cell biology 8

Question 1

what is the extracellular matrix

Answer 1

complex network of macromolecules between cells
- cells make, organise and degrade it

Question 2

what is the functions of the extracellular matrix

Answer 2

• connects cells
• provides support
• regulates cellular survival, development, migration, proliferation, shape and function

Question 3

what are the major classes of macromolecules

Answer 3

• glycosaminoglycans - large, linear, charged proteoglycans
• fibrous proteins - collegen and elastin
• glycoproteins - asparagine- linked oligosaccharides

Question 4

what are glycosaminoglycans (GAGs)

Answer 4

• contain unbranched polysaccharides
• have amino sugars and acidic disaccharide repeats
• long and linear

Question 5

what is the example of a GAG and what is its function

Answer 5

• aggrecan
• have over 100 GAG chains
• major component of cartilage
• can aggregate along hyaluronan molecules

Question 6

what is the structure of basal lamina

Answer 6

• thin layer of specialised extracellular matrix
• lies beneath all epithelial cells

Question 7

what is the function of Basel lamina

Answer 7

• determine cell polarity
• influence cell metabolism
• organise the proteins in adjacent plasma membranes
• promote cell survival, proliferation and differentiation in tissue repair
• highway for cell migration

Question 8

what is laminin

Answer 8

• heterotrimeric glycoprotein - alpha, beta and gamma chains
• primary organiser of the basal lamina

Question 9

that does the basal lamina do in the kidneys glomerulus

Answer 9

• selective filter
• prevents macromolecule loss in urine

Question 10

what happens to the kidney glomerulus when having diabetes

Answer 10

• selective permeability lost
• globular basement thickening
• messangial hyperthrophpy and ECM deposition

Question 11

what are cell matrix adhesion complex made from and what are they used for

Answer 11

• 8 different beta chain genes and 18 different alpha chain genes
• binding to matrix ligands affected by Ca and Mg concentration
• linked to cell cytoskeleton
• some cells need to be attached to ECM to survive

Question 12

where are actin linked cell matrix junctions found

Answer 12

Cellular: Actin filaments
Cellular adaptors: Vinculin, Talin, kindlin
Cell membrane: Integrin
Extracellular Matrix: ECM Proteins

Question 13

where are hemidesmosomes found

Answer 13

• Common in epithelial cells
  Cellular: Intermediate filaments
  Cellular adaptors: Plectin, BP230
  Cell membrane: Integrin, Collagen XVII
  Extracellular Matrix: Lamin

Question 14

what is cell intergrins functions

Answer 14

• Integrins are either active or inactive
• Need to switch between the two to move a cell
• Regulated by GPCR signalling
• Note talin unwinding as a mechanical sensor

Question 15

what are matrix metalloproteinases

Answer 15

• enzymes that degrade ECM
• produced as zymogens - inactivated form

Question 16

what is the function of Matrix metalloproteinases

Answer 16

allows:
- cell penetration
- cell migration
- angiogenesis
- tissue remodelling

Question 17

what are the stages of cell migration

Answer 17

1) Actin polymerisation → protrusion
2) Engorgement of the protruding region
3) Retraction of actin at the neck
4) crosslinking of microtubules into a stable bundle

Question 18

what occurs in neuromuscular synapse adhesion

Answer 18

• muscle is surrounded by basal lamina
• margin secreted from axon into muscle ECM
• binds LRP4/MuSK again receptors

Question 19

what does Rho-GTpases in cell migration do

Answer 19

• active Rho-GTP induces growth cone to collapse
• requires myosin-dependent contractions of actin cytoskeleton

Question 20

what are the features of collagen

Answer 20

• Fibrous protein
• Long, stiff, triplestranded helical structure
• Rich in proline and glycine: Gly-X-Y
• Most abundant proteins in mammals: 25% total protein
• 42 distinct human genes
• > 40 “types” of fibres
• Collagen fibrils resist tensile forces

Question 21

what are the types of collagen

Answer 21

Type I - Fibrillar collagen (Skin and Bone)
Type IX and XII - Fibril-associated collagens
Types IV (Basal lamina) and VII (Anchoring fibrils) - Network-forming collagens

Question 22

what are the stages of collagen synthesis

Answer 22

• ER ribosomes translate preprocollagen
• Selected Pro and Lys are hydroxylated to hydroxyproline and hydroxylysine
  Note: Proline hydroxylation requires ascorbic acid (vitamin C) Scurvy….
• Some hydroxylysines are glycosylated
• Three Pro-α chains combine in a triple-stranded, helical procollagen
• Hydroxyl groups form interchain hydrogen bonds
• N- and C-terminal propeptides cleaved off
  Procollagen → collagen
• Collagen assembles in the extracellular space to form collagen fibrils
• Cross-links formed between modified lysine side chains…….