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74 Cards in this Set
- Front
- Back
Structure (components) and function of the cytoskeleton?
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Function:
-internal scaffolding of the cell -responsible for the shape of cells -driving force behind cell movement Structure: Consists of three major components: 1. intermediate filaments 2. Microtubules 3. Microfilaments (main difference between the 3 is size!) |
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Diameter of microfilaments?
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5 nm
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Diameter of microtubules?
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25 nm
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Diameter of intermediate filaments?
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7-11 nm
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Intermediate filaments - general characteristics
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-ropelike polymers of coiled-coil fibrous polypeptides
-relatively stable -cell type specific --> different types of intermediate filament proteins are associated with different cell types **this characteristic can be used for typing cells (eg. keratins are markers for tumors of epithelial origin) |
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keratin
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a. intermediate filaments
b. markers for tumors of epithelial origin |
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vimentin
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a. intermediate filament
b. marker for tumors of connective tissue cells (sarcomas) |
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Lamins
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intermediate filaments!
**lamins a,b, c !! |
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Intermediate Filament Groups
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4 major groups based on the STRUCTURE of the polypeptide subunits:
Type I - IV |
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Intermediate filament assembly
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The central domains of two individual proteins (a-helices -- repeat for 7 amino acids -- heptad repeats) form a helical dimer
Two dimers line up side by side to form a tetramer Tetramers aggregate end to tend to form a protofilament Eight protofilaments form a cylindrical, 10 nm thick intermediate filament The globular domains at either end project from the surface and accounts for variations between individual types of intermediate filaments |
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Intermediate filament function?
where in the cell are they found? |
-Help to maintain cell structure
-extend from the nuclear envelope to the plasma membrane -they are stable, ie no evidence for a rapid polymerization or depolymerization -particularly prominent in cells that are subject to mechanical stress, such as epithelial and cardiac muscle cells -keratin filaments form a network that crisscross the interior of the cell and attach to SPOT DESMOSOMES |
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Keratin filaments are major structural components of?
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Keratinized structures such as the outer layer of the skin, hair, and nails
-- keratin filaments form a network that crisscrosses the interior of the cell and attaches to spot desmosomes |
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General characteristics, composition of microtubules?
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-single tubules are 25 nm in diameter
-composed of 2 monomers - a- and b-tubulin, which polymerize to form a hollow single microtubule 25 nm in diameter -assembly is regulated by microtubule-associated proteins (MAPs) -Microtubules have a defined polarity -Assembly and disassembly occurs preferentially on one end -Occurs as single, double, or triple tubes |
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Assembly of the (protein subunits) of microtubules is regulated by?
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Assembly of the two monomers -- a- and b- tubulin -- which make up microtubules is regulated by MICROTUBULE-ASSOCIATED PROTEINS (MAPs)
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Which of the microtubule ends grows at a slow rate? At a fast rate? What is this regulated by?
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– end is where microtubule grows at slow rate, + end is end where dimers added more rapidly
Regulated by microtubule-associated proteins (MAPs) |
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What is this an image of?
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Microtubule single, double, or triple tubes
In the doublet, tube B shares part of the complete tube A In the triplet, tube B shares parts of both the complete tube A and the complete tube C |
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Microtubules originate from?
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microtubule organizing center, which contains centrioles that are perpendicular to each other
-microtubules radiate away from this region forming a star like structure termed an aster -amorphous material in this region serves as a nucleating site (or primer) for the formation of cytoplasmic microtubule |
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Functions of microtubules ?
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3 of the major functions of microtubules:
1. make up single apparatus during mitosis where chromosomes line up at equator of cell and are pulled apart as cell divides. Part of spindle apparatus 2. used to transport materials from one part of cell to periphery. 3. Make up structure of flagella and cilia, projections of cell involved in cell motility |
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Kinesin
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-composed of heavy and light chains
-used to walk cargo on microtubules TOWARD THE + END have globular heads that bind to microtubules, and hydrolyze ATP and tails that bind to transported vesicles |
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Dyenin
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-composed of heavy and light chains
-used to walk cargo on microtubules TOWARD THE - END have globular heads that bind to microtubules, and hydrolyze ATP and tails that bind to transported vesicles |
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What proteins walk cargo on microtubules?
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kinesin (--> + end)
dyenin (--> - end) *both proteins have globular heads that bind to microtubules, and hydrolyze ATP and tails that bind to transported vesicles |
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Distribution and function of microtubules?
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-present in almost all vertebrate cells
-form a diverse array of both permanent and transient structure 1. cytoplasmic microtubules are transient in nature -principle structural elements of the cytoplasm during interphase and the mitotic spindle during mitosis -region surrounding the centrioles is termed the MICROTUBULE ORGANIZING CENTER (MTOC) -provide tracks for movement of pigment granules and membrane vesicles *kinesin and dyenin -responsible for axonal transport in neurons -during mitosis bundles of microtubules radiate from the poles of the cells and attach to the chromosomes to form the mitotic spindle -- these microtubules are responsible for separating chromosomes during mitosis |
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What microtubules make up the mitotic spindle?
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-astral
-kinetochore -polar microtubules |
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Centrioles
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-a centriole located at the base of a ciliary axoneme is termed a BASAL BODY
-centrioles can convert into basal bodies and vice verse -both centrioles and basal bodies consist of 9 sets of triple microtubules (1 coplete 2 incomplete) forming a short cylnder 0.2 um x 0.3 um -centrioles usually arise by the duplication of preexisting ones |
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basal body
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-base of cilia
-serves as a nucleation site for the growth of axoneme microtubules -centrioles (formed from microtubules) can convert into basal bodies and vice verse |
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Structure / size of basal bodies v. centrioles?
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-both centrioles and basal bodies consist of 9 sets of triple microtubules (1 coplete 2 incomplete) forming a short cylnder 0.2 um x 0.3 um
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Clila function
how do they move? |
extend from the surface of many epithelial cells, which line the trachea, oviduct, and parts of the male reproductive tract and function to move fluids, mucous, eggs, and sperm
similar structure to flagella move via DYENIN WALKING |
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Flagella function
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function to propel sperm
similar structure to cilia move via DYENIN WALKING |
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dynein walking
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Dynein is a protein associated with individual microtubules in an axoneme
the dynein arms on one set of microtubule doublets interact with adjacent microtubule dublet and hydrolyzes ATP to generate a sligind force between the two sets of microtubules sliding of microtubule doblets is converted into bending of the cilia or flagella -- microtubule doubles are held together by a network of cross-links |
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Axoneme
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AXONEME:
2 singlets in the center + 9 doublets surrounding RADIAL SPOKES +Nexin (connects each doublet together) +Dynein arms make up cilia and flagella |
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Microfilament general characteristics
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-very dynamic
-rapid if polymerization and depolymerization -RESPONSIBLE FOR CELL MOVEMENT -present in all vertebrate cells -can account for a significant fraction of total cellular protein |
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Microfilament structure
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-composed of a helical chain of ACTING
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F- actin
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filamentous actin
polarized and grows faster on one end than the other |
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G-actin
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monomeric actin (globular)
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Proteins that interact with actin to modify its behavior:
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1. cross linkers
-- some proteins can cross-link actin filaments into 3d networks --this is responsible for the reversible gel-sol transitions of actin --may be an important factor in cell movement 2. Fragmenting (or capping) proteins which prevent polymerization, regulating the loss or addition of G-actin -- regulated by Ca2+ ions *these proteins are part of the actin filament and can change the structure and function of the actin filament |
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Gel-sol transitions of actin?
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gel --> cytosol is gel like
sol --> cytosol flows freely |
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Myosin
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-represent a family of proteins that interact with actin (microfilament) to produce tension
-can bind to actin and posess an ATPase -ATP hydrolysis is essential for movement -two major forms have been described: 1. Type 1 (aka minimyosins) 2. Type 2 myosin |
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Type 1 myosin
v Type 2 myosin |
TYPE 1:
aka minimyosins -present only in NONMUSCLE CELLS -contains a short tail that can bind to membrane vesicles, plasma membrane, and microfilaments -responsible for movement of organelles along actin filaments TYPE 2: -present in BOTH MUSCLE and NON MUSCLE CELLS -contains a gobular head that can bind actin and a fibrous tail that can form polymers -in the case of striated muscle the myosin filaments are organized into thick filaments and bind to F- actin |
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Functions of Actin:
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1. intracellular movement
2. muscle contraction 3. membrane structure (microvilli in intestine and sterocilia in choclea of ear and epidimius) 4. locomotion (cortical flow / leading edge) |
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Where does actin interact with the plasma membrane?
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1. Zonula adherens or intermediate junctions
2. Cell cortex |
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Molecules that mediate cell adhesion:
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There are several major families of cell adhesion proteins -- these include:
1. Integrins 2. Immunoglobulin superfamily 3. Selectins 4. Cadherins |
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Integrins
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-family of heterodimers
-function both cell-substratum and cell-cell adhesion -include the fibronectin receptor -attached to the cytoskeleton -Ca2+ dependent -cell survival signal -- lose connection via integrans, lose signal particlar a and b subunit determin what ECM protein an integrin binds to (fibronectin, laminin, collagen ,etc binding depends on subunit) |
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Immunoglobulin superfamily
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-cell-to-cell adhesion during embryogenesis, wound heling, and inflammatory response
-includes N-CAM, the first adhesion molecule to be described have Ig like domains -homophilic binding! |
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N-CAM
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-medites the fasciculation of axons
- important in the attachment of neurons to skeletal muscle cells -immunoglobulin superfamily -homophilic binding |
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Selectins
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-bind specific carbohydrates on target cell
-expressed by some white blood cells and by endothelial cells -mediates an inflammatory response in which leukocytes bind to blood vessle -allows cells to move with respect to one another! |
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Cadherins
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-Ca2+ dependent
-homophilic cell-cell adhesion molecules -developmentally regulated -mediated cell-cell adhesions by serving as anchoring sites for actin filaments (intermediate junctions) -present on most cell types and bindts to itself -Dimers from one cell + dimers from another cell -can be divided into a number of subtypes depending on their distribution and cell binding specificity **junctions can form between cells having the same subtype of cadherin but not between cells having different subtypes **may mediate cell sorting **may control morphoigenesis CATENINS AND OTHER PROTEINS MEDIATE CONNECTION OF CADHERIN TO ACTIN |
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You can us Ab to block what kind of cell-to-cell adhesion?
what's another way you can achieve this same effect? |
Ab to cadherins prevents intermediate junctions
eg. e-cadherins can also us CALCIUM 2+ |
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What holds most epithelial sheets together?
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e-cadherin
-abundant at sides of cell-to-cell contact in epithelia -addition of antibodies to this cadherin cause cultured epithelial cells to detach from each other |
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What molecule may mediate cell sorting?
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cadherins
-when different embryonic tissues are dissociated into individual cells and then allowed to reaggregate, they sort out, ie cells from different tissues segregate into different regions of the aggregate (Can happen between tisseuss with different cadherins, ie. n-cadherin and e-cadhering, or between cells that have high/low levels of the same cadherin) |
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What molecule may control morphogenesis?
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cadherins!
during development, the expression of the various cadherins undergoes dynamic changes the loss of cadhering may be responsible for the epithelial to mesenchymal transformation different germ layers express different forms of cadherins which may account for their separation |
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Zonula adherens aka
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Intermediate Junctions
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Intermediate junctions aka
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Zonula adherens
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Cell cortex
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a layer of actin and associated proteins which is immediately beneath the plasma membrane of many cells
-attached to the plasma membrane by linker proteins -gives mechanical strength to the cell surface and enables the cell to change shape and to move -the thickness varies from cell to cell and between different regions of the same cell |
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Function of intermediate junctions
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1. Structural -- maintain cell surface structures
a. microvilli of the intestine b. stereocilia of epididymis (aids absorption) and in cochlea (hearing) 2. Muscle contraction 3. Movement -- cortical flow and leading edge model |
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Cortical Flow Model
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-one of two models (other being leading edge model) that describes how actin filaments help cells move
-controlled by the flow of actin filaments in the cell cortexs -this flow is governed by the gradients of TENSION in the cortex generated by myosin (flow low --> high tension) -myosin may be responsible for maintaining the tension -during initial stages of cell division, there is an increase in the tension over the entire cell surface -as cell division progresses, the tension at the two polar regions is relaxed, however, tension remains high in the equator leading to an indentation -tension is controlled by the MITOTIC SPINDLE -the contractile ring is a bundle of actin filaments and associated myosin located immediately below the plasma membrane of the cleavage furrow -contains a higher concentration of actin than other areas of the cell surface -cell surface components flow into the cleavage furrow during cytokinesis **bundling of actin filaments in one portion of the cell leads to relaxation of the other portion of the cell |
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Leading edge model
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*mechanism accounting for cell migrationhave cell and get protrusion of leading edge in direction that cell wants to move. Little feet = focal contacts, constantly being formed and broken. In the leading edge model have polymerization of actin occurring in the lamellipodum.. + end.. Extends lamellipodoium then get flow of actin in that direction then focal contact in back of cell breaks. In that way get translocation/locomotion of cell due to polymerization of actin in leading edge of cell and formation of new focal contacts in front and breaking of old in back.
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Communicating gap junctions:
distribution morphology function |
Distribution:
-on epithelial cells and a variety of other cells, especially those that are electrically coupled (smooth and cardiac muscle) -most COMMON type of junction Morphology and composition: -under EM, membranes of adjacent cells are separated by a 2 nm gal (and channel is 1.5 nm in diameter) -Connexons have diameter such that it allows ions, small molecules through, but there is NO ACTIVE TRANSPORT PROCESS GOING ON HERE.5000 and 20000 MW protein cannot pass through connexons but 100 and 1000 MW protein can -composed of several hundered connexons -each connexon is composed of six subunits of a dumbbell-shaped protein called connexin Function: -allows small molecules to pass from cell to cell -the pore size is large enough to pass ions, sugars, and amino acids, but small enough to block the passage of proteins, nucleic acid, and complex carbohydrates _may be important for transmitting nutrients (metabolic cooperation) -can transmit a wave of depolarization from cell to cell -electrical coupling is important for contraction of heart and smooth muscle cells -regulates the coordinated beating of cilia on epithelial sheets |
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Proteins making up gap junctions?
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-composed of several hundered connexons
-each connexon is composed of six subunits of a dumbbell-shaped protein called connexin 2nm space (?) 12 connexins total |
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Zona occludens aka
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Tight (impermeable) junctions
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Tight (impermeable) junctions
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Zona occludens
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Proteins making up zona occludens ?
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occludin and claudin
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Zona occludens
Distribution Morphology Function |
aka tight (impermeable) junctions
Distribution: found between epithelial cells Morphology: -membranes between adjacent cells appear to fuse -freeze fracture shows a series of parallel strands of intramembrane particles -specific proteins in adjacent cells make contact with each other to form the tight junction **flow of tracer is blocked by tight junctions -made of 2 proteins: claudin and occludin -appears to involve Ca2+ dependent proteins Function: serves as PERMEABILITY BARRIER so that material cannot pass between cells -functionally divides the plasma membrane of cells into apical and basolateral regions -many membrane proteins cannot pass this junction -requires divalent cations |
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Desmosomes aka
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Macula Adherens
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Macula Adherens aka
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Hemidesmosomes
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Desmosomes & Hemidesmosomes
Distribution Morphology Function |
aka Macula Adherens
Distribution: -found between adjacent epithelial cells -button like points of contact between cells -transmembrane linker proteins connect the two cytoplasmic plaques -hemidesmosomes in contact with basement membrane -morphology: contain a pair of dense attachment plaques separated by a 20 nm space -otfen has a dense line in the center -KERATIN FILAMENTS fun into the plaque and then course back -there are filaments between the plaques of adjacent cells |
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Hemidesmosomes are located where???
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in regions of epithelial cells in contact with the basement membrane and anchor the cells to the extracellular matrix of the basement membrane
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Gap between desmosomes?
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20 nm space between the plaques
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Protein components of the desmosome?
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cytoplasmic plaque:
-plakoglobin -desmoplakin connecting plaques **20 nm space: -desmoglein and dexmocollin Attached to plaques: KERATIN FILAMENTS |
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Zonula adherens aka
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Intermediate Junctions
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Intermediate Junctions aka
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Zonula adherens
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Intermediate junctions
Distribution Morphology Composition |
aka Zonula adherens
distribution: -occurs as a continuous band around the apical portion of epithelial cells -similar structures occur in intercalated disks of heart muscle Morphology; -contain two plaques into which actin filaments insert -EM shows an ill defined material in the zonula adherens connecting adjacent cells together composition: -contains CADHERINS -family of membrane proteins involved in Ca2+ dependent cell-cell adhesions -present on the cell surface and are closely associated with the zonula adherens |
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Which of the cell junctions are Ca2+ dependent?
What about the CAMs? |
-Zona occludens/tight junctions
-Desmosomes -Zona adherens/intermediate junctions NOT (to my knowledge) gap junctions CAMs: -integrins -cadherins - |
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Proteins associated with intermediate junctions?
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cadherin dimers inside
actin filaments associate with cadherin dimers |
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What mediates the connection of cadherin to actin?
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CATENINS AND OTHER PROTEINS MEDIATE CONNECTION OF CADHERIN TO ACTIN
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