Chapter 7: Interactions between cells and their environment Flashcards
What is glycocalyx?
it is a protective cell coat formed by carbohydrate chains of glycoproteins and glycolipids projecting out of the plasma membrane.
What are the functions of the glycocalyx?
- provide mechanical protection for cell
- serve as a barrier to particles moving toward the cell membrane
- Bind to regulatory factors
- Mediate cell-cell and cell-substratum interactions
Describe the ECM (Extracellular Matrix). Why is it significant?
- its an organized network of extracellular materials beyond the immediate vicinity of the plasma membrane
- It plays a key regulatory role in determining the shape and activities of the cell
What is the basal Lima (Basement Membrane)? How common is it?
- one of the best defined ECM
- shows up in many multiple tissues
1) surrounds nerve fibers, muscles, and fat cells
2) underlies the basal surface of epithelial tissues
3) underlies the inner endothelial lining of blood vessels
What is the function of the basal membrane?
Provide mechanical support to cells attached
Generate signals that maintain cell survival
Serve as a substratum for cell migration
Separate adjacent tissues within an organ
Act as a barrier to the passage of
macromolecules
- Proteins
- Cancer cells
Describe Collagen.
- A fibrous glycoprotein
- Present ONLY in ECM
- Found in all animals
- has highly resistant pulling force: Tensile strength
- the single most abundant protein in the human body: 25% of all proteins
- produced primarily by fibroblast, also can be made smooth muscles and epithelial cells
How many types of collagen proteins exist in the human body?
28 subtypes in the human body
- Each collagen is restricted to particular locations in
the body
What are common features among collagen proteins?
Common features:
o Most collagen molecules are trimers
consisting of 3 α chains
o The 3 α chains of a collagen molecule are
wound around each other to form a unique,
rod-like triple helix along at least part of the
length
- Type I, II, III and some others are fibrillar
collagens
Describe what a collagen molecule looks like.
-triple helix of three
helical alpha chains
-Hydrogen bonds
between proline and
serine hold the triple
helix together
What is a Type IV Collagen?
Type IV is nonfibrillar restricted to the basement
membranes
What is the function of collagen?
- Provides the insoluble framework that determines many of the mechanical properties of the ECM
- Tendon: resist pulling forces
- Cornea: plywood-like structure
What can abnormalities in collagen lead to?
It can lead to serious diseases. Fibrosis • Excessive collagen scar tissue substitutes the normal tissue • Lung: pulmonary fibrosis • Liver: Cirrhosis
What are proteoglycans?
- they are protein-polysaccharide complexes, made of
1) a core protein
2) multiple glycosaminoglycans (GAGs)
* these are repeating chains of disaccharides:
- A-B-A-B-A
* they’re highly acidic and negatively charged - the core proteins of mulitple proteoglycans can bind to hyaluronic (a nonsulfated GAG) to form gigantic complexes
What is the function of proteoglycans?
- They provide resistance to crushing (compression) forces
Negative charged GAGs attract a huge
amount of cations binding to proteoglycans ,
which in turn attract a large amount of H2O
GAG + Cations + H2O form a porous gel
Gel fills the extracellular space with help of
scaffold formed by collagen
What does Fibronectin do for the ECM?
- provides binging sites for numerous components of the ECM, including collagens, protoglycans, and other fibronectin molecules
- it facilitates the establishment of a stable, interconnected network of ECM
- provides binding sites for receptors on the cell surface
- holds ECM in a stable attachment to the cell
- Influence cell’s potential for migration, growth and differentiation
What are Laminins? What are their function?
- Extracellular glycoproteins
- More than 15 types have been found
- Help cell migration, growth and differentiation during
embryonic development - Components of basement membranes lining tissues.
- Bind to cell membrane receptors and other ECM proteins
Explain the Dynamic Properties of the ECM.
Spatially, the ECM can be stretched
during tension
Temporally, the ECM undergoes
constant remodeling by degradation
and reconstruction
How does the cell interact with extracellular materials?
- receptors on the plasma membrane help cells attach to extracellular materials
- these receptors are known as Integrins
What are Integrins?
- a family of integral membrane proteins
- ONLY found in ANIMALS
- made of HETERODIMERS with ALPHA and BETA subunits
- Plays a MAJOR role in:
1) Adhesion of cells to their substratum or
other cells
2)Transmission of signals between the
external environment and the cell interior
How are Integrins inactivated/activated?
- Integrins are inactivated in its “bent” confirmation
- Integrins are activated in its “upright” confirmation
- Signaling of integrin is bi-directional, meaning:
- INSIDE-OUT SIGNALING: Talin binding to cytoplasmic tails separates a and b chains, inducing a conformational change that allows Integrin to bind
extracellular matrix ligands - OUTSIDE-IN SIGNALING: Ligand binds to the extracellular domain of integrin inducing a conformational change that initiates polymerization of actin filaments
- INSIDE-OUT SIGNALING: Talin binding to cytoplasmic tails separates a and b chains, inducing a conformational change that allows Integrin to bind
Explain the role of integrins in platelet aggregation?
- Blood clots form when platelets adhere to one another through fibrinogen bridges that bind to the platelet-integrins
- Integrin binding protein possesses the RGD (arginine-glycine-aspartic acid) domain
In terms of connecting the ECM with the cytoskeleton, what two VERY IMPORTANT specialized structures are Integrins involved in forming?
- Focal Adhesion
- Hemidesmosomes
What are Focal Adhesions? What are its components?
- sub-cellular structures where cells adhere to their substratum and transmit signals in both directions across the plasma membrane
- Components:
Extracellular ligands- Collagen, Fibronectin
Large clusters of integrins
Intracellular adaptor
proteins
-Talin, α-actinin, and vinculin
Actin filaments
What are the properties of Focal Adhesions?
- SCATTERED, DISCRETE SITES
- DYNAMIC: Rapidly assemble and disassemble responding to stimuli or enter mitosis
- may act as a SENSORY STRUCTURE: Collecting extracellular information and transmitting to the cell interior
- function in CELL LOCOMOTION
What are Hemidesmosomes?
- they are differentiated sites at the basal surface of epithelial cells where the cells are attached to the underlying basement membrane
What are some characteristics of Hemidesmosomes?
Contain a dense plaque with Keratin filaments on
the inner surface of the plasma membrane
- Thicker
- Intermediate filaments
- Play a supportive function
- Keratin filaments are linked to the ECM by membrane-spanning integrins
What are some properties of Hemidesmosomes?
The tightest attachment between a cell and its extracellular matrix
Transmit signals from the ECM to the attached epithelial cells
How is cell to cell interaction/adhesion SELECTIVE?
Cells have surface-recognition sites that organize cell-cell interaction/adhesion
- Selectins
- Certain members of the immunoglobulin
superfamily (IgSF)
- Certain members of the integrin family
- Cadherins
What are the three types of SELECTINS?
E-selectin:
endothelial cells
P-selectin:
platelets and endothelial cells
L-selectin:
leukocytes
What is the function of SELECTINS?
- mediate transient interactions between circulating leukocytes and vessel walls at sites of inflammation and clotting
- Ca2+-dependent
What is the functions of the Immunoglobin Superfamily?
- Functions in: cell to cell interaction and immune response
- Mediating interactions of lymphocytes with cells required for an immune response (e.g., macrophages, lymphocytes, and target cells)
- Ca2+-independent
What are CADHERINS?
- Glycoproteins that mediate Ca2+-dependent cell to cell adhesion.
How do CADHERINS work?
- Join cells of similar types to one another by preferential binding to the same cadherin present at the surface of the neighboring cell
How many family of CADHERINS are there? Why is this important?
Family of at least 30 related glycoproteins for cell adhesion
E-cadherin (epithelial)
N-cadherin (neural)
P-cadherin (placental)
The greater the number of interacting cadherins in a cluster, the greater the strength of adhesion between apposing cells
Describe the cell to cell interactions.
Cell to cell adhesive junctions
- Adherens Junctions
- Desmosomes
Epithelial specialized cell to cell junctions
- Tight Junctions
- Gap Junctions
Describe the characteristics of Adheren Junctions?
- Commonly found in the body, especially in epithelia
- Form “belts” to encircle each cell near it apical surface
- Cadherin molecules are responsible for the establishment of AJ (Adheren Junctions)
- The cytoplasmic domain of the cadherin molecule is connected to the actin filaments of the cytoskeleton by linking proteins
What are the functions of AJs?
Anchor cells to other cells
Connect the external environment to the actin cytoskeleton
Provide a signaling pathway for signals from extracellular space to the cytoplasm
Describe Desmosomes.
Disk-shaped adhesive junctions between cells
Found in a variety of tissues (areas of mechanical stress, e.g. skin, gum, cervix).
Cadherins link the two cells across a narrow gap
Intermediate filaments are linked to the cytoplasmic domain of cadherin
What are Tight Junctions? What are their purpose?
- they’re specialized contacts between epithelial cells
- exists at sites where two compartments containing different solute concentrations (I.E. Urinary bladder, skin)
- Located at very apical surface between adjacent cells
- Serves as a barrier to free diffusion of water and solutes from the extracellular matrix compartment
- Some are permeable to specific ions or solutes
What are Gap Junctions? What are their purpose?
- sites between animal cells that are specialized for intercellular communication
- “Pipelines” pass through adjoining cell membranes and open into the cytoplasm of adjoining cells
- made entirely out of integral membrane proteins connexin
- Connexin are organized into a complex called Connexon
How do Gap Junctions mediate intercellular interactions?
Gap-junction intercellular communication (GJIC) allows the passage of low-weight molecules or ions
Gap junctions can allow integration of activities of individual cells into a functional unit
Highly active regulatory substances, such as cAMP
Key metabolites, such as ATP, amino acids, small co-enzymes
What is a Junctional Complex?
A specialized array of junctions for cell-cell interaction lining on the lateral surface of epithelial cells
Composed of
- Tight junctions
- Adherens junction
- Desmosomes
