BIS2D | QZ 3 (11-16) 🦠

• Are made of cells that 1) cover surfaces and create barriers or 2) form glands specialized in secretion


  Epithelial tissues
• What do fibroblasts in connective tissues secrete?


  Extracellular matrix (ECM) molecules
• Examples of Extracellular matrix (ECM) molecules:

  • Proteoglycans
  • Fibrous proteins (Collagen, elastin, fibronectin, laminin)
• Fibrous proteins can also be:

  Adhesive proteins
• Fibrous protein in tendon and cartilage?

  Fibronectin
• Fibrous protein in basal lamina? What does it separate?

  1. Laminin cells
  2. Epithelial cells and the adjacent connective tissue
• What occurs at points of cell-cell and cell-matrix contact in all tissues? It is highly abundant in what?

  1. Specialized cell junctions
  2. Epithelia
• Cell junctions are classified as:

  • Occluding
  • Anchoring
  • Communicating
• Cadherin connects to actin filaments.

  Function: To resist forces that may pull cells apart


  Adherens junctions
• Cadherin connects to intermediate filaments

  Function: To provide mechanical strength (very abundant in epidermis or heart muscle) 


  Desmosomes
• Integrin connects to intermediate filaments inside the cell and to laminin in the basal lamina.

  Function: To keep epithelial cells firmly attached to the basal lamina 


  Hemidesmosomes
• Necessary in epithelial cells to create a barrier so the lumen of the compartment covered by the epithelium is isolated.

  Function: Seal cells together so molecules can’t leak freely across the epithelium establishing apical and basolateral domains 


  Tight junctions
• Connect adjacent cells creating channels from the cytoplasm of a cell to that of the other cells

  Function: Small pore in the channel that allows free transit of inorganic ions and small water soluble proteins 


  GAP junctions
• What connects all cells together in the plant cell walls?

  Cytoplasmic channels of plasmodesmata
• Each what is lined with plasma membrane that is common in 2 connected cells?

  Plasmodesma
• What connects cells to each other or to the ECM?

  Cell adhesion molecules (CAMs)
• Cell adhesion is a what type of process?

  Dynamic
• Cells can alter their adhesive properties and disengage from an epithelium.
• Neutrophil migration is mediated by?


  Dynamic CAM interactions
• Individual CAMs have low affinity for their interacting partner so a single interaction is weak, and as a consequence, transient.
• What enables it to bind in its own characteristic way to other cells and the ECM?

  Each cell has a particular combination and amount of CAMs
• Simultaneous binding of multiple CAMs to other cells and the ECM increases the strength of interactions.
• CAMs must also attach (via anchor proteins) to the cytoskeleton inside the cell.
• What is thought to assist and stabilize the lateral clustering of CAMs?

  The cytoskeleton
• How are epithelial cells organized to create an effective barrier?

  Epithelial tissues form continuous barriers to protect against external environments. Within these tissues, epithelial cells build environment—facing apical membranes, junction complexes that anchor neighboring cells together, and basolateral surfaces that face other cells. There are a variety of connections between epithelial cells that contribute to this barrier.
• How do cells connect with each other and the ECM?

  Specialized cell junctions occur points of cell-cell and cell-matrix contact in all tissues, and highly abundant epithelia.
• Describe the characteristics that cell adhesion molecules (CAMs) have in common.

  Cell adhesion molecules (CAMs) are a subset of cell surface proteins that are involved in the binding of cells with other cells or with the extracellular matrix (ECM), in a process called cell adhesion. CAMs are composed of 3 conserved domains: intracellular domain that interacts with the cytoskeleton transmembrane domain, and extracellular domain. One feature of CAMs is that almost all of their extracellular regions contain repeating copies of structural domains.
• What would happen if cells were not adhesive? If cells were hyper–adhesive?

  If cells were not adhesive, they cannot be packed with each other. For example, if epithelial cells were not adhesive, they can’t be packed together, and the barrier function will be impaired. If cells were hyper-adhesive, they will stick together and cannot migrate to their destination. For example, during embryo development, cells migrate to their own destinations and form 3 different layers. If cells were hyper-adhesive, then the embryo development will be impaired.
• What mechanisms ensure that is cell attaches to an appropriate partner?

  Cells can sort themselves according to the type and level of CAMs they express. Each cell has a particular combination and the amount of CAMs that enables it to bind in its own characteristic way to other cells and the ECM.
• Describe intracellular mechanisms required for stable cell adhesion.

  Intracellular regions of cell-surface proteins interact with the cytoskeleton to promote stable cell adhesion. For example, intracellular domains of cadherins bind to actin filament via anchor proteins that holds the cell adhesion site in place. Other cell-surface adhesion proteins link to other components of the cytoskeleton such as intermediate filaments.
• Most signaling molecules are hydrophilic and are therefore unable to cross the plasma membrane directly. They bind to cell-surface receptors, which in turn generate one or more signals inside the target cell.
• Some signaling molecules are hydrophobic and can diffuse across the plasma membrane.
• Proteins, amino acids, nucleotides, steroids, fatty acids, even light are what?

  Extracellular signals
• This requires cells to be in direct cell-to-cell contact?


  Contact-dependent signaling
• This depends on signals that are released into the extracellular space and act locally on nearby cells?


  Paracrine signaling
• Performed by neurons that transmit signals electrically along their axons and release neurotransmitters at synapses, which are often located far away from the cell body.


  Synaptic signaling
• This depends on endocrine cells, which secrete hormones into the bloodstream that are then distributed widely throughout the body.


  Endocrine signaling
• Signaling protein is activated by the addition of phosphate group and inactivated by the removal of the phosphate.
• Monitoring what?

  Extracellular signals
• How do cells monitor?

  Receptors