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CORNELL BIOMG 1350 - Cytoskeletons and Motor Proteins

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BIOMG 1350 1st Edition Lecture 6Outline of Last Lecture I. Protein structure, formation Outline of Current Lecture II. Regulating by small GTP-binding ProteinsIII.Microtubules and their motorsIV.Microfilaments and their cellsCurrent Lecture- Regulating by small GTP-binding protein:o GTP bind= ono GTP hydrolysis  GDP= ofo Have to be regulated by a signal in and signal out (activate protein kinase) or by timeo GEF= (Guanine nucleotide exchange factor) lets GTP come in, turns switch on o GAP=GTPase Activating protein= faster You can turn it on in one place and of in anothero Over 100 small GTPases encoded in the genome Fall into certain families that each controls a certain activity, lots of regulation. Each has a downstream pathway and each is regulated by a GEF and GAP Ras Family: rat sarcoma, regulates growth control- GDP binds (inactive)- Signal comes in and GEF released (therefore it is active)- GAP turns the system of- Two diferent conformational states- If you disrupt the GAP- you have more GTP bound ras and it will always signals for growth- There is a mutation when the ras protein cannot hydrolyze GTP  Therefore it is always turned ono Microtubules and their Motors: Microtubules Organizing Centers (MTOCs) Structure: - Tubulin (alpha and beta tubulin)- Protofilament: Beta-alpha organizationThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.o There is a plus end (beta) (polymerization) and minus end (alpha) (depolymerization) (structure is said to be polarized). It has nothing to do with charge. o Microtubules grow out of organizing center (MTOCs, centrosome) Nerve cell axon starts at cell body  axon  axon terminal- Have to transport inwards and outwards- Done on microtubules- The minus end is towards the cell body and plus end is towards axon terminal Kinesin: motor transports cargo towards plus end (axon terminal)- Many diferent types for diferent cargo- Same heads, diferent tails- Structure:o Coiled coil dimerization region holding the two coils togethero Has N terminal: motor domain heado C terminal: cargo binding tailo Neck linker: - Couples ATP hydrolysis to conformational changes- Rear head has ADP, front head has ATP- Binding of ATP (to leading head) causes shape change (and ADP release from leading head) and causes neck linker to swing forward and dock into MT. Swings the former trialing head to become the leading head.- The new leading head finds a binding site ahead of its previous site.- Leading head releases ADP and trailing head hydrolyzes ATP and P is realize and the linker becomes undocked- If ATP can’t be hydrolyzed for some reason kinesin will be tightlybound with its cargo- Each step hydrolyzed one ATP molecule- Lots of diferent kinds of kinesins Dynein: transport cargo towards minus end Both of these motors arrange in eukaryotic cells Without ATP: movement stop and cargo falls of of microtubules.- ATP is required! To release the motor from the MT- you need ATP hydrolysis- ATP bound site it has a high affinity for MT Colchicine: extracts of a plant used to treat gout- Depolymerizes microtubules and disturbs internal organization of cellso Microfilaments and their Cells Actin protein:- Subunits of actin that all have same orientation- Helical - Have diferent ends: minus end (disassembly) and plus end (assembly)- Can interact with many diferent proteins: control behavior of actin filaments Myosin: motors that use ATP hydrolysis to do work- Two heavy chains (coiled coil)- ATPase in head domain- Bipolar filaments- Point towards plus end and move towards plus end of actin- When they contract (myosin head interacts), they pull on actin and slide together, shortening sarcomere- Myofibrils  constrain sarcomeres  contractile unit- Sarcomeres:o Actin: thin filamentso Myosin filaments: thick filaments o


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