16.3 Cell-Cell Interactions Flashcards
the 4 types of cell-cell interactions
- adhesion junctions
- tight junctions
- gap junctions
- plasmodesmata
selectivity of cell-cell adhesion is mediated by transmembrane proteins called ()
cell adhesion molecules
cell adhesion molecules can be classified into 4 groups
- selectins
- integrins
- immunoglobulin (Ig) superfamily
- cadherins
cell adhesion molecule that mediates transient interactions between leukocytes and endothelial cells or blood platelets
selectins
the 3 members of the selectin family
- L-selectin - leukocytes
- E-selectin - endothelial cells
- P-selectin - platelets
selectins recognize cell surface ()
carbohydrates
critical role of selectins:
initiate interactions between leukocytes and endothelial cells during leukocyte migration to sites of tissue inflammation
selectins mediate initial adhesion of ()
leukocytes to endothelial cells
cell adhesion molecules that mediate stable interactions between cell surfaces to EC matrix
integrins
cell adhesion molecules that bind to either integrins or each other to mediate selective cell adhesion
immunoglobulin (Ig) superfamily
adhesion junctions are formed when integrins bind to ()
intercellular adhesion molecules (ICAMs)
binding of integrins to intercellular adhesion molecules (ICAMs) is an example of a ()
heterophilic interaction
how is binding of integrins to intercellular adhesion molecules (ICAMs) a heterophilic interaction
adhesion molecule on the surface of one cell (e.g. ICAM) recognizes a different molecules on the surface of another cell (e.g. integrin)
other members of the Ig superfamily mediate () an adhesion molecule on the surface of one cell binds to the same molecule on the surface of another cell → selective adhesions between cells of the same type
homophilic interactions
examples of Ig superfamily members that mediate homophilic interactions
neural cell adhesion molecules (NCAMs) on nerve cells
cell adhesion molecules that are primarily responsible for the maintenance of stable junctions between cells in tissues; mediates largely homophilic interactions
cadherins
cadherins are also involved in the selective adhesion between (1) and the formation of specific (2) in the nervous system
- embryonic cells
- synapses
associates epithelial cells to each other
E-cadherin
many adhesive interactions between cells are ()-dependent
divalent cation
stable adhesion junctions are usually based on cadherins; have 2 types:
- adherens junction
- desmosomes
adhesion junction wherein cadherins link to actin filaments
adherens junction
describe cadherin function in adherens junctions
cadherins bind to catenins, which in turn bind to vinculin (associate to actin filaments)
adhesion junction wherein cadherins link to intermediate filaments
desmosomes
describe cadherin function in desmosomes
- desmoplakin is associated to intemediate filaments and recruits plakoglobin and plakophilin
- plakoglobin and plakophilin are in turn associated to desmosomal cadherins (desmoglein and desmocollin)
role of cadherins in linking the cytoskeletons of adjacent cells is analogous to that of the ()
integrins forming stable junctions between cells and the EC matrix
() are critically important in epithelial cell sheets as barriers between fluid compartments; closest known contacts between adjacent cells
tight junctions
tight junctions bind (1) → divides and separates (2)
- 2 plasma membrane bilayers tightly together
- plasma membrane domains
functions of tight junctions in epithelial sheets
- seals the space between epithelial cells
- separates apical and basolateral domains of epithelial PM
what is the purpose of sealing the space between epithelial cells (via tight junctions)
prevents the free passage of molecules (including ions) between cells of epithelial sheets
what is the purpose of separating the apical and basolateral domains of the epithelial PM (via tight junctions)
prevents the free diffusion of lipids and membrane proteins between PM domains
() in the apical and basolateral domains are able to control the traffic of molecules between distinct extracellular compartments
specialized transport systems
similarities between gap junctions and plasmodesmata
both form continuous channels between adjacent cells
differences between gap junctions and plasmodesmata
- gap junctions are found between animal cells while plasmodesmata are found between plant cells
- gap junctions are formed using proteins called connexins while plasmodesmata are formed through the incomplete separation of daughter cells at cell division
provide direct connections between cells within an individual animal tissue
gap junctions
main functions of gap junctions
- regulate channels through PM
- couple both the metabolic activities and the electric responses of the cells they connect
- allow communication between most cells in animal tissues (e.g. epithelial, cardiac and smooth muscle)
gap junctions are composed of () (transmembrane protein family)
connexins
6 connexins assemble to form a cylinder with an aqueous pore in its center called a ()
connexon
in gap junctions () form a continuous channel between adjacent cells
2 connexons (one on each PM of 2 cells)
in gap junctions, adjacent cells are separated by a gap corresponding to the space occupied by the ()
connexin extracellular domains
specialized assemblies of gap junctions on nerve cells form an () → when open, allow the rapid passage of ions between 2 nerve cells
electrical synapse
plant cell adhesions are mediated by their ()
cell walls
specialized pectin-rich region of plant cell walls that acts as a glue that holds adjacent cells together
middle lamella
rigidity of plant cells means () are not required for the formation of stable associations between plant cells
cytoskeletal links
plant cells communicate with each other through cytoplasmic connections called (); function analagously to gap junctions as a means of direct communication between adjacent cells in tissues
plasmodesmata
why do plasmodesmata play an important role in plant cell signaling
plasmodesmata allow regulatory molecules (e.g. transcription factors and miRNAs) to travel directly between cells
plasmodesmata can form from () following plant cell mitosis
incomplete separation of daughter cells
() allows ions and small molecules are freely able to pass between the cells through plasmodesmata
shared ER as a result of smooth ER extension through the pore formed by plasmodesmata
