Membranes compartmentalize the interior of the cell and facilitate a variety of metabolic activities. Chloroplasts and a rigid cell wall are what distinguish a plant cell from an animal cell. A typical animal cell contains a variety of membranous organelles. Rough Ribosomes Rough Smooth Golgi apparatus Smooth Microtubule Not in most plant cells Flagellum Lysosome Not in animal cells Central vacuole Chloroplast Cell wall Intermediate filament Microfilament Cytoskeleton Centriole Peroxisome Ribosomes Golgi apparatus Mitochondrion Cytoskeleton Microtubule Intermediate filament Mitochondrion Plasma membrane Peroxisome Plasma membrane Microfilament ORGANELLES OF THE ENDOMEMBRANE SYSTEM The nucleus is the genetic control center. Chromatin is DNA attached to proteins. Chromosomes are composed of chromatin. Nucleolus Pore Chromatin Two membranes of nuclear envelope The nucleus is enclosed by a nuclear envelope, which is a double membrane with perforations allowing for the passage of materials in and out of the nucleus. The nucleolus is a prominent structure in the nucleus that forms the building blocks for ribosomes. Following instructions from the DNA, the nucleus synthesizes RNA. One type of RNA, messenger RNA, is carried to the ribosomes in the cytoplasm to be translated into the amino acid sequence of proteins. Ribosomes Rough
Cell organelles of the endomembrane system are connected directly or indirectly through the movement of vesicles. The endomembrane system is a collection of membranous organelles that manufactures and distributes cell products. Smooth, or smooth ER --Synthesizes lipids --Processes toxins and drugs in liver cells --Stores and releases calcium ions in muscle cells Rough ER is called such due to the presence of ribosomes embedded in the membrane. Rough ER manufactures more membrane and synthesizes and modifies proteins to be transported out of the cell (secretory proteins), embedded in membranes (such as glycoproteins) or transported to other organelles. The Golgi apparatus finishes, sorts, and ships cell products. 4 Receiving side of Golgi apparatus Transport vesicle from ER Golgi apparatus Golgi apparatus New vesicle forming Shipping side of Golgi apparatus Transport vesicle from the Golgi TEM 130,000
Lysosomes are sacs of digestive enzymes that help to provide the cell with nutrients and provide the cell with a recycling mechanism. Damaged organelles are enclosed in a vesicle which lysosomes can fuse with to breakdown and recycle. Read connection section on abnormal lysosomes. Vacuoles function in the general maintenance of the cell Plant cells contain a large central vacuole, which has lysosomal and storage functions. The central vacuole of plants can also harbor secondary metabolites that attract pollinators and deter plant-eating predators. Central vacuole Chloroplast Colorized TEM 8,700 ENERGY-CONVERTING ORGANELLES Transport vesicles help to tie all of the endomembrane system together into a cohesive, functioning community. These vesicles transport membranes and the chemical components within them to other organelles of the endomembrane system. They are also responsible for the acquisition or release of macromolecules that may not be able to pass through the cellular membrane. Chloroplasts, in all photosynthetic eukaryotes, are the organelles that are responsible for the conversion of light energy to chemical energy in the form of sugars. This conversion is integral to the sustenance of all living organisms. No human engineered system comes close to duplicating the efficiency of photosynthesis.
The granum (plural-grana) is the site where chloroplasts trap the solar energy and convert it to chemical energy. Mitochondria are the organelles in eukaryotic organisms reponsible for converting chemical energy in the form of sugars into ATP (adenosine triphosphate). ATP is the primary energy source for all cellular activity. Chloroplast Enzyme molecules that make ATP are embedded in the inner membrane. Mitochondrion Outer membrane Figure 4.14 Stroma Inner and outer membranes Granum Intermembrane space TEM 9,750 Why might energy producing organelles have double membranes? Why might the inner membrane have so many folds? Intermembrane space Inner membrane Cristae Matrix TEM 44,880 The Cytoskeleton The cell s internal skeleton helps organize its structure and activities. Microfilaments help maintain cell shape. Intermediate filaments reinforce cell shape and anchor some organelles. Microtubules have many functions, including forming tracks for the movement of vesicles and organelles. Microfilaments of actin enable cells to change shape and move. Microfilaments are solid rods made of globular proteins. Intermediate filaments reinforce the cell and anchor certain organelles. They are made of fibrous proteins. Do such things as hold the nucleus in place. Actin subunit Fibrous subunits Tubulin subunit Microtubules give the cell rigidity and provide anchors for organelles and act as tracks for organelle movement. They are hollow tubes of globular proteins. 7 nm 10 nm 25 nm Microfilament Intermediate filament Microtubule
Cilia and Flagella Cilia and flagella are the locomotive appendages of certain cells. Cilia are short appendages, often numerous, that help protists move through the water and assist in the movement of fluids across tissues in animals. It is the action of the paired microtubules that cause the whipping action of the cilia and flagella. Flagellum Electron micrographs of cross sections: Flagella are longer appendages, often less numerous, that are found on flagellated sperm of plant and animals. Colorized SEM 4,100 LM 600 Outer microtubule doublet Central microtubules Radial spoke Dynein arms Plasma membrane Basal body (structurally identical to centriole) Flagellum Basal body TEM 206,500 TEM 206,500 Figure 4.17A Figure 4.17B The surfaces of cells are important for the structural support, protection of the cell, and for joining to other cells. In plant cell walls it is cellulose and lignin that provide rigidity to the plant, allowing it to stand upright and maximize ability to photosynthesize. Plant cells are joined by plasmodesmata which are channels that allow for a transfer of cytoplasmic fluid. Vacuole Walls of two adjacent plant cells Plasmodesmata Animal cells are embedded in an extracellular matrix that bind cells into tissue providing support and protection. Animal cells are joined by three types of junctions: Tight junctions form cells into a leakproof sheet (digestive tract). Anchoring junctions join cells with cytoskeletal fibers (skin tissues). Gap junctions allow for the transfer of small molecules between cells (similar to plasmodesmata in plants). Layers of one plant cell wall Cytoplasm Plasma membrane
Eukaryotic organelles fall into four functional groups: Manufacturing Breakdown Energy processing Support, movement, and communication between cells All life forms: 1) consist of cells bound by membranes 2) have DNA as genetic material Remember: Structure determines function. 3) carry out metabolism involving the interconversion of energy and chemical compounds.