BIOLOGY 1408 Chapter 4 : Tour of the cell part II Golgi Apparatus n The Golgi apparatus functions in conjunction with the ER by modifying products of the ER Products travel in transport vesicles from the ER to the Golgi apparatus One side of the Golgi apparatus functions as a receiving dock for the product and the other as a shipping dock Products are modified as they go from one side of the Golgi apparatus to the other and travel in vesicles to other sites Receiving side of Golgi apparatus Golgi apparatus Golgi apparatus Transport vesicle from ER New vesicle forming Shipping side of Golgi apparatus Transport vesicle from the Golgi 1
Lysosomes n A lysosome is a membranous sac containing digestive enzymes The enzymes and membrane are produced by the ER and transferred to the Golgi apparatus for processing The membrane serves to safely isolate these potent enzymes from the rest of the cell Lysosomes n One of the several functions of lysosomes is to remove or recycle damaged parts of a cell The damaged organelle is first enclosed in a membrane vesicle Then a lysosome fuses with the vesicle, dismantling its contents and breaking down the damaged organelle n White blood cells engulf bacteria, which then become chewed to pieces in the lysosomes Lysosomes Digestive enzymes Plasma membrane Lysosome Digestion Food vacuole 2
Lysosomes n When lysosomes membranes leak, their enzymes will eat the cell and thus cause cell death (necrosis). n There are more than 50 diseases associated with malfunctioning lysosomes. Since lysosomes do not work, many proteins that need to be destroyed accumulate causing cells to malfunction or burst. n There are strong indications that getting older is due to mitochondria and lysosomes gone bad. Lysosomes n A recent science report indicates scientists blocked the ageing process in mice livers by stopping the build-up of harmful proteins inside the organ's cells. n In healthy organisms, specialized molecules, the "chaperones", dispose of cell debris by directing it to lysosomes where the chaperones dock with special transporter proteins n As organs age, the docking proteins start failing. These researchers supplied extra copies of the docking proteins and turned old livers into young livers.. Vacuoles n Vacuoles are membranous sacs that are found in a variety of cells and possess an assortment of functions. Examples are: the central vacuole in plants with hydrolytic functions pigment vacuoles in plants to provide color to flowers, contractile vacuoles in some protists to expel water from the cell 3
Plant Vacuole Nucleus Central vacuole Chloroplast Protist vacuole Nucleus Contractile vacuoles Paramecium with contracting vacuoles EndoMembrane System n The membranes within a eukaryotic cell are physically connected and compose the endomembrane system n From what we seen, those organelles with membranes within an eukaryotic cell are : n n Rough and smooth endoplasmic reticulum (ERs), Golgi apparatus, n lysosomes, vacuoles, and the plasma membrane 4
Endo-Membrane System n Some components of the endo-membrane system are able to communicate with others with formation and transfer of small membrane segments called vesicles One important result of communication is the synthesis, storage, and export of molecules n The following figure summarizes the relationships among the major organelles of the endomembrane system Nucleus Nuclear membrane Rough ER Smooth ER Transport vesicle Transport vesicle Golgi apparatus Lysosome Vacuole Plasma membrane Energy Converting Organelles n Within the cell we have additional organelles of extreme importance to the viability of the cell. n These are the organelles that transform one energy form into another energy form n What energy forms are there? n Light energy n Chemical energy n Mechanical energy n Life forms convert Light energy Chemical energy Mechanical energy 5
Biological Energy Chemical energy into chemical energy and mechanical energy Light energy into chemical energy Chemical energy into chemical energy and mechanical energy Biological Energy Plants use sunlight to make sugars (carbohydrates) from CO 2 and H 2 O Thus the energy from sunlight is used to make covalent bonds and link carbons from CO 2 together with H 2 O and form C 6 H 12 O 6 Sun energy is thus converted into chemical energy e.g. a series of covalent bonds! Every aerobic organism (e.g. plant and animal cells) liberates that energy in the covalent bonds of a carbohydrate with the use of O 2 in the mitochondria and reforms CO 2. The released energy is now transferred into molecules of ATP. Cells use ATP to make everything work in a cell. Chloroplasts n Chloroplasts convert solar energy to chemical energy n Chloroplasts are the photosynthesizing organelles of plants (animal cells do not have chloroplasts!). n In photosynthesis, light energy, CO 2 and water are converted into sugar molecules ( = chemical energy) n Just like mitochondria, chloroplasts also have 2 membranes surrounding them 6
Chloroplasts Chloroplasts are partitioned into compartments. The important parts of chloroplasts are : the stroma, thylakoids, and grana Chloroplast Stroma Inner and outer membranes Granum Intermembrane space Chloroplasts Micrograph of the cells of a moss species, Plagiomnium. The round green organelles are chloroplasts. Mitochondria n Mitochondria harvest chemical energy from food n This process occurs in most eukaryotic cells and is called cellular respiration, which occurs inside the mitochondria n Cellular respiration involves conversion of chemical energy in foods to chemical energy in ATP (adenosine triphosphate) n ATP is the universal energy molecule used by most living cells 7
Mitochondria n Mitochondria are encased by two membranes : the outer and inner mitochondrial membrane n Space between the 2 membranes is called the intermembrane space n The inner mitochondrial membrane encloses the mitochondrial matrix where materials necessary for ATP generation are found n Every cell that requires O 2 to survive has mitochondria : the place where O 2 is used are the mitochondria! n The more active a cell, the more mitochondria in that cell. Mitochondrion Intermembrane space Outer membrane Inner membrane Cristae Matrix Endo-Symbiosis Hypothesis n The hypothesis of endosymbiosis proposes that mitochondria and chloroplasts were formerly small prokaryotes that began living within larger cells n Symbiosis benefited both cell types n When compared, you find that mitochondria and chloroplasts have (1) DNA and (2) ribosomes The structure of both DNA and ribosomes is very similar to that found in prokaryotic cells, and mitochondria and chloroplasts replicate much like prokaryotes 8
Mitochondrion Engulfing of photosynthetic prokaryote Some cells Engulfing of aerobic prokaryote Host cell Chloroplast Mitochondrion Host cell Cytoskeleton n In addition to all the membraneous cellular organelles, cells also contain a network of protein fibers, called the cytoskeleton, that functions in cell structural support and motility n These are NOT surrounded by membranes n Evidence indicates that cellular motility/flexibility and cellular regulation result when the cytoskeleton interacts with proteins called motor proteins Cytoskeleton n The cytoskeleton is composed of three kinds of protein fibers Microfilaments (actin filaments) support the cell s shape and are involved in motility Intermediate filaments reinforce cell shape and anchor organelles Microtubules (made of tubulin) shape the cell and act as tracks for motor protein 9
Actin subunit Microfilament 7 nm Cytoskeleton n This picture shows a fluorescent microscope image of a cell, where only the actin proteins are tagged with a red fluorescent tag. n Actin is almost always involved in some kind of motion activity. n Microfilaments are the smallest of the cytoskeleton fibers Nucleus Cytoskeleton n Here, the intermediate filaments are tagged with a green fluorescent tag. Fibrous subunits Intermediate filament 10 nm n We can see that these filaments are like cobwebs, spanning almost the entire cell n They re-inforce the cell shape and keep organelles in place Cytoskeleton Nucleus n In this image, the tubulin proteins are tagged with a green tag. n Once again, their presence in the cell is quite abundant Tubulin subunit 25 nm n Microtubules are the largest of the cytoskeleton filaments and very important for the dynamics of cellular trafficking. Microtubule 10
Cytoskeleton Microtubules play an important role in forming the spindle apparatus in the separation of chromosomes during cell division (left image), and during transport of larger structures ( such as vesicles, organelles) inside cells. chromosomes Spindle apparatus Cilia and Flagella n Microtubules are at the basis of some important movement initiators n Two important structures made from microtubules are n Cilia : short and often numerous per cell n Flagella : longer and often few per cell Cilia n Cilia are present on some protists for locomotion and feeding n Cilia are present in multi-cellular cells for creating currents and move things above the cells n In general, cilia are not found in pro-karyotes. 11
Cilia Parmecium, a uni-cellular protist, with cilia for locomotion and feeding A rotifer, a multi-cellular animal, with a ring of cilia around the mouth for creating currents for feeding. Cilia Microscopic view of the lining of the trachea, showing cells with cilia. Flagella n Flagella are present in both prokaryotes and eukaryotes; the are used to move the the cell Flagellum E.coli, a bacterium, powered by flagella Almost all sperm cells are flagellated. The human sperm cell is the only cell with a flagella in the human body ( similar in other mammals). 12
Structure of Cilia/Flagella n Although differences exist, flagella and cilia have a common structure and mechanism of movement n Both flagella and cilia are made of microtubules wrapped in an extension of the plasma membrane n A ring of nine microtubule doublets surrounds a central pair of microtubules n This arrangement is called the 9 + 2 pattern and is anchored in a basal body with nine microtubule triplets arranged in a ring. Structure of Cilia/Flagella ExtraCellular Matrix n Cells synthesize and secrete the extracellular matrix (ECM) that is essential to cell function n The ECM is composed of strong fibers of collagen, which holds cells together and protects the plasma membrane n ECM attaches through connecting proteins that bind to membrane proteins called integrins n Integrins span the plasma membrane and connect to microfilaments of the cytoskeleton 13
Glycoprotein complex with long polysaccharide EXTRACELLULAR FLUID Collagen fiber Connecting glycoprotein Integrin Plasma membrane Microfilaments CYTOPLASM Animal Cell Junctions n Adjacent cells in animals communicate, interact, and adhere through specialized junctions between them Tight junctions prevent leakage of extracellular fluid across a layer of epithelial cells Anchoring junctions fasten cells together into sheets Gap junctions are channels that allow molecules to flow between cells Tight junctions Anchoring junction Gap junctions Plasma membranes of adjacent cells Extracellular matrix 14
Plant Cells n Plant, but not animal cells, have a rigid cell wall It protects and provides skeletal support that helps keep the plant upright against gravity Plant cell walls are composed primarily of cellulose n Plant cells have cell junctions called plasmodesmata that serve in communication between cells Walls of two adjacent plant cells Vacuole Plasmodesmata Primary cell wall Secondary cell wall Cytoplasm Plasma membrane Things to Know 1. Describe microscopes and their importance in viewing cellular structure 2. Who were the early pioneers in microscopy? 3. What sizes are we dealing with when looking at cells? Distinguish between the size of a prokaryotic and eukaryotic cell. 4. What is the relationship between size and surface to volume ratio 5. What are the basics of a cell organization and what makes the difference between prokaryotic and eukaryotic cells.? 6. Describe the term membraneous organelle. What different organelles are in the cell and what is their function? 7. Discuss ways that cellular organelles are involved in the manufacture and breakdown of important cellular molecules 15
Things to Know 8. What is the endo-membrane system? 9. Describe the structure of cell membranes and how membrane structure relates to function 10. What energy forms are important in biology? How are they converted? Which organelles are important in energy transformation? What is the endo-symbiotic hypothesis? 11. What is the cytoskeleton? Which different protein filaments are part of it and what is their main function? 12. Compare and contrast cilia and flagella. 13. What is the Extracellular Matrix? 14. What structures and junctions are typical for animal cells but not for plant cells and visa versa? 16