Cell Biology Review. The key components of cells that concern us are as follows: 1. Nucleus

Transcription

1 Cell Biology Review Development involves the collective behavior and activities of cells, working together in a coordinated manner to construct an organism. As such, the regulation of development is intimately tied to the regulation of cells and cellular activities. As developmental biologists we need to understand how cells! Proliferate! Migrate! Signal! Respond to signals! Secrete specialized extracellular matrices! Undergo programmed cell death! Form specialized structures (e.g. axons or filapodia)! Fuse! Etc., etc. Furthermore, to understand the regulation of these processes, we have to consider the roles of specific regulatory molecules, such as! Transcription factors! Cell surface receptors! Calcium channels on the ER! Neurotransmitters in secretory vesicles To understand these processes, it is important to consider the subcellular organelles or structures that mediate them. We must therefore understand basic concepts regarding how the cell is compartmentalized, the functions of various structures, and how intracellular trafficking is regulated. Without this foundation of cell biology, we won t be able to understand and appreciate the dynamic processes that control developmental events. We therefore need to briefly review some of the key aspects of cell biology as they relate to development. Unfortunately the text does not contain such a review. If you still have your cell biology text, it would be worth flipping through it. Otherwise there is a nice concise description of cell biology in the Wikipedia online encyclopedia: The key components of cells that concern us are as follows: 1. Nucleus! Bound by a double membrane (the nuclear envelope)! Contains chromosomes/genes! Site of gene transcription and mrna processing! Very important for controlling the properties of a cell! Stores all the genetic information to be passed from generation to generation of both cells and organisms! Changes in cell fate usually involve changes in gene expression, therefore changes in nuclear activity

2 2. Cell membrane (plasmamembrane) more than a lipid bilayer! Separates cell contents from the environment! Substances entering or exiting the cell must cross! Contains many proteins, which funciton as channels, receptors and more! Site of perception for many environmental cues such as developmental signals! Site of emination for many cell signals 3. Cytoplasm everything inside the plasmamembrane except the nucleus! Cytosol the liquid/gelatinous contents of cells! Organelles units of structure and function! Cytoskeleton! Ribosomes synthesize proteins from mrna! Information exchange between the nucleus and plasmamembrane must be transduced across the cytoplasm (signal transduction) 4. Rough endoplasmic reticulum! Part of the endomembrane system important for the secretory system! Important for the synthesis and processing of membrane proteins and secreted proteins! Has ribosomes attached to its cytosolic face! Proteins are inserted into the RER as they are translated! Transport vesicles bud off and move to the golgi 5. Golgi apparatus! consists of organized stacks of membrane-enclosed compartments! Processes and sorts proteins destined for the plasmamembrane, secretion, lysosomes, vacuoles! Pinches off vesicles for transport of cargo to the various membranes! RER and Golgi important if a cell needs to signal another cell or change its surface characteristics 6. Mitochondrion! Energy production: ATP from glucose (TCA cycle + electron transport system+oxidative phosphorylation)! Controls programmed cell death! Double membrane bound! Contains DNA encoding some mitochondrial proteins 7. Plastids

3 ! Photosynthesis and starch synthesis! Synthesis of some plant hormones! Double membrane bound! Contains DNA encoding some plastidal proteins 8. Vacuole! membrane bound! Storage of ions (Ca ++ ), conjugated hormones! Fluid balance (turgor)! particularly important in plants for driving cell expansion (growth) 9. Endosomes! Vesicles formed during endocytosis.! Receptor-mediated endocytosis is a means to import selected extracellular macromolecules! Plasmamembrane can be recycled or turned over to remove receptors, etc. 10. Lysosome! Membrane bound! Turnover of cell components (degrades proteins, lipids, carbohydrates) and organelles! Destination for many endocytic vesicles 11. Cytoskeleton--protein fibers inside the cell A. Microfilaments! Made by polymerization of the protein actin! Polymerization and depolymerization are reversible and can be controlled! Interact with myosin for motive force! In animal cells, important for cell shape, cell movement, and cytokinesis (microvilli and pseudopodia) B. Microtubules! Made by polymerization of the protein tubulin! Polymerization and depolymerization are reversible and can be controlled! interact with dyneins and kinesins for motive force! cilia and flagella! Important for directing vesicle traffic, organellar movement and chromosome separation during nuclear division! In plant cells, important in establishing cell shape by controlling cellulose deposition C. Intermediate filaments! Heterogeneous population of fibrous proteins! More stable than actin filaments or microtubules! Provide internal structure to cells

4 12. Extracellular Matrix (Cell wall in plants)! Fibrous matrix outside the cells! In animals, contains glycoproteins! In plants, contains cellulose and other carbohydrates, as well as proteins! Dynamic changes during development! Has both structural and regulatory functions! Important for pathfinding during cell migration 13. Cell junctions--occur at points of cell-cell and cell-matrix contact. a. Occluding junctions (tight junctions) seal epithelial cells together and prevent molecules from leaking from one side of an epithelial sheet to another. b. Anchoring junctions (for example adherens junctions; desmosomes) create a link between cell-cell or cell-ecm junctions and intracellular networks of actin or intermediate filaments. These structures allow sheets of cells to undergo coordinated shape changes. Anchoring junctions also include proteins that initiate intracellular signaling cascades in response to extracellular signals. c. Communicating junctions include gap junctions and plasmodesmata (plants). They form direct cytoplasmic connections. 2 main kinds of animal cells epithelia form sheets rest on an ECM layer called basal lamina line body cavities and organ surfaces external side often contains microvilli extensive contacts with neighboring cells often form tight junctions with neighbors mesenchyme sparse contacts with neighbors surrounded by ECM sometimes migratory Cell Division: Mitosis produces two daughter cells with the same genetic composition as the mother cell = proliferative Meiosis produces 4 daughter cells each with half the chromosome number as the mother cell! Important for gamete formation

5 Subcellular localization! an important mechanism for regulating cell activities or signaling events.! Protein-protein interactions, lipid modifications, or compartmentalization can cause two molecules (e.g. an enzyme and its substrate) to be co-localized! can prevent inappropriate interactions.