Chapter 20

Question 1

What is the ECM?

Answer 1

Extracellular matrix, structural component of tissues that influences their development and physiology

Question 2

What is the ECM made of (3)?

Answer 2

Structural components (collagen), adhesive glycoproteins (fibronectins), and matrix components (proteoglycans)

Question 3

What are the cells that live in the ECM?

Answer 3

connective tissue cells both inhabit and manufacture the ECM, and are called fibroblasts or osteoblasts (bone)

Question 4

In general, how are macromolecules added to the ECM?

Answer 4

synthesized internally, secreted by exocytosis, assemble into huge, cohesive aggregates

Question 5

Describe connective tissue?

Answer 5

tissues such as bone, tendons, and the dermis of the skin, in which ECM makes up the bulk of the tissue and carries the mechanical load

Question 6

Describe bone vs cartilage vs connective tissue

Answer 6

bone → hard and dense

cartilage → resilient and shock absorbing

connective tissue → flexible

Question 7

Define collagen

Answer 7

a helical triple-stranded fibrous protein that is a major component of the ECM and connective tissues

Question 8

Describe the structure of collagen (base unit → structure in tissues)

Answer 8

three collagen polypeptides wind around each other to form a ropelike superhelix

some of these assemble into fibrils, which can then pack into collagen fibers that are arranged both longitudinally and in a cross section

Question 9

How is collagen produced? What modifications are made?

Answer 9

Fibroblasts/Osteoblasts produce collagen molecules in a precursor form called procollagen with additional peptide extensions that prevent premature assembly

Extracellular enzymes called procollagen proteinases cut off the terminal extensions to allow assemble once in the extracellular space

Question 10

What is the purpose of collagen?

Answer 10

Provides tensile strength to resist stretching

Question 11

Define fibronectin

Answer 11

Extracellular matrix protein that helps cells attach to the matrix by acting as a linker, binding a cell-surface integrin molecule on one end and a matrix component (e.g collagen) on the other

Question 12

Describe the structure of fibronectin

Answer 12

Made of two polypeptides that are covalently bonded through disulfide bonds at their C-terminus

Question 13

Define integrins and describe their structure

Answer 13

Family of transmembrane proteins present on cell surfaces that enable cells to make/break connections to the ECM, allowing them to crawl through a tissue

Made of two heterodimers, 𝞪 and 𝜷

Question 14

Describe how integins are used in cell crawling. Include what their extracellular domain and intracellular domains bind to.

Answer 14

Cells can grab the ECM at their front end (focal adhesions or focal contacts) and release at the back end

Extracellular domain binds to fibronectin, intracellular domain binds to actin filaments

Question 15

What is the secondary role of integrins? (not cell crawling)

Answer 15

Also involved in signaling to cells when bound to ECM and responding from signals inside the cell, allowing them to change their adhesion to the ECM

Question 16

Define GAGs. What are they used for (when alone)?

Answer 16

GAGs (glycosaminoglycans) are polysaccharide chains that form a space filling gel in the ECM of connective tissue by attracting ions (and therefore water)

Help animal tissues resist compression and is tough and resilient

Question 17

Define proteoglycans

Answer 17

Molecules that have one or more GAG chains attached to a glycosylated core protein

Question 18

What are proteoglycans used for?

Answer 18

Aggregates can form gels that regulate the passage of molecules through the ECM and guide cell migration

Question 19

What is the basal lamina? What is its major/general purpose?

Answer 19

Thin, tough sheet of ECM secreted by epithelial cells, upon which the cells sit

Barrier between epithelial cells and connective tissue

Question 20

What is the basal lamina composed of? What are their roles?

Answer 20

Composed mainly of collagen and a protein called laminin

Laminin provides adhesive sites for integrin molecules in the basal plasma membranes of epithelial cells, and therefore serves a linking role similar to that of fibronectin

Question 21

Define epitheium

Answer 21

a sheet of cells covering an external surface or lining an internal body cavity creating a barrier between the tissue and the outside

Question 22

What is the general and specific role of tight junctions?

Answer 22

Hold cells together

Prevent the movement of water-soluble molecules and membrane proteins

Question 23

What are tight junctions made of?

Answer 23

Formed by claudins and occludins arranged in strands

Question 24

What is the general and specific role of adherens junctions?

Answer 24

Hold cells together

May form a continuous adhesion belt, connecting bundles of actin filaments from cell to cell

Question 25

What are adherens junctions made of?

Answer 25

Actin filaments tethered to many cadherin molecules

Question 26

What is the general and specific role of desmosome junctions?

Answer 26

Hold cells together

Join ropelike filaments of kerain (IFs) of adjoining cells by cadherin

Question 27

Describe keratin

Answer 27

a type of intermediate filament that provides tensile strength in epithelial cells

Question 28

What is the general role of hemidesmosomes?

Answer 28

Anchor epithelial cells to basal lamina

Question 29

What are hemidesmosomes made of?

Answer 29

Extracellular domains of integrins bind to laminin, intracellular domains bind to keratin (IF)

Question 30

Describe the “plaques” in desmosomes and hemidesmosomes

Answer 30

Both desmosomes and hemidesmosomes have electron-dense protein plaques between the keratin filaments and the cell membrane

Question 31

What is the general and specific role of gap junctions?

Answer 31

Hold cells together

Allows ions and small molecules to move directly from the cytosol of one cell to that of another, creating an electrical and metabolic coupling

Question 32

What are gap junctions made of?

Answer 32

Gap between cells is spanned by transmembrane protein connexons that lie in the plasma membrane of two apposed cells and are aligned end-to-end to form narrow, water-filled channels

Question 33

Define cadherin

Answer 33

Ca+2 dependent protein

Mediate the attachment of one cell to another in animal tissues in both adherens junctions and desmosomes

Question 34

How to cadherins work?

Answer 34

Cadherin molecule in the plasma membrane of one cell binds directly to an identical cadherin molecule in the plasma membrane of its neighbor