w10 txtbk Flashcards
tissues
cooperative assembly of cells and matrix woven together to form a distinctive multicellular unit with a specific function
extracellular matrix
complex network of polysaccharides and proteins secreted by cells
- a structural component of tissues that also influences their development and physiology
what causes a leaf to wilt?
osmotic swelling of the cell, limited by the resistance of the cell wall, can keep the chamber bloated
mass of swollen chambers forms a semirigid tissue
if water is lacking, the cells shrink and the leaf wilts
turgor pressure
a swelling pressure that develops as the result of an osmotic imbalance b/w the interior of the plant cell and its surroundings
how is a 2nd cell wall produced
once cell growth stops and the wall no longer needs to expand, it’s produced either by thickening of the primary wall or by deposition of new layers with a different composition underneath old ones
cellulose microfibils
long thin polysaccharide fiber that helps strengthen plant cell walls
resists compression and tension
how do cellulose microfibrils aid the cell in changing structure
for plant cell to grow/change, cell wall has to stretch or deform
-because the cellulose microfibrils resist stretching, their orientation governs the direction in which the growing cell enlarges
by controlling the way it lays down its wall, the plant cell controls its own shape and direction of growth of the tissue
what guides enzyme complexes?
microtubules serve as tracks that help direct movement of enzyme complexes
-cytoskeleton controls shape of plant cell and modeling of plant tissues
connective tissue
bulk of tissue occupied by extracellular matrix, and the cells that produce the matrix are scattered within it
the tensile strength is provided by fibrous proteins
collagens
triple-stranded, fibrous protein thats a major component of the extracellular matrix and connective tissues; its an abundant main protein in animal tissues
osteoblasts
the cells that manufacture collagen and live within connective tissues’ extracellular matrix and are named according to the tissue type in which they reside
fibroblasts
cell type that produces the collagen-rich extracellular matrix in connective tissues such as skin and tendon
also produce other macromolecules of the matrix
consequence of assembly occurring prematurely?
before secretion, the cell would become choked with its own products
in the case of collagen, the cells avoid this by secreting collagen in a precursor form called procollagen, which has additional peptide extensions at each end (collagen fibrils)
integrins
family of transmembrane proteins present on cell surfaces that allow cells to make and break attachments to the extracellular matrix, helping them to crawl through tissue
don’t interact directly with collagen fibers
undergo conformational changes
fibronectin
extracellular matrix protein that helps cells attach to the matric by acting as a “linker” that binds to a cell-surface integrin molecule on one end and to a matrix component (e.g. collagen) on other
glycosaminoglycans (GAGs)
polysacc. chain that can form a gel that acts as a “space filler” in the extracellular matrix of connective tissues; helps animal tissues resist compression
-negatively charged
proteoglycans
molecule consisting of one or more glycosaminoglycan chains attached to a core protein
these aggregates can form gels that regulate the passage of molecules through the extracellular medium and guide cell migration
how do GAGs cause swelling pressure?
even at low conc, GAGs form hydrophilic gels
-their negative charges attract a cloud of positive cation that draw large amounts of water into matrix
this hydration gives rise to a swelling pressure, whichs balanced by tension in collagen fibers interwoven with the GAGs
when the matrix is rich in collagen and large qty’s of GAGs are trapped in the mesh, both the swelling pressure and counterbalancing tension are big = resistant to compression
Which of the following determines the direction in which cellulose microfibrils are laid down in the extracellular space of a plant cell?
1. amount of turgor pressure within cell
2. availability of sugar monomers for cellulose microfibril elongation
3. orientation of microtubules in cell wall
4. orientation of microtubules on cytoplasmic side of plasma membrane
- orientation of microtubules on cytoplasmic side of plasma membrane
Microtubules beneath the cell wall serve as tracks that guide the movement of the enzyme complexes that synthesize the cellulose microfibrils.
Fibroblasts are the major cellular component in which tissues?
connective
Fibroblasts are the major cellular component in connective tissues. Fibroblasts manufacture and inhabit the extracellular matrix in skin, tendon, and many other connective tissues
epithelium
sheet of cells covering an external surface or lining an internal body cavity
-some mainly act as a protective barrier(+takes up nutrients) and others have biochemical functions
-cover the external surface of the body and line all internal cavities
structure of epithelial sheet
2 faces:
Apical surface
-free and exposed to air or to bodily fluid
Basal surface
-attached to thin, tough sheet of extracellular matrix called basal lamina
-composed of specialized collagen and protein called laminin (provides adhesive sites for integrin molecules)
Differ bc each contain a diff. set of molecules that reflect the polarized organization of individual epithelial cells
-this polarity is crucial for function
-imports food from gut lumen to apical surface and exports food from basal surface into tissue
what does polarity depend on in epithelial cells?
depends on the junctions that the cells form with one another and with the basal lamina
-these cell junctions control the arrangement of system of membrane-associated intracellular proteins
tight junction
cell-cell junction that seals adjacent epithelial cells together, preventing the passage of most dissolved molecules from one side of epithelial sheet to the other
-seal neighboring cells tg so water-soluble molecules cant easily leak b/w them
w/o tight junctions to prevent leakage, the pumping activities of absorptive cells like those in the gut would be pointless
+ the composition of extracellular fluid would become the same on BOTH sides of epithelium
