chapter 20
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intestine is constructed from _, _, and _. Each tissue is an organized assembly of _, held together by _, _, or both.
epithelial tissues _ connective tissues _ muscle tissues _ cells - cell-cell adhesions _ extracellular matrix
Collagen fibrils are organized into _
bundles.
collagen assembly steps:
from individual polypeptide chains to triple-stranded collagen molecules, then to fibrils and, finally, fibers.
fibroblast secretes:
secretes collagen and other extracellular matrix components.
Collagen is the main protein in
animal connective tissues, like bone, skin, and tendons.
_ is the main protein in animal connective tissues, like bone, skin, and tendons.
Collagen
_ can cause the skin to be hyperextensible. In some individuals, this condition arises from a lack of _; in others, it is caused by a defect in _.
Incorrect collagen assembly _ an enzyme that converts procollagen to collagen _ procollagen itself
Incorrect collagen assembly can cause _
the skin to be hyperextensible.
Fibronectin and transmembrane integrin proteins help _
attach a cell to the extracellular matrix.
_ help attach a cell to the extracellular matrix.
Fibronectin and transmembrane integrin proteins
Fibronectin molecules bind to _.
collagen fibrils outside the cell
Integrins in the plasma membrane bind to _
the fibronectin and tie it to the cytoskeleton inside the cell.
(fig.14) The integrin molecule transmits _ across the _: it is anchored inside the cell via _ to the actin cytoskeleton and externally via _ to other extracellular matrix proteins
tension _ plasma membrane _ adaptor proteins _ fibronectin
An integrin protein _ when it binds to molecules on either side of the plasma membrane.
switches to an active conformation
An integrin protein consists of two different subunits, _, both of which can switch between a _, _ form and an _, _ form. The switch to the activated state can be triggered by _ or _ that then _ (see Figure 20–14). In both cases, the conformational change alters the integrin so that _. In this way, the integrin establishes a _ mechanical linkage across the plasma membrane.
α and β _ folded _ inactive _ extended _ active _ binding to an extracellular matrix molecule (such as fibronectin) _ to intracellular adaptor proteins _ link the integrin to the cytoskeleton _ its opposite end rapidly forms a counterbalancing attachment to the appropriate structure _ reversible
In the extracellular matrix (ECM), different components handle different tasks: Collagen provides _. Glycosaminoglycans (GAGs) and proteoglycans _.
strength to resist stretching _ help resist compression
In the extracellular matrix (ECM), different components handle different tasks: _ provides strength to resist stretching. _ help resist compression.
Collagen _ Glycosaminoglycans (GAGs) and proteoglycans
(fig. 17) Proteoglycans and GAGs can form large aggregates. it is built up from _ subunits bristling with numerous _—chondroitin sulfate (long blue lines) and keratan sulfate (short blue lines)—attached to a _ (light green). These subunits then aggregate via _ (green) to the _
aggrecan GAG chains core protein link proteins GAG hyaluronan
The basal surface sits on a _ called the basal lamina
specialized sheet of extracellular matrix
Tight junctions allow epithelial cell sheets to serve as _.
barriers to solute diffusion
cells are sealed together by branching strands (C) of transmembrane proteins (green), called _
claudins and occludins
Cadherin proteins mediate _ attachment of one cell to another.
mechanical
Identical cadherin molecules in the plasma membranes of adjacent cells bind to each other extracellularly; inside the cell, they are attached, via _, to _—either _ or _.
linker proteins cytoskeletal filaments actin filaments keratin intermediate filaments
when epithelial cells in culture touch one another, their cadherins become concentrated at the point of attachment, leading to _
the formation of adherens junctions.