Cell Interactions Between Space and their Environment

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Interactions Between Space and their Environment:

Reporter: Ma. Chrischelle A. Ferreras Professor: Dr. Maricel Gomez Source: Cell and Molecular Biology. Concepts and Experiments, 7 th Edition by Gerald Karp Interactions Between Space and their Environment

Outline:

Extracellular Space Interactions of Cells with Non-cellular Substrates Interactions of Cells with other Cells Tight Junctions: Sealing the Extracellular Space Gap Junctions and Plasmodesmata : Mediating Intercellular Communication Cell Walls Outline

Slide3:

An overview of how cells are organized into tissues and how they interact with one another and with their extracellular environment.

The Extracellular Space:

The Extracellular Space

The Extracellular Matrix an organized network of extracellular materials that is present beyond the immediate vicinity of the plasma membrane :

The extracellular matrix (ECM) of cartilage cells. (Top) Scanning electron micrograph of a portion of a colony of cartilagecells (chondrocytes) showing the extracellular materials secreted by the cells. (Below) The ECM of a single chondrocyte has been made visible by adding a suspension of red blood cells (RBCs). The Extracellular Matrix an organized network of extracellular materials that is present beyond the immediate vicinity of the plasma membrane

Slide6:

The ECM is more than an inert packing material or a nonspecific glue that holds cells together; it provides both physical and biochemical signals that can play key regulatory roles in determining the shape and activities of the cell. For example, enzymatic digestion of the ECM that surrounds cultured cartilage cells or mammary gland epithelial cells causes a marked decrease in the synthetic and secretory activities of the cells.

basement membrane (or basal lamina) a continuous sheet 50 to 200 nm thick that surrounds nerve fibers, muscles, and fat cells, underlies the basal surface of epithelial tissues, such as the epidermis of the skin, or the lining of the digestive and respiratory tracts, and underlies the inner endothelial lining of blood vessels. :

basement membrane (or basal lamina) a continuous sheet 50 to 200 nm thick that surrounds nerve fibers , muscles, and fat cells, underlies the basal surface of epithelial tissues, such as the epidermis of the skin, or the lining of the digestive and respiratory tracts, and underlies the inner endothelial lining of blood vessels.

Basement membranes also serve as a barrier to invasion of tissues by cancer cells. Those cells that do not lie on a basement membrane sheet, such as the fibroblasts of a connective tissue, are typically surrounded by a less organized ECM consisting largely of threadlike fibrils. :

Basement membranes also serve as a barrier to invasion of tissues by cancer cells. Those cells that do not lie on a basement membrane sheet, such as the fibroblasts of a connective tissue, are typically surrounded by a less organized ECM consisting largely of threadlike fibrils.

Collagens comprise a family of fibrous glycoproteins that are present only in extracellular matrices. Collagens are found throughout the animal kingdom and are noted for their high tensile strength, that is, their resistance to pulling forces. :

Collagens comprise a family of fibrous glycoproteins that are present only in extracellular matrices. Collagens are found throughout the animal kingdom and are noted for their high tensile strength, that is, their resistance to pulling forces.

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It is estimated that a collagen fiber 1 mm in diameter is capable of suspending a weight of 10 kg (22 lb ) without breaking. Collagen is the single most abundant protein in the human body—constituting more than 25 percent of all protein—a fact that reflects the widespread occurrence of extracellular materials.

Slide11:

Collagen is produced primarily by fibroblasts, the cells found in various types of connective tissues, but also by smooth muscle cells and epithelial cells. To date, 27 distinct types of human collagen have been identified. Each collagen type is restricted to particular locations within the body, but two or more different types are often present together in the same ECM.

The cornea is also a remarkable tissue; it must serve as a durable, protective layer at the surface of the eyeball but must also be transparent so that light can pass through the lens to the retina. :

The cornea is also a remarkable tissue; it must serve as a durable, protective layer at the surface of the eyeball but must also be transparent so that light can pass through the lens to the retina. The corneal stroma consists largely of layers of collagen fibrils of uniform diameter and spacing. The molecules of alternate layers are arranged at right angles to one another, resembling the structure of plywood.

Slide13:

The type IV collagen network of the basement membrane. Electron micrograph of a basement membrane from human amniotic tissue that had been extracted with a series of salt solutions to remove noncollagenous materials. The treatment leaves behind an extensive, branching, polygonal network of strands that form an irregular lattice. Evidence indicates that this lattice consists of type IV collagen molecules covalently linked to one another in acomplex three-dimensional array

Slide14:

The chains of collagen molecules contain large amounts of proline, and many of the proline (and lysine) residues are hydroxylated following synthesis of the polypeptide. The hydroxylated amino acids are important in maintaining the stability of the triple helix by forming hydrogen bonds between component chains. Failure to hydroxylate collagen chains has serious consequences for the structure and function of connective tissue s.

Slide16:

Ascorbic acid is required as a coenzyme by the enzymes that add hydroxyl groups to the lysine and proline amino acids of collagen.

Slide21:

Ehler-Danlos Syndrome

Proteoglycan consists of a core protein molecule to which chains of glycosaminoglycans (GAGs) are covalently attached. Each glycosaminoglycan chain is composed of a repeating disaccharide; that is, it has the structure -A-B-A-B-A-, where A and B represent two different sugars. :

Proteoglycan consists of a core protein molecule to which chains of glycosaminoglycans ( GAGs ) are covalently attached. Each glycosaminoglycan chain is composed of a repeating disaccharide; that is, it has the structure -A-B-A-B-A-, where A and B represent two different sugars.

Slide24:

The extracellular matrix of bone is also composed of collagen and proteoglycans, but it becomes hardened by impregnation with calcium phosphate salts. Both sulfated and nonsulfated GAGs are taken widely as health supplements with the aim of improving the condition of skin and joints.

Fibronectin consists of a lincear array of distint “building blocks” that gives each polypeptide a modular construction. :

Fibronectin consists of a lincear array of distint “building blocks” that gives each polypeptide a modular construction.

Slide27:

Each of the two polypeptide chains that make up a fibronectin molecule contains: 1. Binding sites for numerous components of the ECM, such as collagens, proteoglycans, and other fibronectin molecules. These binding sites facilitate interactions that link these diverse molecules into a stable, interconnected network . Binding activities of fibronectin molecules are enhanced by mechanical forces that pull on these fibrous proteins and unfold its component modules. Unfolding of these modules exposes binding sites that would otherwise have remained buried.

Slide28:

2. Binding sites for receptors on the cell surface. These binding sites hold the ECM in a stable attachment to the cell.

Slide29:

The importance of fibronectin and other extracellular proteins is particularly evident during embryonic development. Development is characterized by waves of cell migration during which different cells follow different routes from one part of the embryo to another.

Laminins a family of extracellular glycoproteins that consist of three different polypeptide chains linked by disulfide bonds and organized into a molecule resembling a cross with three short arms and one long arm :

Laminins a family of extracellular glycoproteins that consist of three different polypeptide chains linked by disulfide bonds and organized into a molecule resembling a cross with three short arms and one long arm

Slide31:

At least 15 different laminins have been identified. Like fibronectin , extracellular laminins can greatly influence a cell’s potential for migration, growth, and differentiation.

Slide32:

For example, laminins play a critical role in the migration of primordial germ cells. These cells arise in the yolk sac, which is located outside the embryo itself, and then migrate by way of the bloodstream and embryonic tissues to the developing gonad, where they eventually give rise to sperm or eggs. During their migration, the primordial germ cells traverse surfaces that are particularly rich in laminin. Primordial germ cells possess a cell-surface protein that adheres strongly to one of the subunits of the laminin molecule.

Slide33:

Dynamic Properties of the ECM ECM fibrils can be seen to stretch several times their normal length as they are pulled on by cells and con-tract when tension is relieved. Temporally, the components of an ECM are subject to continual degradation and reconstruction.

Slide34:

Dynamic Properties of the ECM The degradation of extracellular materials, along with cell surface proteins, is accomplished largely by a family of zinc-containing enzymes called matrix metalloproteinases (MMPs) that are either secreted into the extracellular space or anchored to the plasma membrane.

Slide35:

Dynamic Properties of the ECM As a group, MMPs can digest nearly all of the diverse ECM components, although individual family members are limited as to the types of extracellular molecules they can attack. The physiological roles of MMPs are not well understood, but they are thought to be involved in tissue remodeling , embryonic cell migration, wound healing, and the formation of blood vessels.

Interactions of Cells with Extracellular Materials :

Interactions of Cells with Extracellular Materials

Integrins family of membrane proteins found only in animals that play a key role in integrating the extracellular and intracellular environments. :

Integrins family of membrane proteins found only in animals that play a key role in integrating the extracellular and intracellular environments.

Slide38:

On the outer side of the plasma membrane, integrins bind to a remarkably diverse array of molecules (ligands) that are present in the extracellular environment. On the intracellular side of the membrane, integrins interact either directly or indirectly with dozens of different proteins to influence the course of events within the cell. Integrins are composed of two membrane-spanning polypeptide chains, an chain and a chain, that are noncovalently linked.

Slide39:

Eighteen different subunits and eight different subunits have been identified. Although more than a hundred possible pairings of and subunits could theoretically occur, only about two dozen different integrins have been identified on the surfaces of cells, each with a specific distribution within the body.

Slide40:

Classification of Integrin Receptors Based on Recognition of RGD Sequences

Slide42:

Integrins have been implicated in two major types of activities: adhesion of cells to their substratum (or to other cells) and transmission of signals between the external environment and the cell interior.

Focal Adhesions and Hemidesmosomes: Anchoring Cells to Their Substratum :

Focal Adhesions and Hemidesmosomes : Anchoring Cells to Their Substratum

Slide45:

When fibroblasts or epithelial cells spread onto the bottom of a culture dish, the lower surface of the cell is not pressed uniformly against the substratum. Instead, the cell is anchored to the surface of the dish only at scattered, discrete sites, called focal adhesions.

Slide46:

Focal adhesions are dynamic structures that can be rapidly disassembled if the adherent cell is stimulated to move or enter mitosis. The plasma membrane of a focal adhesion contains large clusters of integrins. The cytoplasmic domains of the integrins are connected by various adaptor proteins (e.g., talin , - actinin , and vinculin) to actin filaments of the cytoskeleton.

Slide47:

Focal adhesions may act as a type of sensory structure, collecting information about the physical and chemical properties of the extracellular environment and transmitting that information to the cell interior, which may lead to changes in cell adhesion, proliferation, or survival.

Slide50:

Focal adhesions are most commonly seen in cells grown in vitro, although similar types of adhesive contacts are found in certain tissues, such as muscle and tendon. Within the body, the tightest attachment between a cell and its extracellular matrix is seen at the basal surface of epithelial cells where the cells are anchored to the underlying basement membrane by a specialized adhesive structure called a hemidesmosome .

Slide52:

The importance of hemidesmosomes is revealed by a rare disease, bullous pemphigoid , in which individuals produce antibodies that bind to proteins (the bullous pemphigoid antigens ) present in these adhesive structures.

Slide53:

A similar inherited blistering disease, epidermolysis bullosa , can occur in patients with genetic alterations in any one of a number of hemidesmosomal proteins, including the 6 or 4 integrin subunit, collagen VII, or laminin-5.

Interactions of Cells with other Cells :

Interactions of Cells with other Cells

Slide56:

Four distinct families of integral membrane proteins play a major role in mediating cell–cell adhesion: (1) selectins , (2) certain members of the immunoglobulin superfamily ( IgSF ), (3) certain members of the integrin family, and (4) cadherins .

Selectins comprise a family of integral membrane glycoproteins that recognize and bind to a particular arrangement of sugars in the oligosaccharides that project from the surfaces of other cells:

Selectins comprise a family of integral membrane glycoproteins that recognize and bind to a particular arrangement of sugars in the oligosaccharides that project from the surfaces of other cells

There are three known selectins: E-selectin, present on endothelial cells; P-selectin, present on platelets and endothelial cells; andL-selectin, present on leukocytes (white blood cells).:

There are three known selectins: E-selectin, present on endothelial cells; P-selectin, present on platelets and endothelial cells; andL -selectin, present on leukocytes (white blood cells).

The Immunoglobulin Superfamily (IgSF) Antibodies, which are a type of protein called an immunoglobulin (or Ig), were found to consist of polypeptide chains composed of a number of similar domains. Most members of the IgSF are involved in various aspects of immune function, but some of these pro-teins mediate calcium-independent cell–cell adhesion.:

The Immunoglobulin Superfamily ( IgSF ) Antibodies, which are a type of protein called an immunoglobulin (or Ig), were found to consist of polypeptide chains composed of a number of similar domains. Most members of the IgSF are involved in various aspects of immune function, but some of these pro- teins mediate calcium-independent cell–cell adhesion.

Most IgSF cell-adhesion molecules mediate the specific interactions of lymphocytes with cells required for an immune response (e.g., macrophages, other lymphocytes, and target cells). :

Most IgSF cell-adhesion molecules mediate the specific interactions of lymphocytes with cells required for an immune response (e.g., macrophages, other lymphocytes, and target cells).

Cadherins a large family of glycoproteins that mediate Ca2 dependent cell–cell adhesion and transmit signals from the ECM to the cytoplasm.:

Cadherins a large family of glycoproteins that mediate Ca 2 dependent cell–cell adhesion and transmit signals from the ECM to the cytoplasm.

Cadherin-mediated adhesion is thought to be responsible for the ability of like cells to “sort out” of mixed aggregates. In fact, cadherins may be the single most important factor in molding cells into cohesive tissues in the embryo and holding them together in the adult. :

Cadherin-mediated adhesion is thought to be responsible for the ability of like cells to “sort out” of mixed aggregates. In fact, cadherins may be the single most important factor in molding cells into cohesive tissues in the embryo and holding them together in the adult.

Adherens Junctions and Desmosomes: Anchoring Cells to Other Cells:

Adherens Junctions and Desmosomes: Anchoring Cells to Other Cells

Adherens junctions found in a variety of sites within the body. They are particularly common in epithelia, such as the lining of the intestine, where they occur as “belts” (or zonulae adherens) that encircle each of the cells near its apical surface, binding that cell to its surrounding neighbors:

Adherens junctions found in a variety of sites within the body. They are particularly common in epithelia, such as the lining of the intestine, where they occur as “belts” (or zonulae adherens ) that encircle each of the cells near its apical surface, binding that cell to its surrounding neighbors

Like the integrins of a focal adhesion, the cadherin clusters of an adherens junction (1) connect the external environment to the actin cytoskeleton and (2) provide a pathway for signals to be transmitted from the cell exterior to the cytoplasm. :

Like the integrins of a focal adhesion, the cadherin clusters of an adherens junction (1) connect the external environment to the actin cytoskeleton and (2) provide a pathway for signals to be transmitted from the cell exterior to the cytoplasm.

Desmosomes (or maculae adherens) are disk-shaped adhesive junctions approximately 1 µm in diameter that are found in a variety of tissues. Like adherens junctions, desmosomes contain cadherins that link the two cells across a narrow extracellular gap. :

Desmosomes (or maculae adherens ) are disk-shaped adhesive junctions approximately 1 µm in diameter that are found in a variety of tissues. Like adherens junctions, desmosomes contain cadherins that link the two cells across a narrow extracellular gap.

The importance of cadherins in maintaining the structural integrity of an epithelium is illustrated by an autoimmune disease (pemphigus vulgaris) in which antibodies are produced against one of the desmogleins. The disease is characterized by a loss of epidermal cell–cell adhesion and severe blistering of the skin.:

The importance of cadherins in maintaining the structural integrity of an epithelium is illustrated by an autoimmune disease (pemphigus vulgaris) in which antibodies are produced against one of the desmogleins . The disease is characterized by a loss of epidermal cell–cell adhesion and severe blistering of the skin.

Slide73:

The Role of Cell-Adhesion Receptors in Transmembrane Signaling

Tight Junctions: Sealing The Extracellular Space:

Tight Junctions: Sealing The Extracellular Space

Tight Junctions specialized contacts between neighboring epithelial cells:

Tight Junctions specialized contacts between neighboring epithelial cells

Slide79:

TJs serve as a barrier to the free diffusion of water and solutes from the extracellular compartment on one side of an epithelial sheet to that on the other side. Tight junctions also serve as “fences” that help maintain the polarized character of epithelial cells. Tight junctions are also involved in signaling pathways that regulate numerous cellular processes.

Slide80:

Tight junctions are also present between the endothelial cells that line the walls of capillaries. These junctions are particularly evident in the brain where they help form the blood–brain barrier, which prevents substances from passing from the blood-stream into the brain.

Slide82:

Gap Junctions and Plasmodesmata : Mediating Intercellular Communication

Gap junctions sites between animal cells that are specialized for intercellular communication :

Gap junctions sites between animal cells that are specialized for intercellular communication

Slide85:

A number of inherited disorders have been associated with mutations in genes encoding connexins . Consequences of these disorders include deafness, blindness, cardiac arrhythmias, skin abnormalities, or nerve degeneration.

Slide87:

Plasmodesmata (singular, plasmodesma ) are cytoplasmic channels that pass through the cell walls of adja -cent cells

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Cell Wall

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The matrix of the cell wall is composed of three types of macromolecules: 1. Hemicelluloses are branched polysaccharides whose backbone consists of one sugar, such as glucose, and side chains of other sugars, such as xylose. Hemicellulose molecules bind to the surfaces of cellulose microfibrils, cross-linking them into a resilient structural network.

Slide93:

The matrix of the cell wall is composed of three types of macromolecules: 2. Pectins are a heterogeneous class of negatively charged polysaccharides containing galacturonic acid. Like the glycosaminoglycans of animal cell matrices, pectins hold water and thus form an extensive hydrated gel that fills in the spaces between the fibrous elements. When a plant is attacked by pathogens, fragments of pectins released from the wall trigger a defensive response by the plant cell. Purified pectin is used commercially to provide the gel-like consistency of jams and jellies.

Slide94:

The matrix of the cell wall is composed of three types of macromolecules: 3. Proteins, whose functions are not well understood, mediate dynamic activities. One class, the expansins , facilitate cell growth. These proteins cause localized relaxation of the cell wall, which allows the cell to elongate at that site in response to the turgor pressure generated within the cell. Cell wall-associated protein kinases span the plasma membrane and are thought to transmit signals from the cell wall to the cytoplasm.

Summary:

Summary

Slide96:

The extracellular space extends outward from the outer surface of the plasma membrane and contains a variety of secreted materials that influence cell behavior.

Slide97:

The major components of extracellular matrices include collagens, proteoglycans, and a variety of proteins, such as fibronectin, and laminin.

Slide98:

Integrins are cell-surface receptors that mediate interactions between cells and their substratum.

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Cells attach to their substratum by means of cell-surface specializations such as focal adhesions and hemidesmosomes .

Slide100:

The adhesion of cells to other cells is mediated by several distinct families of integral membrane proteins, including selectins, inte -grins, cadherins , and members of the immunoglobulin superfam-ily ( IgSF ).

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Strong adhesions between cells are facilitated by the formation of specialized adherens junctions and desmosomes.

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Tight junctions are specialized sites of contact that block solutes from diffusing between the cells in an epithelium.

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Gap junctions and plasmodesmata are specialized sites of communication between adjoining cells in animals and plants, respectively.

Slide104:

Plant cells are surrounded by a complex cell wall composed of cellulose and a variety of secreted materials that provide mechanical support and protect the cell from potentially damaging influ-ences .

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