Week 11 Textbook Flashcards
what are tissues
cooperative assembly of cells and matrix woven together to form a distinctive multicellular unit with a certain function
nervous, muscular, epithelial, connective
what is the extracellular matrix
complex network of polysaccharides and proteins secreted by cells
a structural component of tissues that also influence their development and physiology
cellulose, collagen
explain the function of the cell wall
mechanically strong fibrous outer layer that animals do not have
they protect, immbolilze and shape the cells
what is the turgor pressure
the driving force for cell growth = swelling pressure
it develops the osmotic imbalance between the interior of the plant cell and its surroundings
explain how the cell wall in plants is essentially formed
primary cell wells are first made, they can slowly expand to accommodate cell growth
more rigid secondary cell wall is produced by thickening the primary cell wall or by the deposition of new layers with a different composition underneath the old ones
- when they come specialized they can have more adapted types of cell walls like wax, waterproof ability, hard, think, woody walls for xylem cells of the stems
what are cellulose microfibrils
long, thin, polysaccharide fiber that helps strengthen plant cell walls
explain the structure of cellulose
long unbranched chains of glucose, each glucose unit is linked to the adjacent with their 1 and the others 4
they stack on top of each other to make a cellulose microfibril and hydrogen bonding between each microfibril hold it in place
- cellulose microfibrils provide tensile strength- resisted stretching
- when turgor pressure becomes uniform in all directions of a cellulose microfibrils, each cell tends to elongate in a direction perpendicular to the orientation of the microfibrils = great tensile strength
explain how cellulose is produced in most extracellular macromolecules
they can be synthesixed on the outer surface of the cell by enzyme complexes which are embedded in the plasma membrane
these complexes activate glucose monomers in from of UDP-glucose and incorporate them into a growing chain of cellulose chains to make a cellulose microfibril
the complex dictates the orientation in which cellulose deposits in the cell wall
- microtubules serve as track on the inside of the cell to help direct the movement of the enzyme complexes
the complexes are connected to the MT via connector proteins
what are connective tissues
tissues such as bone, tendons, the dermis of the skin
its where extracellular matric makes up the bulk of the tissue and carries the mechanical load
t/f the various kinds of connective tissues are due to the type of collagen they contain
true
a variety of specialize polysaccharide molecules give other connective tissues their distinctive properties
what is the rubbery protein in arteries
elastin
makes the vessel withstand high pressure of blood
explain the structure and function of collagen
triple stranded helical fibrous protein that is the major component of extracellular matrix and connective tissues
long, stiff, wrap around each other like a rope
abundant protein in animal tissues and can be in different forms in skin, tendon, bone, cartilage and vessels
some types of collagen molecules turn into collagen fibrils which are thin cables that pack together to make a thicker collagen fiber
what are osteoblasts and fibroblasts
a type of collagen that lives in the connective tissue in the extracellular matrix
they are in the bone and called osteoblasts or in the skin/tendon and other connective tissues called fibroblasts
how does collagen strands stop from assembling prematuraly
since they are made in the intracellular matric of a vesicle, they can prematurely bundle up into fibril - they have precursor forms called procollagen which has additional peptide extensions at each end that obstruct premature assembly into collagen fibrils
extracellular enzymes called procollagen proteinases cut off these terminal extensions to allow the assembly of the collagen fibril only after they move into the extracellular matrix
what happens when incorrect collagen assembly occurs
skin = hyperextensible
elastic skin
can be caused by the defect in procollagen or the enzyme that converts the procollagen to collagen
how does fibroblast influence the alignment of collagen fibers
during development of the tissue, they work on the collagen they have secreted by crawling over and pulling on it to help compact it into sheets and pull into cables
- when fibroblast are on a randomly oriented meshwork of collagen fibrils they tug on it and compact it
fibroblast migration is also important in healing wounds
what are integrins
one of the families of transmembrane proteins on the cell surface that enable cells to make and break attachments to the extracellular matrix, helping them crawl thru the tissue
integrins do not directly interact with collagen fibers
has a alpha and a beta subunit side by side inside the plasma membrane
activated state can be triggered by binding to an extracellular matrix molecule such as fibronectin or intracellular adaptor proteins (adaptor + actin)
what are fibronectins
extracellular matrix protein that help cells attach to the matric by acting as a linker that binds to the cell surface integrin molecule on one end and to the matrix component like collagen on the other end
the fibronectin binds to the integrins via adaptor proteins to an actin filament inside the cell
for many cells it is the formation and breakage of these attachments on either end of the integrin molecule that allows the cell to crawl thru the tissue
integrins undergo these conformational changes - when binding to a molecule on one side of the plasma membrane, it causes the integrin to stretch out and extend (activated) so that the on the other side they can latch
binding to an external structure can switch on alot of intracelluar signalling pathways by activating protein kinases that associate with the intracellular end of the integrin
what is the disease leukocyte adhesion deficiency caused by
integrin on leukocytes (WBCs) help the cells crawl out of the blood vessel when there is an infection
lacking these integrins = this disease
what is the other group of macromolecules in the extracellular matrix of animal tissues that provide the function of resisting compression
as collagen resists stretching, glycosaminoglycans (GAGs) are negatively charged polysaccharide chains made of repeating disaccharide units
- they form a gel that acts as a space filler in the extracellular matrix of connective tissues
chains of GAGs are covalently linked to a core protein to = proteoglycans
alot of GAG chains bind to one protein and then link to another GAG chain
EX: aggrecan in cartilage has lots of GAG chains on a single core protein
- chains of GAG all around a core protein attached via linker protein
t/f there is high proportions of GAGs in connective tissues like tendon, bone
false
small proportion
large proportion of collagen
t/f there is a high proportion of GAG in jellylike substances
true
small amounts of collagen
GAGs are strong hydrophilic
they are space fillers in the extracellular matrix of connective tissues
how does the matric balance swelling
GAGs are negatively charged –> which also attract + charges like Na+ –> attracts water –> swelling pressure
balanced by tension in collagen fibers that are woven with the GAGs
when you have alot of collagen and GAGs the swelling and tension are both strong making the matrix tough, springy, hard to compress - like the cartilage in ur knee
what are the other functions of proteoglycans besides hydrating spaces around cells
they form gels with different sizes and charges that act like filters
they help control what molecules move thru the area
bind to growth factors and signals that help cells respond to their environment
help guide or block how cells move
t/f the matrix can affect how cells behave and the cells can shape the matrix as well
true
interactions with cell development and tissue structure
which type of tissues are fibroblast the major cellular component
connective tissue
what is the epithelium
sheets of cells covering an external surface or lining an internal body cavity
sometimes it can be thick or stratified as in the epidermis like the outer layer of the skin or it can be a simple epithelium which is only one cell thick - lining of our gut
some might be for protection like the epidermis, some line the gut and absorb nutrients, sense light, sense sound
what are the 4 ways cells can be packaged together in the epithelial sheet
- columnar - stretched out vertically
- squamous - lined and compressed vertically
- cuboidal - lining
- stratified - large sheets of many cells compact together and thin
what are the 2 faces on the epithelial sheet
apical surface is free and exposed to the air or bodily fluids (if lining internal structures)
basal surface is attached to a thin, tough, sheet of extracellular matrix = basal lamina
what is the basal lamina made out of
supportive fibrous mat that is made up of specialized collagen and a protein called laminin
provides adhesive sites for integrin molecules in the basal plasma membranes of epithelial cells
- serves as a linking role
what line the faces of the simple columnar epithelium that is in the small intestine
contains absorptive cells which take up nutrients and goblet cells which secrete mucus that protects and lubricates the gut lining
the absorptive cells import food molecules from the gut lumen through their apical surface and export these molecules from their basal surface into the underlying tissues - need different membrane transport proteins in their apical and basal plasma membranes
both surfaces are polarized - but it depends on the junctions that the cells form with one another and with the basal lamina
what are cell junctions
provide a tight seal to prevent the leakage of molecules across the epithelium thru the haps between its cells
- some provide mechanical attachments
- some provide intercytosolic exchange
what are tight junctions
barrier function
seal neighboring cells together so that water-soluble molecules cannot easily leak between them
they are formed by proteins called claudins and occludins which are arranged in strands along the lines of the junction to create the seal
without tight junctions - pumping activities of absorptive cells would not work and the extracellular fluid would become the same on both sides of the epithelium
t/f tight junctions maintain the polarity of the epithelial cells
true
the tight junctions on the apical region prevent diffusion of proteins in the plasma membrane so keeping the contents separate
what are the three types of junctions that form strong mechanical attachements
- adherens junctions
- desmosomes
- bind one epithelial cell to another
3. hemidesmosomes - binds epithelial cells to the basal lamina
- proteins that form the junction span the entire plasma membrane and are linked inside the cell to cytoskeletal filaments which extend the networking from one cell to another in a sheet
what transmembrane protein are built around adherens junctions and desmosomes
cadherins family
- cadherin molecule binds directly to an identical cadherin molecule in the plasma membrane of the adjacent cell
= homophilic binding - binding to the same molecule
to bind in the extracellular fluid between the 2 cells side by side, there needs to be Ca2+ present
-
explain adherens junctions
holds together epithelial cells in a sheet of epithelium - actin filaments inside the cell attach to its cytoplasmic face
each cadherin molecule is tethered inside the cell with linker proteins binded to actin filaments
- they usually form a continuous adhesion belt around each of the interacting epithelial cells - the belt is near the apical end of the cell
- bundles of actin filaments are thus connected from cell to cell across the epithelium
how does a sheet of epithelial cells form into a tube
tightening along adhesion belts in selected regions of cell sheet, starts to bend into a circle
- epithelial tube pinches off from overlying sheet of cells into epithelial tubes to form into neural tubes - common in embryological development
what is a desmosome
formed between 2 epithelial cells that connect the rope like kertain filaments of the joining cells together - providing tensile strength
in between = intercellular space between 2 plasma membranes = cadherin proteins
the keratin filaments are anchored to cytoplasmic plaque
- this is not enough for epidermal cells to be firmly attached to each other - they need to be anchored securely to the underlying connective tissue
what are hemidesmosomes
anchor the keratin filaments in a epithelial cell to the basal lamina
what are gap junctions
regions where the 2 plasma membranes lie close together with a very narrow gap
the gap is not empty, it has transmembrane protein complexes called connexons
the cytosolic channel allows inorganic ions and small water soluble molecules to move directly from the cytosol of one cell to the next
creates electrical and metabolic coupling between the cells - composed of 6 protein subunits
*the junctions can be closed or open depending on the extracellular or intracellular signals like neurotransmitters = dopamine reduces the gap junction communication between certain neurons in the retina when responding to an increase in light intensity
the reduction in the gap allows a pattern of electrical signalling and helps the retina switch from using rod to cones which are better in colour
explain the dye injected in the retina of the rabbit neuron
before dopamine - the dye can allow us to visualize all the branches and axons bc it diffuses rapidly between the gap junctions
- after dopamine is injected into 1 cell only, the dye allows us to visualize only the one injected because the dopamine closed the gap junctions - allowing no nutrients or dopamine to flow from that injected cell to the adjacent
t/f plants have all the same cell junctions that animals have
false
they do not have any
but they have a similar structure to gap junctions
like plasmodesmata
what is plasmodesmata
in plant cells, the cytoplasm of adjacent cells are connected via plasmodesmata
the cytoplasm is continuous between one cell to the next
this allows the passage of small and some larger molecules including proteins and regulatory RNA to flow between
this
what is the order of the junctions in epithelial cells
tight junctions
adherens junctions
desmosomes
gap junctions
hemidesmosomes
what are the cell to cell anchoring junctions
adherens junctions
desmosomes
what are cell-extracellular matrix anchoring junctions
hemidesmosomes
what are tight junctions
creates a tigh seal between cells to prevent the extracellular environments
prevents mixing of membrane proteins - apical and basolateral are kept separate
what are tight junctions composed of
2 transmembrane proteins = claudin and occludin
needed in both cells
homophilic binding meaning that they bind to themselves on the adjacent cell
claudin - claudin
occludin-occludin
what is the main purpose of anchoring junctions (desmosomes + aderens, hemidesmosomes)
to provide mechanical strength by linking cytoskeletons of neighboring cells together
the hemidesmosomes link the cytoskeleton to the basal lamina
what are the transmembrane adhesion proteins
the EXC has the adhesion proteins from the neighboring cell or from the basal lamina (EXC)
the intracellular domina interacts with the linker proteins
they link transmembrane adhesion proteins to cytoskeletal filaments
EX: cadherins for aderens junctions
explain what adherens junctions are
form an adhesion belt
the transmembrane adhesion proteins = cadherins
the proteins interact with each other in the EXC as both have cadherins sticking out
- link cadherin proteins to actin filaments
- homophobic interactions with cadherins
explain desmosomes and hemidesmosomes
they link intermediate filaments
like keratin filaments
- most strength
intermediate provides the most structural strength
desmosomes: link to keratin filaments that connect to the neighbouring cell
hemidesmosomes: anchor keratin filaments to the basal lamina
explain the structure of desmosomes
they have specific cadherin family members called desmoglein and desmocollin
which bind homophilic (to each other same)
and bind to can also be heterophilic (to one another)
then there’s intracellular linker proteins that link the desmoglein and desmocollin to the keratin filaments inside the cell (IF)
explain the structure of hemidesmosomes
transmembrane adhesion proteins
- integrins - bind to laminin in the basal lamina
with intracellular linker proteins that link the integrins to keratin filaments inside the cell
explain the structure of gap junctions
allow for communication between cells
cell to cell opening pores
- cytosol of one connects to the cytosol of the other
1 monomer = connexin
6 connexions - form connexin (hemichannel)
2 connexions form intercellular channel
the 2 connexions line up
- they pass ions and metabolites and exchange materials - any can pass thru its not selective
although large molecules like proteins,nucleic acids and macromolecules cannot
t/f gap junctions are gated
true
they can be in the open or closed state by extracellular or intracellular signals
- dopamine closes the gap junctions
- increase in Ca2+ inside the cell closes gap junction (to prevent the imbalance from occurring to the neighboring cells)
t/f plant cells do not have the same cell junctions
true
they have cell wall which provides most of their strength
they do have plasmodesmata
what is plasmodesmata
allows communication between plant cells
gaps between the cells - different structure than gap junctions
- links cytoplasm together (gap junctions linked cytosol tg)
- creates a continuous plama membrane and ER across plasmodesmata
*small sugars, ions and nutrients can pass thru easily - larger molecules = controlled gating like proteins, RNAs, etc
how does the gating work in plasmodesmata
blocking movement of larger soluble molecules
callose is a deposition in the cell wall = plant polysaccharide
- controls how closed or narrow the spacing between the 2 cells are
(callose builds up in the corners of the cell wall)
what is the layering of animal cells
epithelium
basal lamina
connective tissue
what is the epidermis
the outer layer of the surface
such as the skin
compare connective tissue and epithelial tissue
epithelial: intestinal lining
- cells are close together and attached to each other
- has a think basal lamina with cytoskeletal filaments for mechanical stress
connective tissue: bone, tendon, cartilage
- not connected
- attached to the EXCM
- the EXCM provides resistance to mechanical stress
EX: fibroblast
what are the 3 major classes of macromolecules in the EXCM
- glysoaminoglycans (GAGs) and proteoglycans
- fibrous proteins - collagens, elastin
- glycoproteins - laminin, fibronectin
t/f EXCM gives tissues its different properties
true
it is the primary component in the connective tissues
and has different compositions to give different tissue properties
what are GAGs
glycosaminoglycans
- long, linerar chains of repeating disaccharide
very negatively charged so it attracts Na+ and h2o
they form hydrated gels and become space-filling and resist compression
- synthesizes in the Golgi and moved to EXCM by exocytosis
what is hyaluronan
a simple GAG
synthesizes in PM
long repeating disaccharide subunits
very large
attracts Na+
makes lots of gel
explain proteoglycans
subclass of glycoproteins
protein + sugar chain that must be a GAG
form aggregate which is the hyaluronan long chain with multiple aggrecans sticking out (composed of protein + GAG) attached with linker proteins
what is collagen
fibrous protein
provides tensile strength
resists stretching
- makes up extracellular components
3 chains wound up around each other in a triple helix –> collagen fibril –> pack together into collagen fibres
secreted as procollagen by fibroblasts (skin, bone) and osteoblasts (bone)
- once the procollagen is secreted outside it is processed to become mature collagen fibril
- in a vesicle, has protective ends (procollagen), once released from vesicle proteinase cleaves terminal procollagen extensions and self assembles into fibril in EXCM
how do cells interact with collagen in the EXCM
attached to the plasma membrane are integrin dimers which attach to fibronectin that holds the collagen fibril
the integrin dimer is a transmembrane protein attached to the actin filaments via adaptor proteins inside the cell
on the fibronectin there is an area where the integrin domain binds and where the collagen fibril domain binds
what is elastin
it is a connective tissue in the EXCM
it is a fibrous protein
networks of elastin gives tissue elasticity to stretch and relax = resilience
covalently attached to lots of other elastic = curled meshwork
when relax it bunches up and stretched it straightens up
explain the basal lamina
specialized type of EXCM
under all epithelial cells
influences the cell polarity
- separated the epithelial from tissue
- prevents fibroblasts in underlying connective tissue from interacting with epithelial cells
- anchored by hemidesmosomes
- links integrins to collagen
can be supporting different shapes of epithelial cells like:
- columnar, squamous, cubodial
stratified
what is the basal lamina made out of
laminin (glycoprotein)
type 4 collagen (fibrous protein)
integrin (transmembrane adhesion protein)
what are the main components of the plant cell wall
cellulose, pectin (hydrating gel - meshwork)
cellulose microfibrils provide tensile strength
pectin - space-filling and provides resistance to compression
cellulose synthase complex makes many cellulose molecules and assembled them into microfibril (being added to preexisting wall)
- the MT attach the cellulose tubes to the plasma membrane
