.
when local regulator acts on the cell that produced it. eg. growth hormones.
beta 1- are in cardiac muscle cells. increase contraction of cardiac muscle. beta 2 receptors promote the breakdown of glycogen. alpha receptors in smooth muscle cells cause constriction upon binding epinephrine.
all cells exposed to hormones, but only cells with receptors for the hormone respond to it. amplification. response differs among target organs depending on receptor and pathway triggered.
features of hormonal signalling
calcium dependant adhesion molecules
phosphorylation, isomerization, phosphorylation, hydrolysis, isomerization, redox, SL phosphorylation, mutase reaction, redox, SL phosphorlation.
reactions of glycolysis
part of photosystem that contains a specialized chlorophyll a molecule complexed with protiens. photosystem 1's center is called p700, and photosystem II's is called p680 based on the wavelenth that each absorbs.