* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download The Cell - University of South Carolina
Survey
Document related concepts
Tissue engineering wikipedia , lookup
Cytoplasmic streaming wikipedia , lookup
Biochemical switches in the cell cycle wikipedia , lookup
Signal transduction wikipedia , lookup
Extracellular matrix wikipedia , lookup
Cell encapsulation wikipedia , lookup
Cell membrane wikipedia , lookup
Programmed cell death wikipedia , lookup
Cell nucleus wikipedia , lookup
Cell culture wikipedia , lookup
Cellular differentiation wikipedia , lookup
Organ-on-a-chip wikipedia , lookup
Cell growth wikipedia , lookup
Cytokinesis wikipedia , lookup
Transcript
S l i d e 1 THE CELL Robert W. Ogilvie, Ph.D. Roger H. Sawyer, Ph.D. Professor Emeritus Professor , Biological Sciences Medical University of South Carolina Executive Associate Dean, Visiting Professor College of Arts & Sciences University of South Carolina University of South Carolina This lecture will describe the generic cell, its organelles and inclusions. It will explain how the more than 200 unique cell types in the body are derived from embryological origins and how different cell populations in the adult are maintained by mitosis and two means of cellular death. This lecture is intended to review cell structure and function for those who can recall courses in high school and college that presented cell biology and to serve as basic information for those who may have not had such courses. Most all students who have reached junior status in college have had some exposure to cell structure and function. Cell Structure, Function & Differentiation S l i d e 2 Relevant Resources Textbook Cell Biology Lecture PDF containing slides and narrative text of this lecture Laboratory Exercise WebMic Program WebMic S l i d e 3 Study Guide Unit 1: Study Guide Plan, WebMic Information & Tutorial Learning Outcomes These are the resources that relate to the content of this lecture. The lecture PDF downloadable from the Blackboard Course Website contains all of the slides and the narrative of this lecture. Continue to practice and refine your interaction with WebMic and understanding of the WebMic Study Guide Plan. There is no lab exercise on cell structure. These are the learning outcomes for this lecture. A quiz is offered at the end of the lecture that will assist you in assessing your understanding of the content of this lecture. After completing a study of this lecture, you should be able to: explain the difference between a prokaryotic and eukaryotic cell. describe a generic cell, list organelles and inclusions , their function and explain the difference between them. explain the process of differentiation and how it plays a significant role in the creation of more than 200 different types of cells in the human body. list 3 cell populations in the adult and give examples of each. describe the cell cycle differentiating between the M phase and the Interphase. list the stages of mitosis. distinguish between meiosis and mitosis. define & differentiate between two mechanisms of cell death. 1 S l i d e Vocabulary 4 The Cell Organelles Inclusions Mitochondria Rough Endoplasmic Reticulum Ribosomes Smooth Endoplasmic Reticulum Nucleus Nucleolus Golgi complex Cell membrane Centrioles Euchromatin Heterochromatin S l i d e 5 S l i d e Prokaryotic Vs. Eukaryotic Cells Compartments of the Cell Light & Electron Microscopic Views of a cell Cell Complexity Cell Organelles and Inclusions Cell Factory Analogy Origin of Adult Cells Examples of Differentiated Cells Cell Populations Cell Cycle Mitosis Mitosis vs. Meiosis Cell Death Cell Homeostasis The Cell: in levels of organization 6 Cytoskeleton Microfilaments Intermediate filaments microtubules Cell Cycle Mitosis Meiosis Necrosis Apoptosis Differentiation Homeostasis Static cell population Stable cell population Dynamic cell population Lecture Topics This is the vocabulary of terms that you should be able to define. Look for these terms as you view this lecture and consult with the course glossary for the definitions. Small molecules Macromolecules and aggregates of molecules Cells Tissues Organs Organ Systems Organism Each of the topics listed on this slide is hyperlinked to the first slide that begins that topic. You can jump to any topic. When you reach the first slide for a certain topic, you will find on that slide a button to click that will return to slide. This should make it convenient during review. To begin, let's see where the cell fits into the different levels of organization of a biological organism. The cell is defined as the smallest unit of a living organism capable of independent existence. In this scheme of organization from small molecules to the organism, the cell is the basic living structure that is the ‘block’ or ' brick' with which the body is constructed. Cells and their secretions constitute the material that is used to construct tissues, organs and organ systems. S l i d e The Cell Prokaryotic vs. Eukaryotic Cells Eukaryotic Cell Prokaryotic Cell Without a nucleus Bacteria 7 With a nucleus Plant nucleoid S l i d e Return to outline & Animal Cells nucleus Return to outline Cell Compartments Two Compartments: Cytoplasmic (c) and Nuclear (n) Cytoplasmic/nuclear (c/n) ratio n 8 c n c c n c epithelial cells S l i d e 9 n Return to outline Cytoplasm and Nucleus (stain: hematoxylin & eosin) Satellite cell nucleus (heterochromatin) Nucleus (euchromatin) Cell Limit Nucleolus cytoplasm All cells have two main compartments: the cytoplasmic compartment containing cytoplasm and the nuclear compartment containing nucleoplasm. In normal cells there is a constant ratio of nuclear volume to cytoplasmic volume. The larger the volume of cytoplasm, the larger the volume of the nucleus will be because the information contained within the nucleus and nucleolus has to match the size and activity of the cytoplasm. This normal ratio is upset in cancer cells because cancer cells have a much higher volume of the nucleus to the volume of cytoplasm………..in other words, the nucleus is cancer cells abnormally large. The resulting shape difference between the epithelial and nerve cells illustrated here is the direct result of gene directed differentiation from stem cells. This occurs first in the embryo and fetus and later in the adult, resulting in specialized adult cells like these epithelial and nerve cells as examples of the more than 200 unique cell types in the human body. nerve cells Light Microscope View of a Cell Some cells have nuclei and others do not. All animal cells have nuclei. The term karyose comes from a Greek word meaning “kernal”. Pro means before or no kernal. Eu means true or having a kernal. Biologists use karyo to refer to the nucleus. A prokaryotic cell, example –a bacterium, has no nucleus. It contains the DNA in a circular organization with no end in a region called the nucleoid that is only a region and not bounded or confined by a membrane. Bacteria are so small that all parts of the cell are close together and therefore, there is no need for the organization as in eukaryotic cells. Eukaryotic cells contain a nucleus enclosed by a membrane. The nucleus sequesters the DNA in a chamber for efficient exchange of genetic information with the cytoplasmic structures. Eukaryotic DNA is linear. In this example of a nerve cell stained with hematoxylin and eosin, you can see the extent to which you can resolve cell components in the using a light microscope. In this particular nerve cell, the nucleolus is large and the DNA in the nucleus is fully extended in a form that is called euchromatin. The combination of the extended DNA and the large nucleolus is indicative of very active protein synthesis with the DNA providing the gene code information and the nucleolus providing the source of ribosomal RNA. By contrast, look at the satellite cell nucleus. The nucleolus is not visible and the DNA is condensed in a form called heterochromatin. The morphology of the nucleus where the DNA is condensed is indicative of a cell that is not very active or not active at all in protein synthesis. The cytoplasm of this nerve cell has patches of blue distributed in a background of pink. The blue staining indicates patches of ribosomes containing RNA carrying a negative charge reacting with the positive charged hematoxylin and the pink staining indicates membrane carrying a positive charge reacting with the negatively charged eosin. Observe also that the The Cell S l i d e 1 0 Electron Microscope View of a Cell Rough Endoplasmic Reticulum (tiny dots are ribosomes) Cisterna of endoplasmic reticulum containing newly synthesized proteins showing as flocculent material Heterochromatin of the nucleus Euchromatin of the nucleus Nucleolus detail of the cell membrane cannot be resolved……………only the cell limit. In the following slides, the content of the nucleus, the cytoplasm and the cell membrane will be presented. The purpose of presenting more detail of cell structure that can only be resolved with an electron microscope is to provide an understanding of what is behind your observation of different cell types in this course. In this electron microscope view of a cell, one can see cell components such as the rough endoplasmic reticulum, the endoplasmic reticulum cisterna, the nucleolus, a lysosome and the two expressions of DNA in the nucleus –heterochromatin and euchromatin resolved in greater detail than when using a light microscope. When you encounter the many cell types as you learn histology, keep in mind the structures in the cytoplasm and nucleus that stain blue or pink with the hematoxylin and eosin stain. In this way, you can appreciate whether a cell is active and what components in the cytoplasm are dominant. This is only an approximation but a helpful one. Lysosome S l i d e Cell Complexity 1 1 http://commons.wikimedia.org/wiki/File:Cell_structure_large.png Return to outline This drawing from the commons wiki web site illustrates the complexity of an eukaryotic cell. Just as the body is divided into compartments by epithelial tissues and basement membranes, the cell is also compartmentalized by the cell membrane and intracellular membranes. The next few slides will present the components / compartments of the cell. The Cell S l i d e Cell Organelles and Inclusions Organelles –structures that serve to perform functions that require energy Membranous organelles are mitochondria, endoplasmic reticulum, Golgi complex, lysosomes, cell membrane, microbodies, multivesicular bodies, coated vesicles, secretory granules and the nucleus. Non-membranous organelles are nucleolus, ribosomes, microfilaments, microtubules, centrioles, cilia, flagella and chromosomes 1 2 Inclusions are chemically inert substances that appear and disappear during cell activity S l i d e Inclusions include glycogen, stored lipid, crystals, pigments, keratin Plasma Membrane Membranous Organelle 1 3 Return to outline These molecules projecting from the Plasma membrane surrounds the cell membrane form the cell coat cytoplasm controlling traffic into and out of the cell Carbohydrates Glycolipids Glycoproteins Consists of a lipid bi-layer interspersed with cholesterol molecules and with proteins that float in this layer Proteins serve as lipid Pumps Channels Receptor proteins Linker proteins Enzymes Structural proteins bilayer The cell coat (glycocalyx) serves to give identity to the cell as cells interact in the immune reaction, receptors for hormones and influence cell to cell associations cholesterol molecule microfilaments of the cytoskeleton cytoplasm Organelles are structures in the cell that perform functions that require energy and are contrasted with inclusions that are inert substances that appear and disappear during cell activity. There are two classes of organelles depending on whether or not they are bound by a membrane; membranous or non-membranous organelles. Membranous organelles include mitochondria, endoplasmic reticulum, the Golgi complex, lysosomes, the cell membrane, microbodies, multivesicular bodies, coated vesicles, secretory granules and the nucleus. Non-membranous organelles include the nucleolus, ribosomes, microfilaments, microtubules, centrioles, cilia, flagella and chromosomes. Inclusions include pigments and other substances such as glycogen, lipid that are stored and not a part of a cell structure, crystals such as cholesterol crystals and keratin, the protein that fills the dead cells in the superficial layers of cells in the skin. The following slides will present organelles in more detail. The plasma membrane and other membranes within the cell are of paramount importance in maintaining compartments and regulating ions and water levels. The membranes are semipermeable and composed of two lipid layers (lipid bilayer) with proteins that are fixed or float in that lipid bilayer. Cholesterol molecules inserted into the lipid bilayer provide an element of stiffness to the plasma membrane. The proteins integral within the membrane act as pumps, channels, receptors, linkers, enzymes and provide structure. The proteins provide a link to the extracellular environment. The plasma membrane is intimately connected with the interior of the cell via linker molecules and the microfilaments of the cytoplasm. Molecules projecting from the cell are carbohydrates, glycolipids (complexes of carbohydrates and lipids) and glycoproteins (complexes of carbohydrates and proteins). This forms the cell coat that gives unique identity to each cell, provides receptors for hormones and influences association between cells. S l i d e 1 4 Nucleus membranous organelle S l i d e 1 5 S l i d e 1 6 The Cell Contains DNA Usually in the form of euchromatin and/or heterochromatin Contains genetic information Composed of DNA Thicken to form chromosomes for cellular division Set number per species (23 pairs for humans) Nuclear membrane Surrounds nucleus Composed of two layers Numerous openings (pores) for nuclear-cytoplasmic traffic The nucleus is the main repository of DNA. The DNA takes several forms. If it is uncoiled, it is euchromatin, if coiled it is heterochromatin, and if fully condensed, it is in the form of chromosomes. The nuclear membrane is porous to provide for interchange of information between the nucleoplasm and the cytoplasm. The nucleolus is located within the nucleoplasm and is not bounded by any membrane. It contains RNA that contributes particles called ribosomes that function in protein synthesis in the cytoplasm. Nucleolus Spherical shape Visible when cell is not dividing Contains RNA for protein manufacture The rough endoplasmic reticulum (rER) is a membrane shaped into tubules that form a network that communicates with the nuclear membrane and the plasma membrane. It is involved in synthesis and transport of protein molecules. A reticular membrane without ribosomes attached is called the Smooth Endoplasmic Reticulum (sER). The next slide explains and illustrated sER. Rough Endoplasmic Reticulum membranous organelle Network of tubes or flattened sacs fused to the nuclear membrane Goes through cytoplasm and is continuous with the cell membrane Stores, separates and serves as cell’s transport system Rough type: ribosomes embedded in the reticulum membrane and functions to synthesize proteins Smooth type: lacks ribosomes and functions in steriod synthesis and glycogen metabolism see next slide Smooth Endoplasmic Reticulum membranous organelle Contains no ribosomes metabolism Sequesters calcium in muscle cells Detoxification function in liver cells Glycogen metabolism M Lipid sER M M M M L M = mitochondria, L = Lipid, sER = smooth endoplasmic reticulum M Smooth endoplasmic reticulum (sER) is a network of membranes that lacks any association with ribosomes. It has a large presence in cells that are involved in lipid metabolism. It sequesters calcium in muscle cells to relax muscle. It proliferates in liver cells when excess lipid is in the diet. It contains a variety of detoxifying enzymes that modify and detoxify hydrophobic compounds such as pesticides and carcinogens by converting them into water-soluble products that can be eliminated from the body; sER also contains glycogen metabolizing enzymes. Note in the electron micrograph the network of smooth endoplasmic reticulum (sER) with several mitochondria in intimate association. Note the large lipid droplet (L) around which is a mitochondrion. Mitochondria (M) are involved in lipid metabolism. S l i d e 1 7 S l i d e The Cell Golgi Apparatus & Lysosomes Membranous Organelles Golgi Apparatus-membranous organelle Protein ‘packaging plant’ A membrane structure found near nucleus Composed of numerous layers forming a sac Lysosome-membranous organelle Digestive ‘plant’ containing enzymes for degrading proteins, lipids, and carbohydrates Transports undigested material to cell membrane for removal Vary in shape depending on process being carried out Cell breaks down if lysosome explodes Mitochondrium Membranous Organelle Mitochondriamembranous organelle 1 8 S l i d e Second largest organelle with unique genetic structure Double-layered outer membrane with inner folds called cristae Energy – producing chemical reactions take place on cristae Controls level of water and other materials in cell Recycles and decomposes proteins, fats and carbohydrates and forms urea Ribosome Non-membranous Organelle Ribosomes* 1 9 The Golgi apparatus is a membranous organelle that serves to add to or modify and package products synthesized on the rough endoplasmic reticulum. It also forms lysosomes. The lysosome is a membranous bag which contains hydrolytic enzymes that are used to digest macromolecules. The lysosome contains over 40 enzymes, some of which are the proteases, nucleases, and phopholipases. Each cell contains thousands Miniature ‘protein factories’ Composes 25% or more of cells’ mass if cell is mainly synthesizing protein Stationary type: embedded in rough endoplasmic reticulum Mobile type, unattached to membrane: injects proteins directly into cytoplasm *When ribosomes are not attached to the endoplasmic reticulum they are considered non-membranous organelles, but when attached they are part of a membranous organelle – the rough endoplasmic reticulum. A mitochondrion (plural mitochondria) is a membraneenclosed organelle found in most eukaryotic cells. These organelles range from 0.5 to 10 micrometers (µm) in diameter. Mitochondria are sometimes described as "cellular power plants" because they generate most of the cell's supply of adenosine triphosphate (ATP), used as a source of chemical energy. In addition to supplying cellular energy, mitochondria are involved in a range of other processes, such as signaling, cellular differentiation, cell death, as well as the control of the cell cycle and cell growth. Mitochondria have been implicated in several human diseases, including mitochondrial disorders and cardiac dysfunction, and may play a role in the aging process. The word mitochondrion comes from the Greek: mitos, meaning thread and chondrion, meaning granule. Eukaryotic ribosomes are between 25 and 30 nm (250300 ångströms) in diameter and the ratio of rRNA to protein is close to 1. Ribosomes translate messenger RNA (mRNA) and build polypeptide chains (e.g., proteins) using amino acids delivered by transfer RNA (tRNA). Their active sites are made of RNA, so ribosomes are now classified as "ribozymes". Ribosomes build proteins from the genetic instructions held within messenger RNA. Free ribosomes are suspended in the cytosol (the semi-fluid portion of the cytoplasm); others are bound to the rough endoplasmic reticulum, giving it the appearance of roughness and thus its name. Ribosomes are also bound to the nuclear envelope. S l i d e Vaculoles Membranous Organelles 2 0 S l i d e The Cell Vacuoles Membrane-bound sacs for storage, digestion and waste removal Contains water solution Contractile vacuoles for water removal (in unicellular organisms such as an amoeba) Centrioles Non-membranous Organelles Centrioles-non membranous organelle Paired cylindrical organelles near nucleus arranged at right angles to each other Composed of nine tubes, each with three tubes Involved in cellular division & the formation of cilia 2 1 S l i d e 2 2 Cytoskeleton Non-membranous Organelle The cytoskeleton is a system of microfilaments, microtubules, intermediate filaments The cytoskeleton organizes the cytoplasm by: creating a dynamic organization of cytoplasmic structures providing the means of transport of information and structures through the cytoplasm creating and maintaining the different morphological design and shape that is unique to each the more than 200 different cell types in the body A vacuole is a membrane-bound organelle which is present in all plant and fungal cells and some protist, animal and bacterial cells. Vacuoles are essentially enclosed compartments which are filled with water containing inorganic and organic molecules including enzymes in solution, though in certain cases they may contain solids which have been engulfed. Vacuoles are formed by the fusion of multiple membrane vesicles and are effectively just larger forms of these. The organelle has no basic shape or size, its structure varies according to the needs of the cell. A centriole is a barrel-shaped cell structure found in most animal eukaryotic cells, though absent in higher plants and most fungi. The walls of each centriole are usually composed of nine triplets of microtubules (protein of the cytoskeleton). An associated pair of centrioles, arranged perpendicularly and surrounded by an amorphous mass of dense material (the pericentriolar material) constitute the compound structure known as the centrosome (the center of the cell). Centrioles are involved in the organization of the mitotic spindle in mitosis and in the completion of cytokinesis in cell division. Centrioles are a very important part of centrosomes, which are involved in organizing microtubules in the cytoplasm. The position of the centriole determines the position of the nucleus and plays a crucial role in the spatial arrangement of the cell. Centrioles are the source of basal bodies that lie just within the peripheral aspect of some epithelial cells. Basal bodies form cilia. As the human body has shape and form due to the bones that comprise the skeleton, each cell of the body has its own skeleton resulting in unique shape and form. The cytoskeleton of each cell consisting of microfilaments, microtubules and intermediate filaments is responsible for this. In addition, the cytoskeleton provides the solid state structures upon which some organelles, such as secretory granules and coated vesicles, are transported within the cytoplasm of the cell. Without the cytoskeleton, the cytoplasm would be like a soup with its components suspended, but, no chance for organized movement of its components. The next slide illustrates two cytoskeletal components, microfilaments and microtubules. The Cell S l i d e Cytoskeletal Components Microfilaments 2 3 Microtubules S l i d e 2 4 S l i d e 2 5 Actin protein Diameter, 6-8 nm Core of microvilli, beneath plasma membrane, contractile element in muscle Tubulin Diameter, 20-25 nm Form the core of cilia, present in all cells – especially numerous in neurons where neuronal transport with the nerve cell processes is made possible by microtubules Cell – Factory Analogy The nucleus (1) is the managing director of the factory consulting the blueprint (the chromosomes) (2); The mitochondria (3) supply the power The ribosomes (4) make the products; The chloroplasts of plant cells (5) supply the fuel (food) The Golgi apparatus (6) packages the products ready for dispatch; The ER (7) modifies, stores and transports the products around the factory; The plasma membrane is the factory wall and the gates (8); The lysosomes dispose of the waste and worn-out machinery. Return to outline Microfilaments (mf) and microtubules (mt) are illustrated. Microfilaments are composed of actin, have diameter of 6-8 nm and form the core of microvilli. They also form a network at the peripheral aspect of the cytoplasm of most cells. Microfilaments made of actin are also one of the contractile elements in a muscle cell. Microtubules are composed of subunits of the protein tubulin, have a diameter of 20-25 nm and form the core of cilia. They play a very important role in the transport of molecules throughout the extensive processes of nerve cells. This illustration and analogy comparing a cell to a factory may be helpful in understanding cell structure and function. The nucleus is like the manager of a factory giving out instructions for all cell activity. The mitochondria supply the electricity. The ribosomes are like the employees of a factory making the products. The Golgi apparatus is like the wrapping and packaging department where the products are prepared for shipping. The ER (endoplasmic reticulum) is like a system of transport devices or vehicles in a factory that carry out transportation of components used to make the products. The plasma membrane is like the external walls, doors, gates of a factory that control what comes in and what leaves the factory. The lysosomes are like recycling processes in a factory where some materials are recycled and others are disposed of in dumpsters. So, where do specialized adult cells come from? Of course, the most early origin is the fusion of the sperm and egg to form a zygote. The earliest form where cells can be traced back to in the embryo is the blastocyst containing the inner cell mass where experimenters obtain stem cells for experimentation. In this scheme that displays the pathways of differentiation of cells from the three germ layers, you can see where the Trilaminar Disc of Early Embryological Development fits into the context of the overall process of development. It is the next stage in development after the blastocyst stage where the inner cell mass contains the totipotential cells that give rise to all of the cells of the human body. Following the color scheme, we can see the components of the body that are derived from the three germ layers. Cellular differentiation is the process where Gene expression results in uniquely different cell types. Genes determine the final differentiation of each of the more than 200 cell types in the human body resulting 1) the final shape and size of the cell, 2) the shape of the nucleus, and 3) the unique presence and proportion of the cytoplasmic components – for example, the quantity and proportion of smooth and rough endoplasmic reticulum, the number of lysosomes and intracellular vacuoles, the quantity and organization of intracytoplasmic microtubules and microfilaments. The next slide will illustrate and explain specifically what happens in the trilaminar disc stage. S l i d e The Cell The Trilaminar Disc of the Embyro 2 6 The more than 200 cell types of the human body begin to take on their unique shape and composition just after the blastocyst stage of human embryological development when a trilaminar disc shaped structure forms as the result of migration of embryonic cells. The cells in the three layers are pluripotential, meaning that they can each differentiate into multiple cells types. The top layer (blue) consists of neuroectodermal cells that give rise to nerve and epithelial tissue cells. The middle layer (red) consists of mesodermal (mesenchymal) cells that will form muscle and connective tissue. The lower layer (yellow) consists of cells that will form the epithelium that lines the gastrointestinal tract and the glands associated with the intestinal tract. Process of differentiation produces >200 Cell Types & their products that make up body structures & organs S l i d e Return to outline Examples of Differentiated Cells erythrocyte neuron monocyte fibroblast goblet cell eosinophil 2 7 plasma cell Skeletal muscle cell thyroid cell mast cell Here are some examples to illustrate the variety of cells that are derived from the cells of the trilaminar disc by the process of differentiation creating cells that have unique architectures and perform unique functions. From left to right and top to bottom: • erythrocyte (from mesoderm) that is a cell that loses its nucleus and assumes a biconcave disc shape to maximize the surface area for carrying oxygen. • The neuron (from neuro ectoderm) with its large nucleus mostly of euchromatin and a prominent nucleolus is constantly synthesizing protein (e.g. acetylcholine esterase) and transporting it down the long axons via a microtubule associated transport system. • The monocyte (from mesdoderm) with its large nucleus to support the formation of many lysosomes for phagocytosis. • The fibroblast (from mesoderm) with its elongated shape lies along collagen fibers and synthesizes collagen protein (thus the blue staining rough endoplasmic reticulum). • • parietal cell • • • • • • • • • duct cell Intestinal cell taste bud cell Fat cell The goblet cell (from endoderm) becomes engorged with mucus and then spits it out in cycles. The eosinophil (from mesoderm) loaded with granules interacts and neutralize parasites. The plasma cell (from mesoderm) with lots of rough endoplasmic reticulum for manufacturing antibodies (protein). The skeletal muscle cell (from mesoderm) composed mostly of actin (thin) and myosin (thick) filaments for contraction for movement. The thyroid follicular cell (from endoderm) that synthesizes thyroglobulin and thyroid hormone. The mast cell (from mesoderm), full of eosinophilic granules that store and release histamine and a variety of other substances. The parietal cell (from endoderm), the hydrochloric acid producing cell of the stomach that has a very red acidophilic cytoplasm because of the large amount of mitochondria it contains to provide the energy for the membrane pumps that create the hydrochloric acid. A duct cell (from oral ectoderm) that lines, for example, the ducts of salivary glands………….the cell acts to add and remove substances from the secretion of the gland….its acidophilic cytoplasm reflects basal infoldings of the plasma membrane with lots of mitochondria. The intestinal cell (from endoderm) responsible for absorption of molecules from the intestinal lumen has a border rich in tiny projections called microvilli that increase the surface area for absorption. The taste bud cell (from ectoderm) with it projections into the pore in the oral cavity for picking up ions and transducing them into taste. And finally, the fat cell (from mesoderm) that stores fat. It looks empty because the lipid that it contained in its huge vacuole was dissolved by the chemicals use to process the tissue for microscopy. Note the single flattened nucleus to one side within a very thin rim of cytoplasm…………..the majority of the cell is the lipid in a large vacuole. Hopefully this tour 15 of the more than 200 cell types in the human body has helped in your appreciation of the process of differentiation and the importance of unique architecture designed for function. As you proceed through the course consider listing each cell type you learn logging in a brief description and its function. This will not only help you realize how many cell types you learn, but will also serve to put the structure and function of organs into context because cells are the key S l i d e Return to outline Cell Populations Three cell populations Static: no longer divide (post mitotic) Neurons, 2 8 The Cell Stable: cardiac or skeletal muscle cells divide episodically and slowly Smooth muscle and lining cells of blood vessels Dynamic and Renewing: regular reoccurring mitosis Blood cells in the bone marrow Epithelial cells S l i d e Skin is example of slow, every 2 two weeks cells are renewed Oral cavity lining is example of fast, every three days epithelial lining is renewed Return to outline Cell Cycle State Phase Abbreviation quiescent / senescent Gap 0 G0 A resting phase where the cell has left the cycle and has stopped dividing Interphase Gap 1 G1 Cells increase in size in Gap 1. The G1 checkpoint control mechanism makes certain that everything is ready for DNA synthesis. Synthesis S DNA replication occurs during this phase Gap 2 G2 During the gap between DNA synthesis and mitosis, the cell will continue to grow. The G2 checkpoint control mechanism makes certain that the cell is ready to enter the M (mitosis phase and divide. Mitosis M Cell growth stops at this stage and cellular energy is focused on the orderly division into two daughter cells. A checkpoint in the middle of mitosis (metaphase) makes certain the cell is ready to complete cell division. 2 9 Cell division Description The cells of the body fall into three different populations: 1) Static, 2) Stable and 3) Dynamic. The static population consists of cells that are post-mitotic in the adult human meaning that these cells cannot divide at all and if lost, then the organ is less those cells. In the brain, a stroke usually results in the death of a variable number of neurons that are not replaced. In the heart after a heart attack, a variable number of cardiac myocytes die depending on the severity of the infarct. These cells are replaced by scar tissue, not cardiac myocytes, so the function of the heart may be weakened. Another population category is call Stable and these cells divide, but only episodically and slowly. Cells, like smooth muscle cells that make up part of the structure of the walls of blood vessels and the gastrointestinal tract, may divide, but very slowly and intermittently. A third population category is called Dynamic or Renewing. Cells in this population undergo regular recurring mitosis. In the bone marrow, as one example, a huge number of cells are constantly dividing to provide replacements for the equally huge number of blood cells that are destroyed in the normal function of the body. Epithelial tissue cells divide often, very often in the GI tract and slower in the skin. Every two weeks the surface layer of your skin is renewed by cell division producing replacements for the epidermal cells that fall off of the body constantly. Now, let's consider the cell cycle, a dynamic process in which cells are either resting, preparing for mitosis or undergoing mitosis. There are two phases of the cell cycle – the Interphase and Mitosis. Cells in interphase are preparing to divide and in the mitosis phase, they are dividing. Preparing for cell division in interphase, a cell first increases in size while checking that all is ready for DNA synthesis and this is termed the Gap 1 phase. Next, DNA is replicated and this is the synthesis phase of interphase. Next, the cell enters a gap between synthesis and mitosis when the cell increases further in size and continues checking for readiness of cell division and this is the Gap 2 phase. Finally, when ready, the cell enters the mitosis phase known as the M phase. Cells that have left the cycle and stopped dividing are referred to as quiescent / senescent and are designated to be in the Gap 0 phase. Mitosis is the process of chromosome segregation and nuclear division followed by cell division that produces two daughter cells with the same chromosome number and DNA content as the parent cell. S l i d e The Cell Return to outline Mitosis prophase > metaphase > anaphase > telophase 3 0 Drawing copied from http://en.wikipedia.org/wiki/Mitosis S l i d e 3 1 Mitosis and Meiosis Compared Return to outline prophase > metaphase > anaphase > telophase Drawing copied from http://en.wikipedia.org/wiki/Mitosis Four haploid cells Drawing copied from http://en.wikipedia.org/wiki/Meiosis Mitosis is the process by which a eukaryotic cell separates the chromosomes in its cell nucleus into two identical sets and sequesters the chromosomes in two nuclei. This process undergoes 4 main phases: 1) prophase, when the chromatin in the nucleus condenses and forms chromosomes followed shortly by the disappearance of the nuclear membrane, 2) metaphase, when the chromosomes align along a plate region in the center of the cell, 3) anaphase, when, by shortening of the microtubules, the duplicate chromosomes are separated moving to the two poles of the cell, and finally, 4) telophase, when the two groups of chromosomes are surrounded by nuclear membranes that is immediately followed by an uncoiling of the DNA with simultaneously disappearance of the chromosomes and the beginning of cytokinesis as evidence by the presence of a cleavage furrow. Mitosis is generally followed immediately by cytokinesis, which divides the nuclei, cytoplasm, organelles and cell membrane into two cells containing roughly equal shares of these cellular components. Mitosis and cytokinesis together define the mitotic (M) phase of the cell cycle—the division of the mother cell into two daughter cells, genetically identical to each other and to their parent cell. This accounts for approximately 10% of the cell cycle. So now, let's compare mitosis with meiosis, the process that produces a sperm and egg. Mitosis is the process by which a eukaryotic cell separates the chromosomes in its cell nucleus into two identical sets in two nuclei. It is generally followed immediately by cytokinesis, which divides the nuclei, cytoplasm, organelles and cell membrane into two cells containing roughly equal shares of these cellular components. Meiosis involves two sequential nuclear divisions followed by cell divisions that produce gametes containing half the number of chromosomes and half the DNA found in somatic cells. Anaphase I and telophase I are similar to the same phases in mitosis except the centromeres do not split. The sister chromatids remain together. At the completion of meiosis I the cytoplasm divides. Each daughter cell is haploid in chromosome number (1n) but the cell is still diploid in DNA content (2d). After meiosis I the cells enter meisois II without passing through the S phase. Sister chromatids are now separated and after passing through prophase II, metaphase II, anaphase II, and telophase II, the chromosome number is haploid (23 chromosomes N) and the DNA content is haploid (1d). S l i d e Cell Death: Two Mechanisms The Cell Return to outline Necrosis Accidental cell death due to injury Rapid cell swelling and lysis Inflammatory response 3 2 Apoptosis Programmed External cell death and internal signals Fig. 3.18, p. 89, Ross & Pawlina, 5th edition S l i d e 3 3 Cellular Homeostasis Return to outline When the rate of cell division and cell death are similar a condition known as homeostasis exists. The following illustration demonstrates this. The body maintains cell populations by mitosis and death. We now have an understanding of mitosis and cell proliferation. Cell death is an important component of maintaining normal population levels of cells. Cells die by two mechanisms – Necrosis and Apoptosis. Necrosis is cell death as a result of injury. In necrosis, injury can be due to hypoxia (low oxygen) or anoxia (no oxygen) due to inadequate blood flow or complete stoppage of blood flow due to clotting and thrombosis. The mitochondria of the cell stop producing energy that, in turn, upsets the integrity of the membranes. The plasma membrane then leaks and calcium (which is much higher in concentration outside of the cell) rushes in and completely overwhelms the mitochondria that normally can handle a slight increase in calcium. Immediately, water is taken into the cell and it swells…..then ultimately, the cell breaks apart and its components attract inflammatory cells and macrophages that eventually resorb the cell fragments. Apoptosis occurs differently and is the mode of cell death that occurs under normal physiologic conditions. The cell is an active participant in its own demise (cellular suicide). One external mechanism of apoptosis involves cytotoxic T lymphocytes in which pores are induced in the cell and endonucleases are activated resulting in DNA fragmentation. So, by means of regulated cell proliferation and cell death, a balance or homeostasis is achieved. The top drawing illustrating a balanced teeter totter illustrates two new cells being formed while two cells are dying. This is homeostasis of body cell population that occurs in the normal condition. Pathological conditions may tip the balance one way or another. When cell deaths exceed cell division, pathological conditions characterized by loss of cells occurs such as in AIDS, Alzheimer’s, Parkinsons, Aplastic Anemia and Myocardial Infarction. When cell division exceeds cell death, abnormal cell numbers accumulate creating pathological disorders such as benign and malignant cancer, lupus, glomerulonephritis and viral infections. S l i d e 3 4 Summary The Cell Prokaryotic and eukaryotic cell prototypes were illustrated and explained. Cellular Compartments: Plasma Membrane, Cytoplasm and Nucleus were presented. Light microscope and Electron Microscope views of a cell were compared Cell complexity was emphasized Cell organelles and inclusions were defined, listed and their structure and function was presented. The embyrological origin of cells was presented and examples of differentiated cells were illustrated. Three populations of cells –static, stable and dynamic, were defined and examples given. Two mechanisms of cell death, necrosis and apoptosis, were defined and illustrated. Finally, cellular homeostasis was defined and two examples given where homeostasis was interfered with by either excessive cell proliferation or death. .