Multi-cellualr organisation

Question 1

collagen production

Answer 1

1 Procollagen synthesized into ER lumen, where they assemble into a triple helix.
2. Procollagen is secreted outside of cell.
Extension sequences are
removed, to form collagen.
3. Removal of extension sequences allows collagen to assemble into fibrils.
4 Collagen fibrils assemble into larger
collagen fibers.

Question 2

In vertebrates, the most abundant are glycosaminoglycans (GAGs)

Answer 2

Long, unbranched polysaccharides with a repeating disaccharide unit
Highly negatively charge attracts positive ions and water
Structure of chondroitin sulfate (cartilage)

Question 3

adherens junction and desmosomes: cadherins

Answer 3

CAM that create cell-to-cell junctions
Ca2+ dependent adhering molecule
Extracellular domain of two cadherins, each in adjacent cells, bind to each other to promote cell-to-cell adhesion
Inside the cell, linker proteins connect cadherins to the cytoskeleton
By expressing only certain types of cadherins, each cell will only bind to other expressing same type

Question 4

focal adhesions:
Hemidesmosomes
Integrins

Answer 4

Group of cell-surface receptor proteins
2nd type of CAMs
Creates connections between cells and ECM
Do not require Ca2+ to function
Extracellular domain to bind to ECM
Intracellular domain for binding to cytoskeleton
Focal adhesions: link to actin
Hemidesmosomes: link to intermediate filaments

Question 5

tight junctions

Answer 5

Also known as occluding junctions
Forms tight seal between adjacent cells
Prevents leaking between cells
Tight junctions 
Made by occludin and claudin
Bind to each to form tight seal
Not mechanically strong, not bound to cytoskeleton

Question 6

gap junction

Answer 6

Small gap between plasma membranes of cells at junction
Six connexin proteins in one cell align with six connexin proteins of an adjacent cell to form a connexon
Connexon allows passage of ions and small molecules
Allows adjacent cells to share metabolites and directly signal each other

Question 7

apical side

Answer 7

faces air or extracellular

region such as the lumen of the intestine

Question 8

basal side

Answer 8

faces inside

the body toward the blood