CAM

Question 1

Cells can adhere to one another (cell-cell adhesion) through ____________ that often cluster into specialized cell junctions

Answer 1

cell adhesion molecules (CAMs)

Question 2

Junctional Adhesion Mechanisms:

Cell-Cell Adhesion

Answer 2

1. Tight Junctions (Claudins)
   - Seal neighboring cells to prevent leakage.
   - Maintain cell polarity by restricting movement of membrane proteins.
2. Adhesion Belts (Cadherins)
   - Connect actin filaments between cells via cadherins.
   - Important in tissue morphogenesis.
3. Desmosomes (Cadherins)
   - Provide strong adhesion by linking intermediate filaments.
   - Cadherins involved: desmogleins and desmocollins.
4. Gap Junctions (Connexins)
   - Channels allowing direct communication between cells.
   - Permit ions and small molecules to pass.

Question 3

Junctional Adhesion Mechanisms:

Cell-Matrix Adhesion

Answer 3

1. Hemidesmosomes (Integrins)
   - Anchor intermediate filaments of the cytoskeleton to the ECM.
   - Provide strong, stable attachments.
2. Focal Adhesions (Integrins)
   - Link actin filaments to the ECM via integrins.
   - Dynamic structures important in cell signaling and migration.

Question 4

Non-Junctional Adhesion Mechanisms

Cell-Cell adhesion

Answer 4

1. Cadherins
   - Calcium-dependent adhesion proteins involved in homophilic binding (same cell types).
2. Ig-like CAMs (Cell Adhesion Molecules)
   - Immunoglobulin-like domains; mediate calcium-independent adhesion.
   - Involved in immune responses and neuron guidance.
3. Integrins
   - Mediate cell-ECM and cell-cell adhesion.
   - Signal bidirectionally between ECM and cytoskeleton.
4. Selectins
   - Bind to carbohydrates on neighboring cells.

Question 5

Non-Junctional Adhesion Mechanisms

Cell-Matrix adhesion

Answer 5

1. Integral Membrane Proteoglycans
   - Participate in ECM binding, cell signaling, and structural support.
2. Integrin

Question 6

Types of Cell Adhesion Molecules (CAMs)

Answer 6

Homophilic interactions
- Cadherins (E-cadherin)
- Ig-superfamily CAMs (NCAM)
Heterophilic interactions
- Integrins
- Selectins

Question 7

• Mediate Ca2+-dependent cell-cell adhesion
• Cause compaction during development
• Blastomeres become tightly packed and joined by intercellular junctions
  *Highly selective recognition, enabling cells of similar type to stick together

Answer 7

Cadherins

Question 8

Cadherin-dependent cell-cell adhesion guides the organization of developing tissues sorting out according to their origins

Question 9

Cadherin binds preferentially to similar type of cell

Question 10

• Strengthen the binding of the blood cells to the endometrium
• Heterophilic binding to specific proteins
• Principal cell-surface receptors used by animal cells to bind to the extracellular matrix (ECM)
• transmembrane linkers between the ECM and cytoskeleton

Answer 10

Integrins

Question 11

Some types of integrin

α5β1 - Ligand is Fibronectin
- Phenotype when α subunit is mutated = Death of embryo; defects in blood vessels, somites, neural crest
- Phenotype when β subunit is mutated = Early death of embryo (at implantation)

α6β1 - Ligand is Laminin
- Phenotype when α subunit is mutated = Severe skin blistering; defects in other epithelia also
- Phenotype when β subunit is mutated = Early death of embryo (at implantation)

αIIβ3 - Ligand is Fibrinogen
- Phenotype when α subunit is mutated = Bleeding; no platelet aggregation (Glanzmann disease)
- Phenotype when β subunit is mutated = Bleeding; no platelet aggregation (Glanzmann disease); mild osteoporosis

α6β4 - Ligand is Laminin
- Phenotype when α subunit is mutated = Severe skin blistering; detects in epithelia also
- Phenotype when β subunit is mutated = Severe skin blistering; detects in other epithelia also

Question 12

__________
* Cell-surface carbohydrate-binding proteins (_______) that mediate transient cell-cell adhesions in the bloodstream
* Heterophilic binding to specific oligosaccharides on glycoproteins and glycolipids
* Control the binding of WBC to endothelial cells, enabling the blood cells to migrate out of the bloodstream (________)

Answer 12

Selectins; lectins; extravasation

Question 13

Selectins and integrins act in sequence to let WBC leave the bloodstream and enter tissues.

Answer 13

Weak adhesion and rolling - selectin-dependent

Strong adhesion and emigration
integrin-dependent

Question 14

• Ca2+ independent cell-cell adhesion
• Contain one or more Ig-like domains that are characteristic of antibody molecules

Answer 14

Immunoglobulin (Ig) superfamily of proteins

Question 15

Members of Ig superfamily

Answer 15

1. Neural cell adhesion molecule (NCAM) - nerve cells
   - has type III fibronectin repeats
2. ICAM - intercellular cell
3. Nectin - collaborates with cadherin to help build and strengthen adherens junctions in many tissue

Question 16

• Bind to integrins on blood cells when blood cells migrate out of the bloodstream

Answer 16

Intercellular adhesion molecules (ICAMs)

Question 17

Mucin-like CAMS
- has selectin

Integrin
- has fibronectin

Question 18

Anchoring junctions

Cell-cell
- Adherens junction
- Desmosome

Cell-matrix
- Actin-linked cell-matrix junction
- Hemidesmosome

Question 19

Intracellular adaptor proteins of:

adherens junction
- α-Catenin, β- Catenin, p120-Catenin, vinculin

desmosome junction
- Plakoglobin, plakophilin, desmoplakin

Actin-linked cell-matrix junction
- Talin, kindin, vinculin, paxillin, focal adhesion kinase (FAK)

Hemidesmosome
- Plectin, BP230

Question 20

Intracellular cytoskeletal attachment of:
Adherens junction and Actin-linked cell-matrix junction

Answer 20

Actin filaments

Question 21

Intracellular cytoskeletal attachment of:
Desmosome and Hemidesmosome

Answer 21

Intermediate filaments

Question 22

Transmembrane adhesion proteins of:
Adherens junction = Classical cadherins

Desmosome = Nonclassical cadherins (desmoglein, desmocolin)

Actin-linked cell-matrix junction = Integrin

Question 23

Types of Cell Junctions

Answer 23

1. Tight junction
   - interlocking junctional proteins
2. Anchoring junctions
   a. Adhering junctions
   b. Desmosome
   c. Hemidesmosome
3. Gap junction
   - channel between cells formed by connexons

Question 24

• Block the passageways through the gaps between epithelial cells, preventing extracellular molecules from leaking from one side to the other

Question 25

Tight junction proteins

Answer 25

Claudin Occludin

Question 26

* Impermeable to macromolecules, however permeability to small molecules varies in different epithelia - In small intestine 10,000x more permeable to inorganic salts than urinary bladder * For maintenance of vectorial transport function of cells

Answer 26

Tight junctions (vertebrates)

Question 27

* Mechanically attach cells (and their cytoskeletons) to their neighbors or to the extracellular matrix * Abundant in tissues that are subjected to severe mechanical stress * Heart, muscle, and epidermis

Answer 27

Anchoring junctions

Question 28

Anchoring junctions *Three types

Answer 28

* Adherens junctions * Desmosomes * Hemidesmosomes

Question 29

Adherens junctions - Takes in a form of adhesion belt

Question 30

* Are button-like points * Rivet (fasten) cells together, connect intermediate filaments of adjoining cells to distribute tensile or shearing forces * Mechanical strength

Answer 30

Desmosomes

Question 31

_____________ * Severe blistering of the skin, with leakage of body fluids into the loosened epithelium * Due to antibodies against one of desmosomal cadherin proteins, ___________.

Answer 31

Pemphigus vulgaris ;desmogleins 1 and 3

Question 32

______________ * Or half-desmosomes, resemble desmosomes morphologically and in connecting intermediate filaments * Connect the basal surface of the epithelial cell to the underlying basal lamina * Transmembrane linker proteins are ___________ - Has keratin filaments

Answer 32

Hemidesmosomes ;integrins

Question 33

Autoimmune disease directed against hemidesmosome antigens

Answer 33

Bullous pemphigoid

Question 34

* Cell-matrix junctions * Actin filament attachment sites

Answer 34

Focal adhesions

Question 35

* Allow cell to cell communication * Mediate the passage of chemical or electrical signals from one interacting cell to its partner

Answer 35

Gap junctions

Question 36

Connexon is made up of 6 connexin monomers or heteromers 2 connexons form an intercellular channel (homotypic or heterotypic) They form a hydrophilic channel

Question 37

* Is spanned by channel-forming proteins (connexons) * Cells connected by ___________ share many of their inorganic ions and other small molecules and are therefore chemically and electrically coupled

Answer 37

Gap junctions

Question 38

Functional significance of Gap junctions

Answer 38

* Coordinates activities of electrically active cells * Allow action potentials to spread rapidly from cell to cell, without delay that occurs at chemical synapses * Synchronizes contractions of heart and smooth muscle cells

Question 39

* Only intercellular junctions in plants * Function like gap junctions

Answer 39

Plasmodesmata

Question 40

A functional classification of Cell Junctions

Answer 40

Anchoring junctions Actin filament attachment sites 1. cell-cell junction = adherens junction 2. cell-matric junctions = actin-linked cell-matrix adhesion Intermediate filament attechment sites 1. cell-cell junction = desmosomes 2. cell-matric junctions = hemidesmosomes Occluding junctions 1. Tight junctions (vertebrates) 2. Septate junctions (invertebrates) Channel-forming junctions 1. Gap junctions (animals) 2. Plasmodesmata (plants) Signal-relaying junctions 1. Chemical synapses (nervous system) 2. Immunological synapses (immune system) 3. Transmembrane ligand-receptor cell-cell signaling contacts