Cell-to-cell interactions

Question 1

What are the 3 basic features in multicellular animals?

Answer 1

• Formation of diverse kinds of tissue
• Cells being able to communicate w/ each other
• Cells having markers of individual identity

Question 2

What kind of proteins do the 3 basic features involve?

Answer 2

-Membrane proteins & proteins secreted by cells

Question 3

What are the 7 kinds of connections between cells?

Answer 3

• Surface markers
• Septate junctions & tight junctions
• Desmosome (adhesive junction)
• Adherens junction (adhesive junction)
• Hemidesmosome/ focal adhesion (adhesive junction)
• Gap Junction (communicating junction/ Animals)
• Plasmodesmata (communicating junction/ Plants)

Question 4

What are the 3 types of Adhesive Junctions?

Answer 4

• Desmosomes
• Adherens Junction
• Heridesmosome/ Focal adhesion

Question 5

What are the 2 types of Communicating Junctions?

Answer 5

• Gap junction

- Plasmodesmata

Question 6

What functions to mark the surfaces of cells?

Answer 6

-A key set of genes

Question 7

When cells of the same tissue recognize each other, what do they do?

Answer 7

-They respond by forming connections between their surfaces to better coordinate their functions

Question 8

What are Glycolipids?

Answer 8

• They’re surface markers for tissue-specific cells

- They’re lipids w/ carbohydrate heads

Question 9

What blood types are the Glycolipids on the surface of RBD responsible for?

Answer 9

-A,B, and O blood types

Question 10

What is an example of the function of the cell-surface markers?

Answer 10

-The recognition of “self” & “non-self” by the immune system= vital for multicellular organisms to defend themselves against invaders

Question 11

What is Major Histocompatibility Complex (MHC)?

Answer 11

-Proteins= makers that vertebrates use to distinguish self from non-self

Question 12

What is vital for a tissue to maintain its characteristic architecture?

Answer 12

-Cell junctions

Question 13

What are Adhesive Junctions & where are they found?

Answer 13

• They mechanically attach the cytoskeleton of a cell with the cytoskeleton of other cells or to the extracellular matrix
• They’re found in tissues subject to mechanical stress= muscle & skin epithelium

Question 14

What are Adherens Junctions & where are they found?

Answer 14

• They’re based on the protein Cadherin

- They’re found in animals ranging from jellyfish to vertebrates

Question 15

What is Cadherin & how does it help adherens junctions?

Answer 15

• A protein that is Ca2+ dependent adhesion molecule w/ very wide phlyogenetic distribution
• It’s a single-pass transmembrane protein w/ extracellular domain of a cadherin in an adjacent cell to join cells together

Question 16

How does Cadherin interact on the cytoplasmic side?

Answer 16

-They interact indirectly through other proteins w/ actin to form flexible connections between cells

Question 17

What are Desmosomes?

Answer 17

• They are a cadherin-based junction unique to vertebrates

- They join adjacent cells= support tissues against mechanical stress

Question 18

What 2 types of Cadherin do desmosomes have & what do they do?

Answer 18

-Desmocollin & Desmoglein= interact w/ intermediate filaments of cytoskeletons INSTEAD of actin

Question 19

What are Hemidesmosomes & Focal adhesions?

Answer 19

• They connect cells to the basil lamina or other ECM
• Also connect the cytoskeleton of cells= actin filaments at focal adhesions & intermediate filaments at hemidesmosomes

Question 20

What are the proteins that interact w/ the ECM in hemidesmosomes & focal adhesions?

Answer 20

-Integrins= Cell-surface receptors that bind to a protein component of the ECM

Question 21

What are Septate Junctions?

Answer 21

-They’re found in both invertebrates & vertebrates & form a barrier that can seal off a sheet of cells

Question 22

What are Tight Junctions?

Answer 22

• They’re unique to vertebrates & contain proteins called Claudins= abilty to occulde/block subtances from passing between cells
• IS A BRICK WALL

Question 23

What are Communicating Junctions?

Answer 23

• Allow communication between cells by diffusion though small openings
• They permit small molcules or ions to pass from one cell to another

Question 24

What are Gap Junctions?

Answer 24

• They’re found in both invertebrates & vertebrates (in invertebrates they’re formed by protein pannexins while the vertebrates= connexons)
• Provide passageways large enough to permit small substances (amino acids, simple sugars) to pass from one cell to the next but small enough to prevent passage from bigger molecules (proteins)

Question 25

How do Gap Junctions form?

Answer 25

-When the pannexins/ connexons of 2 cells align perfectly= creates open channel that spans the membrane between the cells

Question 26

What are Gap Junction channels?

Answer 26

• They’re dynamic structures that can open or close in response to a variety of factors (Ca2+ &H+ ions)
• Prevents damage from spreading by closing when Ca2+ tries to flow in due to the plasma membrane becoming leaky

Question 27

What are Plasmodesmata?

Answer 27

• They function like gap junctions but they are for Plant cells & w/ a more complex structure
• They’re cytoplasmic connections that form across the touching plasma membranes of adjacent cells
• They’re lined w/ plasma membrane & contain a central tubule that connects the endoplasmic reticulum to the 2 cells