Interactions b/w cells & their environments

Ch. 9 & 10

Extracellular Matrix

Large network of proteins and other molecules that surround, support, and give structure to cells and tissues in the body

Carbohydrate projections form part of the _____ on the outer surface of the PM.

Glycocalyx

Glycocalyx Functions

• Mediator of cell–cell and cell–substratum interactions

• Mechanical protection

• Barrier to molecular movement

One of the best-defined extracellular matrices (ECM) is the ___ membrane that surrounds muscles that nerves & fat cells

Basement

• Underlies the epidermis of the skin, the digestive and respiratory tract and the lining of blood vessels

ECM Components

1. Collagen

2. Proteoglycans

3. Fibronectin

4. Laminin

Single most abundant protein in the body

Collagen

Collagen is produced by:

Fibroblasts, smooth muscle and epithelial cells

Collagens comprise a family of:

Fibrous glycoproteins present only in the ECM

Triple helix of three helical alpha chains

Collagen Molecule

Collagen provides the:

Insoluble framework that determines many of the mechanical properties of the matrix

Protein-polysaccharide complex, with a core protein attached to glycosaminoglycans (GAGs)

Proteoglycans

 Common in basement membranes, attract water, forming gel

Hyaluronic acid is popular in topical creams and skin care because of its:

Water-retaining properties

Consists of a linear array of 30 Fn domains to give a modular construction

Fibronectin

Fn-type domains are found in:

Blood clotting factors and receptors

Fibronectin and other extracellular proteins have important roles during:

Embryonic development (heart cells —> heart, brain cells —> brain)

Several organs (e.g., salivary gland, kidney, and lung) are formed by a process of:

Branching/cleft formation

___ & ___ are also fibronectin-dependent

Cell adhesion & shape determination

Laminin has three polypeptide chains linked by disulfide bonds – What type of protein structure?

Quaternary

Railroad tracks; greatly influence a cell’s potential for migration, growth, and differentiation

Laminin

Laminin has a role in development of ___ & in strengthening the ___ membrane.

Neuronal outgrowth; basement

Degrades ECM materials

Matrix metalloproteinases (MMPs)

The physiological roles of MMPs are thought to be involved in:

Tissue remodeling, embryonic cell migration, wound healing, and the formation of blood vessels

How do cells interact with extracellular materials?

1. Integrins

2. Focal adhesions

3. Hemidesmosomes

Family of membrane proteins unique to animals

Composed of two membrane-spanning polypeptide chains, an α chain and a β chain

Integrins

The bent conformation of integrin corresponds to its ___ state, Integrins with a bound ligand are found in an ___ conformation

Inactive; upright

Can send the signal inside the cell to alter intracellular function in response to integrins becoming unbent

Talin

Cultured cells are anchored to the surface of the dish only at scattered, discrete sites

Focal adhesions

Focal adhesions play a key role in cell ___.

Locomotion

Cell-matrix attachment in vivo is seen at the basal surface of epithelial cells, anchored to the underlying basement membrane

Hemidesmosomes

Hemidesmosomes contain a dense:

Cytoplasmic plaque with keratin filaments

___ filaments are linked to the ECM by integrins

Keratin

Experiments demonstrated that separated cells would redistribute themselves so that each cell adhered only to ___.

Cells of the same type

How do cells interact with other cells in close proximity?

Cell Adhesion Molecules (CAMs)—help cells stick to each other & provide signals for cellular crosstalk

Types of CAMs

1. Selectins

2. Immunoglobulins

3. Cadherins

4. Integrins - help cells interact w/ ECM material & other cells

Family of membrane glycoproteins that bind to specific oligosaccharides

Selectins

[Key] “Lectin,” is a term for a compound that binds to specific:

Carbohydrate groups [Lock]

Selectins have a small cytoplasmic segment, a ___, & a ___.

Single membrane-spanning domain, and a large extracellular portion

Leukocytes recruitment has focused on three types of cell adhesion molecules:

Selectins, integrins, and IgSF proteins

Endothelial cells that line venules become more adhesive to circulating ___ through display of __ & __-selectins

Neutrophils; P-; E-

On endothelial cells stimulates an increase in the integrin binding activity on neutrophils

Platelet activating factor (PAF)

Bound neutrophils then ___ and squeeze between adjacent ___ cells into the damaged tissue

Change their shape; endothelial

Immunoglobulin

Original function likely cell-adhesion mediators (Ca2+ independent) Developmental roles in neuronal growth and circuitry

Both of these aids in neuronal growth

Laminin & Immunoglobulin

Cadherins

Glycoprotein family

Typically join cells of similar type to one another (Ca2+ dependent)

[Cadherins] Possibly the single most important factor in molding cells into cohesive tissues in the ___ & holding them together in the ___.

Embryo; adult

Two types of Cadherins

E-cadherin (epithelial) & N-cadherin (neural)

Govern which cells will become epidermis (ectoderm) and which will form the neural tube (brain and spinal cord)

Cadherin signaling pathways

Tight junctions occur b/w:

Neighboring epithelial cells

[TJ] Prevent solute distribution where ___ solute concs. are in ___ compartments

Different; adjacent

[TJ] The points of cell–cell contact are sites where __ proteins of two adjacent membranes meet within the __ space

Integral; extracellular

How do cells engage in intercellular communication at close distances? (w/o fusion)

1. Gap junctions

2. Plasmodesmata

Molecular “pipelines” that pass through the adjoining plasma membranes and open into the cytoplasm of the adjoining cells

Sites b/w animal cells that are specialized for intercellular communication

Gap junctions

[GJ] composed of an integral membrane protein ____ , & organized into multi-subunit complexes, ____, that span the membrane

Connexin; connexons

____ membranes of a gap junction contain channels that connect the cytoplasm of one cell with the cytoplasm of the adjoining cell

Plasma membranes

Plasma membranes come very close to one another but ___ at gap junction.

Do not make direct contact

For cell-cell communication, most plant cells are connected by ___, cytoplasmic channels that pass through the cell walls of adjacent cells

Plasmodesmata

Plasmodesmata allow ___ molecules to pass since the pore is capable of ___.

Larger; dilation

Plant cells produce their own ___ through proteins that regulate the flow of proteins and ___ from cell to cell

Movement; RNAs

The cells of nearly all organisms other than ___ are enclosed in a protective outer envelope

Animals

Provides the fibrous component of the cell wall

Cellulose

___ & ___ provide the matrix

Proteins; pectin

Cellulose molecules are organized into:

Rod-like microfibrils

The matrix of the cell wall is composed of three types of macromolecules:

1. Hemicelluloses

2. Pectins

3. Proteins

Branched polysaccharides whose backbone consists of one sugar & side chains of other sugar

Hemicellulose

(-) polysaccharides containing galacturonic acid

Pectin

Mediate dynamic activities

Proteins