Ch.20 - Tissues, Stem Cells, Cancer Flashcards Preview

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Flashcards in Ch.20 - Tissues, Stem Cells, Cancer Deck (106)
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1

Summarize the general diffs b/w animal and plant tissue, partic wrt ECM.

Plants are sedentary: tissues are mostly rigid, although cells are weak/fragile if isolated fr ECM/cell wall.

  • Cell wall is a boxlike structure that encloses, protects, and constrains the shape of cells.
  • Common principle of tissue construction: many tiny cells attached t/g via CJs.

Animal tissues are more diverse.

  • Cells/ECM are orgz in many diff ways: some tissues (bone, tendon) have abundant ECM, others (muscle, epidermis) have scant ECM → cytoskeletons themselves carry mechanical load.

2

T/F: Plant cell cytoskeletons lack intermediate filaments.

True

Plant cell cytoskeletons lack tension-bearing ifils found in animal cells → have virtually no tensile strength of their own, i.e. rely almost entirely on cell wall for mech strength.

3

T/F: all cell walls are tough and rigid.

False

Cell wall is tough, but not always rigid: provides turgor pressure during osmotic swelling → forms semirigid tissue, e.g. a crisp lettuce leaf.

  • If water is lacking → cells shrink → leaf wilts.

4

Summarize the formation of three types of cell walls.

Most newly formed cells initially make relatively thin primary cell walls slowly expand (via osmotic swelling; turgor pressure) to accommodate cell growth.

A more rigid secondary cell wall is typ produced once cell growth stops—either by thickening of primary wall or by deposition of new layers w diff composition underneath.

Specialized cell walls form when plant cells become specialized, e.g. waxy, waterproof walls for surface epidermal cells of a leaf; hard, thick, woody walls for xylem cells of a stem; etc.

5

Like all ECMs, plant cell walls derive tensile strength fr ____ (long/short) fibers oriented ______ (along/perpendicular to) lines of stress.

Like all ECMs, plant cell walls derive tensile strength fr long fibers oriented along lines of stress.

6

In higher plants, long fibers of the cell wall are typ made fr _______, a type of _________.

In higher plants, long fibers of the cell wall are typ made fr cellulose, a type of polysaccharide.

  • E.g. woody tissue: highly cross-linked network of lignin (complex polymer of aromatic alcohol groups) is deposited w/i this matrix to make it more rigid and waterproof.

7

For plant cell to grow/change shape, cell wall must stretch/deform. Describe how cellulose microfibrils govern the orientation of growth.

Cellulose microfibrils resist stretching → orientation governs direction in wh growing cell enlarges.

  • I.e. turgor pressure is uniform in all directions → cell will elongate in direction perpendicular to orientation of microfibrils.
  • E.g. if arranged circumferentially → grows more readily in length than girth.

8

Cellulose is produced in radically diff way fr most other ECM components, wh are typ synth'd inside cell and exported by exocytosis. Explain how cellulose production differs.

Cellulose is synthd by enzymes embedded in pmem (cellulose synthase complex), wh xprt sugar monomers across pmem (in → out) and incorporate into set of growing polymer chains at their points of mem attachment on EC surface.

  • Ea set of chains assembles to form a cellulose microfibril.
  • Enzyme complexes move in mem → lay down trail of oriented cellulose microfibrils behind them.

9

Cellulose synthase complex moves laterally in pmem and lays down a trail of oriented cellulose microfibrils. What guides the path of this enzyme and thus controls plant cell shape/tissue modeling?

Path of enzyme complex is guided by mtubs just beneath pmem that are aligned exactly w EC cellulose microfibrils; i.e. serve as tracks for enzyme movement.

  • Thus, cytoskeleton controls shape of plant cell and modeling of tissues.

10

Cells in the stem of a seedling grown in the dark orient their mtubs horizontally. How would you expect this to affect growth?

Horizontal mtub orientation → horizontal cellulose microfibril orientation (deposited in cell walls) → vertical plant growth.

11

What are the four major types of tissues in animals? Wh type of tissue has distinct architecture?

Four major types of tissues in animals: connective, epithelial, nervous, and muscular; w conn tissue (CT) having distinct architecture.

  • In CT, ECM is plentiful and carries mechanical load; in other tissues, ECM is scant and cells are directly joined t/g and carry mech load thru cytoskeleton.

12

Animal CTs are enormously varied: can be tough/flexible (tendons, dermis), hard/dense (bone), resilient/shock-absorbing (cartilage), or soft/transparent (vitreous humor of eye).

Regardless, bulk of tissue is _______. In all CT, tensile strength—whether great or small—is chiefly provided by ________.

Animal CTs are enormously varied: can be tough/flexible (tendons, dermis), hard/dense (bone), resilient/shock-absorbing (cartilage), or soft/transparent (vitreous humor of eye).

Regardless, bulk of tissue is ECM. In all CT, tensile strength—whether great or small—is chiefly provided by collagen (a fibrous protein).

  • Various types of collagen (and interwoven molecules) → various types of CT.
  • E.g. elastin is interwoven w collagen of ECM of arterial walls → provide flexible resilience as blood pulses thru.

13

________ provides tensile strength in animal CT.

Collagen provides tensile strength in animal CT.

  • Long, stiff, triple-helical structure of collage polypeptide chains.
  • Collagen fibrils are ordered polymers of collagen → can pack into still thicker collagen fibers.
  • Other types of collagen decorate the surface of collagen fibrils and link fibrils t/g and to other components in ECM.

14

Mutations in genes encoding collagens are often detrimental, partic those that effect glycines, wh are reqd at every third position in collagen polyp chain to assemble into triple-helical rod.

Would you expect collagen mutations to be detrimental if only one of the two copies of a collagen gene is defective?

As three collagen chains have to come t/g to form triple helix, a defective molecule will impair assembly, even if normal collagen chains are present at same time. Therefore, collagen mutations are dominant; that is, they have a deleterious effect even in presence of a normal copy of the gene.

15

Mutations in genes encoding collagens are often detrimental, partic those that effect glycines, wh are reqd at every third position in collagen polyp chain to assemble into triple-helical rod.

A puzzling observation is that the change of a glycine residue into another AA is most detrimental if it occurs toward amino terminus of the rod-forming domain. Suggest an explanation.

Diff severity of mutations results fr polarity in assembly process. Collagen monomers assemble into triple-helical rod starting fr their amino-terminal ends. A mutation in an “early” glycine therefore allows only short rods to form, whereas a mutation farther downstream allows for longer, more normal rods.

16

CT cells that manufacture/inhabit ECM are named according to tissue, such as _________ in skin/tendon/other CTs and _________ in bone.

CT cells that manufacture/inhabit ECM are named according to tissue, such as fibroblasts in skin/tendon/other CTs and osteoblasts in bone.

17

Fibro/osteoblasts synth collagen, in its precursor form, as well as other macromolecules of ECM → secreted → assemble into huge, cohesive aggregates.

Describe the precursor form of collagen, and what would happen if collagen was instead synth'd directly.

Fibro/osteoblasts synth collagen, in its precursor form of procollagen, as well as other macromolecules of ECM → secreted → assemble into huge, cohesive aggregates.

  • Procollagens contain unstructured extensions at ea end that obstruct premature assembly into collagen fibrils → secreted → emerge into EC space → procollagen proteinases cleave extensions to enable assembly.
  • If collagen was synthd directly, assembly would occur before secretion → cell would become choked w own products.

18

For tissues to grow, repair, and renew cells, or to allow migratory cells (e.g. macrophages) to burrow thru, tissue cells must also degrade ECM, often thru __________ (enzyme).

For tissues to grow, repair, and renew cells, or to allow migratory cells (e.g. macrophages) to burrow thru, tissue cells must also degrade ECM, often thru matrix proteases.

  • Also play part in many disease processes, e.g. arthritis (break down cartilage) and cancer (help cancer cells invade normal tissue).

19

Orientation of collagen fibrils fits function and is det by CT cells that synth collagen. Describe how fibril orientation fits function in skin vs tendons.

Skin - fibrils are woven in wickerwork pattern, or in alt layers w diff orientations so as to resist tensile stress in multiple directions.

Tendons (muscle to bone) - fibrils are aligned in parallel bundles along major axis of tension.

20

Fibroblasts influence alignment of collagen fibers, and collagen fibers in turn affect distribution of fibroblasts. Explain.

Fibro/osteoblasts first deposit collagen in an oriented fashion, then rearrange. I.e. during tissue dev, fibroblasts secrete collagen then crawl over and pull on it → compact it into sheets and draw it out into cables.

21

________ are xmem receptor proteins that couple the ECM to the cytoskeleton, while ______ are ECM proteins that provide linkage to collagen.

Integrins are xmem receptor proteins that couple ECM to cytoskeleton, while fibronectins are ECM proteins that provide linkage to collagen.

  • Cells do not attach well to bare collagen; req linkage via fibronectin.

22

Formation/breakage of attachments on either end of integrin enable cell to crawl thru tissue → attach ECM at its front end and releasing its grip at rear.

Describe how integrins coord cell movement thru signif conform changes.

Integrin's EC domain binds fibronectin → IC domain binds (thru set of adaptor molecules) to mfil (actin).

Binding fibronectin (and EC collagen) causes integrin to stretch out into an extended, activated state → can latch onto actin on IC side, and vice-versa.

  • I.e. IC signal can activate integrin fr cytosolic side → integrin extends/attaches EC struc, e.g. collagen. Likewise, binding an EC structure can activate IC signal paths (e.g. protein kinases) that assoc w IC side of integrin.

23

Collagen provides tensile strength (resists stretching), but _________________ resist compression.

Collagen provides tensile strength (resists stretching); glycosaminoglycans (GAGs) resist compression.

  • Neg charged polysacch chains.
  • Covalently link to ECM proteins → proteoglycan.
  • Strongly hphilic → osmotically active: attract cations (Na+) and form extended conforms → high volume-to-mass ratio, i.e. "space-fillers".
    • Swelling pressure counterbalanced by tension fr interwoven collagen fibers.
    • GAG-to-Collagen ratio is small in dense, compact tissue (tendon, bone) and high in jelly-like tissue (aqeous humor).
  • Proteoglycans also bind secreted EC signals and regulate their passage thru ECM; imp in cell differentiation.

24

GAGs are _____ (neg/pos) charged ________ (polysacch/polypep) chains made of repeating ______ (disacch/di-peptide) units; typ ________ (non/covalently) linked to core proteins to form ________, wh are v diverse in size, shape, and chemistry.

GAGs are negatively charged polysacch chains made of repeating disacch units; typ covalently linked to core proteins to form proteoglycans, wh are v diverse in size, shape, and chemistry.

  • Typ, many GAG chains are attached to single core protein → linked at one end to another GAG, creating enormous aggregate resembling a bottlebrush.

25

In wh type of tissues are glycosaminoglycans (GAGs) more abundant: bone or the aqueous humor of the eye?

GAGs are more abundant in aqueous humor.

  • Typ, GAGs are strongly hphilic and tend to adopt highly extended conforms → occupy huge volume relative to mass → “space fillers” in ECM of CTs.
  • In dense, compact CTs (tendon, bone), proportion of GAGs is small, ECM consists almost entirely of collagen (or, collagen w Ca2+-Phos crystals in bone).
  • In jelly-like humor in interior of eye, abundant GAG (plus water) and only small amount of collagen.

26

Even at v low concens, GAGs form hphilic gels: multiple neg charges attract cloud of cations (chiefly Na+) that are osmotically active, i.e. draw large amount of water to ECM → swelling pressure → balanced via tension in collagen fibers interwoven w proteoglycans.

In what type of tissue might an ECM rich in collagen and a large qty of GAGs be desireable?

In tough, resilient, compression-resistant CT (cartilage matrix of knee joint), ECM is rich in collagen w large qty of GAGs trapped in meshwork → enormous swelling pressure and counterbalancing tension.

27

Proteoglycans are characterized by the abundance of negative charges on their sugar chains. How would these props differ if negative charges were not as abundant?

The remarkable ability to swell and thus occupy a large volume of space deps on negative charges, wh attract a cloud of cations (chiefly Na+) → draw in large amounts of water (via osmosis) → give proteoglycans unique props.

Uncharged polysacchs such as cellulose, starch, and glycogen, by contrast, are easily compacted into fibers or granules.

28

_______ are sheets in wh cells are joined t/g side-to-side; may be many cells thick (stratified, e.g. epidermis) or only one cell thick (gut lining).

Epithelia are sheets in wh cells are joined t/g side-to-side; may be many cells thick (stratified, e.g. epidermis) or only one cell thick (gut lining).

  • Many forms: tall (columnar), squat (cuboidal), or fat (squamous).

29

T/F: w/i a given sheet, all epithelial cells are of the same type.

False

W/i given sheet, cells may be all the same type or a mix.

  • Functions vary: some protect, some secrete specialized products (hormones, milk, tears), absorb nutrients (e.g. gut lining), or detect signals (e.g. photoreceptors, hair cells).

30

Epithelial sheets are ______ (non/polarized) and rest on a ___________.

Epithelial sheets are polarized and rest on a basal lamina.

  • An epithelial sheet has two faces: apical surface is free/exposed to EC space (air/watery fluid); basal surface is attached to a sheet CT (basal lamina).