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89 Cards in this Set
- Front
- Back
- 3rd side (hint)
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What are two major differences between plant cells and animal cells?
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1. Plant cells have semi-rigid walls surrounding them
2. Plant cells contain an organelle known as a central vacuole. |
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What is the selectively-permeable membrane of the central vacuole called?
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The tonoplast.
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Is the normal state of a plant cell called? What does it mean?
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Turgid, which means that the cell wall will resist entry of water from a hypotonic solution in the state of turgidity.
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What helps non-woody plants to stay upright against gravity?
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Turgidity
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Why do plants wilt?
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because their cells are flaccid or dehydrated.
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What is water potential? In what direction does water move?
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The tendancy of water to move from one location to the next.
Water always moves from a location of higher water potential to a location of lower. (from Higher to Lower or from Positive to Negative) |
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When is pressure and solute potential of water zero?
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An open container at sea level has a pressure potential ᵠp of zero. Pure water (no dissolved solutes of any kind) has a solute potential ᵠs of zero.
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Why do plants need water?
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1. For electrons for photosynthesis
2. To carry out metabolic reactions 3. Move sugar in the phloem 4. Structural Support 5. Evaporative cooling |
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What is the evaporative water loss from the aerial portion of the plant called?
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Transpiration
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How do plants control how much water is lost through the stomata?
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Through guard cells.
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How do the guard cells work?
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In order to make the guard cells turgid, the guard cell pumps out protons (not osmotically active) and takes up K+ ions (and Cl- ions). Water will follow into the guard cells and they swell and uncover the stoma. K+ and Cl- ions leave the cell and water follows when the cell goes from turgid to flaccid (when the plant needs to close that stomata).
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Where are stomata located and why? When do most plants open their stomata?
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Stomata are located on the bottom of leaves in order to lessen dehydration Most plants open their stomata at first light when photosynthesis occurs.
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How does water move from the roots to the tops of tall trees?
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Bulk Flow: movement of fluid driven by a pressure difference. Ultimately, the plant expends no energy to move water up the Xylem to the leaves even is the tree is 100 meters tall. The transpiration (driven by sunlight) places a pull (tension) on the column of water in the Xylem and this pull is transmitted all the way to the bottom of the tree.
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How does a plant absorb water even when the soil is dry? What process does it use?
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The plant uses co-transport. In secondary transport no energy is used.
The plant pumps out protons (not osmotically active) so these protons displace cations in interaction with the negatively charged soil particles. Once those osmotically active cations are free in the soil solution, the root hair cell can specifically take up some of these ions which lowers the megapascals below that of the clay soil. Then the water can follow the cations into the root hair cells. |
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What is the living portion of the plant cell known as?
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The symplast
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What is the space made up of cell walls and extra cellular spaces is known as? The nonliving portion of the plant.
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The apoplast
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Can water and ions enter into the Xylem and flow up into the plant through the apoplastic route?
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No, Water and ions can follow the apoplastic route from the epidermis to the endodermis or the symplastic route or the transmembrane route. However, in order to get into the Xylem, water & ions must cross the plasma membranes and enter the symplast
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What is the waxy band that surrouns the endodermal cells and prevents water and ions from flowing from the apoplast into the symplast
called? |
The Casparian Strips
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What must the water cross in order to make it to the stele, which houses the Xylem? Why?
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Water must cross through the plasma membrane. This allows the plant to protect itself against metals such as lead, zinc and iron from entering.
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What two different cell types make up the Xylem cells?
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Vessel elements and tracheids. Both are dead at functional maturity. The cell walls are made up of hydrophilic cellulose and there are perforations in these walls that allow water and ions (xylem sap) to move to adjacent vessel elements or tracheids
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Once water is in the Xylem, what helps to pull it up?
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Cohesion between the water molecules themselves and adhesion between the water molecules and the cellulose of the cell walls.
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What is the main purpose that plants open their stomata?
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In order to take in CO2 needed for photosynthesis
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What is transpirational pull?
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The evaporative water loss from the spaces in the leaf (out into the atmosphere) places a pull on the water that is at the are liquid interface. The loss of a water molecule from this interface causes another water molecule to try to move into its place and since this water molecule is cohering to water molecules adjacent to it, there is a pull on the entire column of water. This pull is relayed all the way down the plant root Xylem. It is a negative pressure that moves water up the Xylem that is solar-powered.
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Are their any benefits to transpiratoin?
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Cooling of the plant.
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What is the direction of water flow in the Xylem? Describe how the water moves.
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Movement in Xylem in unidirectional from the roots to the shoots. Movement is based on Bulk Flow and pressure in the Xylem is a negative pressure.
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Are Xylem Cells dead or alive?
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Once mature, they are dead.
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Are Phloem cells dead or alive?
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Phloem cells are living at functional maturity although they have cleared out the major organelles and the smaller ones that are left are still in the Phloem cells are pushed to the periphery.
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What are companion cells?
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The adjacent cells to the phloem are considered companion cells and provide all the macromolecules that the sieve tube members of the phloem cannot make themselves because they do not have the organelles.
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How does sap travel in the phloem, how is is similar or different to sap travel in the Xylem?
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Flow of phloem sap is also by bulk flow but it is a positive pressure. While within a single phloem tube, movement is unidirectional, some phloem tubes move phloem sap against gravity while others move it from top to bottom (with gravity). It is called from source to sink.
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In a plant, what is a source and what is a sink?
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A source produces sucrose while a sink consumes or stores it.
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How can plants move sucrose from production (mesophyl cells) against its concentration gradient to storage?
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If at any point, sucrose movement from one cell to the other is not a passive movement (b/c the concentration gradient doesn’t favor movement in that direction) the sucrose molecule can exit out into the cell wall. The cell wall space contains a high concentration of protons b/c the proton pump pumped them there and this H+ gradient can be used to translocate sucrose into the companion and/or sieve tube member against its concentration gradient. The plasma membranes of companion cells and sieve tube members contain H+/sucrose cotransporters ( in addition to the proton pumps) so as H+ move down their concentration gradient from the cell wall into the cell, they can bring along sucrose molecules against their gradient.
Once sucrose is loaded into the sieve tube members of the phloem, the water potential of these cells is lowered beneath that of the water potential of the Xylem, thus water moves (H2O) from the Xylem to the Phloem and builds up pressure. The phloem sap them moves from the higher pressure region to a lower pressure region. The lower pressure region of the phloem exists because sugar is unloaded at the sink (site of storage or net consumption of sugar) Once sugar leaves the sieve tube member cells, this increases the Megapascals in that cell and allows water to leave and re-enter the Xylem. |
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Is loading of the phloem active or inactive, what about unloading?
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While loading of the phloem is considered active due to the energy expenditure of the proton pumps in the plasma membrane of the companion cells, the unloading of the phloem can be either active or passive. If sucrose exits the phloem and moves through cells that have a lower and lower concentration of sucrose (because the cells are using it up or converting it into a molecule or macromolecule other than sucrose), then the unloading is passive.
If sucrose is stored as sucrose in a central vacuole of a cell or the cytoplasm of a root cell, the plant has to expend energy at some point to move/transport the sucrose into that location. Unloading is active. (not necessarily active all along but in the end it is active) |
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Xylem
1. What is the souce of flow? 2. What is the site of flow? 3. Pressure potential in Sap? 4. Movement is due to? |
1. Transpiration puts negative pressure on Xylem Sap
2. Tachoids and vessel elements 3. Negative 4. Bulk Flow |
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Phloem
1. What is the souce of flow? 2. What is the site of flow? 3. Pressure potential in Sap? 4. Movement is due to? |
1. Active loading of sucrose allows H2O to flow in and puts positive pressure on phloem sap
2. Living cells w/o organelles: sieve tube members 3. Positive 4. Bulk Flow |
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In Griffith's pathogenicity experiment, testing "S", smooth coat bacteria (harmful) and "R" rough coat bacteria (harmless), what happened to the mice when he:
1. Injected the "S" strain into the mice 2. Injected the "R" strain into the mice 3. Killed the "S" strain with heat, then injected it into the mice 4. Mixed the heat-killed "S" with living "R" and injected it into the mice. |
1. Mice died
2. Mice lived 3. Mice lived 4. Mice died |
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In 1928, what did Griffith conclude from his pathogenicity experiment with the two strains of bacteria?
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, The heat-killed “S” strain released some molecules that were taken up by the living “R” cells. The “R” cells acquired the ability to make a capsule and become the “S” strain. The “R” strain cells picked up some molecules that directed their production of a capsule so the “R” cells were transformed into “S” cells by this uptake.
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Avery, McCarty, Macleod tested the macromolecules of the "S" strain bacteria from Griffith's experiment to see what was responsible for transforming the non-pathogenic "R" strain into pathogenic "S" strain. They tested Carbohydrates, Proteins, Lipids and DNA by radioactively tagging atoms, phosphorus (DNA) & sulphur (protein), what was responsible for transforming the "R" strain to "S" strain?
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DNA was the transforming factor, since radioactive phosphorus was found in the new bacteria (phages).
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Why did Hershey and Chase use Radioactive Phosphorus to see what was the transforming factor in the "R" and "S" strain bacteria experiments?
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Phosphorus is contained in DNA but not in Protein so feeding radioactive phosphorus to growing bacteria phages would result in radioactive DNA.
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Why did Hershey and Chase use Radioactive Sulfur to see what was the transforming factor in the "R" and "S" strain bacteria experiments?
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Sulfur is found in 2 amino acids (cysteine and methionine) so proteins would incorporate radioactive sulfur while DNA would not
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Why were Hershey-Chase able to determine that either protein or DNA were the transforming or heritable factors when they tested the bacteria with the radioactive sulphur and phosphorus?
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They chose a simple T2 E.Coli bacteria that is composed of only proteins and DNA.
They initially labeled the proteins only with radioactivity and then allowed the infection to occur and examined which macromolecule was injected into the E.Coli by inspecting the E.Coli for traces of radioactivity. When phage proteins were made radioactive, the E.Coli did not contain any radioactivities after the infection was allowed to occur. When phage DNA was made radioactive, the E.Coli contained radioactivity after the infection was allowed to occur. The first half of the experiment proved the proteins were not the genetic material while the second half of the experiment proved that DNA was the genetic material. |
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If a typical chromosome is 150 nucleotides long and a DNA polymerase only adds 50 nt/sec, how can the DNA polymerase copy chromosomes in a more efficient fashion?
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There are many DNA polymerase copying chromosomes simultaneously.
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DNA to DNA is called?
DNA to RNA is called? RNA to Protein is called? |
Replication
Translation Transcription |
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Where does replication begin? Why
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Replication begins at “origins of replication” or “Ori”, which are specific sequences of DNA that are rich in A-T base pairs (easier to open than a sequence with lots of G-C base pairs). Proteins specifically recognize the oris and bind at these regions and ready the DNA for the DNA replication complex to arrive. Oris are located all along the length of the linear chromosomes spaced anywhere from 30,000 to 250,000 nucleotides apart from one another.
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In the DNA double helix, which parental strand serves as a template for new strands of DNA?
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Both strands of a DNA double helix serve as templates for new strands of DNA once the parental strands are separated from one another.
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What are the three hypothesis that Meselson and Stalal tested in order to determine how DNA replication occured?
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1. Conservative Replication - two parental strands would find one another after serving as templates
2. Semi conservative replication - each parental strand stayed paired with the new strand it coded 3. Dispersive Replication - each DNA duplex contained portions of its double helix that were fully prental and other portions that were fully new. |
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What experiment did Meselson and Stalal do in order to determine how DNA replication occured? Which of the three hypothesis were proved accurate?
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1. Take bacteria and grow them exclusively in media containing heavy nitrogen otherwise known as N15. Take some DNA out and centrifuge it in a tube.
2. Transfer the bacteria to media containing “light” nitrogen N14, and allow only one round of replication to occur before isolating the DNA. What types of densities of DNA molecules were found after this first round of replication would determine whether replication was conservative or by another mechanism. A single band of a hybrid duplex (14N15N) was found after a round of replication. When the bacteria was allowed to grow in this 14N containing media for another replication round, a new band showed up Therefore DNA replication is by a semi-conservative mechanism. If we continued to allow these bacteria to grow in 14N media, the 14N14N band would get thicker but the 14N15N would always remain |
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1. DNA polymerase synthesizes in what direction?
2. What does it attached the next nucleotide to? 3. DNA polymerase reads the DNA in what direction? |
DNA polymerase must synthesize in the 5’ to 3’ direction. They add the next nucleotide to the free (unattached) hydroxyl group that is connected to the 3’ carbon of the sugar deoxyribose. DNA polymerase reads the DNA in the 3’ to 5’ direction
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What is a telomere?
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A telomere is a repeating DNA sequence (for example, TTAGGG) at the end of the body's chromosomes. The telomere can reach a length of 15,000 base pairs. Telomeres function by preventing chromosomes from losing base pair sequences at their ends. They also stop chromosomes from fusing to each other. However, each time a cell divides, some of the telomere is lost (usually 25-200 base pairs per division). When the telomere becomes too short, the chromosome reaches a "critical length" and can no longer replicate. This means that a cell becomes "old" and dies by a process called apoptosis. Telomere activity is controlled by two mechanisms: erosion and addition. Erosion, as mentioned, occurs each time a cell divides. Addition is determined by the activity of telomerase.
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What is telomerase?
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Telomerase, also called telomere terminal transferase, is an enzyme made of protein and RNA subunits that elongates chromosomes by adding TTAGGG sequences to the end of existing chromosomes. Telomerase is found in fetal tissues, adult germ cells, and also tumor cells. Telomerase activity is regulated during development and has a very low, almost undetectable activity in somatic (body) cells. Because these somatic cells do not regularly use telomerase, they age. The result of aging cells is an aging body. If telomerase is activated in a cell, the cell will continue to grow and divide. This "immortal cell" theory is important in two areas of research: aging and cancer.
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What are cells that no longer divide called?
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Senescent cells, they have exited out of the cell cycle.
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What is the repeated sequence at the end of a linear chromosome called?
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Telomeres. These telomeres will shorten in any somatic cell that does not have (very) active telomerase. This enzyme maintains the telomeric sequence.
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Are Telomeres transcribed?
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No, Telomeres are not transcribed, they are recognized by proteins that bind in the region & protect the end b/c double-stranded breaks will activate the DNA repair machinery.
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What are hela cells?
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Hela cells came from Hennrietta Lacks who died of cancer. Her cancer cells have made it to just about every lab around the world. her cancer cells never die since they have turned on the telomerase.
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MLC'S, districts, and CO's of HQ units may authorize the purchase of office furniture, exceptions must be in writing and reviewed at least every ___ years?
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2 years
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1
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What human cells have telomerase turned on/off?
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Adult stem cells (bone marrow, skin) in our bodies naturally retain expression of telomerase. Most somatic cells have turned telomerase off so chromosomes are shortening with each division.
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Do chromosomes in our bodies shorten with each division until they stop dividing at a certain point? What is this called?
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Yes, this is called the Hayflick limit.
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In addition to DNA polymerase proof-reading and correcting errors, proteins scan and look out for mismatched pairs, how do they know which strand of DNA is the parental strand and which is the new strand with the error? How do they know which to correct?
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because the new strand has “nicks” in the sugar-phosphate backbone for a short period of time. The enzymes correct the “nicked” strand. Nicked means The strand that hasn’t yet connected all the okazaki fragments and or leading strands to the okazaki fragments from a replication bubble.
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How do adjacent cells communicate with each other?
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Cells that are adjacent to one another may communicate by engagement of cell surface receptors or by sharing ions/molecules through gap junctions if you’re an animal cell or plasmadesmata if you are a plant cell.
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How do cells that are not adjacent to one another communicate with each other?
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Cells that are not adjacent to one another can communicate with one another by sending out soluble signals. In order for a cell to respond to the signals, it must have a specific receptor for the signal. A non-target cell will not have a receptor for a particular signaling molecule.
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Two cells close to each other communicating via soluble molecules is called
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Paracrine signaling.
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A cell secretes a signaling molecule onto itself, this is called
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Autocrine signaling
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Two cells at a distance to each other communicating via soluble molecules is called
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Endocrine signaling. A secreting cell sends out its signaling molecules and these difuse to the blood stream and are carried to cells at a distance. Cells at a distance, of course have to have receptors for the signaling molecules in order to be able to respond. Cells are responding to many signals at any one point in time. Cells are integrating information from all of these signals in order to carry out a coordinated behavior.
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What are the 4 types of receptors?
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1. Intracellular receptors (located in cytoplasm or nucleus)
2. Ion Channel receptors (neurotransmitters often bind to them) 3. G-Protein linked receptors 4. Protein kinase receptors (these receptors have an enzyme portion) |
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Where does a cell receive a signal from? What is a signal?
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Cells are receiving signals from many different places at one time and receiving signals from both adjacent cells and distance cells simultaneously. The signals are molecules secreted by a cell and they may be either polar or non-polar and they may find their receptors on a target cell in different locations.
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What happens when a signaling molecule binds to a receptor?
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Once the signaling molecule binds the receptor, the receptor undergoes a conformational charge and this change in shape will dictate a change in function. (Usually) the receptor changes from inactive to active upon binding signaling molecule.
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What are the two types of signaling molecules? Where are the receptors that receive them?
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Polar signaling molecules:
Polypeptides Some Amino Acid Derivatives Receptor is embedded in plasma membrane (on cell surface) Non-Polar molecules: Steroid hormones Modified from the cholesterol backbone Receptor either in the cytoplasm or in the nucleus |
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How do steroid hormones work?
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Steroid hormones bind their receptors and this hormone-receptor complex becomes a transcription factor. Often the receptor is not located in the nucleus but in the cytoplasm instead, by the binding, this will result in translocation of the complex into the nucleus. Transcription results in the production of new proteins. These newly synthesized proteins will take the cell in a new direction. (behavior wise)
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What produces a faster response? A polar or non polar signaling molecule?
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A polar molecule. Non-polar molecules like steroid hormones can take anywhere from 30 minutes to a couple of hours to develop a response.
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What is a Ligand?
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means signaling molecule or hormone. It can be soluble (meaning secreted) or embedded in plasma membrane (when two cells have to physically contact each other).
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Is ligand binding reversible?
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Bear in mind that ligand binding is reversible. The ligand binds, receptor is activated (by shape change), then ligand diffuses away and receptor becomes inactive. Some receptors for ligands are actually channels for ions. The binding of the ligand changes the receptors/channels shape and usually, the channel opens and allows ions to flow through and when the ligand diffuses away, the receptor channel will close once more. The Ligand is an example of a gated channel.
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Waht is The process by which a signal on a cell’s surface is converted to a specific cellular response in a series of steps called?
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a signal transduction pathway
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Describe the steps involved in a Signal transduction pathway
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1. The signaling molecule binds to the receptor at the cell surface (Reception)
2. Activation of a series of proteins or so called "relay" molecules (transduction) 3. Activation of cellular response (Response) involving many proteins, the relay molecule allows for complexity of the response and integration of many signaling molecules and pathways so that the cell can coordinate its behavior or response. |
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What are examples of cellular responses?
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- In altered metabolism (by activating or inactivating metabolic enzymes)
- Altered gene expression - Cytoskeletal proteins may be (activated) modified so that the call can move in a particular direction |
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How does a cell respond to a polar signaling molecule?
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The cell can respond to a polar signaling molecule binding by altering the function of preexisting proteins (fast acting, seconds) and/or altering protein synthesis (slower acting, 30 minutes to hours). The cell can carry out both responses simultaneously.
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What is the main type of receptor that responds to polar signaling molecules
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G-protein coupled receptors are the main class of receptors to respond to polar signaling molecules. They are embedded in the plasma membrane and cross the plasma membrane 7 times. All of these G-protein coupled receptors have similar structures but they may bind different ligands. We have hundreds of different G-protein coupled receptors with different ligand specificities.
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What is a G-protein?
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A protein that can activate channels and enzymes that are embedded in the plasma membrane.
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What dictactes whether a G-protein is active?
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Which guanine nucleotide it is bound to. If bound to GDP, G protein is off/inactive. If bound to GTP, G protein is on/active.
What determines which of these nucleotides is bound? The G-protein coupled receptor must have found its ligand. (then it activates the G-protein) |
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What does an activated G-protein do?
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An activated G-protein (bound to GP) can activate an enzyme. The enzyme can make many second messengers that can travel throughout the cytoplasm activate other proteins in them. The message that the ligand has found the receptor can now travel throughout the cell plasma membrane into the cellular interior. Where is amplification (and through increase in speed) of the signal?
1. 1 ligand binding to 1 GPCR can lead to the activation of many G-proteins 2. Each G protein activating an enzyme allows for the production of many small, soluble second messengers. Many second messengers can activate many proteins which bring about the cell’s response. |
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Termination of a signal is as important as the arrival and activation of a signal. Termination of signaling through a G-protein coupled receptor includes:
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1 Diffusion of the ligand away from the GPCR = Receptor assumes its inactivation conformation
2. The G-protein hydrolysis of its bound GTP to GDP. A G-protein bound to GDP is in the inactive conformation 3. When the G-protein is no longer bound to the enzyme, the enzyme assumes its inactive conformation & enzyme stops catalyzing its reaction 4. Any second messenger generated has to be destroyed or if the second messenger was a release of an ion, the ion has to be re sequestered. |
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Many signal transduction pathways operate through phosphorylation cascades. These cascades involve a series of kinases being made active by their own phosphorylation.
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1. Inactive kinase, you put an active phosphate on it and it’s phosphorylated or “Activated”.
2. Once activated, these kinases will work on their kinases and activate them by phosphorylating them. This is a rapid pathway b/c it involves the minor modification (phosphorylation) of existing proteins and much amplification since the proteins activated are enzymes. 3. The last active kinase in the phosphorylation cascade will phosphorylate the target protein that will bring about the cellular response. |
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How can we reverse the activation of kinases?
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By removing the phosphate groups that were attached to them. Proteins (enzymes) called phosphatases dephosphorylates the activated kinases.
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In the trasduction pathway, how do Kinases and Adenylyl Cyclases work?
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1. They activate the signal transduction pathway
2. They must be actived 3. They are reversible |
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In the trasduction pathway, how do Phosphatases and Phosphodieterases work?
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1. They terminate the signal
2. They are always active, ready to terminate a siganl like garbage disposal 3. They are reversible |
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Example of a cell’s response to a hormone using a phosphorylation cascade. The binding of adrenaline, known as epinephrine to a GPCR activates G-protein:
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1. activates adenylyl cyclase
2. activates cAMP 3. activates Protein Kinase A………(phosphorylation cascade activates many kinases) 4. activates Final Kinase 5. activates glycogen which phosphorylase breaks down to release glucose which is cells response is to release glucose from starch when adrenaline binds. |
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Does phosphorylation of proteins or enzymes always lead to their activation?
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Sometimes phosphorylation inactivates a protein or enzyme (shuts it off). This is also seen in response to the binding of adrenaline since the cell phosphorylates & turns off the enzyme responsible for starch synthesis. Activate the starch breakdown pathway and inactivate the starch synthesis pathway
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What is an abundant second messenger seen inside of cells other than cyclic nucleotides?
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Ca2+. Ca2+ is kept low in the cytosol by pumping out of the cell and also pumping into the ER. When Ca2+ concentration in the cytoplasm increase, proteins that are responsive to Ca2+ (b/c they bind it or a protein they interact with binds it) can be activated (or inactivated).
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What are second messengers? How do they work?
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Signaling through gene protein coupled receptors can lead to the activation of enzymes that break down particular phospholipids. Components of the cleaved phospholipids can serve as 2nd messengers e.g. IP3, while other components of the cleaved phospholipid stays tethered to the membrane and activates molecules from that position. Second messengers are classically defined as molecules or ions that take the message that a signal has arrived at the plasma membrane into the interior of the cell. They are generally small and soluble & travel by diffusion. They diffuse freely through the cytoplasm
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What is Receptor Tyrosine Kinase? How does it work?
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receptors that have enzymatic activity. They bind their signaling molecule or ligand molecule(s) and dimerize. This event leads to the autophosphorylation of the receptor by its subunits. The kinase activity phosphorylates tyrosines on the cytoplasmic side of the receptor. Autophosphorylation leads to the activation of this receptor. “Relay” proteins can then bind to these phosphorylated tyrosines, become active, and send the message onward.
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How can a phosphorylation cascase get activated / shut off?
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Phosphorylation cascades can be activated in response to the activation of receptor tyrosine kinases. Phosphorylation cascades can terminate in the modification of existing proteins (see adrenaline example) or terminate with new gene transcription.
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