Week 5 BIO 130 Readings

Tissues

Cooperative assemblies of various cell types that work together to carry out a unified function

Extracellular matrix

• The material that cells secrete around themselves that gives supportive tissues like bone or wood their strength

Cell wall

• ECM of plant cells

• Plant cells themselves will synthesize, secrete and control this structure that forms a box aorund cells

• helps to imobilize, protect and enclose cells

• Can be thick like in wood or thin and flexible like a leaf

• Important as cells without cell walls are easily ruptured, as they lack the strong intermediate filament cytoskeleton that helps animal cells hold their shape

• Doesn,t have to be rigid - ex. lettuce leaves are rigid due to osmotic swelling

Primary cell walls

• formed in newly made plant cells

• only 200 nm thick

• Can slowly expand to accomodate cell growth

Turgor pressure

• The driving force for cell growth

• Develops as a result of an osmotic imbalance between the interior of the plant and its surroundings

Secondary cell wall

• produced when a cell stops growing and the wall does not need to expand

• done by thickening the primary one or adding new layers with different composition under the old ones

• When cells are specialized they produce specialized forms fo these walls

  • ex. waxy and waterproff ones for the surface of epidermal cells of leaves, hard and thick woody walls for those of the xylem

Cellulose microfibrils

• Long fibers of the polysaccharide cellulose that are used to provide tensile strength along the stress lines of the plant cell wall

• Interwomen with other polysaccharides and some structural proteins that are bonedeted to form a complex structure

• Can resist compression and tension

• Cellulose molecules are long and unbranched chains of glucose with each unit inverted with respect to each other and connected by a beta-1,4-glycosidic linnkage

• this repeates hundres of times to create a cellulose moleulce

• 18 of these are held together by hydrogen bonds to make this polymer

Cellulose microfibrils and growth

• Orientiation of these determiens how a cell grows due to their rigidity

• If they are arrangeld like a corset cell will grow more upwards in length rather than in girth

• controlling the way it makes it’s wall allows a cell to control its shape

Cellulose synthase complexes

• Produce cellulose

• embeded in the outer surface of the cell as integeral membrane proteins that are made up of six enzyme trimers, acts as an enzyme complex to make cellulose

• transport activated glucose monomers in the form of UDP-gluclose from the cytosol across the plasma mrembrane and incorporat them into a growing cellulsoe chain at the points of membrane attachment which then assemble to form a cellulose microfibril

• distal ends of microfibrils are integrated into cell wall and elongation pushes these complexes along the plane 9blue arrows)

Microtubule

• Guides cellulose synthase complexes and alligns with the growing cellulose microfibrils outside of the cell

• act as tracks taht direct the moevment of this enzyme complex, indireclty shapingthe plant cell and its tissues

• .attached to plasma membrane by transmembrane proteins

Connective tissues

• Cells in which the extracellular matrix is abundant and carries the mechanical load themselves

• Many cells are classed under this tissue for example

  • the dermis of the skin

  • bone

  • cartilage

  • jelly in the interior of the eye

• Bulk of the tissue is occupied by the extracellular matrix in which the cells are scattered in

• Tensile sterngth of ecm provided by fibrous proteins that are mainly collagens

• Specific character of tissues is attributed to the type and quanity of collagen it contains as well as the other molecules in between in various propotions

• Elastin for example is a rubbery proteins in artieries that helps to make the vessels resilient and allows them to withstand blood pulsing through them

Collagens

• Family of proteins

• mammals have over 40 genes that code for various kinds of these proteins that support the strucuture and function of tissues

• Chief protein in skin, tendon and bone

• Make up 25% of the protein mass of a mammal- more than any other protein

• Characteristic feature = long and stiff triple stranded helical strucutre where 3 polypeptide chains of these monomers are wonund around each other in a rope like super helix

Type 1 collagen

most abundant form, makes up 90% of bodies collagen

Collagen fibrils

• Thin cables 10-300 nm in diameter and many micrometers long

Collagen fibers

• Thick asosociations of collagen fibrils that are 0.5 to 3 micromeeters in diameter

Osteoblasts

• Cells in the ecm of the bone tha make collagen

• Produce most of the other macromolecules of the matrix

• molecules synthesized intracellularly and form huge cohesive agregartes outside of the cell

Fibroblasts

• Cells in the connective tissue that make collagen

• Produce most of the other macromolecules of the matrix

• molecules synthesized intracellularly and form huge cohesive agregartes outside of the cell

• Dr. Matt Buechler studies these!

Procollagen

• As mature collagens are designed to form huge aggreates inside of a osteo/fibroblast this could cause a cell to become chocked with its own products

• Therefore osteo/fibroplasts secrete this preliminary form of collagen that has additional peptide extensions at the end to obstrucutre the premature assembly into collagen fibrils