Fluent Essays

12 questions with notes provied Cell Questions: The Eukaryotic Cell Name _________________________ Total points = 92 Your grade = your score/92 x 100 1. Describe the arrangement of the phospholipid molecules in the Cell Membrane as explained by the Fluid Mosaic (Singer) model. Use and define the terms hydrophyllic and hydrophobic in your discussion. Also describe the arrangement and explain the function of the protein molecules in the cell membrane. 10 points 2. What is the function of the Cell Membrane? Define the term selectively permeable and explain its importance to the cell. 4 points 3. Describe the 9 + 2 structure of cilia and flagella. Describe the 9 + 0 structure of centrioles and basal bodies. 4 points 4. Describe the parts of the mitochondrion. Discuss the function of the mitochondrion by going over the main points of cellular respiration and the electron transport chain, metabolic processes that happen within it. 10 points 5. Explain the endosymbiotic theory. Name two organelles that it applies to. 6 points 6. What is the endoplasmic reticulum? Name the two types of endoplasmic reticulum and give the functions of each. 6 points 7. Describe the structure of ribosomes. What is the function of ribosomes? 4 points 8. Describe the structure of the Golgi apparatus. Explain the function of the Golgi apparatus. What are lysosomes? What is their function? 8 points 9. Review the makeup and operation of the endomembrane system. Identify the organelles that are included in it and trace the flow of materials through it. 10 points 10. List and describe the parts of the nucleus. What is the function of the nucleus? 10 points 11. Describe the structure of the chloroplast. Include the membranous structures outside and inside and the liquid interior. What is the function of the chloroplast? 10 points 12. Compare animal and plant cells. 10 points The Cellular Basis of Life Introduction Definition A cell is the basic unit of a living organism that contains genetic material and protoplasm, which is surrounded by a cell membrane. The cell is the structural unit of the organism, carries out its life processes, and forms new cells in the process of cell division. Discovery of Cells and Historical Development of the Cell Theory Discovery of Cells 1. Robert Hooke, an Englishman, discovered cells in 1665. Using a microscope that he made, Hooke observed thin slices of dried cork. Under the microscope, the cork appeared to be made up of tiny boxes. Hooke called these boxes cells, because they resembled the cells or rooms in monasteries of his day. Hooke was the first to use the word “cells” to describe the tiny compartments that together make up an organism. The cork cells that Hooke observed were not living cells. However, he observed living cells in elderberry plants. 2. Anton van Leeuwenhoek, a Dutch inventor and scientist examined many kinds of living cells. Leeuwenhoek used his microscope to examine all sorts of living material including the muscle fibers of a whale, the scales of his own skin, and the lens of ox eyes, various insects, and the wood of trees. One day he examined a drop of water from a pot that he used to measure rainfall outside in his garden. Imagine his amazement as he saw countless tiny animals swimming around inside the drop. Prior to this time, no one could have imagined that a tiny drop of water could teem with so many living creatures. Using his microscope, Leewenhoek had discovered a new world in a drop of water filled with previously unknown living creatures. Leewenhoek called the tiny organisms that he observed “animalcules”, meaning tiny animals. Cell Theory The Cell Theory was developed in the years 1838 and 1839 by two German Scientists, Schleiden and Schwann. Matthias Schleiden was a botanist. After studying many different kinds of plant tissues, he concluded that all plants were composed of cells. Theodor Schwann, a zoologist, reported that all animal tissues were also composed of cells. The Cell Theory, as developed by Schleiden and Schwann stated that all living organisms were composed of one or more units known as cells. In 1855, Rudolf Virchow, a German physician, contributed the concept that cells can arise only from previously existing cells. The Cell Theory in its modern form states that: 1) All living organisms are composed of one or more units called cells. 2) The metabolic reactions of a living organism, including its energy-releasing processes and its biosynthetic reactions, take place within cells. 3) Cells arise from other cells. 4) Cells contain the genetic information of living organisms, and this information is passed from parent cell to daughter cell. Types of Cells – Prokaryotic and Eukaryotic There are two main types of cells: prokaryotic cells and eukaryotic cells. Prokaryotic cells 1. Lack a membrane-bound nucleus 2. Lack membrane-bound organelles. 3. Have genetic material in the form of a single, circular molecule of DNA 4. Are found in Archaea, bacteria, and Cyanobacteria Eukaryotic Cells A eukaryotic cell is a cell having a membrane-bound nucleus, membrane-bound organelles, and chromosomes in which DNA is combined with histone proteins. Eukaryotic Cells: 1. Have a membrane-bound nucleus containing genetic material. 2. Contain membranous organelles. 3. Have rod-shaped chromosomes containing linear DNA bound to special proteins known as histones. 4. Are found in Protists, Fungi, Plants, and Animals. Structure of the Prokaryotic Cell Structures External to the Cell Wall Among the structures external to the cell wall are the: Capsule (slime layer) Flagella Axial filaments, and Pili (fimbriae) Capsule, or Slime Layer A capsule is a jelly-like coating that surrounds the cells of certain bacteria. Chemically, the capsule is composed of a gelatinous polymer of polysaccharide, polypeptide, or both. Functions: 1. It appears to prevent desiccation (drying) of the organism under adverse conditions. 2. Capsules often protect pathogenic bacteria from phagocytosis by cells of the host. Flagella Flagella are long threadlike appendages used for locomotion in certain bacteria. Bacteria can swim by rotating their flagella. Structure The flagellum has three basic parts: 1. The filament, the outer threadlike part composed of the protein flagellin. 2. Hook – a curved portion attached to the proximal end of the filament. 3. Basal body – anchors the flagellum to the cell wall and cytoplasmic membrane. The structure of the flagellum of bacteria is completely different from the cilia and flagella of eukaryotic cells. Mechanism of Movement In the basal body there is a helical rotor powered by a proton gradient that pushes the cell by spinning either clockwise or counter clockwise around its axis. Axial Filaments Axial Filaments consist of numerous fibrils that arise from both poles of the cell and are encased within a sheath. Axial filaments are found only in the spirochetes. These are corkscrew-shaped bacteria. One of the best-known spirochetes is Treponema pallidum, the causative agent of syphilis. The axial filaments are similar in structure to flagella but instead of being found outside the cell as flagella are, they are found inside the cell. They are attached to both poles of the cell and spiral around the organism between the plasma membrane and the cell wall. The function of axial filaments is movement. As they rotate or contract, the axial filaments cause the spirochete cell to turn in a corkscrew-like manner. Pili and Fimbriae Pili and fimbriae are filamentous projections that extend from the surface of certain bacteria. Fimbriae are shorter in length than pili and present in high numbers. Fimbriae function in the attachment of a bacterium to a surface. Neisseria gonorrhoeae, the bacterium that causes the disease gonorrhoeae, uses fimbriae to adhere to the cell it infects. Pili function in the process of bacterial conjugation in which genetic material is exchanged between two bacterial cells. Non-sex pili also function in attachment of bacteria to surfaces. The Cell Wall The cell wall is a semi rigid structure that surrounds the bacterial cell. The cell wall protects the cell when it is in a dilute environment. The high concentration of solute within the bacterial cell creates a high osmotic pressure that leads to the entry of water into the cell. The cell wall resists the pressure created by the inward flow of water preventing the cell from bursting. Structure of the Cell Wall The bacterial cell wall is composed of a material called peptidoglycan (poly-N-acetylglucosamine and N-acetylmuramic acid). The Gram Stain Bacteria can be divided into two large groups on the basis of a differential staining technique called the gram stain. One large group is called gram-positive and the other, gram-negative. Following the gram-staining procedure, gram-positive organisms will appear purple, gram-negative organisms will appear pink or red. This staining procedure is based upon differences in the structure of the cell wall between the two groups. Gram-positive bacteria have a thicker peptidoglycan wall. The cell wall contains polyalcohols called teichoic acids, some of which are lipid-linked to form lipoteichoicacids. Lipoteichoic acids link the peptidoglycan to the cytoplasmic membrane. Gram-negative bacteria contain less peptidoglycan. In the gram-negative bacteria, a thin layer of peptidoglycan is sandwiched between the plasma membranes and a second outer membrane. The outer membrane contains phospholipids and lipopolysaccharide, lipids with polysaccharide chains attached. Procedure for the Gram Stain 1. A bacterial smear is prepared and then stained with the purple stain crystal violet. 2. The slide is washed off with distilled water. 3. The slide is covered with Gram’s iodine, which is a mordant. The iodine combines with crystal violet to form a compound or precipitate that remains in gram-positive bacteria, but can be removed from gram-negative bacteria by washing with ethyl alcohol. 4. The slide is flooded with ethyl alcohol until the purple dye no longer appears in the alcohol flowing from the slide. If the bacteria are gram-positive, they will not be decolorized. The crystal violet dye will remain in the cells. Gram-negative bacteria are decolorized by the alcohol, losing the purple color of the crystal violet. 5. The slide is washed using distilled water, stopping the action of the alcohol. 6. The bacterial smear is counterstained using the red dye safranin. Gram-positive bacteria will retain the purple color of the crystal violet stain. Decolorized gram-negative bacteria will be stained pink by the safranin. 7. The slide is washed, blotted dry, and allowed to dry at room temperature. Microscopic Examination This slide is examined microscopically. Gram-positive bacteria will appear purple. Gram-negative bacteria will appear pink. Structures Internal to the Cell Wall Plasma (Cell) Membrane The plasma membrane is a thin membrane internal to the cell wall that encloses the protoplasm of the cell. It is composed of protein and phospholipid molecules. Functions of the Cell Membrane 1. It controls the transport of most compounds entering and leaving the cell. 2. Produces a separation of protons (H+) from hydroxyl ions (OH-) generating a proton motive force. This force is responsible for driving functions such as transport, motility, and synthesis of ATP. Cytoplasm Cytoplasm is the substance contained within the cell membrane. Cytoplasm consists mostly of water. Dissolved and suspended in the water there are many substances including inorganic ions, nucleic acids, proteins, carbohydrates, lipids, inorganic ions, and a variety of compounds of low molecular weight. There are no membranous organelles in the cytoplasm of a bacterial cell, but there are ribosomes, internal membranes, a cytoskeleton, and storage granules. Internal Membranes In photosynthetic bacteria, internal membranes within bacterial cells may serve as a location for photosynthetic reactions. Cytoskeleton The prokaryotic cytoskeleton consists of structural filaments within the protoplasm. The Cytoskeleton functions in cell division, or to produce changes in cell shape. Storage Granules Storage granules contain phosphate or sulfur. Magnetosomes are particles of the iron mineral magnetite – Fe3O4. They allow bacteria to respond to a magnetic field. Ribosomes Ribosomes are small granules that are composed of RNA and protein. Ribosomes are the site of protein synthesis. Ribosomes are numerous in the cytoplasm of bacterial cells. Observation with the electron microscope shows that the cytoplasm is quite densely packed with ribosomes. Several antibiotics, such as streptomycin, neomycin, and tetracycline exert their antimicrobial effects by inhibiting protein synthesis. Nuclear Area The nuclear area, or nucleoid, of bacterial cells contains a single, long, circular molecule of DNA, referred to as the bacterial chromosome. This is the cell’s genetic information. Unlike the chromosomes of eukaryotic cells, bacterial chromosomes are not surrounded by a nuclear envelope. Eukaryotic cells have rod-shaped chromosomes containing linear DNA bound to special proteins known as histones. Bacteria often contain, in addition to the bacterial chromosome, small cyclic DNA molecules called plasmids. Plasmids Plasmids are extrachromosomal genetic elements; that is, they are not connected to the main bacterial chromosome. Plasmids are used to transfer genetic material from one cell to another. Plasmids can pass from one cell to another cell by passing through the cell wall. When it enters the cell that receives it, it introduces new genetic information into that cell. Plasmids are now used in Genetic Engineering Research to introduce genetic material into recipient cells. Endospores Endospores are highly durable, dehydrated bodies with a thick wall. Endospores are formed by bacterial cells in response to harsh conditions such as lack of food, lack of water, high temperatures, freezing temperatures, etc. They are formed inside the bacterial cell wall. Since one vegetative cell forms a single endospore, which after germination remains one cell, sporogenesis in bacteria is not a means of reproduction. There is no increase in the number of cells. Endospore formation is important from a clinical viewpoint, because endospores are quite resistant to processes that normally kill vegetative cells. Such processes include heating, freezing, desiccation, use of chemicals, and radiation. Whereas temperatures above 70º C kill most vegetative cells, endospores may survive in boiling water for an hour or more. Endospore-forming bacteria are a problem in the food industry, since some species produce toxins that result in food spoilage and disease. Reproduction Asexual Reproduction Binary fission – bacteria reproduce asexually by binary fission. First, the single chromosome duplicates and then the two chromosomes move apart into separate areas; then the cell membrane grows inward and partitions the cell into two daughter cells, each of which now has its own chromosome. Under favorable growth conditions, fission may occur in approximately 20 to 30 minutes. Sexual Reproduction Three types of genetic recombinations are known in bacteria – conjugation, transformation, and transduction. Conjugation – the transfer of genetic material between two bacterial cells that are temporarily joined. In the process of conjugation, two cells, an F+ cell and an F- cell come together side by side. The F+ acts as a donor cell or “male” cell to transfer genetic material to the F- cell which acts as a recipient cell or “female” cell. F+ cells contain an F plasmid. The F plasmid contains genes that code for the production of an F pilus by the donor cell. The F pilus attaches to a specific receptor on the F+ cell and then retracts, drawing the cells together. The F pilus serves as a protoplasmic bridge that connects the two cells. Within the donor cell, one strand of the plasmid DNA is nicked and this single strand moves through the F pilus into the F+ cell. Replication of DNA by the rolling circle mechanism then replaces the transferred strand in the donor cell. The single strand that enters the F+ cell is also replicated. This results in two F+ cells. Transformation – a genetic change in a recipient bacterium resulting from the absorption of DNA released from another cell. Transduction – a virus-mediated transfer of bacterial DNA from one bacterium to another. Structure and Function of a Eukaryotic Animal Cell The Structure and Function of Cellular Organelles The Cell Membrane Functions of the Cell Membrane 1) It serves as a boundary or barrier that maintains the cell’s integrity 2) It controls the transport of substances into or out of the cell. The cell membrane or plasma membrane surrounds the cell and encloses the protoplasm. The cell membrane allows substances that the cell needs, such as oxygen, glucose, amino acids, fatty acids and glycerol to enter the cell, and wastes such as carbon dioxide and urea to leave the cell. The cell membrane is described as selectively permeable. This means that the cell membrane allows certain substances such as water to pass through it, but does not allow certain others, such as polysaccharides to pass through. The Structure of the Cell Membrane The structure of the cell membrane is described by the Fluid-Mosaic or Singer model. The cell membrane is composed of lipid and protein. The lipid layer is composed of a double layer of phospholipid molecules. The Phospholipid molecules that comprise the cell membrane have a hydrophilic end containing a phosphate group that is attracted to water, and a hydrophobic tail composed of fatty acid molecules that are repelled by water. In the cell membrane, one layer is arranged so that the hydrophilic “heads” (polar ends) of the molecules face the outside of the cell. There, they are close to the water that is found on the outside of the cell. Similarly, in the inner layer of phospholipid molecules, the hydrophilic “heads” all face toward the inside, toward the water inside the cytoplasm of the cell. The fatty acid tails of the phospholipid molecules in both layers face inward. They are hydrophobic, or repelled by water, and the tails swing inward to get as far away from the water as possible In addition to the phospholipid molecules, the cell membrane also contains proteins. In the fluid mosaic model, the phospholipids bilayers are viewed as fluid. The globular proteins are inserted into the lipid bilayer. The hydrophobic ends of the proteins are embedded deeply in the interior of the lipid bilayer, in contact with the hydrophobic lipid “tails”, while the hydrophilic end of the protein remains at the surface, in contact with the hydrophilic lipid “heads” and the aqueous medium surrounding the membrane. The proteins have been compared to icebergs floating in a sea of lipid. Some of the proteins, which were large enough to span the entire thickness of the membrane, had two protruding hydrophilic ends and a hydrophobic embedded interior. Some of the proteins that extend through the membrane contain channels. Their function is to control the transport of substances through the cell membrane. The Cytoskeleton The cytoskeleton is a network of protein filaments that extends throughout the cytoplasm of a eukaryotic cell. Functions: The cytoskeleton is responsible for producing various types of movements in cells. These include such movements as changes in cell shape, the crawling of cells on a substratum, the transport of organelles in the cytoplasm, and the separation of chromosomes during mitosis. Structure The cytoskeleton is composed of three types of protein filaments: 1. Microfilaments Microfilaments are composed of the protein actin. They are essential for many movements of the cell, especially those on its surface. Microfilaments are smaller than microtubules. Microfilaments are involved in changes in cell shape during development and motility, and in protoplasmic streaming in plant cells. 2. Microtubules Microtubules are tiny tubes composed of the protein tubulin. They are thought to be the primary organizers of the cytoskeleton. Microtubules form the spindle fibers of dividing cells, on which chromosome movement takes place. Microtubules are also found in the cilia and flagella of motile cells. They are found in the pseudopods of certain protozoans or in the extremely elongated axons of nerve cells. 3. Intermediate filaments Intermediate filaments, composed of fibrous proteins such as vimentin or lamin, seem to have the function of providing cells with mechanical strength. Motor Proteins Cytoskeletal filaments also serve as supports for intracellular transport. Motor proteins generate the movements. They can move along either actin filaments or microtubules using the energy from the breakdown of ATP. An example of a motor protein is myosin. This is the protein that causes muscle contraction by moving along actin filaments. Kinesins are motor proteins that move along microtubules. They are involved in the movement of chromosomes along spindle fibers during cell division. They also function in the movement of mitochondria, Golgi bodies, and vesicles. Cytoplasmic dyneins are involved in the transport of vesicles and organelles. Cilia and Flagella Cilia Cilia are minute, hair-like, motile processes that extend from the surfaces of the cells of many animals. Functions: 1. Locomotion of single-celled organisms such as Paramecia through their aquatic environment. 2. Propulsion of fluids and materials across the surfaces of epithelial cells. Ciliated epithelial cells in the trachea propel dust-ladened mucus lining the surface of the cells toward the mouth, clearing the respiratory system of particles of dirt. This mechanism is a dust-removal or filtration system. 3. Cilia sweep eggs along the oviduct. Flagella A Flagellum is a long whip-like structure that extends from the surface of certain animal cells. They are found in flagellated protists, animal spermatozoa, and sponges. Structure of Cilia and Flagella The cilium and flagellum are both made up of nine pairs (doublets) of microtubules surrounding a central pair of microtubules that runs down the center of the shaft. This arrangement is called the “nine-plus-two” pattern. Cilia are shorter than flagella and more numerous per cell. Flagella are longer than cilia, and there are fewer per cell in comparison to cilia. The distinction between cilia and flagella is that a cilium propels water parallel to the surface to which the cilium is attached whereas a flagellum propels water parallel to the main axis of the flagellum. The molecular basis for the movement of cilia or flagella (in eukaryotic cells) is the same. It should be noted that the flagella of bacteria are completely different from the cilia and flagella of eukaryotic cells. The protein dynein generates the movement of cilia and flagella. The interaction of ciliary dynein with adjacent microtubules generates a sliding force between the microtubules. Because the adjacent microtubules are linked together, the sliding movement is converted to a bending motion. Centrosomes The centrosome is the major microtubule-organizing center in almost all animal cells. In interphase it is typically located to one side of the nucleus, close to the outer surface of the nuclear envelope. Embedded in the centrosome is a pair of cylindrical structures arranged at right angles to each other in an L-shaped configuration. These are centrioles. The centrosome duplicates and splits into two equal parts during interphase, each half containing a duplicated centriole pair. These two daughter centrosomes move to opposite sides of the nucleus when mitosis begins, and they form the two poles of the mitotic spindle. Not all microtubule-organizing centers contain centrioles. Plant cells lack centrioles. Centrioles Centrosomes consist of two centrioles, which are seen as a pair of cylinders situated at right angles to each other. Centrioles organize the microtubules that serve to separate chromosomes during cell division. The wall of each cylinder is composed of nine groups of microtubules. Each group consists of a triplet of microtubules (9 + 0). Basal Bodies Basal bodies are found at the base of cilia and flagella. The basal bodies have the same structure as centrioles (9 + 0). Microvilli Microvillus - a cylindrical projection with a rounded top found on the surface of many animal cells. Function Microvilli increase the surface area of the cell for absorption. For example, microvilli greatly increase the surface area of the epithelial cells lining the intestine. This leads to increased absorption of nutrients such as amino acids, simple sugars, glycerol and fatty acids from the intestine. Junctional Complexes between Cells Tight Junction A tight junction is a region of actual fusion of cell membranes between two adjacent cells. Desmosome A Desmosome is a discoid structure that serves as an intracellular connection. Gap Junctions Gap junctions – formed from tiny canals between cells so that the cytoplasm becomes continuous, and molecules can pass from one cell to another. Gap junctions provide a means of intercellular communication. Cytoplasmic Organelles Cytoplasm - the cytoplasm is the protoplasm that is located between the cell membrane and the nuclear membrane. The cytoplasm contains organelles. The organelles are small internal organs of the cell – organized units of living substance having specific functions in cell metabolism. The cell organelles include: Centrioles (centrosomes), Microtubules, Mitochondria, Endoplasmic reticulum, Golgi apparatus, Lysosomes, and Peroxisomes. Mitochondria Mitochondria are small rod-shaped bodies located in the cytoplasm and which function in the production of energy. Size – 0.2 to 5.0 μm Mitochondria are found in all types of eukaryotic cells. Location – mitochondria are especially concentrated in areas of cellular activity. For example, mitochondria are numerous in muscle tissue and at nerve endings. Structure A double-layered membrane surrounds the mitochondrion. The outer membrane surrounds the outside of the mitochondrion. The inner membrane is folded inward forming partitions or cristae. The intermembrane space lies between the outer membrane and the inner membrane. The matrix is the fluid-filled interior of the mitochondrion. It lies inside the inner membrane. Function The mitochondria complete the breakdown of glucose to carbon dioxide and water. The energy released in this process is used to make ATP. The breakdown of glucose to carbon dioxide, water, and energy is known as cellular respiration. The reaction for cellular respiration is: C6H12O6 + 6O2 → 6CO2 + 6H2O + energy The breakdown of glucose begins in the cytoplasm outside the mitochondrion. There glucose is broken down into pyruvic acid. The pyruvic acid enters the mitochondrion. The pyruvic acid is broken down into an acetyl group and combined with coenzyme A forming acetyl coenzyme A. The acetyl coenzyme A then enters the reactions of the Citric Acid Cycle. As the molecules in the Citric Acid Cycle are oxidized, energy is released. The energy is captured in the form of ATP. ATP production – occurs in the mitochondrial membrane in what is known as the electron transport chain. Mitochondria Contain DNA Mitochondria contain DNA. The fact that mitochondria contain DNA supports the hypothesis that mitochondria were once free-living bacterial cells that were captured by another cell that evolved into eukaryotic cells. This theory is called the endosymbiotic theory. It will be discussed more fully later. Endomembrane System A eukaryotic cell contains a system of membranes that extends throughout its cytoplasm. This system, known as the endomembrane system includes the endoplasmic reticulum, the Golgi apparatus, lysosomes, and vesicles. These organelles are interconnected and function together. They provide surfaces for the synthesis of lipids and proteins, divide the cell into compartments, and serve as a transportation system throughout the cell. Endoplasmic Reticulum The endoplasmic reticulum is a system of membranes that extends throughout the cytoplasm of a eukaryotic cell. The endoplasmic reticulum extends from the nuclear membrane on the inside to the plasma membrane on the outside of the cell. Function Function – the endoplasmic reticulum is concerned with the synthesis of lipids and proteins. Types of Endoplasmic Reticulum There are two types of endoplasmic reticulum: rough and smooth. Rough Endoplasmic Reticulum Rough endoplasmic reticulum is associated with tiny granules known as ribosomes. Ribosomes are tiny granules that are composed of protein and ribonucleic acid (RNA). They are the sites of protein synthesis. Rough endoplasmic reticulum functions in protein synthesis. Smooth Endoplasmic Reticulum Smooth endoplasmic reticulum, or smooth ER lacks bound ribosomes. Smooth Endoplasmic Reticulum synthesizes lipids and detoxifies lipid-soluble drugs including amphetamines, morphine, codeine and phenobarbital, as well as various harmful compounds produced by metabolism. The endoplasmic reticulum also regulates the accumulation and release of Ca2+ from the cytosol (the part of the cytoplasm that contains organic molecules and ions in solution). Other Functions of the Endoplasmic Reticulum In addition to its role in synthesis, the endoplasmic reticulum has the following functions: 1) It is a kind of cytoskeleton 2) Provides surfaces for chemical reactions (keeps chemical reactions in the cell separated and prevents them from interfering with one another) 3) It serves as a pathway for transport of materials 4) Collection depot for synthesized materials (prepares synthesized materials by forming vesicles that are transported to the Golgi apparatus) Ribosomes Ribosomes are granules that consist of RNA and protein. Function: protein synthesis. Ribosomes are often found in clusters known as polyribosomes. The Golgi Apparatus The Golgi apparatus is composed of stacks of parallel, double-layered membranes. It is named after its discover, Camillo Golgi, the nineteenth-century Italian physician. The Golgi apparatus (also called the Golgi complex) is a major site of carbohydrate synthesis. It combines carbohydrate with proteins (brought to them through the canals of the endoplasmic reticulum) to form compounds called glycoproteins. It also sorts, packages and distributes the products of the ER to the plasma membrane, lysosomes, and secretory vesicles. Each Golgi stack has a receiving end, known as the cis face (or entry face), which is usually located near the ER, and a discharging end called the trans face (or exit face). Lysosomes Lysosomes are vesicles that contain powerful digestive enzymes. The Golgi apparatus forms lysosomes. Functions of Lysosomes 1) Digestion of large particles that enter the cell (intracellular digestion) 2) Digestion of substances external to the cell (extracellular digestion) 3) The digestion of the cell itself Microbodies Microbodies …