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I. Intercellular Junctions
Explain the study of cells adhering to substrates in vitro.
- i. cell is rounded until it contacts substratum, when it sends out projections that form stable attachments
- 1. eventually, the cell flattens and spreads out on the substratum
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a. when fibroblasts or epithelial cells spread onto bottom of a culture dish, the lower surface of the cell is not pressed uniformly against the substratum; instead, it is __
anchored to the surface of the dish only at scattered, discrete sites, called focal adhesions
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i. dynamic structures that can be rapidly disassembled if the adherent cell is stimulated to move or enter mitosis
1. the plasma membrane of the focal adhesion contains large clusters of __
2. the __domains of the __are connected by various __to __ of the __
- integrins
- cytoplasmic
- iintegrins
- adaptor proteins
- actin filaments
- cytoskeleton
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a. __ may act as type of __, collecting information about the __of the extracellular environment and transmitting that information to the __, which may lead to changes in __, __, and __ i. also play a key role in cell __, with extracellular materials
- Focal adhesions
- sensory structure
- physical and chemical properties
- cell interior
- cell adhesion, proliferation, or survival
- locomotion
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a. Focal adhesions are capable of creating __ or responding to such forces
i. these properties are expected from a structure that contains __ and __, two of the cell’s major contractile proteins
- mechanical forces
- actin and myosin
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a. acting in opposite directions, mechanical forces applied to the surfaces of cells can be converted by __ into __in the cytoplasm
i. this process of __ is called __, and the __ is acting as a __by recognizing the physical properties of the environment
- focal adhesions
- biochemical signals
- signal conversion
- mechanotransduction
- focal adhesion
- mechanosensor
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1. the ability of cells to respond to __ is important in many cellular behaviors and can be illustrated by a study in which cells were allowed to bind to beads that had been covered with a coating of __
a. when the membrane-bound beads were pulled by an optical tweezer, the mechanical stimulus was __ where it generated a wave of __
- physical forces
- fibronectin
- transmitted into the cell interior
- Src kinase activation
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1. __is mediated by conformational changes in some of the adaptor proteins, such as __, that are induced by stretching
a. such conformational changes can expose important __ in these proteins that were previously hidden, allowing additional protein molecules ot be recruited to the __
- mecahnotransduction
- talin
- binding sites
- adhesion complex
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a. activation of the __ can transmit signals throughout the cell, including the cell nucleus, where they can promote changes in __
i. activation of either FAK or Src can alter __
- protein kinases
- gene expression
- cell behavior
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a. importance of the physical properties of a cell’s environment in influencing cellular behavior is illustrated with __ cells from adult bone marrow
i. when grown on __substratum, they differentiated into __
ii. when grown on __one, they became __
iii. even __led to __
- mesenchymal stem
- soft
- nerve cells
- stiff
- muscle cells
- stiffer
- skeletal tissue
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a. __ are most commonly seen in cells grown in vitro, although similar types of adhesive contacts are found in certain tissues
i. in the body, tightest attachment between a cell and its extracellular matrix is seen at __where the cells are anchored to the underlying __ by a specialized adhesive structure called a __
- focal adhesions
- basal surface of epithelial cells
- basement membrane
- hemidesmosome
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Explain hemidesmosomes.
1. hemidesmosomes contain a dense plaque on the inner surface of the plasma membrane with filaments coursing outward into the cytoplasm
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i. unlike filaments of focal adhesions, which consist of actin, the filaments of the hemidesmosome are __and consist of the __
1. __ are classified as __filaments, which serve primarily in a __function
- thicker
- protein keratin
- keratin-containing filaments
- intermediate
- supportive
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1. __filaments of the __are linked to the extracellular matrix by __, which also transmit signals from the __that affect the shape and activites of the attached epithelial cells
- keratin
- hemidesmosome
- membrane-spanning integrins
- ECM
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a. importance of __seen in disease __, in which individuals produce antibodies that bind to proteins present in these adhesive structures
i. presence of __causes the lower layer of the epidermis to lose attachment to the underlying __
1. the leakage of fluid into the space between the epidermisà __of skin
- hemidesmosomes
- bullous pemphigoid
- autoantibodies
- basement membrane
- blistering
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a. Adherenes Junctions and Desmosomes: Anchoring Cells to Other Cells
i. cells of certain tiessues, especially epithelia and cardiac muscle, are difficult to separate from one another because they are __ by specialized __
- held together tightly
- calcium-dependent adhesive junctions
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Two types of adhesive junctions
- 1. adherens junctions
- desmosomes
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i. in addition to __, epithelial cells often contain other types of cell junctions along their lateral surfaces near the __
1. when arranged in a specific array, this assortment of surface specializations is called a __
- adhesive junctions
- apical lumen
- junctional complex
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Adherens junctions
1. found in several sites, especially epithelia as __ that __each of the cells near its __, binding that cell to its surrounding neighbors
2. in this, cells are held together by __ formed between the __ of __molecules that bridge the 30-nm gap between neighboring cells
- belts that encircle
- apical surface
- calcium-dependent linkages
- extracellular domains
- cadherin
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a. the __domain of these __is linked by __ and __ __ to a variety of cytoplasmic proteins, including __filaments of the cytoskeletom
i. thus, like the __of a __, the __clusters of an __ connect the external environment to the __ and provide a pathway for signals to be transmitted from the __to the __
- cytoplasmic
- cadherins
- alpha and beta catenins
- actin
- integrins
- focal adhesion
- cadherin
- adherens junctions
- actin cytoskeleton
- cell exterior
- cytoplasm
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i. desmosomes
1. What are they?
2. numerous in what kind of tissues?
3. they contain __that link the two cells across a narrow __
a. __of __different from those of __= called __ and __
- disk-shaped adhesive junctions approximately one micrometer in diameter
- tissues under mechanical stress, like cardial and epithelial of skin and cervix
- cadherins
extracellular gap
- cadherins
- desmosomes
- adherens
- desmogleins and desmocollins
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Desmosomes
1. dense __ on the inner surface of the plasma membranes serve as sites of __for __ similar to those of __
2. the 3D network of ropelike __ provides __ and __ to the entire sheet of cells
- cytoplasmic plaques
- anchorage
- looping intermediate filaments
- hemidesmosomes
- intermediate filaments
- structural continuity and tensile strength
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1. intermediate filaments are linked to the __ of the __ by additional proteins
a. importance of cadherins in __ illustrated in autoimmune disease in which antibodies are produced against one of the desmogleins
- cytoplasmic domains of the desmosomal cadherins
- maintaining structural integrity
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i. one of the roles of integral membrane proteins is to ?
transfer information across the plasma membrane, called transmembrane signaling, in which all cell-adhesion molecules can carry out
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1. __ and __ can transmit signals from the extracellular environment to the cytoplasm by means of __and with __
a. __ activate their target protein through __, whereas __ activate their protein targets through __
integrins and cadherins
- linkages with the cytoskeleton
- cytosolic regulatory molecules
- protein kinases
- phosphorylation
- G proteins
- physical interaction
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1. the engagement of an __with its __can induce a variety of responses within a cell, including changes in __, __, and __.
a. these changes can alter a cell's __(4)__
- integrin
- ligand
- cytoplasmic pH or Ca2+ concentration
- protein phosphorylation
- gene expression
- cell’s growth potential, migratory activity, state of differentiation, or survival
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