Advanced Biology Cell Structure Chapter 5

All organisms are composed of cells  Prokaryotes have a single circular molecule of DNA, while eukaryotic cells have a nucleus, bounded by a nuclear membrane and containing DNA.

All organisms are composed of cells  Cytoplasm fills the interior of the cell, exclusive of the nucleus, and a plasma membrane encloses the cell and separates it from its surroundings. The plasma membrane contains several types of proteins that allow the cell to interact with its environment.

All organisms are composed of cells  Early cell theory included three principles: (1) All organisms are composed of one or more cells; (2) cells are the smallest living things; and (3) cells arise only by division of previously existing cells.

All organisms are composed of cells  Smaller cells are more advantageous than larger cells due to the limitations of communication in relation to surface area-to-volume ratios.

Eukaryotic cells are more structurally complex than prokaryotic cells.  Most prokaryotic cells are encased by a strong cell wall and can be classified using the Gram staining procedure.  Gram Positive – thicker cell wall retains the violet stain  Gram Negative – thinner wall, does not retain violet stain, but will appear pink due to the second stain applied.

Eukaryotic cells are more structurally complex than prokaryotic cells.  Some prokaryotes use a flagellum for locomotion.  Because prokaryotic cells lack membrane-bounded organelles, all cytoplasmic constituents have access to all areas of the cell.

Eukaryotes: Cells with Complex Interiors  Eukaryotic cells have extensive internal compartmentalization, with multiple membrane-bounded organelles carrying out specific functions.

The Nucleus: Information Center for the Cell  The nucleus is the repository for the genetic information that directs cell activities.  The surface of the nucleus is bounded by two phospholipid bilayer membranes that form the nuclear envelope.

The Nucleus: Information Center for the Cell  DNA is organized into chromosomes located in the nucleus.

The Endomembrane System  The endoplasmic reticulum is an extensive system of folded membranes that compartmentalizes the cell's interior.  The Golgi apparatus collects, packages, modifies, and distributes molecules throughout the cell.

The Endomembrane System  Lysosomes contain digestive enzymes that catalyze the rapid breakdown of proteins, nucleic acids, and carbohydrates.

Ribosomes: Sites of Protein Synthesis  Two ribosomal subunits join to form a ribosome when they attach to messenger RNA to direct protein synthesis.

The Cytoskeleton: Interior Framework of the Cell  The cytoplasm of all eukaryotic cells is meshed by a network of protein fibers called the cytoskeleton, which supports the shape of the cell and anchors its organelles.

The Cytoskeleton: Interior Framework of the Cell  Eukaryotic cells may contain three types of cytoskeletal fibers: actin filaments, microtubules, and intermediate filaments.

Not all eukaryotic cells are the same.  Vacuoles and Cell Walls Plant cells usually contain a large central vacuole for storage, and are encased by thick cell walls and often even by strong secondary walls.

Not all eukaryotic cells are the same.  The Extracellular Matrix Animal cells lack the thick cell walls of plants, but secrete a mixture of glycoproteins to form an extracellular matrix, which helps coordinate the behavior of all the cells in a particular tissue.