Cell and Molecular Biology Concepts and Experiments, 6th Edition By Karp
Email: Richard@qwconsultancy.com
CHAPTER 1 INTRODUCTION TO THE STUDY OF CELL & MOLECULAR BIOLOGY OBJECTIVES Present a brief outline of the early history of Cell Biology. Familiarize students with the basic properties of all cells. Describe the differences between prokaryotic and eukaryotic cells. Specify the types of prokaryotic cells. Emphasize cell specialization as it relates to eukaryotic cells. Discuss the relevance of multicellularity and the significance of cellular differentiation. Review the dimensions important to Cell Biology (micrometer, nanometers, Ångstroms). Clarify the structure and function of the different types of viruses. Define the mechanisms by which viral infections proceed. Explain the traits that distinguish viroids from viruses.
LECTURE OUTLINE Introduction I.
Cell & molecular biology is reductionist – based on the view that knowledge of the parts of the whole can explain the character of the whole A. Can lead to replacement of the wonder & mystery of life by the need to explain everything in terms of the workings of the machinery of living systems which many consider a loss B. Can replace this loss by a strong appreciation for the beauty & complexity of the mechanism underlying cellular activity
II.
Cell biology began as a result of the discovery that curved glass surfaces can bend light & form images A. Spectacles were first made in Europe in the 13th century B. First compound (double-lensed) microscopes were made by the end of the 16th century C. By the mid-1600s, a handful of scientists had used handmade microscopes to uncover a previously unseen world
The Discovery of Cells I.
Robert Hooke (1665), English microscopist (at age 27, became curator of the Royal Society) A. Described chambers in cork (part of the bark of trees); called them cells (cellulae) since they reminded him of cells occupied by monks living in a monastery B. Found them while trying to explain why cork stoppers could hold air in a bottle so effectively C. Was looking at empty cell walls of dead plant tissue; no internal structure – walls originally made by the living cells they surrounded
II.
Anton van Leeuwenhoek (1665-1675), Dutch seller of clothes & buttons – in spare time, he ground lenses & made microscopes of remarkable quality A. He was the first to describe living single cells; his results were checked and confirmed by Hooke B. Saw “animalcules” in pond water (first to do this) using the scopes that he made C. First to describe various forms of bacteria from tooth scrapings & water in which pepper was soaked
D. Soon, he became a celebrity visited by Russia's Peter the Great & the queen of England IV. 1830s - full & widespread importance of cells realized A. Matthias Schleiden, German lawyer turned botanist (1838) – realized that, despite differences in tissue structures, all plant tissues were made of cells & that plant embryos arise from single cell B. Theodor Schwann, German zoologist (1839) – realized cellular basis of animal life; concluded that plants & animals are similar structures C. Schwann then proposed first two tenets of Cell Theory 1. All organisms are composed of one or more cells. 2. The cell is the structural unit of life for all organisms. D. However, the Schleiden-Schwann view of cell origin was less insightful - both felt cells could arise from noncellular materials -> eventually disproved by others; it took time due to their prominence E. Rudolf Virchow, German pathologist (1855) – made good case for & added third tenet of Cell Theory derived from his cell division observations; it ran counter to Schleiden-Schwann view of cell origins 1. Cells can arise only by division from a preexisting cell. Basic Properties of Cells I.
Life – most basic property of cells; they are the smallest units to exhibit this property; plant or animal cells can be removed from organism & cultured in laboratory A. Can grow and reproduce for long time in culture, unlike their parts, which soon deteriorate if isolated 1. If mistreated, they may die; death can also be considered one of the most basic properties of life, since only a living entity faces this prospect 2. Remarkably, cells within the body generally die by their own hand 3. They are the victims of an internal program that causes cells that are no longer needed or cells that pose a risk of becoming cancerous to eliminate themselves B. George & Martha Gey, Johns Hopkins U. (1951) - first human cell culture (HeLa cells); donor was Henrietta Lacks (from her malignant tumor); descendants from this sample are still grown in labs today C. Cultured cells are simpler to study than cells in body; cells grown in vitro (in culture, outside the body) have become essential tool of cell & molecular biologists
II. Cells are highly complex and organized A. Each level of structure in cells has a great level of consistency from cell to cell – each cell type has consistent appearance in EM; organelles have particular shape & location in all individuals of species B. Organelles have consistent macromolecular composition arranged in a predictable pattern C. Cell structure is similar from organism to organism despite differences in higher anatomical features 1. Thus, information obtained from studying cells of one organism often has a direct application to other forms of life 2. Many of the most basic processes (protein synthesis, membrane structure, etc.) are remarkably similar in all living organisms 3. In evolutionary terms, many molecules in our cells must be very similar to those present in our primitive cellular ancestors that lived more than 3 billion years ago III. Cells possess genetic program & the means to use it (a blueprint); encoded in collection of genes A. Genes are the blueprint for constructing cellular structures & ultimately organisms – this vast amount of information is packaged into a set of chromosomes occupying the very small cell nucleus 1. Genes constitute the directions for running cell activities 2. Genes constitute the program for making more cells B. Changes in genetic information from generation to generation lead to the variations that form the basis of biological evolution IV. Cells are capable of producing more of themselves - mitosis and meiosis A. Cells reproduce by division; process whereby “mother” cell contents are distributed to 2 “daughter” cells
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B. Before division, genetic material is faithfully copied; each daughter cell gets complete & equal share of genetic information C. Usually, daughter cells have roughly equal volume; however, during egg production, one cell gets nearly all of the cytoplasm & half of genetic material V. Cells acquire & use energy – every biological process requires energy input (photosynthesis, respiration, etc.) A. Virtually all energy utilized by life on Earth arrives in form of electromagnetic radiation from the sun B. This energy is trapped by light-absorbing pigments in photosynthetic cells C. Light energy is turned to chemical energy by photosynthesis; stored in energy-rich carbohydrates D. Most animal cells get energy prepackaged, often as glucose (released to blood by liver in humans) E. Once in cell, glucose disassembled; most of its energy is stored as ATP & used to run cell's energyrequiring activities 1. Cells expend an enormous amount of energy simply breaking down & rebuilding the macromolecules & organelles of which they are made 2. This continual turnover maintains integrity of cell components in face of inevitable wear & tear to which they are subjected & enables cell to respond rapidly to changing external conditions VI. Cells carry out a variety of chemical reactions - sum total of chemical reactions in cells (metabolism); to do this, cells require enzymes (molecules that greatly increase rate of chemical reactions) VII. Cells engage in numerous mechanical activities based on dynamic, mechanical changes in cell, many of which are initiated by changes in the shape of "motor" proteins (require constant energy to keep working): A. Material moved from place to place B. Structures assembled and disassembled C. Cells move from place to place VIII. Cells are able to respond to stimuli whether organisms are uni- or multicellular - have receptors that sense environment & initiate responses (move away from object in path or toward nutrient source) A. Most cells covered with receptors that interact in specific ways with substances in environment 1. Receptors bind to hormones, growth factors, extracellular materials, surfaces of other cells 2. Allow ways for external agents to evoke specific responses in target cells B. Cells may respond to specific stimuli by: 1. Altering their metabolic activities 2. Preparing for cell division 3. Moving from one place to another, or 4. Even committing suicide IX. Cells are capable of self-regulation A. Importance of regulatory mechanisms most evident when they break down 1. Failure of cell to correct error in DNA replication -> may lead to debilitating mutation 2. Breakdown in growth-control safeguards -> may lead to cancer cell & maybe death of whole organism B. Example: Hans Driesch, German embryologist (1891) - separate first 2 or 4 cells in sea urchin embryo -> each produces normal embryo; the cells regulated their activities to make whole embryos C. Cell processes are a series of ordered steps – the information for these steps & product design reside in nucleic acids & construction workers for these processes/designs are primarily proteins 1. In cell, the workers act without benefit of conscious direction 2. Each step in process must occur spontaneously so that the next step is automatically triggered 3. Each type of cell activity requires unique set of highly complex molecular tools & machines, the products of eons of natural selection & biological evolution D. Primary goal of cell & molecular biologists is to understand structure & role of each component in particular activity, the way in which they interact & mechanisms by which interactions are regulated
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X. Cells evolve A. It is presumed that cells evolved from some type of precellular life form, which in turn evolved from nonliving organic molecules that were present in primordial seas B. While cell origin is shrouded in mystery, evolution of cells can be studied by examining organisms that are alive today 1. Observe bacterial cell in human respiratory tract & cell that is part of lining of human intestinal tract; you would be struck by their differences 2. Yet both evolved from a common ancestral cell that lived >3 billion years ago 3. Structures shared by these two distantly related cells (similar plasma membranes, ribosomes) must have been present in ancestral cell C. Evolution is not simply an event of the past, but an ongoing process that continues to modify cell properties that will be present in organisms yet to appear Two Fundamentally Different Classes of Cells: Prokaryotes and Eukaryotes I. With advent of EM, 2 basic classes of cells were distinguished by size/types of internal structures (organelles) A. The existence of 2 distinct classes of cells, without any known intermediates, represents one of the most fundamental evolutionary divisions in the biological world B. The structurally simpler, prokaryotic cells include bacteria; the structurally more complex eukaryotic cells include protests, fungi, plants & animals II. General information about prokaryotes & eukaryotes A. Prokaryotes (pro - before; karyon - nucleus) – all bacteria, cyanobacteria (blue-green algae); structurally simpler; not sure when prokaryotic cells first appeared on Earth 1. Compelling evidence of prokaryotic life obtained from rocks ~2.7 billion year old rocks (Australia, S. Africa); prokaryotes now living seem very similar to those fossilized in rocks 2. They were sole life on planet for nearly 2 billion years before the first eukaryote 3. These rocks also contain complex organic molecules characteristic of particular types of prokaryotic organisms, including cyanobacteria 4. It is unlikely that such molecules could have been synthesized abiotically (without living cells) B. Eukaryotes (eu - true) - structurally more complex; protists, fungi, plants, animals 1. Their origin is also uncertain – complex multicellular animals appear suddenly in fossil record ~600 million years ago 2. However, there is considerable evidence that simpler eukaryotes were present >1 billion years earlier 3. It is clear that life arose quickly after the formation of Earth & the cooling of its surface; it took longer for the subsequent evolution of complex plants & animals III. Similarities between prokaryotes and eukaryotes reflect the fact that eukaryotes almost certainly evolved from prokaryotic ancestors A. Both types of cells encode genetic information in DNA using an identical genetic code B. Both types of cells share a common set of metabolic pathways (glycolysis, TCA cycle) C. Both types of cells share common structural features – similarly constructed plasma membrane that serves as selectively permeable barrier & cell walls (same function, different structure) D. Similar mechanisms for transcription & translation of genetic information, including similar ribosomes E. Similar apparatus for conservation of chemical energy as ATP (located in plasma membrane of prokaryotes & mitochondrial membrane of eukaryotes) F. Similar mechanism of photosynthesis (between cyanobacteria & green plants) G. Similar mechanism for synthesizing & inserting membrane proteins H. Proteasomes (protein digesting structures) of similar construction (between archaeabacteria & eukaryotes)
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