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161 Cards in this Set
- Front
- Back
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What are the three components that make up the cytoskeleton?
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Microfilaments, microtubules, and intermediate filaments
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What is the primary constituent of microfilaments?
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actin
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How many strands do microfilaments have?
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two, twisted around each other
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Which is more flexible microtubules or microfilaments
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microfilaments
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What is the primary constituent of microtubules?
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alpha and beta tubulin
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What is the cell cortex?
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The actin cage that lies just below the plasma membrane
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What are filopodia?
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spikes that stick out of a cell, made of actin
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What is the lamellipodium?
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the leading/mobil edge of a cell, made of actin
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The actin on rate is dependent on?
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concentration
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The actin off rate is dependent on?
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Nothing, its a constant
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What is it called when the + end grows as the - end shrinks but the length of the filament doesn't change?
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Actin Treadmilling
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Which end of the actin filament do actin polymerize onto?
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the + end
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Which end of the acting filament do the actin depolymerize off of?
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the - end
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Describe the steps of actin polymerization and depolymerization that power actin tread milling
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1. ATP binds
2. Actin attaches Filament grows 3.ATP is hydrolyzed 4.ADP actin dissociates |
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What is the function of formins?
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the are proteins that accelerate of decelerate the growth of actin filaments
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What is the purpose of fimbrin?
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it has two actin binding domains so it can be used to hold two filaments together
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what is the purpose of alpha-actinin?
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alone it only have one actin binding domain, but when dimerized it can be used to cross link filaments
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Why does the listeria virus spread so quickly?
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because it hardnesses actin polymerization to propel itself out of the host cell into another cell.
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What is the purpose of Arp2/3?
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Its an actin branching nucleator. It binds to the side of an actin filament and allows for the formation of a branch off the side (at 70degrees)
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At what angle does a daughter filament emerge from the mother filament?
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70 degrees
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What does WASp do?
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It is the activation domain for Arp2/3 that causes a conformational change that allows branching to begin
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What does Arp2/3 require to start nucleating a daughter actin branch?
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WASp activation domain
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What is the purpose of the capping proteins in the lamelipodia?
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they don't allow for futile polymerization.... or basically the addition of actin to branches that are not close to the plasma membrane (pushing on it)
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What is the name of the actin capping protein?
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CapZ
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How does the capping protein know to only cap the branches that aren't pressing on the plasma membran
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only because its really slow and doesn't know any better and in its (1 second) lag time... it doesn't cap the new filaments until they are no longer pushing on the membrane
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To which end of the actin filament does capZ bind?
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+ end
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What does profilin do?
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accelerates actin recycling,
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What does ADF/Cofilin do?
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It cuts actin filaments. It binds to the middle, unwraps it and causes the middle to break down. This is because the rate of actin recycling is not always fast enough to meet the demand
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What do Listeria posses that give them their properties?
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They have "Act A"... which is an Arp 2/3 activator... so it causes branching on an actin filament which is uses as propulsion
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How do formins interact with the actin filament?
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They dimerize around the + end of the filament and each half of the FH2 domain rocks up and down with growing actin dimers. They also have an FH1 domain that recruits actin to help in acceleration
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An amoeba swimming towards cAMP is an example of....?
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Chemotaxis
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Why do amoeba's emit cAMP when they are hungary?
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So that other amoebas congregate around it and then they throw one of the amoebas out far away (in search of food)
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What do the Rho family GTPases do?
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they are the master regulators on the actin cytoskeleton. Cause different actin structures to form.
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What actin structure does RHO promote?
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Stress Fibres
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What actin structure does Rac promote?
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Extending of the Lamellipodia
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What actin structure does Cdc42 promote?
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filopodia (spikes)
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How would one know if Rho is turned on?
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It's bound to GTP
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What does GEF stand for?
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GTP exchange factor
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What does GAP stand for?
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GTPase activating protein.
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What protein turns GTPase proteins?
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GES (it exchanges GDP for GTP)
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What proteins turn off GTP associated proteins?
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GAP (GTPase activating protein) because it activates they hydrolysis of GTP to GDP)
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Why is cross-talk between the RHO-family proteins important?
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because it directs the signalling pathway... eg. active RHO inhibits active RAC. or Active Cdc42 activates Rac.
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Why does a dominant negative form of one of the three signalling proteins (for actin) cause a wound to not heal
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because they all cross-talk and are mutually dependent... a wound cannot close without all three of the proteins...and if one is dominant negative it cannot be activated it wont close
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What does Cdc42 activate?
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It activates Arp2/3 through binding with WASp, causing an conformational change or "opening" of the complex that allows it to polymerize actin
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What does Rho activate?
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It activates formins, causing a confomational change from closed (inactive) to open (active)
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What detects the chemotactic gradient?
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the G-protein coupled receptors in the plasma membrane
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How does such a small chemotactic gradient cause such a large cellular action?
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The receptors have a positive feedback system that amplifies the signal
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What is unique about myosin as a protein?
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It can transform chemical energy to mechanical work
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How does myosin move?
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It has an actin binding doman and ATP hydrolysis causes a large scale conformational change (causing motion)
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Describe class 1 myosin
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Monomeric, associated with membranes
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Describe class 2 myosin
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associated with contradiction of stress fibres and muscles. Two heads form a dimer
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Describe class 5 myosin
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two myosin heads that can translocate along actin filaments
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What is the name for the bipedal protein?
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Kinesin
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Towards which direction does Kinesin walk?
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Towards the plus end of the actin filament.
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Where does the tail of Kinesin bind?
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They bind to the cargo. The heads bind to the filament.
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How many steps can Kinesin take before it dissociates
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About 100 steps
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Which type of cells are typically multinucleated?
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Muscle Cells
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Which does the reaching out a grabbing? (actin or myosin)
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Myosin
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Why do you get rigamortus in your muscles after you die?
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Because myosin binds to muscles and contracts and stays stuck like that.
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How does the myosin head detach from the actin filament?
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ATP hydrolysis
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What is the primary signal in the muscle that causes contraction?
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Release of Ca++ into cytoplasm from sarcoplasmic reticulum
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Where does the muscle store Ca++?
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The Sarcoplasmic reticulum
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Why does Ca++ cause muscle contraction?
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Tropomyosin lines actin and usually blocks the myosin from attaching. When Ca++ binds to tropomyosin it moves out of the way.
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How many protofilaments make up the average microtubule?
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13
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Why do human cells have more of a need for microtubules than bacterial cells?
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Microtubules serve as highways for long rang transportation around the cell, bacterial cells are significantly smaller and require much less transportation.
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Where do microtubules emanate from?
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a centrosome
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Which cytoskeletal structure causes the segregation of daughter cell's chromosomes during mitosis?
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The Mitotic Spindle.
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What is the purpose of microtubules in neurons?
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Neurons can have dendrites far away from their cell bodies, and microtubules provide the long-range transport needed.
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What is at the centre of a centrosome? (when its beginning)
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Two centrioles, made of microtubule triplets, surrounded by the pericentriolar materia, and contain gamma-Turcs which are the nucleation factors for microtubules.
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What are Gamma-turcs ?
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They are the nucleation factors for microtubules?
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What are the nucleation factors for microtubules?
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Gamma-TURCS
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What do depolymerases do to microtubules?
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They trigger a catastrophe, either through actively depolymerizing, or slowing the growth rate
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What is XMAP215?
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a depolymerase and polymerase of microtubules, its reaction is dependent on tubulin concentration... can accelerate polymerization by a factor of 5
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What is MCAK?
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a microtubule depolymerase
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How fast can kinesin walk?
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100 steps per second
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Which protein walks towards the minus end?
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Dynein
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What does Dynein do?
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It walks down mircrotubules, towards the minus end, in the opposite direction of kinesin
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How do cargo proteins know to take specific proteins to specific places?
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The microtubules have indicators, analogous to road signs indicating where they go.
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Which protein drives the beating of flagella?
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Dynein
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How do the centres of daughter cells start?
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Two centrosomes are pushed apart and form the mitotic spindle
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What does Kinesin-5 do?
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It cross links and slides anti-parallel pushing two filaments in opposite directions, and in mitosis push apart the centrosomes
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What are dynein's major role in mitosis?
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They attach the microtubule to the plasma membrane and walk to the minus end, which since they are attached causes them to pull the centrosomes to the poles and into place... if you don't have this you can get asymetric separation
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What is the role of Kinesin-13 in mitosis ?
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It causes poleward flux of the microtubules, by depolymerizing microtubules at the minus end, causing them to be sucks towards the poles
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What is the main driving force behind chromosome separation?
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Mostly the depolymerization of the filaments but there are also motor proteins present in the kinetochore
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Which protein is responsible for the poleward flux?
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Kinesin-13
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How do cells know when to replicate?
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Time, or well concentration that builds over time. Concentration of Cyclins.
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What is the primary 'timer' molecule?
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Cyclin
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What produces the active MPF (maturation promoting factor) molecule?
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Cyclin bound to cdc2
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What does MPF do?
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It phosphorylates a lot of substrates, and the accumulation of phosphorylated product is the timer for the cell
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Does the concentration of cyclins increase or decrease after undergoing mitosis?
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It decreases... ALOT ... to almost nothing
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What does Wee1 do?
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It is a kinase that can shut down cyclin-CDK... an excess of it causes elongated cells that don't divide.
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What does Cdc25 do?
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It turns on cyclin-CDK, an excess of these causes tiny cells that have over divided.
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How is DNA replication initiated?
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By Cyclin-CDK phosphorylating pre replication complex which causes DNA duplication
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How is the nuclear envelope broken down?
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Cyclin-CDK phosphorylation
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What process signals a protein for degredation?
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poly-ubiquitination
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Once a protein gets poly-ubiquitinated what happens next?
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It gets unfolded and fed into a proteosome
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What is APC?
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Anaphase promoting complex, it is a ubiquitin ligase, it targets M-phase cyclins (the ones that need to be broken down at the end of anaphase) and pretty much flags them for death
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What activates APC?
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Cdc20 - initiating metaphase-anaphase transition.
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What is the significance of Cdc20 in mitosis?
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It causes degredation of metaphase cyclins causing the initiation of the metaphase anaphase transition
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What does securin do?
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It is a protein that inhibits the breakdown to Cohesins that hold sister chromosomes together.
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How do cells prevent the onset of anaphase?
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The inhibit Cdc20 - which thus inhibits the breakdown of securins that hold the chromosomes together.
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What are Cohesins?
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They are ring molecules that hold sister chromosomes together.
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Separase does what?
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It cuts the Cohesin proteins that hold the sister chromosomes apart. It is inhibited by securin.
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How does the cell inhibit Cdc20?
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Mad 2. Which in the closed conformation 'hugs' cdc20 inhibiting its actions
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How do unaligned chromosomes tell the cell to not go into anaphase?
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They catalyze the conversion of Mad2 to its open conformation so it can close on a cdc20 molecule and thus inhibit it. This happens because mad1 recognizes the unattached kinetochore and signals accordingly.
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What does Mad2 do?
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It inhibits cdc20 preventing onset of anaphase
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How does the final orientation of the last chromosome trigger the onset of anaphase?
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the mad1-mad2 tetramere is released and it interacts with P31, which breaks apart the Mad2-Cdc20 complex and lets active Cdc20 initiate anaphase.
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How does the kinetochore know if its bioriented or not?
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Probably because of tension in either direction
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What are the three classes of intracellular messenger molecules?
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1. Steroids (Testosterone)
2. modified amino acids (epinephrine) 3. Peptides (insulin) |
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What is the term for signalling by hormones that are released into the blood?
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Endocrine signalling
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What is paracrine signalling?
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The release of the signalling molecule in close proximity to the cell that is responding. Synaptic neurotransmission for example.
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What type of signalling is it called, when a cell stimulates itself by releasing a signalling molecule.
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Autocrine signalling
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What is the term for signaling via intimate contact between the two cells?
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Contact mediated signalling
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How do lipid soluble intercellular signals work?
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They diffuse across the membrane, and their receptors are either cytoplasmic or nuclear and are usually transcription factors. This means that the processes they initiate are usually prolonged and gradual
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How do water soluble intercellular signals work?
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They cannot cross the membrane so they usually will activate a receptor on the plasma membrane, and their effects are usually more immediate.
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What are the three types of receptors in cells??
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1. G-protein coupled receptors
2. Receptor Protein Kinases 3. Ion Channels |
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What are most steroid hormones derived from?
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Cholesterol
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How does the sun give us vitamin D?
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Vitamin D is generated from Cholesterol by the action of UVB `
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What are the conserved elements found in lipophilic receptors?
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- Variable domain(not conserved) that interacts with other transcription factors
- DNA binding domain (recognizes response elements on target gene) highly conserved -ligand binding domain (at C-terminal) also conserved |
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how do steroids activate cytoplasmic (homodimeric) receptors
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The steroid usually displaces a bound inhibitor that prevents the receptor from entering the nuclear envelope
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What are the two classes of hormone response elements?
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Homodimer and Heterodimers.
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What is the Zinc-finger motif?
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A cytoplasmic hormone receptor that as a dimer binds to paired response elements on the DNA, with an alpha helix that lies in the major groove.
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What are the three subunits of the G-protein ?
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Alpha, beta and gamma
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What acts as the 'switch' for turning on and off G-protein coupled receptors ?
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GDP -> GTP (or the opposite)
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The activated G-protein coupled receptor binds to which subunit of the G-protein?
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It binds to the alpha subunit
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Which of the three subunits exchanges GDP for GTP in the G-protein?
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Alpha
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How many transmembrane alpha-helices do G-protein coupled receptors have?
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Seven
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What shuts off an activated G-protein ?
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GAP
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What protein turns on G-proteins?
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GEF
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What activates adenylate cyclase?
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active G-proteins?
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What does adenylate cyclase do?
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It converts ATP into cAMP
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What does cAMP do?
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It activated PKA (protein Kinase A) which is the final common path for most signalling systems
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What turns off cAMP?
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cAMP phosphodiesterase
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how do GAPS affect G-Proteins?
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They are GTPase Activating Proteins that cause activation of GTPase which hydrolyzes GTP to GDP... turning off the G-protein
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What is cAMP converted to by cAMP phosphodiesterase
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adenosine 5-monophosphate
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How does Cholera act?
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It is a toxin that prevents the alpha subunit of G from releasing GTP.... so it is always active... and causes a constant flow of food from the gut and causes diarrhea
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How are Whooping Cough and Cholera opposites?
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Cholera locks G-protein(alpha) into the activated position, and Whooping cough locks G-Protein(alpha) in the inactive state
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How is PKA involved in negative feedback preventing over-stimulation of receptors?
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If PKA is over active it will phosphorylate the G-protein receptor (on the serine or threonine residues) which reduce its signaling effectiveness
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What is heterologous desensitization?
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When PKA phosphorylated all the G-protein coupled receptors in the cell (reducing their efficiency)
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What is the effect of BARK on receptors?
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It phosphorylates different amino acids on receptors to create a docking site for the inhibitory protein B-arrestin (which stops the interaction with the G-protein and and causes endocytosis of the receptor)
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Why does cocaine make it so that our brains DA levels can no longer maintain our sense of well-being?
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Because the over excitation of the DA receptors causes either desensitization through PKA phosphorylation or endocytosis from BARK & B-arrestin
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What does AKAP do?
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AKAP = A Kinase anchoring protein... and it anchors PKA in the nuclear membrane
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Describe the negative feedback system involving PKA and cAMP....
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When cAMP increases it causes activation of PKA.... which activates PDE (phosphodiesterase) which degrades cAMP (lowering the concentration)... thus reducing the activation signal to PKA
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When an egg is fertilized how does it immediately prevent the entering of another sperm
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A wave of calcium sweeps across the cell (egg), causing a reaction around the membrane making it impermeable
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What does Calmodulin do?
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It mediates and amplifies calcium signals in the cell. Calcium binds to it and causes a conformational change. Also once a single Ca++ binds its affinity for Ca++ rises dramatically (amplification of signal) .... Calmodulin can activate different kinases and phosphatases in the cell.
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What is the primary action of viagara?
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It blocks Phosphodiesterases (PDEs) that break down cGMP... and allows muscles to contract again... allowing for contraction of blood vessels and an erection
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Describe Tyrosine Kinases
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They have one transmembrane alpha helix, an extracellular receptor site, and an cytoplasmic tail with enzymatic activity
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What happens to a Tyrosine kinase receptor once it becomes activated
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Its cytoplasmic tails dimerize and become active
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What is HER?
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Human EGF Receptor 2.... it doesn't bind to a ligand, its always active... and interacts with HER1, HER3 or HER4.... and expression of HER2 is found in many cancers
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What is the effect of Ras on the cell?
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A cascade of activated kinases that cause cell proliferation
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How does Ras cause transcriptional change?
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Ras activates Raf that activates MEK that activates MAPK which translocated into the nucleus and phosphorylates a transcription factor ... which transcribe more transcription factors... causing a wave of gene expression changes
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Where does an neuron receive information?
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In the dendrite (post-synaptic cleft)
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Where does the neuron send information/signals?
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Down its Axon to the pre-synaptic terminal
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What two factors can cause an increase of axon firing speed
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Myelination and thickening of the axon
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What is the typical resting charge of the inside of a nerve cell ?
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Negative
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When the resting potential moves towards zero what is it called?
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Depolarization (it moving from negative to zero or positive)
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When the resting potential becomes relatively negative it is called?
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Hyperpolarization
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Typically in the cell membrane which side has more Na+ ?
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Outside
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Typically in the cell membrane which side has more K+
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Inside
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What happens when a cell membrane is made permeable to Na+?
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Na+ goes rushing INWARDS and leaves a negative charge on the outside (a membrane potential)
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What happens when a cell membrane is made permeable to K+?
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The K+ goes rushing OUT of the cell... leaving a negative charge inside the cell (membrane potential)
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