Week 11 Textbook

Question 1

what are tissues

Answer 1

cooperative assembly of cells and matrix woven together to form a distinctive multicellular unit with a certain function
nervous, muscular, epithelial, connective

Question 2

what is the extracellular matrix

Answer 2

complex network of polysaccharides and proteins secreted by cells
a structural component of tissues that also influence their development and physiology
cellulose, collagen

Question 3

explain the function of the cell wall

Answer 3

mechanically strong fibrous outer layer that animals do not have
they protect, immbolilze and shape the cells

Question 4

what is the turgor pressure

Answer 4

the driving force for cell growth = swelling pressure
it develops the osmotic imbalance between the interior of the plant cell and its surroundings

Question 5

explain how the cell wall in plants is essentially formed

Answer 5

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

Question 6

what are cellulose microfibrils

Answer 6

long, thin, polysaccharide fiber that helps strengthen plant cell walls

Question 7

explain the structure of cellulose

Answer 7

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

Question 8

explain how cellulose is produced in most extracellular macromolecules

Answer 8

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

Question 9

what are connective tissues

Answer 9

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

Question 10

t/f the various kinds of connective tissues are due to the type of collagen they contain

Answer 10

true
a variety of specialize polysaccharide molecules give other connective tissues their distinctive properties

Question 11

what is the rubbery protein in arteries

Answer 11

elastin
makes the vessel withstand high pressure of blood

Question 12

explain the structure and function of collagen

Answer 12

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

Question 13

what are osteoblasts and fibroblasts

Answer 13

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

Question 14

how does collagen strands stop from assembling prematuraly

Answer 14

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

Question 15

what happens when incorrect collagen assembly occurs

Answer 15

skin = hyperextensible
elastic skin
can be caused by the defect in procollagen or the enzyme that converts the procollagen to collagen

Question 16

how does fibroblast influence the alignment of collagen fibers

Answer 16

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

Question 17

what are integrins

Answer 17

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)

Question 18

what are fibronectins

Answer 18

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

Question 19

what is the disease leukocyte adhesion deficiency caused by

Answer 19

integrin on leukocytes (WBCs) help the cells crawl out of the blood vessel when there is an infection
lacking these integrins = this disease

Question 20

what is the other group of macromolecules in the extracellular matrix of animal tissues that provide the function of resisting compression

Answer 20

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

Question 21

t/f there is high proportions of GAGs in connective tissues like tendon, bone

Answer 21

false
small proportion
large proportion of collagen

Question 22

t/f there is a high proportion of GAG in jellylike substances

Answer 22

true
small amounts of collagen
GAGs are strong hydrophilic
they are space fillers in the extracellular matrix of connective tissues

Question 23

how does the matric balance swelling

Answer 23

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

Question 24

what are the other functions of proteoglycans besides hydrating spaces around cells

Answer 24

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

Question 25

t/f the matrix can affect how cells behave and the cells can shape the matrix as well

Answer 25

true interactions with cell development and tissue structure

Question 26

which type of tissues are fibroblast the major cellular component

Answer 26

connective tissue

Question 27

what is the epithelium

Answer 27

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

Question 28

what are the 4 ways cells can be packaged together in the epithelial sheet

Answer 28

1. columnar - stretched out vertically 2. squamous - lined and compressed vertically 3. cuboidal - lining 4. stratified - large sheets of many cells compact together and thin

Question 29

what are the 2 faces on the epithelial sheet

Answer 29

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

Question 30

what is the basal lamina made out of

Answer 30

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

Question 31

what line the faces of the simple columnar epithelium that is in the small intestine

Answer 31

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

Question 32

what are cell junctions

Answer 32

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

Question 33

what are tight junctions

Answer 33

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

Question 34

t/f tight junctions maintain the polarity of the epithelial cells

Answer 34

true the tight junctions on the apical region prevent diffusion of proteins in the plasma membrane so keeping the contents separate

Question 35

what are the three types of junctions that form strong mechanical attachements

Answer 35

1. adherens junctions 2. 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

Question 36

what transmembrane protein are built around adherens junctions and desmosomes

Answer 36

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 -

Question 37

explain adherens junctions

Answer 37

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

Question 38

how does a sheet of epithelial cells form into a tube

Answer 38

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

Question 39

what is a desmosome

Answer 39

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

Question 40

what are hemidesmosomes

Answer 40

anchor the keratin filaments in a epithelial cell to the basal lamina

Question 41

what are gap junctions

Answer 41

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

Question 42

explain the dye injected in the retina of the rabbit neuron

Answer 42

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

Question 43

t/f plants have all the same cell junctions that animals have

Answer 43

false they do not have any but they have a similar structure to gap junctions like plasmodesmata

Question 44

what is plasmodesmata

Answer 44

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

Question 45

what is the order of the junctions in epithelial cells

Answer 45

tight junctions adherens junctions desmosomes gap junctions hemidesmosomes

Question 46

what are the cell to cell anchoring junctions

Answer 46

adherens junctions desmosomes

Question 47

what are cell-extracellular matrix anchoring junctions

Answer 47

hemidesmosomes

Question 48

what are tight junctions

Answer 48

creates a tigh seal between cells to prevent the extracellular environments prevents mixing of membrane proteins - apical and basolateral are kept separate

Question 49

what are tight junctions composed of

Answer 49

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

Question 50

what is the main purpose of anchoring junctions (desmosomes + aderens, hemidesmosomes)

Answer 50

to provide mechanical strength by linking cytoskeletons of neighboring cells together the hemidesmosomes link the cytoskeleton to the basal lamina

Question 51

what are the transmembrane adhesion proteins

Answer 51

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

Question 52

explain what adherens junctions are

Answer 52

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

Question 53

explain desmosomes and hemidesmosomes

Answer 53

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

Question 54

explain the structure of desmosomes

Answer 54

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)

Question 55

explain the structure of hemidesmosomes

Answer 55

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

Question 56

explain the structure of gap junctions

Answer 56

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

Question 57

t/f gap junctions are gated

Answer 57

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)

Question 58

t/f plant cells do not have the same cell junctions

Answer 58

true they have cell wall which provides most of their strength they do have plasmodesmata

Question 59

what is plasmodesmata

Answer 59

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

Question 60

how does the gating work in plasmodesmata

Answer 60

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)

Question 61

what is the layering of animal cells

Answer 61

epithelium basal lamina connective tissue

Question 62

what is the epidermis

Answer 62

the outer layer of the surface such as the skin

Question 63

compare connective tissue and epithelial tissue

Answer 63

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

Question 64

what are the 3 major classes of macromolecules in the EXCM

Answer 64

1. glysoaminoglycans (GAGs) and proteoglycans 2. fibrous proteins - collagens, elastin 3. glycoproteins - laminin, fibronectin

Question 65

t/f EXCM gives tissues its different properties

Answer 65

true it is the primary component in the connective tissues and has different compositions to give different tissue properties

Question 66

what are GAGs

Answer 66

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

Question 67

what is hyaluronan

Answer 67

a simple GAG synthesizes in PM long repeating disaccharide subunits very large attracts Na+ makes lots of gel

Question 68

explain proteoglycans

Answer 68

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

Question 69

what is collagen

Answer 69

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

Question 70

how do cells interact with collagen in the EXCM

Answer 70

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

Question 71

what is elastin

Answer 71

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

Question 72

explain the basal lamina

Answer 72

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

Question 73

what is the basal lamina made out of

Answer 73

laminin (glycoprotein) type 4 collagen (fibrous protein) integrin (transmembrane adhesion protein)

Question 74

what are the main components of the plant cell wall

Answer 74

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