1. Cell structure & functions.pdf

DEPARTMENT OF ZOOLOGY 100 LEVEL COURSES Courses Title LH PH Units Status ZOO 112 The Mammalian Body 45 0 3 C ZOO 114 Principles of Cell Biology and 30 0 2 C Genetics ZOO 115 Introductory Ecology...

DEPARTMENT OF ZOOLOGY 100 LEVEL COURSES Courses Title LH PH Units Status ZOO 112 The Mammalian Body 45 0 3 C ZOO 114 Principles of Cell Biology and 30 0 2 C Genetics ZOO 115 Introductory Ecology 30 0 2 C ZOO 116 Introductory Invertebrate Zoology 30 0 2 C ZOO 117 Introductory Vertebrate Zoology 30 0 2 C ZOO 118 Practical Zoology 0 90 2 C  ZOO 114 (PRINCIPLES OF CELL BIOLOGY & GENETICS PERIOD LECTURE SYNOPSIS LECTURER 3 weeks Cell structure and function Prof. A. A. Bakare 3 weeks Cellular basis of biological organization. Dr. Chiaka I. Macromolecular basis of life Anumudu 3 weeks Genetic inheritance and variation Charles Latunji Information transfer 2 weeks Energy production and utilization. Dr. G. C. Alimba Principles of Bioethics. 2 weeks Embryogenesis and growth Dr. Roseangela Nwuba  Some useful Biology Textbooks ❑ BSCS Biology A Human Approach. Richard; Parravano, Carlo; Girard, Jan Chalatain; Handy, Mark; Hill, Becky; Sauerhagen, Brent; Third Edition 2006. Kendall Hunt Publishing Company. ❑ Glencoe Biology Alton Biggs, Whitney Crispen Hagins, William G. Holliday, Chris L. Kapicka, Linda Lundgren, Ann Haley MacKenzie, William D. Rogers, Marion B. Sewer and Dinah Zike. First Edition 2007. Mcgraw-Hill, New York ❑ Integrated Principles of Zoology Hickman, C. P., Roberts L. S., Keen S.L., Eisenhour, D. J. Larson Allan, L’Anson Helen. Fifteenth Edition. 2011 McGraw Hill. ❑ Biology An Exploration of Life. Carol H. McFadden, William T. Keeton. First Edition. 1995. W. W. Niston and Company Inc. ❑ Advance Biology. Mary Jones and Geoff Jones. First Edition. 1997. Cambridge University Press. ❑ Biology Today. Sandra S. Gottfried. First edtion1993. Mosby Year book Inc. ❑ Biology. Peter H. Raven, George B. Johnson, Kenneth A. Mason, Jonathan Losos, Susan Singer Ninth Edition.2011. McGraw Hill ❑ Biology The Dynamic Science. Peter J. Russell and Paul E. Hertz. Second edition 2011. Brooks/Colle Cengage learning. ❑ Vertebrates Kenneth V. Kardong Fourth Edition. 2006. McGraw Hill. ❑ Biology of the Invertebrates. Pechenick J. A. Sixth edition. 2010. McGraw Hill. ❑ Invertebrate Zoology Fatik Baran Mandal. First edition. 2012. PHI Learning.  CELL STRUCTURE AND FUNCTION The Cell Theory Cell is the basic functional unit of life. The cell theory was formulated in 1839 and it includes three basic principles: 1. All living things are made up of one or more cells. 2. The smallest living unit of structure and function of all organisms is the cell. 3. All cells arise from pre-existing cells. Two kinds of cells exist; 1. Prokaryotic cells (organisms as prokaryotes) 2. Eukaryotic cells (organisms as eukaryotes)  PROKARYOTIC CELLS These are structurally simple but biochemically diverse e.g. bacteria, blue green algae and other lower organisms. A bacteria cell (an example of a prokaryote)  CHARACTERISTICS OF PROKARYOTIC CELLS ✓The cell is a whole organism but may exist in colonies. ✓They have no membrane-bound organelles e.g. mitochondria, golgi bodies, etc. ✓No defined nucleus. ✓The genetic material consists of a single DNA molecule which is found floating in the cytoplasm. ✓DNA is naked. The chromosome consists of only nucleic acid and is relatively free of protein. ✓Those that have flagella are without the 9-2 fibrillae structure. ✓They may contain chlorophyll but the chlorophyll is not contained within a chloroplast. ✓Stages of protein synthesis are coupled. Most proteins attached to the DNA are associated with replication, transcription and control and occur in a large variety of colour and sizes.  EUKARYOTIC CELLS Eukaryotic cells differ remarkably from prokaryotic cells because of the following: They possess membrane-bound organelles. Genetic or hereditary material is constrained in a membrane bound nucleus. Genetic material is organised into chromososme and the chromosomes have some proteins attached to them. Stages of protein synthesis are separate i.e. transcription occurs in the nucleus and translation occurs in the cytoplasm. Eukaryotic cells are found in higher organisms i.e. higher plants and animals and these organisms are made up of various cells arranged at different levels of cellular organisation. A generalised representation of an animal cell showing the major organelles  LEVELS OF BIOLOGICAL/CELLULAR ORGANISATION The levels of organization in the correct order are: cells --> tissues --> organs --> organ systems --> organisms A tissue is composed of many cells usually very similar in both structure and function and these cells are bound together by intercellular material. An organ is composed of various tissues not necessarily similar but grouped together into a structural and functional unit. A system can be defined as a group of interacting organs that cooperate as a functional complex in the life of an organism. Organisms: Entire living things that can carry out all basic life processes.  TYPES OF TISSUE Different types of tissues can be found in different organs. In humans, there are four basic types of tissue: EPITHELIAL, CONNECTIVE, MUSCULAR, AND NERVOUS There may be various sub-tissues within each of the 10 tissues. 1. EPITHELIAL TISSUE Epithelial tissue covers the body surface and forms the lining for most internal cavities. The major function of epithelial tissue includes protection, secretion, absorption, sensation, and filtration. The skin is an organ made up of epithelial tissue which protects the body from dirt, dust, bacteria and other microbes that may be harmful. Cells of the epithelial tissue have different shapes: can be thin, flat to cubic to elongated.  Epithelial tissue can de distinguished on the basis of shape e.g Squamous, cuboidal and columnar. They can also be classified by the number of layers: simple layer, stratified layer, pseudostratified layer  2. CONNECTIVE TISSUE ❖Connective tissue is the most abundant (e.g. cartilage and bone). ❖It is the most widely distributed of the tissues. ❖Connective tissues perform a variety of functions including support and protection. ❖The following connective tissues are found in the human body, loose connective tissue, adipose/fat tissue, elastic connective tissue, reticular connective tissue, dense fibrous tissue, cartilage, bone, blood, and lymph. Collagen fibres and adipocytes  MUSCULAR TISSUE There are three types in Vertebrates: SKELETAL, SMOOTH, AND CARDIAC. Skeletal muscle is a voluntary type of muscle tissue that is used in the contraction of skeletal parts. Smooth muscle is found in the walls of internal organs (e.g. digestive tract, uterus) and blood vessels. It is an involuntary type. The cardiac muscle is found only in the walls of the heart and is involuntary in nature.  NERVOUS TISSUE ✓Nerve tissue is composed of specialized cells (two types: Neurons and Glial cells) ✓Glial cells support and nourish the neurons ✓Functions: Receive stimuli and conduct impulses to and from all parts of the body. ✓Nerve cells or neurons are long and string-like.  THE PLASMA MEMBRANE (ORGANELLES) ✓Also known as Plasmalemma or cell membrane ✓This is a thin sheet that keeps the cell together. ✓ It regulates what passes in and out of the cell. ✓It also functions in cell-to-cell recognition. ✓It is often seen to be continuous with the cell’s internal membrane systems such as the endoplasmic reticulum and the Golgi complex. ✓It has two main components: phospholipid and proteins. ✓The cell membrane may be supported or supplemented by the cellulose cell wall as found in plants or pellicle as found in Paramecium. ✓This membrane actually has a tripartite structure giving it a dark-light-dark band structure. ✓Dark band contains protein while the light band contains lipid. Unit membrane structure of plasma membrane  THE CYTOPLASM The cytoplasm of the cell is the viscous fluid containing all cell organelles. The major components of the cytoplasm are: 1. A gel-like fluid known as the cytosol. 2. Storage substances 3. A network of interconnected filaments and fibers. 4. Cell organelles. The fluid part of the cytoplasm is made up of approximately 75% water and 25% proteins. Non-protein molecules involved in the various chemical reactions of the cell, such as ions and ATP, are also dissolved in this fluid.  CELL CYTOSKELETON ✓These are long, fine filaments of protein that crisscrossed the cytosol. ✓They are of three types. 1. The first and the thinnest of the filaments are actin filaments, ✓ which are present in all eukaryotic cells but occur in especially ✓ large numbers inside muscle cells, where they serve as part of ✓the machinery that generates contractile forces. 2. The second type are called microtubules. ✓They are so called because they have the form of minute ✓hollow tubes. ✓They are the thickest and are reorganised into spectacular arrays in dividing cells, where they help pull the duplicated chromosomes in opposite directions and distribute them equally to the two daughter cells. 3. Intermediate in thickness between actin filaments and microtubules are the intermediate filaments, which serve to strengthen the cell mechanically. These three types of filaments together with other proteins that attach to them, form a system of girders, ropes and motors that give the cell its mechanical strength, control its shape and drive and guide its movements. Apart from this, animal cells and plant cells alike depend on the cytoskeleton to separate their internal components into two daughter sets during cell division. The Nucleus The nucleus, or control center of the cell is made up of an outer, double membrane that encloses the chromosomes and one or more nucleoli.  This membrane is called the nuclear envelope and is continuous with the endoplasmic reticulum. This membrane is interrupted at various spots on its surface to form openings called nuclear pores which serve as passageways for molecules entering and leaving the nucleus. Within the nucleus is the hereditary material, DNA, which determines the characteristics or traits of all living organisms. It controls all activities of the cell. ❖DNA bound to proteins in the nucleus, forms a complex called chromatin. ❖When a cell divides, the DNA condenses into compact structures called chromosomes. ❖The nucleolus is a darkly staining region within the nucleus and consists of DNA, ribosomal RNA (rRNA) and ribosomal proteins.  THE ENDOPLASMIC RETICULUM The ER is an extensive system of interconnected membranes that forms flattened channels and tube-like canals within the cytoplasm. The channels are used to help move substances from one part of the cell to another. There are two types of ER: ROUGH AND SMOOTH. The surface of the rough ER which is in contact with the ground cytoplasmic matrix is heavily coated with spherical structures called RIBOSOMES and this gives it a rough appearance under the microscope hence the name rough endoplasmic reticulum.  It is in this network of channels that lipids and proteins of cell membrane as well as materials destined for export from the cell are synthesized. The smooth ER lacks ribosomal attachment and as a result appears smooth and does not manufacture proteins. Instead, smooth ER has enzymes bound to its inner surfaces that help build carbohydrates and lipids. The Endoplasmic Reticulum  RIBOSOMES These are visible as small granules. They are molecular structures consisting of RNA and proteins. A ribosome is an organelle that takes part in protein synthesis. Each ribosome is clearly divided into two unequal but constant sized subunits. There are three types of ribosomes: 1. Polyribosomes, also known as attached ribosome, are chains of ribosomes attached to the endoplasmic reticulum and are actively involved in protein synthesis. 2. Single ribosomes are temporarily inactive ribosomes and are also attached to the endoplasmic reticulum. Proteins manufactured by the polyribosomes and single ribosomes are usually exported out of the cell. 3. Free ribosomes build proteins with which the cell makes new parts as well as reproducing itself. They represent about 10% of total ribosome population in the cell and are found lined free in the cytoplasm.  MITOCHONDRIA These are oval, sausage-shaped or thread-like organelles about the size of bacterial that have their own DNA. They are normally referred to as the power house or power plant of the cell because they provide energy for the cell during cellular or tissue respiration. Chemical analysis shows that it consists of 70% protein, 25% lipids and 5% miscellaneous. The 5% includes a small amount of DNA and RNA. DNA found in mitochondria is responsible for extra-nuclear inheritance. Each mitochondrion is bounded by a double membrane.  The outer of the two membranes is smooth and defines the shape of the organelle. The inner membrane however has many folds called the CRISTAE that dip into the interior of the mitochondrion. A mitochondrion  The cristae show variable forms and arrangement. It may be tubular, flattened, sparse or numerous. The cristae appear to be more extensively developed in the mitochondria of cell with high energy requirement. The number of mitochondria in the cell is also highly varied; The higher the energy requirement of the cell, the higher the number of mitochondria in the cell.  GOLGI COMPLEX OR BODIES This organelle is involved in the synthesis, modifying, sorting, packaging and transport of macromolecules for secretion or for delivery to other organelles. They show considerable variation in size, number and position. It can simply be defined as a system of flattened stacks arranged in parallel rolls much like microscopic stacks of pancackes in the cytoplasm. Animal cells contain 10 to 20 sets of these flattened membranes. Plant cells however, may contain several hundreds because the Golgi bodies are involved in the synthesis and maintenance of plant cell walls.  Golgi bodies are well developed in secretory cells and neurons. Each Golgi stack has three areas referred to as cis and trans faces, with a medial region between. The cis face is located nearest the nucleus and functions to receive materials from transport vesicles from the endoplasmic reticulum. The trans face, nearest to the plasma membrane, packages molecules in vesicles and transports them out of the Golgi. GOLGI COMPLEX OR BODIES  LYSOSOMES This is a membrane enclosed body that apparently functions as a storage vesicle for many powerful digestive hydrolytic enzymes. These enzymes break down old cell parts or materials brought into the cell from the environment. They are usually called ‘suicide bags’. Lysosome may exist in four different phases: 1. Storage granule or primary lysosome 2. Digestive granule or secondary lysosome 3. Residual body 4. Autophagic vacuole The different phases of the lysosome  PEROXISOMES These are about the size of lysosomes and are bound by a single membrane. They are filled with enzymes of which catalase is the most characteristic. Catalase catalyses the breakdown of hydrogen peroxide (H2O2), a potentially dangerous product of cell metabolism. They may also break down other toxic molecules that get into the cell, such as beverage, alcohol and many other drugs. In animals, peroxisomes appear to be confined to cells of the liver and kidney. In plants, they occur in a variety of cell types and often contain protein that is crystallised.  THE CENTROSOME The centrosome consists of a pair of centrioles located in the cytoplasm just outside the nucleus. They serve as the microtubule organising center of animal cells which function during cell division. In certain cells, the centrioles also duplicate to produce the basal bodies of cilia and flagella.  CILIA AND FLAGELLA These are whip-like appendages found on the exterior of many kinds of eukaryotes. If there is only one or a few of these structures, we call them flagella. If there are many of them, we call them cilia. Both are locomotor structures for many single cells.  CHLOROPLASTS This is only found in plants and algae, not in cells of animals or fungi. They are large green organelles that have in addition to the two surrounding membranes, stacks of membrane containing the green pigment chlorophyll inside the organelle. Chloroplasts enable plants to obtain energy directly from sunlight by the process of photosynthesis. The chloroplasts generate both the food molecules and the oxygen that all mitochondria use. Like mitochondria, chloroplasts contain their own DNA and can also reproduce themselves by dividing into two. CHLOROPLAST  VACUOLES Vacuoles are most often found in plant cells where they play a major role in helping plant tissues stay rigid. Certain single celled eukaryotes, the protists and some yeasts also contain vacuoles. In these organisms, it is a storage depot for excess water and waste products. However, in most cases, it serves as a dustbin where harmful substances are dumped so as not to interfere with the normal metabolism of the cell. Many protists also have food vacuoles, where food is stored and eventually digested by fusion with lysosomes.