Plasma Membrane and Cell Surface Nucleus and Ribosomes Endomembrane System Figure 4.6a Plasma Membrane Cell Surfaces The plasma membrane separates the living cell from its nonliving surroundings. Most cells secrete materials for coats of one kind or another That are external to the plasma membrane. Extracellular coats help protect and support cells facilitate interactions between cellular neighbors in tissues Plant cells and bacterial cells have cell walls, Which help protect the cells, maintain their shape, and keep the cells from absorbing too much water. Animal cells have an extracellular matrix, Which helps hold cells together in tissues and protects and supports them (not shown). Plasma Membrane and Cell Surface Nucleus and Ribosomes Endomembrane System 1
The Nucleus: Genetic Control of the Cell The nucleus is the manager of the cell. Genes in the nucleus store information necessary to produce proteins. Prokaryotes do not have nuclei. Their genes (on DNA) are in the nucleoid region Ribosomes: Protein Synthesis Ribosomes are responsible for protein synthesis. Structure and Function of the Nucleus The nucleus is bordered by a double membrane called the nuclear envelope. It contains chromatin and a nucleolus. Chromatin: long strands of DNA and associated proteins. The DNA stores the genetic information (genes). Nucleolus: assembles ribosomes How DNA Controls the Cell DNA controls the cell by transferring its coded information into RNA. The information in the RNA is used to make proteins. The Endomembrane System: Manufacturing, Distributing, and Storing Cellular Products Plasma Membrane and Cell Surface Nucleus and Ribosomes Endomembrane System Not found in bacterial cells! 2
The Endoplasmic Reticulum The endoplasmic reticulum (ER) Produces an enormous variety of molecules. Is composed of smooth and rough ER. Rough ER Smooth ER The smooth ER lacks the surface ribosomes of rough ER and produces lipids, including steroids. Rough ER The roughness of the rough ER is due to ribosomes that stud the outside of the ER membrane. The roughness of the rough ER is due to ribosomes that stud the outside of the ER membrane. The functions of the rough ER include: The functions of the rough ER include: Producing two types of membrane proteins Producing two types of membrane proteins Membrane proteins Secretory proteins Membrane proteins Secretory proteins Producing new membrane After the rough ER synthesizes a molecule, it packages the molecule into transport vesicles. These vesicles head off to the Golgi Apparatus Producing new membrane The Golgi Apparatus The Golgi apparatus Works in partnership with the ER. Refines, stores, and distributes the chemical products of cells. 3
are membranous sacs. Contractile vacuoles of protists get rid of excess water. Central vacuoles of plants store nutrients, absorb water, contain some pigments or poisons. A lysosome is a membraneenclosed sac that contains digestive enzymes to break down macromolecules. A review of the endomembrane system An amazing system that manufactures, distributes, and stores cellular products! Plasma Membrane and Cell Surface Nucleus and Ribosomes Endomembrane System Energy Conversion: Chloroplasts & Mitochondria Cells require a constant energy supply to do all the work of life. Not found in bacterial cells! Chloroplasts Chloroplasts are the sites of photosynthesis, the conversion of light energy to chemical energy. All little green circles are chloroplasts Cell walls 4
Mitochondria Mitochondria are the sites of cellular respiration, which involves the production of ATP from food molecules. Plasma Membrane and Cell Surface Nucleus and Ribosomes Endomembrane System The : Cell Shape and Movement The cytoskeleton consists of a network of fibers. Mechanical support to maintain cell shape Can change cell shape to allow movement Also, recently found in bacterial cells! Cilia and flagella are motile appendages. Plasma Membrane and Cell Surface Nucleus and Ribosomes Endomembrane System Not found on most plant cells! 5
Flagella propel the cell in a whiplike motion. Cilia move in a coordinated back-and-forth motion. Plasma Membrane and Cell Surface Nucleus and Ribosomes Endomembrane System Membrane-bound organelles found only in plants Amyloplast stores starch (stained blue with iodine) All little green circles are Cell walls chloroplasts Chloroplast performs photosynthesis Chromoplast stores pigments (little orange circles) 6