BIOL 225 - Cell Biology - Chapter 1 Notes
BIOL 225 - Cell Biology - Chapter 1 Notes BIOL 225
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This 11 page Class Notes was uploaded by MelLem on Saturday January 23, 2016. The Class Notes belongs to BIOL 225 at Simmons College taught by Dr. Lopilato in Fall 2016. Since its upload, it has received 42 views. For similar materials see Cell Biology in Biology at Simmons College.
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Date Created: 01/23/16
BIOL 225 Cell Biology Professor Lopilato Chapter 1: Introduction to the Study of Cell and Molecular Biology 1.1 The Discovery of Cells • Because of the cells small size, they can only be seen with the aid of a microscope. • The first compound light microscope was constructed by the end of the 16 century. • The discovery of cells is often credited to Robert Hooke, an English microscopist. o When Hooke examined his cork under the microscope, he saw what he called “cells”, these cells were actually the cell walls of dead plant cells. • Leeuwenhoek – was the first to examine pond water under the microscope. o He observed teeming microscopic “animalcules” o Was also the first to describe various forms of bacteria • Schwann conducted that: o The cells of plants and animals are similar in structure and proposed two tenets of the cell theory: ▯ All organisms are composed of one or more cells. ▯ The cells is the structural unit of life. 1.2 Basic Properties of Cells • Just as plants and animals are alive, so too are cells. o Life is the most basic property of cells o Cells are the smallest unity that exhibits this property (life). • Whole cells can be removed from an animal or plants and be cultured in a lab. o Here they can grow and be reproduced for an extended amount of time so that they can be studied and a part of research. • Death can also be considered a basic property of life. o Cells within the body tend to die by themselves. o Other times, cells that pose a threat or are damaged can die and deteriorate. • The first culture of human cells began in 1951 at Johns Hopkins by George and Martha Grey. o The cells were obtained from a malignant tumor of Henrietta Lacks. o The cells were named HeLa cells after her. o Her cervical cancer cells are still being grown in laboratories around the world today, and are being used in colleges and research for learning purposes. • Cells are much easier to study when they are outside of the body in a petri dish. o In Vitro – cultured outside the body. o In Vitro grown cells have become essential for cell and molecular biologists. Cells are Highly Complex and Organized • The complexity of life has many different levels – over the course of the class, we will discuss several: o Organization of atoms into small molecules o Organization of small molecules into giant polymers o And the polymers into subcellar organisms. • Fortunately for cell and molecular biologists, evolution has moved very slowly at the levels of biological organization. • When looking at a cat and human, there are many anatomical differences, but the organelles and structures that make up the cells are similar. • Many of the basic processes, such as: o Synthesis of proteins o Conservation of chemical energy o Or the construction of a membrane – are very similar in all living organisms. Cells Possess a Genetic Program and the Means to use it • Organisms are build according to information that is encoded in a collection of genes o Genes – constructed of DNA • The amount of information packaged into the chromosomes in the nucleus is approximately 100 times smaller than the dot on the ‘i’ • Genes constitute the blueprints for constructing cellular structures and running cellular activities, and the program of making more of themselves. • The molecular structure of genes allows for changes in the genetic information (mutations). o Mutations – lead to variation among individuals, which forms the basis of biological evolution. Mutations can be harmful, and in some cases be helpful to the organism. Reproduction of Cells • Cells reproduce by division. The contents of the “mother” cell are divided into two “daughter” cells • Prior to division, the genetic material is duplicated; each daughter cell receives a complete and equal amount of material. • In most cases, the cells have approximately the same volume. However, it is sometimes possible for one of the cells to retain nearly all of the cytoplasm, even though it has ½ of the genetic material. Cells Acquire and Utilize Energy • Every biological process requires the input of energy. • The energy of light, from the sun is trapped in the light absorbing pigments present in the membranes of the photosynthetic cells of plants. • Light energy is converted by photosynthesis to chemical energy that is stored in energy rich carbohydrates, such as sucrose and starch. • For most animals, energy comes pre-‐packaged in the form of glucose. o In humans, glucose is released by the liver into the blood where it is then able to circulate. Energy is brought to all of the cells in the body. o Glucose is then disassembled and stored (usually as ATP) in the body. • Cells expend an enormous amount of energy when they break down and rebuild the macromolecules and organelles that they’re comprised of. Cells Carry out a Variety of Chemical Reactions • Cells function similarly to “chemical plants” • Even the simplest form of bacteria undergoes and is capable of hundreds of different chemical transformations • Virtually all chemical reactions that take place in the cell require enzymes. o Enzymes – molecules that greatly increase the rate at which a chemical reaction occurs. A catalyst. o Metabolism – The sum total of the chemical reactions in a cell. Cells engage in Mechanical Activities • Cells are very active: o Material are transported from places to other places. o Structures are assembled and then rapidly disassembled. o In many cases, the cell moves itself from one site to another. • Motor proteins are one of the many types of molecular “machines” employed by the cell to carry out mechanical activities. Cells are able to Respond to Stimuli • Some cells respond to stimuli in obvious ways o Single celled protists – moves away from an object in its path or towards a source of nutrients. • Cells possess receptors to: o Hormones o Growth factors o Extracellular materials o As well as substances on the surfaces of other cells. • A cells receptors provide a pathway for an external stimuli (signal) to evoke a specific reaction in the target cells. • Many cells may respond to a stimuli by: o Alternating their metabolic activities o Moving from one place to another o Or – committing suicide Cells are capable of self-‐regulation • If fluctuations within the cell occur, specific feed back circuits are activated that serve to return the cell to the appropriate state. • An ordered state requires constant regulations • Many processes within the cell require a specific series of ordered steps. Cells Evolve • It is resumed that cells evolved from a pre-‐cellular life form o Pre-‐cellular life forms are thought to have evolved from non-‐living organic materials that were present in the primordial seas. • According to one of the tenets of moderns biology, all living organisms have evolved from a single common ancestral cell that lived more than 3 billion years ago. • Evolution is not an event from the past, but an on going one that continues to modify the properties of cells of future organisms. 1.3 Two Fundamentally Different Classes of Cells (pg 7) • Once the electron microscope became widely available, biologists were able to examine the internal structures in a large variety of cells. • These studies determined that there was two different types of cells o Prokaryotes o Eukaryotes • The two cell types can be distinguished between by looking at their structure, size and internal organelles o Organelles – internal structures of a cell. • Prokaryotic cells o Structurally simpler o They include – bacteria • Eukaryotic Cells o Structurally more complex o They include – protists, fungi, plants and animals • There is no known time of appearance of prokaryotes, but there is evidence of them in rocks from 2.7 billion years ago. o The rock contains complex organic molecules that are characteristic of particular types of prokaryotes (cyanobacteria) o Cyanobacteria appears 2.4 billion years ago, this is when 02 was infused into the atmosphere. o O2 is the by product of photosynthetic activity Characteristics that Distinguish Prokaryotic and Eukaryotic Cells • There are many differences and similarities between prokaryotes and eukaryotes. • The shared similarities almost certainly evolved from prokaryotes o Due to common ancestry, both types of cells share an identical genetic language, a common set of metabolic pathways, and many common structural features. • Both types of cells are bounded by plasma membranes. o Serves as selectively permeable barrier between the living and non-‐ living worlds. • Although the cell walls of prokaryotes and eukaryotes may be similar functions, their chemical composition is very different. • Internally, eukaryotic cells are much more complex – both structurally and functionally. Prokaryotic: • The genetic material of prokaryotes is found in the nucleoid. • Nucleoid – a poorly demarcated region of the cell that lacks a boundary membrane to separate it from the surrounding cytoplasm. Eukaryotic: • In contrast, eukaryotic cells posses a nucleus. • Nucleus – a region bounded by a complex membranous structure called the nuclear envelope. DNA: • Prokaryote cells contain relatively small amounts of DNA. o The DNA content of bacteria ranges from about 600,000 to 8 million base pairs. o This encodes for about 500 – several thousand proteins. • Eukaryotic cells tend to contain considerably more genetic information. • Both prokaryotes and eukaryotic cells have DNA containing chromosomes. • Eukaryotic cells possess a number of separate chromosomes. Each containing a single linear molecule of DNA. • Nearly all prokaryotes however contain a single circular chromosome. • Most importantly, eukaryotic cells chromosomal DNA is tightly associated with proteins to forma complex nucleoprotein known as chromatin. The cytoplasm • The cytoplasm of the two different types of cells is very different. • The cytoplasm of a eukaryotic cell is filled with a large amount of diverse structures (plant & animal cells) • Even yeast, the simplest Eukaryote is more complex than the average bacterium. Eukaryotic Organisms’ cells contain an array of membrane bound organelles • Eukaryotic Organelles: o Mitochondria – Where chemical energy is made available to fuel cellular activities. “The power house of the cell” o Endoplasmic Reticulum – where many of the cell’s proteins and lipids are manufactured. o Golgi complexes – Where materials are sorted, modified, and transported to specific cellular destinations. • Variety of simple membrane bound vesicles of varying dimension. • Plan cells contain additional membranous organelles o Chloroplasts – the site of photosynthesis. Pigmented cells. o Single large vacuole – occupies a large volume of the cell, waste storage (sometimes). • The cytoplasmic membranes of eukaryotic cells form a system of interconnecting channels and vesicles. o Function in the transport of substances from one part of a cell to another • In Prokaryotic cells, intracytoplasmic communication is less important because of their small size. o The necessary movement of materials can be accomplished by simple diffusion. • Eukaryotic cells also have structures that lack a surrounding membrane. o Elongated tubules o Filaments of the cytoskeleton. • Prokaryotic and Eukaryotic cells contain ribosimes. o Ribosomes – non membranous particles that function as “workbenches” on which the proteins of the cell are manufactured. • The cytoplasm of eukaryotic cells is extremely crowded, this leaves little space for the soluble phase of the cytoplasm (cytosol). Eukaryotic Cell – structures Prokaryotic Cell – Structures • Eukaryotes divide by the complex process of mitosis o Duplicated chromosomes condense into compact structures that are segregated by an elaborate microtubule containing apparatus. o Mitotic-‐Spindle – allows each daughter cell to receive an equivalent array of genetic material. • In the prokaryotic cells, there is no compacting of the chromosome and no mitotic spindle. • Prokaryotes for the most part are non-‐sexual organisms o They only contain one copy of their single chromosome and have no processes comparable to meiosis, gamete formation, or true fertilization. • Eukaryotic cells possess a variety of complex locomotor mechanisms, whereas those of prokaryotes are relatively simple. o The movement of a prokaryotic cell may be accomplished by a thin protein filament called a flagellum. o Flagellum – use for locomotion, protrudes from the cell and rotates. These rotations propel the cell by exerting pressure against the surrounding fluid. • Certain Eukaryotic cells such as protists and sperm also possess flagella, this is however much more complex than a thin filament. • The eukaryote cell flagellum also uses a different mechanism for the locomotion. • Even the most metabolically talented cells in your body require a variety of organic compounds including a number of vitamins and other essential substances that they cant make on their own. o Most of these essential dietary items re produced by the bacteria that normally live in the large intestine. Types of Prokaryotic Cells • The distinction between prokaryotic and eukaryotic cells is base on structural complexity and not on phylogenetic relationship. • Prokaryotes are divided into two major taxonomic groups, or domains. o Archaea (archaeabacteria) o Bacteria (Eubacteria) • Numbers if the archaea are more closely related to eukaryotes than they are to bacteria. • Most cyanobacteria are capable not only of photosynthesis, but also of a process known as nitrogen fixation. o Nitrogen fixation – the conversion of nitrogen (N2) gas into reduced forms of nitrogen such as ammonia. • The species that are able to photosynthesis and nitrogen fixate are usually the first organisms to colonize – this is because all they need is N2, CO2, Water and light to survive. Types of Eukaryotic cells: Cell Specialization • Complex unicellular organisms represent one evolutionary pathway o The other pathway has led to the evolution of multicellular organisms in which different activities are conducted by different types of specialized cells. • Specialized cells are formed by a process known as differentiation. • The pathway of differentiation followed by each embryonic cell depends on the signals its receiving from its external and nearby environment. o Signals depends on the position of the cells in the embryo. • As a result of differentiation, different types of cells acquire a distinctive appearance and contain unique materials. • For example, skeletal muscles contain a network of precisely aligned filaments composed of contractile proteins. Model Organisms • There are 6 model organisms that are commonly used in research (there are however more than 6 model organisms). o 1 prokaryote o 5 eukaryote • Each of these organism has specific advantages that make it particularyly useful as a research subject. The size of cells and their contents • Two units of linear measure are most commonly used to describe structures within the cell. -‐6 o Micrometer (um) – equal to 10 meters o Nanometer (nm) – equal to 10 -‐meters o Angstrom (Å) – equal to 1/10 of a nanometer • Highly elongated proteins are over 100 nm • DNA is approximately 2 nm wide • Cells and their organelles are more easily defined in micrometer. o Nuclei for example are 5-‐10 um in diameter. • Prokaryotic cells typically range in length from about 1-‐5 um. • Eukaryotic cells range from 10 -‐30 um. • Most cells are small because: o Eukaryotic cells possess a single nucleus that only has 2 copies of most genes o As cells increase in size, their surface area/volume ration decrease. The ability of a cell to exchange substances with its environment is proportional to its environment. o If the cell grew too large, its surface would not be sufficient to take up substances needed for metabolic activities. o Cells tend to depends greatly on the random movement of molecules (diffusion) Synthetic biology • Goal is to create some minimal type of living cells in the laboratory essentially from ‘scratch’ • A more modest goal is to develop forms from existing organisms. • Following the “DNA” transplant in come cases, the new bacterium takes on the characteristics of the species from which the DNA was derived from. 1.4 Viruses • By the end of the 19 century, the work of Louis pasteur (and others) convinced the scientific world that infectious diseases of plants and animals were from bacteria o BUT Tobacco mosaic disease and hoof mouth disease in cattle pointed to another type of infectious agent. • Ivanovsky concluded in 1892 that certain diseases were caused by pathogens that were caused by pathogens that were even smaller and presumably simpler o These pathogens became known as viruses • Viruses are responsible for many human diseases including: o AIDS o Polio o Influenza (flu) o Cold sores o Measles o And some types of cancers (+ More diseases) • Viruses come in many shapes, sizes, and constructions, but all share certain common properties o Intracellular parasites in a sense – they cant reproduce unless they are present within a host cell. o Outside of a cell, the virus exists as a particle, or virion. o The virion contains a small amount of genetic material, that depending on the virus may be single or double stranded, DNA or RNA. o The genetic material or the virion is surrounded by a capsule known as a capsid o Viruses are not deemed living nor an organism because they’re unable to reproduce, metabolize, or carry out any activities associated with life. • Viral capsids are generally made up of a specific number of subunits o Viruses only need one or a few genes to code for its protein container • Many viruses have a capside whose subunits are organized into a polyhedron – a structure having planar faces • A common polyhedron shape of viruses is the 20-‐sided icosahedron. • In many animal viruses, the protein capsid is surrounded by a lipid containing an outer envelope that is derived from the modified plasma membrane of the host cell as the virus buds from the host cell surface • Bacteriophages -‐ bacterial viruses are among the most complex viruses o They are also the most abundant biological entities on Earth. • Each virus has on its surface a protein that’s able to bind to a particular surface component of its host cell. • Some viruses have a wide host range meaning they are able to infect cells from a variety of different organs, or host species. • There are two basic types of viral infections: o In most cases, the viruses arrests the normal activities of the host and has the cell use its available resources to manufacture viral nucleic acids and proteins, which assemble new virions. o In other cases, the infecting virus does not lead to death of the host cell, but instead inserts its DNA into the DNA of the hosts cell – the integrated viral DNA is called a provirus. Viroids • In 1971, it was discovered that viruses are not the simplest types of infectious agents. • Viroid – a pathogen that lacks a protein coat, and consists of a small circular RNA molecule. • Viroids are though to cause disease by interfering with the cells normal path of gene expression Synopsis – Chapter 1 • The cell theory has three tenets o All organisms are composed of one or more cells. o The cell is the basic organizational unit of life o All cells arise from pre-‐existing cells • The properties of life, are exhibited by cells. Can be described by a collection of properties. o Cells are very complex and their substructure is highly organized and predictable o Genes are encoded with the information to make cells o Cellular reproduction occurs due to division, all activitie including reproduction are fueled by chemical energy • Cells are either prokaryotic or eukaryotic o Prokaryotic cells are found only among archaebacteria and eubacteria. o Eukaryotic cells are all other types of organisms – protists, fungi, plants, and animals • Cells are microscopic in size o They must be examined under the microscope and are recorded in nm and um. o The organelles and structure of the cells are small and must also be examined under the microscope
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