Cell Concepts PDF

WHAT IS BIOLOGY?  The word "biology" is derived from the Greek words "bios" (meaning life) and "logos" (meaning "study"). Biology is the study of life. the study of living organisms, divided into many specialized fields that cover their morphology, physiology, anatomy, behaviour, or...

WHAT IS BIOLOGY?  The word "biology" is derived from the Greek words "bios" (meaning life) and "logos" (meaning "study"). Biology is the study of life. the study of living organisms, divided into many specialized fields that cover their morphology, physiology, anatomy, behaviour, origin, and distribution  What makes something “alive”? Anyone could deduce that a galloping horse is alive and a car is not, but why? CHARACTERISTICS OF LIVING ORGANISMS Cellular organization - All organisms consist of one or more cells. Ordered complexity - All living things are both complex and highly ordered. Your body is composed of many different kinds of cells, each containing many complex molecular structures. Sensitivity - All organisms respond to stimuli. Plants grow toward a source of light, and the pupils of your eyes dilate when you walk into a dark room Growth, development, and reproduction - All organisms are capable of growing and reproducing, and they all possess hereditary molecules that are passed to their offspring Energy utilization - All organisms take in energy and use it to perform many kinds of work. Homeostasis - All organisms maintain relatively constant internal conditions that are different from their environment, a process called homeostasis. For example, your body temperature remains stable despite changes in outside temperatures. Evolutionary adaptation - All organisms interact with other organisms and the nonliving environment in ways that influence their survival, and as a consequence, organisms evolve adaptations to their environments Biological Sciences embrace the fields of: 1. Zoology – science of animals – A branch of zoology specializing in the study of insects is termed Entomology – Another branch of zoology dealing with parasitic animals is called Parasitology 2. The science of plants is known as Botany or Phytology 3.The study of fungi is termed as Mycology 4.The study of Bacteria is covered in the discipline of biology called Bacteriology 5.The special study of viruses is termed Virology 6.The fields of bacteriology, mycology and virology constitute a major discipline of biology called Microbiology. Microbiology is the study of microscopic organisms (bacteria, fungi, viruses) 7. The branch of biology dealing with heredity and biological variation is called Genetics Biology can be studied from several angles that embrace such branches as: 1. Morphology – a field which deals with the form and structure of organisms 2. Anatomy – a field that involves the study of the internal structures of organs and associated tissue types 8. Ecology – the study that involves the interactions between organisms (plants and animals) and their environment  INTRODUCTION All living things are made up of cells Cells are the basic unit of structure and function in an organism (basic unit of life) Living things may be unicellular or multi-cellular. Cell structure is diverse but all cells share common  MICROSCOPE The cells are so minute that they can only be studied under the microscope. A microscope is a device that allows people to view specimens in detail too small for the naked eye to see. They do this by magnification and resolution. Magnification is how many times the object is enlarged within the viewing lens. Resolution is how detailed the object appears when viewed. TYPES OF MICROSCOPES THE LIGHT MICROSCOPE The light microscope can magnify the cell structure to about 1,000 times the normal size. The light microscope which consists of a system of lenses, floods the specimens with light waves Light Microscopy  Electron Microscope The electron microscope, developed in the 1950s, is yet another innovation which can reveal much finer detail (or ultra- structure) of cell components The electron microscope floods the specimens with a beam of electrons. The electron microscope can magnify the image to about 250,000 times or more. The two main features of the microscope are: I. Magnification II. Resolving power  MAGNIFICATION Magnification is the factor by which an image appears to be enlarged. It will be a whole number greater than 1 and is usually followed by an “x”, as in 10x magnification.  is the ability of a microscope to enlarge specimens for the viewer  How to calculate magnification for a light microscope: Magfinal = Magocular X Magobjective  RESOLVING POWER Resolving power – is the ability of the microscope to reveal fine detail of the specimen Resolving power is determined by: – The wavelength of light, power of the objective and ocular lenses Therefore, microscopes are essential tools for studying cell structures  transmission electron microscope (TEM) designed to reveal internal structures of the specimen. scanning electron microscope (SEM) designed to reveal the surface features of the specimen.  Microscopy Two types of microscopes used in the laboratory are: i. Transmission types ii. Dissecting types In transmission microscopes, the light waves are transmitted through the specimen whereas in electron microscopes, electrons are transmitted through the specimen  Microscopy In dissecting microscopes, the light is reflected on the surface of the specimen to reveal surface features or ornamentations A variant of the powerful dissecting microscope is the scanning electron microscope (SEM) – It is designed to reveal surface features of the specimen – Resolution ~ 0.05nm  Microscopy A variant of the transmission microscope is the transmission electron microscope (TEM) – It is designed to reveal internal structures of the specimen – Resolution ~ 0.4nm – 3D view CELLS  ROBERT HOOKE English natural philosopher Robert Hooke first described cells in 1665 when he used a microscope he had built to examine a thin slice of a non-living tissue found in the bark of certain trees. Hooke observed a honeycomb of tiny, empty (because the cells were dead) compartments. He called the compartments cellulae (Latin, “small rooms”), and the term has come down to us as cells. ROBERT HOOKE  antonie van Leeuwenhoek The first living cells were observed a few years later by the Dutch naturalist Antonie van Leeuwenhoek, who called the tiny organisms that he observed “animalcules,” meaning little animals. Antonie van Leeuwenhoek  Beginning of the Cell Theory For another century and a half, however, biologists failed to recognize the importance of cells. In 1838, a German botanist named Matthias Schleiden concluded that all plants were made of cells. Schleiden is a co-founder of the cell theory made a careful study of plant tissues and developed the first statement of the cell theory. He stated that: “all plants are aggregates of fully individualized, independent, separate beings, namely the cells themselves.” Matthias Schleiden  Theodore Schwann In 1839, a German zoologist named Theodore Schwann concluded that all animals were made of cells. Schwann also co-founded the cell theory  Rudolph Virchow In 1855, a German medical doctor named Rudolph Virchow observed, under the microscope, cells dividing He reasoned that all cells come from other pre-existing cells by cell division Rudolph Virchow  The Cell Theory Explains relationship between cells and living things – foundation of modern biology THE CELL THEORY, in its modern form, includes the following three principles: 1. All organisms are composed of one or more cells, and the life processes of metabolism and heredity occur within these cells. 2. Cells are the smallest living things, the basic units of organization of all organisms. 3. Cells arise only by division of a previously existing cell.  When cells were visualized with microscopes, two basic cellular architectures were recognized: eukaryotic and prokaryotic. These terms refer to the presence or absence, respectively, of a membrane-bounded nucleus that contains genetic material.  Prokaryotes and Eukaryotes 1. prokaryotic (pro = before; karyon– = nucleus) The single-celled organisms which includes bacteria and Archaea 2. Eukaryotes (eu = true). Animal cells, plant cells, fungi, and protists are eukaryotes (eu = true).  Prokaryotic cells comprise bacteria and archaea. They typically have a diameter of 0.1–5 μm, and their DNA is not contained within a nucleus. Instead, their DNA is circular and can be found in a region called the nucleoid, which floats in the cytoplasm. Prokaryotes are organisms that consist of a single prokaryotic cell. cell wall composed of peptidoglycan PROKARYOTES  Prokaryotes are very important in the ecology of living organisms. Some harvest light by photosynthesis, others break down dead organisms and recycle their components. Still others cause disease or have uses in many important industrial processes. Prokaryotes have two main domains: archaea and bacteria.  Eukaryotic cells are found in plants, animals, fungi, and protists. They range from 10–100 μm in diameter, and their DNA is contained within a membrane-bound nucleus. Eukaryotes are organisms containing eukaryotic cells. EUKARYOTES EUKARYOTES Prokaryotes versus Eukaryotes Prokaryotes—bacteria and archaea—differ from eukaryotes in numerous important features. These differences represent some of the most fundamental distinctions that separate any groups of organisms. 1. Multicellularity. All prokaryotes are fundamentally single- celled in comparison to multicellular eukaryotes  2. Cell size - Most prokaryotic cells are only 1 micrometer or less in diameter. Most eukaryotic cells are well over 10 times that size. 3. Chromosomes - Eukaryotic cells have a membrane-bound nucleus containing chromosomes made up of both nucleic acids and proteins. Prokaryotes do not have membrane- bound nuclei. Instead, their naked circular DNA is localized in a zone of the cytoplasm called the nucleoid.  4. Cell division and genetic recombination - Cell division in eukaryotes takes place by mitosis and involves spindles made up of microtubules. Cell division in prokaryotes takes place mainly by binary fission Binary Fission in Prokaryotes Mitosis in Eukaryotes  5. Internal compartmentalization. In eukaryotes, the enzymes for cellular respiration are packaged in mitochondria. In bacteria, the corresponding enzymes are not packaged separately but are bound to the cell membranes. The cytoplasm of prokaryotes, unlike that of eukaryotes, contains no internal  6. Flagella. Prokaryote flagella are simple in structure, composed of a single fibre of the protein flagellin, spinning like propellers. Eukaryotic flagella are complex have a whip-like motion. 7. Metabolic diversity. Only one kind of photosynthesis occurs in eukaryotes, and it involves the release of oxygen. Prokaryotes have several different patterns of anaerobic and aerobic photosynthesis, involving the formation of end products such as sulphur, sulphate, and oxygen  BACTERIA all bacteria may be classified into two types based on differences in their cell walls detected by the Gram staining procedure. Danish microbiologist Hans Christian Gram, who developed the procedure to detect the presence of certain disease-causing bacteria.  Two types of bacteria can be identified using a staining process called the Gram stain, hence their names. Most bacteria are encased by a strong cell wall composed of peptidoglycan, which consists of a carbohydrate matrix (polymers of sugars)  Gram-positive bacteria have a thick, single-layered cell wall that retains a violet dye from the Gram stain procedure, causing the stained cells to appear purple under a microscope. whereas the Gram-negative bacteria contain less peptidoglycan and do not retain the purple-coloured dye. These gram-negative bacteria can be stained with a red counter-stain and then appear dark pink  Gram stain test Gram stain testing is a method for classifying bacteria based on their cell wall. It allows scientists to determine whether an organism is gram-positive or gram-negative. The test, which uses a microscope, was created by Hans Christian Gram in 1884. During the procedure, crystal violet dye is applied to a sample of bacteria. This chemical dye can stain thick peptidoglycan layers. Under a microscope, gram-positive bacteria appear purple-blue because their thick peptidoglycan membrane can hold the dye. The bacteria is called gram-positive due to the positive result. Gram-negative bacteria stain pink-red. Their peptidoglycan layer is thinner, so it doesn’t retain the blue color. The test result is negative. In a medical setting, a doctor can send a sample of your blood, urine, or tissue to a lab for Gram stain testing. This may help them diagnose a bacterial infection.  Gram stain procedure - Gram staining a sample 1. Gently flood the smear with crystal violet and leave for 1 minute. Tilt the slide slightly and gently rinse with tap water or distilled water. Crystal violet is a water-soluble dye which enters the peptidoglycan layer in the bacterial cell wall. 2. Gently flood the smear with Gram’s iodine and leave for 1 minute. Tilt the slide slightly and gently rinse with tap water or distilled water. The smear will now appear purple. Gram's iodine solution (iodine and potassium iodide) is added to form a complex with the crystal violet, which is much larger and is insoluble in water. 3. Decolorize the smear using 95 % ethyl alcohol or acetone. Tilt the slide slightly and apply the alcohol drop by drop until the alcohol runs almost clear (5-10 seconds). Immediately rinse with water to avoid over-decolorizing. Decolorizer dehydrates the peptidoglycan layer, shrinking and tightening it. In Gram positive bacteria, the large crystal violet-iodine complexes are then unable to penetrate and escape the thick peptidoglycan layer, resulting in purple stained cells. However, in Gram negative bacteria, the outer membrane is degraded, the thin peptidoglycan layer is unable to retain the crystal violet-iodine complexes and the color is lost. 4. Gently flood with safranin counterstain and leave for 45 seconds. Tilt the slide slightly and gently rinse with tap water or distilled water. Safranin is weakly water soluble and will stain bacterial cells a light red, enabling visualization of Gram negative cells without interfering with the observation of the purple of the Gram positive cells. 5. Blot the slide dry on filter paper then view the smear using a light-microscope under oil-immersion.  Though both groups of bacteria can cause disease, they require different treatments. If you have a bacterial infection, the Gram stain will determine what kind of medication you need.  The major difference is the outer lipid membrane. It’s difficult to penetrate, which gives gram- negative bacteria extra protection. Gram-positive bacteria don’t have this feature. Because of this difference, gram-negative bacteria are harder to kill. This means gram-positive and gram-negative bacteria require different treatments. Though gram-negative bacteria are harder to destroy, gram-positive bacteria can still cause problems. Many species result in disease and require specific antibiotics.