ch 11 Cell-Cell Interactions flashcards

Cell–Cell Interactions

• Cells modify their environment and interact through social networks.

• Crucial for both unicellular and multicellular organisms.

• Focus on cell surface, cell-cell attachments, and communication.

11.1 The Cell Surface

• The plasma membrane defines the boundary between life and nonlife.

• Cells secrete extracellular material (ECM) for support and attachment.

• ECM is a fibre composite with filaments resisting tension and ground substance resisting compression.

• Animal ECM contains collagen and proteoglycans.

• Plant cell walls contain cellulose microfibrils and pectins.

• Integrins link the cytoskeleton to the ECM in animal cells.

• Plant cells have primary and secondary cell walls for support and protection.

• Turgor pressure is essential in plant cells, and expansins enable cell growth.

11.2 How Do Adjacent Cells Connect and Communicate?

• Intercellular connections maintain tissue structure and function.

• Middle lamella (plants) and ECM (animals) glue cells together.

• Tight junctions form watertight seals in animal cells.

• Desmosomes provide strong adhesions via membrane proteins and intermediate filaments.

• Selective adhesion occurs via cadherins.

• Gap junctions (animals) and plasmodesmata (plants) allow direct cytosolic communication.

11.3 How Do Distant Cells Communicate?

• Cells communicate over long distances using signalling molecules.

• Hormones = signalling molecules secreted into bodily fluids that act on target cells.

• Receptors (in cytosol or on the membrane) initiate signal transduction.

• Lipid-soluble molecules bind to intracellular receptors, often affecting gene expression.

• Lipid-insoluble molecules bind to surface receptors, triggering signal transduction pathways.

• G-protein-coupled receptors activate G proteins and second messengers (e.g., cAMP, Ca^{2+}).

• Second messengers amplify signals and activate protein kinases.

• Enzyme-linked receptors and ion channel receptors are other types.

• Insulin and acetylcholine are examples of signalling molecules that work through these receptors.

• Signals lead to changes in gene expression or protein activity.

• Signal deactivation mechanisms exist to prevent overstimulation.

11.4 Signalling between Unicellular Organisms

• Unicellular organisms use quorum sensing to monitor population density.

• Signalling molecules trigger coordinated activities like biofilm formation.

• Slime molds aggregate in response to quorum sensing.

• Cell signalling enables organisms to respond to environmental changes.

The Cell Cycle

• Cells divide to produce new cells, as proposed by Rudolf Virchow.

• Mitosis leads to somatic cells.

Here are the answers to your questions:

1. Utility of Extracellular Layers:

   • In both animal and plant cells, extracellular layers provide structural support and facilitate cell-cell attachment. These layers are essential for tissue organization and function.

2. Structure of Animal Extracellular Matrix (ECM):

   • The animal ECM contains collagen and proteoglycans. Its composition can vary greatly depending on the tissue. For example:

     • Bone ECM is highly mineralized, providing rigidity and support.

     • Cartilage ECM is more flexible, allowing for cushioning and movement.

3. Structure and Function of Plant Cell Walls:

   • Plant cell walls consist of cellulose microfibrils and pectins.

   • Primary cell walls are thinner and more flexible, enabling cell growth.

   • Secondary cell walls are thicker and more rigid, providing additional support and protection.

   • Turgor pressure is essential in plant cells, and expansins facilitate cell growth.

4. Structure and Function of Cell Junctions in Animal Cells:

   • Tight junctions form watertight seals between cells.

   • Desmosomes provide strong adhesions via membrane proteins and intermediate filaments.

   • Gap junctions allow direct cytosolic communication between adjacent cells.

5. Structure and Function of Plasmodesmata in Plant Cells:

   • Plasmodesmata are channels through plant cell walls that connect the cytoplasm of adjacent cells, allowing the passage of water, nutrients, and signalling molecules. This direct communication is crucial for coordinating activities and maintaining tissue integrity in plants.