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65 Cards in this Set
- Front
- Back
Name the 3 polymers found in the cytoskeleton and the proteins that interact with them.
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1. Microtubules (alpha, beta-tubulin subunits, a heterodimer)
2. Actin Filaments (G-actin subunits, a monomer) 3. Intermediate Filaments |
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Name the characteristics of microtubules.
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-Radiate from nucleating center
-Subunits in polymer point in same direction --> polarity -"plus" and "minus" end, "plus" end grows more readily -Tubulin binds and hydrolyzes GTP |
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What are the functions of microtubules?
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Mitosis, cilia, and intracellular transport of organelles and other cargo (over long distances)
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Name the characteristics of actin filiaments.
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-Concentrated at cell cortex
-Subunits point in same direction -Actin binds and hydrolyzes ATP |
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What are the functions of actin filaments?
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Contraction in muscle and other cells, cell migration, and intracellular transport (over short distances)
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Name the characteristics of intermediate filaments.
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-Randomly oriented throughout the cell
-IF subunits are related to each other, but differ depending on type -The polymer has NO POLARITY -IF proteins DONT bind or hydrolyze NTPs -Not dynamic |
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What are the different types of IF subunits?
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1. Keratin (skin)
2. Nestin (stem-cells) 3. Neurofilaments (neurons) |
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What is the function of intermediate filaments?
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Mechanical integrity
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What is epidermolysis bullosa?
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An inherited skin disease caused by point mutations in keratin subunits found abundantly in keratinocytes.
The mutations interfere with polymerization of the subunits and cause the epidermis to separate from the dermis, causing blistering. |
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Describe self assembly.
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It is the spontaneous assembly of subunits (typically proteins) to build an ordered structure.
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T/F The formation of the 3 types of cytoskeletal polymers from their subunits requires an enzyme or chaperone?
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False, it occurs through self-assembly. The driving force is non-covalent bonds
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T/F The size/shape of the final structure is governed by the shape and size of the subunits?
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True
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Name examples of self-assembled structures.
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Cytoskeletal polymers, virus coats, bacterial flagella, ribosomes
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Describe Nucleation
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-Nucleating a new filament is slow because each incoming subunit makes only a subset of favorable bonds.
-Nucleation rate is proportional to 1/nth power of the subunit; n=# of subunits in the "critical seed" (actin n=3, tubulin n=6-12) |
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Describe Elongation
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-Elongation is fast because each incoming subunit makes all favorable bonds
-Rate is proportional to concentration of subunits |
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Describe the kinetic barrier to nucleation.
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Prevents polymerization of cytoskeleton subunits at random in the cell. The cell uses special nucleation factors to control where polymers form.
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Describe the general principle for nucleating factors.
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Like all end-binding proteins, nucleating factors recognize only one end (the two ends are structurally different because subunits point in the same direction)
-NFs also cap the minus-end, preventing subunit loss |
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Which end to nucleating factors recognize?
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Minus end --> thus, for both actin filaments and microtubules, nucleating factors determine where the polymer forms and the orientation
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What is the name of the key protein component of the nucleating complex for microtubules?
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γ-tubulin
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What is the name of the key protein component of nucleating complex for actin filaments?
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ARP 2 and 3
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Describe the kinetic barrier to nucleation.
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Prevents polymerization of cytoskeleton subunits at random in the cell. The cell uses special nucleation factors to control where polymers form.
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Describe the general principle for nucleating factors.
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Like all end-binding proteins, nucleating factors recognize only one end (the two ends are structurally different because subunits point in the same direction)
-NFs also cap the minus-end, preventing subunit loss |
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Which end to nucleating factors recognize?
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Minus end --> thus, for both actin filaments and microtubules, nucleating factors determine where the polymer forms and the orientation
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What is the name of the key protein component of the nucleating complex for microtubules?
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γ-tubulin
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What is the name of the key protein component of nucleating complex for actin filaments?
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ARP 2 and 3
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In microtubules, where is the γ-tubulin complex found?
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At the centrosome
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In actin, where is the ARP2/3 complex found?
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At the leading edge of motile cells
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In a motile cell, where does the plus-end of the microtubule radiate outward from?
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A single centrosome (i.e. MTOC)
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In epithelial cells, where is the plus-end of the microtubule found?
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Basal
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In neuronal axons, where is the plus-end of the microtubule found?
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Towards the synapse
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In cilia, where is the minus-end of the microtubule found?
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At the basal body
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In a mitotic cell, where are the plus-ends of the microtubules found?
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In the middle of the two centrosomes
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In a muscle sarcomere, where is the plus-end and minus end of the actin filament found?
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At the z-band and in the middle
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The plus-end of the leading edge of motile cells actin filament is found where?
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At the membrane
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T/F The rear end of a motile cell has anti-parallel arrays of actin filaments, as in muscle?
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True
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T/F Only microtubule arrays serve as directional tracks for motor proteins?
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False, so do actin arrays
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What are the general properties of motor proteins?
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-Motor proteins are enzymes, ATPases, that convert the energy of hydrolysis into a directed walk along the polymer.
-Most are dimers with 2 heads that interact with the polymer -2 domains: Motor and Tail (cargo-binding) |
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Name the 3 families of motor proteins.
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1. Kinesins (MTs)
2. Dyneins (MTs) 3. Myosin (Actin) |
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What are the general principles of the motor protein families?
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-within each family, the motor domain is similar structurally/functionally
-move in one direction only -the different members of each family are distinguished by their tails, which are specific for particular cargo |
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T/F Microtubules support bidirectional movement?
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True, kinesins walk toward the plus-end and dyneins walk toward minus-end
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Name the plus-end microtubule motor and its functions
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Kinesin
Functions-axonal transport, other vesicle transport, mitosis |
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Name the minus-end microtubule motor and its functions
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Dynein
Functions-most are axonemal dyneins involved in cilia/flagella motility. There is one cytoplasmic dynein involved with transport and mitosis. |
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Name the actin motors and there functions
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Myosins
Functions-muscle contraction, terminal steps of vesicle transport, i.e. vesicles leave the microtubules and engage cortical actin network on their way to fuse with the cell membrane. |
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What are 3 examples of motor functions in the cell?
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1. Muscle contraction by myosin
2. Membrane compartment transport by kinesin and dynein 3. Movement of chromosomes in mitotic cells |
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Which direction to the z lines move in muscle contraction?
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Inward
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T/F Golgi and lysosomes associate with cytoplasmic dynein and thereby congregate toward the nucleus
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True
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T/F Secretory vesicles associate with kinesin motors and thereby move away from the nucleus, toward the microtubules plus ends
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True
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T/F Chromosomes have 1 motor?
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False, they have a (plus-end) kinesin motor and a (minus-end) cytoplasmic dynein motor.
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Where are motile cilia found?
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They are present in large numbers on the surface of specialized cells such as respiratory epithelial cells, and oviduct epithelial cells.
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What are the characteristics of primary cilia?
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-Virtually all cells have a single primary cilium with the characteristic 9 doublet microtubules.
-Most are immotile and lack axonemal dynein as well as a central pair of microtubules. |
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What are ciliopathies?
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congenital diseases discovered to be caused by defects in primary cilia biogenesis or function.
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Name some examples of ciliopathies
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Polycystic kidney disease, Bardet-Biedl syndrome, Alstrom syndrome, and Meckel-Gruber syndrome.
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What are basal bodies?
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Nucleation sites for the growth of axonemal microtubules in all cilia, whether motile or primary cilia. They are found at the base of the cilium.
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T/F Bidirectional transport occurs in only motile cilia?
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False, it occurs in both primary and motile cilia
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Which motor is responsible for inward movement of complexes during intraflagellar transport?
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Cytoplasmic dynein, NOT axonemal dynein
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T/F Intracellular transport also mediates certain signal transduction pathways (e.g. Sonic Hedgehog signaling)?
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True
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What is NTP hydrolysis used for?
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To weaken the bonds that hold the polymer together.
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What is the name of the protein that dissembles ADP-actin and what is its function?
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Cofilin
The delay in hydrolysis acts like a timer to prevent dissolution of the actin before newly assembled actin causes further protrusion |
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What does the bacterial pathogen Listeria do?
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It hijacks the leading edge actin machinery to propel itself within the host cells it infects
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Name the proteins that create or affect cell structures
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1. Bundling
2. Gel forming 3. Cross-linking |
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Name the proteins that control microtubule or actin dynamics
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1. Severing, depolymerizing
2. Capping 3. Nucleating factors |
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T/F The centrosome contains the γ-tubulin complex that initiates assembly of new microtubules while anchoring and capping their minus-ends
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True
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Name the 3 types microtubules involved with the organization of the mitotic spindle
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1. Kinetochore
2. Polar 3. Astral |
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What is the name of the kinase that initiates mitosis through a gradual increase during interphase?
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Mitotic cyclin dependent kinase, known as cdc2-cyclin B
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What is the function of cdc2-cylin B?
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It phosphorylates many proteins, which triggers these proteins to carry out the various activities that are required for the cell to reorganize its microtubules and chromosomes, leading to metaphase and then anaphase.
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