Life Begins with Cells 授課老師：王啟仲基礎醫學研究所 E-mail: [email protected]

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(1)MOLECULAR CELL BIOLOGY SIXTH EDITION Lodish • Berk • Kaiser • Krieger • Scott • Bretscher •Ploegh • Matsudaira. CHAPTER 1. Life Begins with Cells 授課老師：王啟仲基礎醫學研究所 E-mail: [email protected]. 97/09/26 © 2008 W. H. Freeman and Company.

(2) A single ~200 µm cell, the human egg..

(3) Introduction.

(4) The individual cells that form our bodies can grow, reproduce, process information, respond to stimuli, and carry out an amazing array of chemical reactions. Even simple unicellular organisms exhibit all the hallmark properties of life, indicating that the cell is the fundamental unit of life..

(5) The Diversity and Commonality of Cells.

(6) Cells come in an amazing variety of sizes and shapes. Move rapidly, fast-changing structures stationary and structurally stable.. vs.. Oxygen kills some cells but is an absolute requirement for others. Internal organization (prokaryotic vs. eukaryotic cells) All cells share certain structural features and carry out many complicated processes in basically the same way..

(7) Lactococcus lactis, which are used to produce cheese..

(8) A mass of archaebacteria (Methanosarcina) that produce their energy by converting CO2 and hydrogen gas to methane..

(9) Blood cells: (1) RBC: oxygenbearing erythrocyte, (2) WBC: part of the immune system and fight infection, (3) Platelets: provide substances to make blood clot at a wound..

(10) Large single cells: fossilized dinosaur eggs..

(11) A colonial singlecelled green alga, Volvox aureus. This large spheres are made up of many individual cells, visible as blue or green dots. The yellow masses inside are daughter colonies, each made up of many cells..

(12) A single Purkinje neuron of the cerebellum. It can form more than 100,000 connections with other cells through the branched network of dendrites.. Cell body.

(13) Epithelial sheet in the slice through intestine. Each finger-like tower of cells, a villus, contains many cells in a continuous sheet..

(14) Plant cells are fixed firmly in place in vascular plants, supported by a rigid cellulose skeleton. Spaces between the cells are joined into tubes for transport of water and food..

(15) All Cells Are Prokaryotic or Eukaryotic Prokaryotes include bacteria and archaea. Prokaryotic cells: 1. consists of a single closed compartment that is surrounded by the plasma membrane 2. lacks a defined nucleus 3. has a relatively simple internal organization (no membrane-bounded) 4. Many proteins are localized in the cytosol.

(16) The nucleoid, consisting of the bacterial DNA, is not enclosed within a membrane. E. coli and some other bacteria are surrounded by two membranes separated by the periplasmic space. The thin cell wall is adjacent to the inner membrane..

(17) Eukaryotes include 4 kingdoms: plants, animals, fungi, and protists. Eukaryotic cells contain a defined membranebound nucleus and extensive internal membranes that enclose other compartments called organelles. The region of the cell lying between the plasma membrane and the nucleus is the cytoplasm, comprising the cytosol (aqueous phase) and the organelles. Eukaryotic cells are commonly about 10-100 µm across, generally much larger than bacteria..

(18) The defining characteristic of eukaryotic cells is segregation of the cellular DNA within a defined nucleus, which is bounded by a double membrane. Only a single membrane (plasma membrane) surrounds the cell, but the interior contains many membrane-limited compartments, or organelles..

(19) Process and modify proteins Generate energy Process molecules using oxygen. Digest cell materials to recycle them A factory for assembling proteins. Carry cell materials to the surface to release them.

(20) All cells are thought to have evolved from a common progenitor because the structures and molecules in all cells have so many similarities.. DNA sequences.

(21) Unicellular Organisms Help and Hurt Us Fungi have an important ecological role in breaking down plant and animal remains for reuse. They also make numerous antibiotics and are used in the manufacture of bread, beer, wine, and cheese. Fungal diseases, which range from relatively innocuous skin infections such as athlete’s foot to life-threatening Pneumocystis carinii pneumonia..

(22) Viruses Are the Ultimate Parasites Not all microscopic pathogens are cells. Most viruses have a rather limited host range, infecting certain bacteria, plants, or animals. To survive, a virus must infect a host cell and take over its internal machinery to synthesize viral proteins and in some cases replicate the viral genetic material. When newly made viruses are released by budding from the cell membrane or when the infected cell bursts, the cycle start anew..

(23) Viruses are much smaller than cells, on the order of 100 nm in diameter. A virus is typically composed of a protein coat that encloses a core containing the genetic material, which carries the information for producing more viruses. The coat protects a virus from the environment and allows it to stick to, or enter, specific host cells. In some viruses, the protein coat is surrounded by an outer membrane-like envelope..

(24) Viruses must infect a host cell to grow and reproduce T4 bacteriophage attaches to a bacterial cell via a tail structure..

(25) TMV causes a mottling of the leaves of infected tobacco plants and stunts their growth..

(26) Adenovirus causes eye and respiratory tract infections in humans. This virus has an outer membranous envelope from which long glycoprotein spikes protrude..

(27) Even Single Cells Can Have Sex If genetic material was never shared or exchanged, each individual would be the beginning of a new clone of individuals, and the members of a clone would share most of the same genetic strengths and weaknesses. Sex is a process of mingling genetic variation from two individuals, creating new individuals with a combination of properties unlike either parent and that may be beneficial for survival and reproduction..

(28) Like many other unicellular organisms, yeasts have two mating types that are conceptually like the male and female gametes (eggs and sperm) of higher organisms. Two yeast cells of opposite mating type can fuse, or mate, to produce a third cell type containing the genetic material from each cell. Such sexual life cycles allow more rapid changes in genetic inheritance than would be possible without sex..

(29) Multiply asexually. Mitotic budding (asexual).

(30) After each bud breaks free, a scar is left at the budding site, so the number of previous buds can be counted..

(31) We Develop from a Single Cell Fertilization of an egg by a sperm cell yields a zygote, a visually unimpressive cell 200 µm in diameter. Development begins with the fertilized egg cell dividing into two, four, then eight cells, forming the very early embryo. Continued cell proliferation and the differentiation into distinct cell types gives rise to every tissue in the body..

(32) The first few cell divisions of a fertilized egg set the stage for all subsequent development.. A developing mouse embryo is shown at various cell stages.. Video: Early Embryonic Development.

(33) Stem Cells, Fundamental to Forming Tissues and Organs, Offer Medical Opportunities A division that produces two different daughter cells is sometimes described as an asymmetric cell division. Stem-cell divisions are a special case of asymmetric division. One of the two daughter cells is identical to the parent cell; the other follows a path of differentiation, such as becoming a blood cell. The parent cell, called a stem cell, can go on reproducing itself at every division, at each division also producing another blood cell..

(34) Blood is produced from stem cells that reside in the bone marrow and continue to produce new blood cells for our entire lives. This is the basis of the bone marrow transplants that are used to treat cancer patients who have had their blood stem cells damaged by cancer treatments: what is being transplanted is stem cells. However, blood stem cells produce only more of themselves and blood cells, not other cell types. Each tissue must have its own stem cells, at least during the period of development when the tissue is formed..

(35) The first stem cells are found in early embryos, where all the cells are capable of producing all cell types. In mammals the ultimate stem cell is the fertilized egg, which produces early embryo cells capable of forming all the tissues of the body. Each cell in an eight-cell-stage mouse embryo has the potential to give rise to any part of the entire animal. Cells with this capability are referred to as embryonic stem (ES) cells..

(36) In recent years, nuclei taken from cells of adult animals have been used to produce new animals. In this procedure, the nucleus is removed from a body cell of a donor animal and introduced into an unfertilized mammalian egg that has been deprived of its own nucleus. The egg with its donor nucleus is implanted into a foster mother. Since all the cells in an animal produced in this way have the genes of the single original donor cell, the new animal is a genetic clone of the donor, though the animals may differ anyway due to their distinct environments and experiences..

(37) The majority of embryos produced by this technique do not survive due to birth defects: Æ the donor nuclei may not have all the needed information, or Æthe nuclei may be damaged by the cloning process. Even those animals that are born alive have abnormalities, including accelerated aging.. Five genetically identical cloned sheep.

(38) Of much greater scientific and medical interest is the ability to generate specific cell types starting from embryonic or adult stem cells. This procedure, somatic cell nuclear transfer (SCNT), produces cells that are grown in culture and never turned into an embryo. Æ What signals control? Æ Medical treatments? Drug effects? Æ Cell-transplant therapy?.

(39) Take a break。。。. 960519 朱銘美術館 CCW.

(40) The Molecules of a Cell.

(41) Small Molecules Carry Energy, Transmit Signals, and Are Linked into Macromolecules The locations and concentrations of small molecules and ions within the cells are controlled by numerous proteins inserted in cellular membranes. These pumps, transporters, and ion channels move nearly all small molecules and ions into or out of the cell and its organelles. One of the best-known small molecules is adenosine triphosphate (ATP), which stores chemical energy in two of its chemical bonds..

(42) Other small molecules act as signals both within and between cells; such signals direct numerous cellular activities. Certain small molecules (monomers) in the cellular soup can be joined to form polymers through repetition of a single type of chemicallinkage reaction. Cells produce three types of large polymers, commonly called macromolecules: polysaccharides, proteins, and nucleic acids..

(43) Proteins Give Cells Structure and Perform Most Cellular Tasks Cells string together 20 different amino acids in a linear chain to form a protein. The ”essential” amino acids, from a dietary standpoint, are the eight that we can’t synthesize and must obtain from food. Once a chain of amino acids is formed, it folds into a complex shape, conferring a distinctive threedimensional structure and function on each protein..

(44) Proteins vary greatly in size, shape, and function Each protein has a defined three-dimensional shape (conformation) that is stabilized by numerous chemical interactions..

(45) Some proteins are similar to one another and therefore can be considered members of a protein family. Proteins can serve as: structural components sensors enzymes transcription factors motors extracellular/intracellular signals pump/ion channel/transporter….

(46) Nucleic Acids Carry Coded Information for Making Proteins at the Right Time and Place The information about how, when, and where to produce each kind of protein is carried in the genetic material, a polymer called deoxyribonucleic acid (DNA). The three-dimensional structure of DNA consists of two long helical strands that are coiled around a common axis, forming a double helix. DNA strands are composed of monomers called nucleotides; these often are referred to as bases because their structures contain cyclic organic bases..

(47) Four different nucleotides, abbreviated A, T, C, and G, are joined end to end in a DNA strand, with the base parts projecting out from the helical backbone of the strand. Complementary matching of the two strands is so strong that if complementary strands are separated, they will spontaneously zip back together in the right salt and temperature conditions.. DNA replication.

(48) The information-bearing portion of DNA is divided into discrete functional units, the genes, which typically are 5000 to 100,000 nucleotides long. The genes that carry instructions for making proteins commonly contain two parts: Æ a coding region that specifies the amino acid sequence of a protein, and Æ a regulatory region that controls when and where the protein is made..

(49) Cells use two processes in series to convert the coded information in DNA into proteins. In transcription, the coding region of a gene is copied into a ss ribonucleic acid (RNA). RNA polymerase catalyzes the linkage of nucleotides into a RNA chain using DNA as a template. In eukaryotic cells, the initial RNA product is processed into a smaller mRNA molecule, which moves to the cytoplasm..

(50) In the cytoplasm, ribosome carries out the second process, called translation. During translation, the ribosome assembles and links together amino acids in the precise order dictated by the mRNA sequence according to the nearly universal genetic code..

(51) Recently, RNA has also been found to play a important role in regulating many aspects of gene activity. In many cases small RNAs, 20-200 nucleotides long, specifically regulate: the structure and function of chromosomes, the stability of large RNA molecules, and the translation of mRNA molecules into protein..

(52) The Genome Is Packaged into Chromosomes and Replicated During Cell Division Most of the DNA in eukaryotic cells is located in the nucleus, extensively folded into the familiar structures known as chromosomes. Each chromosome contains a single linear DNA molecule associated with certain proteins. The genome of an organism comprises its entire complement of DNA..

(53) Chromosomes can be “painted” for easy identification This preparation was treated with fluorescent-labeled staining reagents that allow each of the 22 pairs and the X and Y chromosomes to appear in a different color when viewed in a fluorescence microscope. Chromosome painting. Karyotype. Multiplex fluorescence in situ hybridization (M-FISH).

(54) Every time a cell divides, a large multiprotein replication machine, the replisome, separates the two strands of double-helical DNA in the chromosomes and uses each strand as a template to assemble nucleotides into a new complementary strand. The outcome is a pair of double helices, each identical to the original. DNA polymerase, which is responsible for linking nucleotides into a DNA strand. Many DNA polymerase molecules work in concert, each one copying part of a chromosome..

(55) Mutations May Be Good, Bad, or Indifferent Mistakes occasionally do occur spontaneously during DNA replication, causing changes in the sequence of nucleotides. Such changes, or mutations, also can arise from radiation that causes damage to the nucleotide chain or from chemical poisons that lead to errors during the DNA-copying process..

(56) Mutations come in various forms: Æ a simple swap of one nucleotide for another, Æ the deletion, insertion, or inversion of nucleotide(s) in the DNA of one chromosome, and Æ translocation of a stretch of DNA from one chromosome to another. In sexually reproducing animals, mutations can be inherited only if they are present in germ-line cells (egg and sperm) that potentially contribute to the formation of offspring. Mutations that occur in somatic cells never are inherited, although they may contribute to the onset of cancer..

(57) Mutated genes that encode altered proteins or that cannot be control properly cause numerous inherited diseases. Mutations in the nonfunctional DNA regions usually produce no immediate effects – good or bad. Such “indifferent” mutations in nonfunctional DNA may have been a major player in evolution, leading to creation of new genes or new regulatory sequences for controlling already existing genes..

(58) Much of the nonessential DNA in both eukaryotes and prokaryotes consists of highly repeated sequences that can move from one place in the genome to another. These mobile DNA elements can jump (transpose) into genes, most commonly damaging but sometimes activating them..

(59) The Works of Cells.

(60) Any cell is simply a compartment with a watery interior that is separated from the external environment by a surface membrane (the plasma membrane) that prevents the free flow of molecules in and out. Each eukaryotic cell organelle has contents and properties, such as specialized proteins or a certain pH, suited to its job. The plasma membrane and other cellular membranes are composed primarily of two layers of phospholipid molecules..

(61) These bipartite molecules have a “water-loving” (hydrophilic) end and a “water-hating” (hydrophobic) end. The two phospholipid layers of a membrane are oriented with all the hydrophilic ends directed toward the inner and outer surfaces and the hydrophobic ends buried within the interior..

(62) Smaller amounts of other lipids and many kinds of proteins are inserted into the phospholipid framework. The lipid molecules and some proteins can float sidewise in the plane of the membrane, giving membranes a fluid character. This fluidity allows cells to change shape and even move. However, the attachment of some membrane proteins to other molecules inside or outside the cell restricts their lateral movement..

(63) The cytosol and the internal spaces of organelles differ from each other and from the cell exterior in terms of acidity, ionic composition, and protein contents. The unique functions and microclimates of the various cell compartments are due largely to the proteins that reside in their membranes or interior..

(64) Cells Build and Degrade Numerous Molecules and Structures In animal and plant cells, most ATP is produced by large molecular machines located in two organelles, mitochondria and chloroplasts.. Overview Animation: Biological Energy Interconversions.

(65) Cells need to break down worn-out or obsolete parts into small molecules that can be discarded or recycled. This housekeeping task is assigned largely to lysosomes, organelles crammed with degradative enzymes. The interior of a lysosome has a pH of about 5.0, roughly 100 times more acidic than that of the surrounding cytosol Æ this aids in break-down of material by lysosomal enzymes..

(66) Lysosomes are assisted in the cell’s cleanup work by peroxisomes. These small organelles are specialized for breaking down the lipid components of membranes and rendering various toxins harmless.. http://extlifesciences.com/per.gif.

(67) Animal Cells Produce Their Own External Environment and Glues The simplest multicellular animals are single cells embedded in a jelly of proteins and polysaccharides called the extracellular matrix (ECM). Collagen, the single most abundant protein in the animal kingdom, is a major component of the ECM in most tissues. A specialized, especially tough matrix, the basal lamina, forms a supporting layer underlying sheetlike cell layers and helps prevent the cells from ripping apart..

(68) The cells in animal tissues are “glued” together by cell adhesion molecules (CAMs) embedded in their surface membranes. Some CAMs bind cells to one another; other types bind cells to the ECMs, forming a cohesive unit.. http://www.steve.gb.com/images/science/cell_adhesion_summary.png.

(69) The cytosols of adjacent animal or plant cells often are connected by functionally similar but structurally different “bridges” called gap junctions in animals and plasmodesmata in plants. These structures allow cells to exchange small molecules including nutrients and signals, facilitating coordinated functioning of the cells in a tissue.. http://fig.cox.miami.edu/~cmallery/150/cells/plasmodesmata.jpg.

(70) Cells Change Shape and Move Cells changes shape and move (20 µm/sec) because their internal skeleton, the cytoskeleton, exerts forces on the rest of the cells and its contents. Three types of protein filaments, organized into networks and bundles, form the cytoskeleton within animal cells..

(71) All cytoskeletal filaments are long polymers of protein subunits.. http://www.uic.edu/classes/bios/bios100/lecturesf04am/cytoskeleton02.jpg.

(72) The cytoskeleton: Æ prevents the plasma membrane of animal cells from relaxing into a sphere; Æ functions in cell locomotion and the intracellular transport of vesicles, chromosomes, and macromolecules. The cytoskeleton can be linked through the cell surface to the ECM or to the cytoskeleton of other cells, thus helping to form tissues.. http://www.uic.edu/classes/bios/bios1 00/lecturesf04am/cytoskeleton.jpg.

(73) Cells Sense and Send Information A living cell continuously monitors its surroundings and adjusts its own activities and composition accordingly. Cells also communicate by deliberately sending signals that can be received and interpreted by other cells. At any time, a cell may be able to sense only some of the signals around it, and how a cell responds to a signal may change with time..

(74) Both changes in the environment and signals received from other cells represent external information that cell must process. The most rapid responses to such signals generally involve changes in the location or activity of pre-existing proteins..

(75) The ability of cells to send and respond to signals is crucial to development. Many developmentally important signals are secreted proteins produced by specific cells at specific times and places in a developing organism. At least 10-15% of the proteins in eukaryotes function as secreted extracellular signals, signal receptors, or intracellular signal-transduction proteins, which pass along a signal through a series of steps culminating in a particular cellular response..

(76) Cells Regulate Their Gene Expression to Meet Changing Needs In addition to modulating the activities of existing proteins, cells often respond to changing circumstances and to signals from other cells by altering the amount or types of proteins they contain. Gene expression is commonly controlled at the level of transcription, the first step in the production of proteins..

(77) Control of gene activity in eukaryotic cells usually involves a balance between the actions of transcriptional activators and repressors. Binding of activators to specific DNA regulatory sequences called enhancers turns on transcription, and binding of repressors to other regulatory sequences called silencers turns off transcription. Many external signals modify the activity of transcriptional activators and repressors that control specific genes..

(78) The receptors for steroid hormones are located within cells. The hormone-receptor complexes activate transcription of specific target gene, leading to increased production of the encoded proteins..

(79) Take a break。。。. 960519 朱銘美術館 CCW.

(80) Cells Grow and Divide The simplest type of reproduction entails the division of a “parent” cell into two “daughter” cells. This occurs as part of the cell cycle, a series of events that prepares a cell to divide followed by the actual division process, called mitosis..

(81) The chromosomes and the DNA they carry are copied during the S (synthesis) phase. The replicated chromosomes separate during the M (mitotic) phase, with each daughter cell getting a copy of each chromosome during cell division. The M and S phases are separated by two gap stages, the G1 phase and G2 phase, during which mRNAs and proteins are made.. Overview Animation: Life Cycle of a Cell.

(82) Mitosis is an asexual process since the daughter cells carry the exact the same genetic information as the parental cell. In sexual reproduction, fusion of two cells produces a third cell that contains genetic information from each parental cell. Since such fusions would cause an everincreasing number of chromosomes, sexual reproductive cycles employ a special type of cell division, called meiosis, that reduces the number of chromosomes in preparation for fusion..

(83) Cells with a full set of chromosomes are called diploid cells. During meiosis, a diploid cell replicates its chromosomes as usual for mitosis but then divides twice without copying the chromosomes in between. Each of the resulting four daughter cells, which have only half the full number of chromosomes, is said to be haploid. Animals spend considerable time and energy generating eggs and sperm, the haploid cells, called gametes, which are used for sexual reproduction..

(84) Gametes are formed from diploid precursor germ-line cells, which in humans contain 46 chromosomes. In humans the X and Y chromosomes are called sex chromosomes because they determine whether an individual is male or female. In human diploid cells, the 44 remaining chromosomes, called autosomes, occur as pairs of 22 different kinds..

(85) Through meiosis, a man produces sperm that have 22 chromosomes plus either an X or a Y, and a woman produces ova (unfertilized eggs) with 22 chromosomes plus an X. Fusion of an egg and sperm (fertilization) yields a fertilized egg, the zygote, with 46 chromosomes, one pair of each of the 22 kinds and a pair of Xs in females or an X and a Y in males. Errors during meiosis can lead to disorders resulting from an abnormal number of chromosomes..

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(87) Cells Die from Aggravated Assault or an Internal Program When cells in multicellular organisms are badly damaged or infected with a virus, they die. Cell death resulting from such a traumatic event is messy and often releases potentially toxic cell constituents that can damage surrounding cells. Cells also may die when they are fail to receive a life-maintaining signal or when they receive a death signal..

(88) In this type of programmed cell death, called apoptosis, a dying cell actually produces proteins necessary for self-destruction. Death by apoptosis avoids the release of potentially toxic cell constituents. Apoptosis is important to Æ eliminate virus-infected cells, Æ remove cells where they are not needed, Æ destroy immune system cells that would react with our own bodies..

(89) Apoptotic cells break apart without spewing forth cell constituents that might harm neighboring cells. WBC. normal. apoptosis.

(90) Investing Cells and Their Parts Biologists are interested in objects ranging in size from small molecules to the tallest trees..

(91) Cell Biology Reveals the Size, Shape, Location, and Movements of Cell Components. The goal of cell biologists is to understand how a cell is able to Æ control its own shape and surface properties, Æ transport materials to the right locations, Æ copy itself, and Æ receive and send signals….

(92) Microscopy is most powerful when particular components of the cell are stained or labeled specifically, enabling them to be easily seen and located within the cell. If a cell or tissue is treated with a detergent that partially dissolves cell membranes, fluorescent antibodies can drift in and bind to the specific protein they recognize. Introduce an engineered gene that codes for a hybrid protein: X-GFP in living cells with intact membranes..

(93) Chromosomes are visible in the light microscopy only during mitosis, when they become highly condensed. About halfway through mitosis, the replicated chromosomes begin to move apart. Microtubules participate in this movement of chromosomes during mitosis.. microtubules.

(94) Electron microscopes use a focused beam of electrons instead of a beam of light. In transmission electron microscopy (TEM), specimens are cut into very thin sections and placed under a high vacuum, precluding examination of living cells. The resolution of TEM, about 0.1 nm, permits fine structural details to be distinguished, and their powerful magnification would make a 1-µm-long bacterial cell look like a soccer ball..

(95) Biochemistry and Biophysics Reveal the Molecular Structure and Chemistry of Purified Cell Constituents To purify a particular protein of interest, a purification scheme is designed so that each step yields a preparation with fewer and fewer contaminating proteins, until finally only the protein of interest remains. Purification of a protein is a necessary prelude to studies on how it catalyzes a chemical reaction or carries out other functions and how its activity is regulated..

(96) Biochemical purification of a protein from a cell extract requires several separation techniques. Three types of column chromatography that separate proteins by electrical charge, size, or binding affinity for a particular small molecule..

(97) The folded, three-dimensional structure, or conformation, of a protein is vital to its function. The most widely used method for determining the complex structures of proteins, DNA, and RNA is x-ray crystallography, one of the powerful tools of biophysics. Computer assisted analysis of the data often permits the location of every atom in a large, complex molecule to be determined.. http://content.answers.com/main/content/wp/encommons/thumb/9/9d/300px-X_ray_diffraction.png.

(98) Genomics Reveals Differences in the Structure and Expression of Entire Genomes Genomics-based methods for comparing thousands of pieces of DNA from different individuals all at the same time. DNA microarrays can simultaneously detect all the mRNAs present in a cell, thereby indicating which genes are being transcribed. To find out which genes are directly regulated by a TF, chromatin containing the protein of interest can be purified with an antibody and the associated DNA analyzed on microarrays, a procedure called chromatin immunoprecipitation..

(99) Microarray analysis.

(100) The entire complement of proteins in a cell, its proteome, is controlled in part by changes in gene transcription. The regulated synthesis, processing, localization, and degradation of specific proteins also play roles in determining the proteome of a particular cell.. http://www.proteomics-services.com/images/2demousebrain.jpg.

(101) Developmental Biology Reveals Changes in the Properties of Cells as They Specialize Many of the differences among differentiated cells are due to production of specific sets of proteins needed to carry out the unique functions of each cell type. Only a subset of an organism’s genes is transcribed at any given time or in any given cell. Transcription can change within one cell type in response to an external signal or in accordance with a biological clock..

(102) Differential gene expression can be detected in early fly embryos before cells are morphologically different..

(103) In the developing organism, Æ cells grow and divide at some times and not others, Æ they assemble and communicate, Æ they prevent or repair errors in the developmental process, and Æ they coordinate each tissue with others. Developmental studies involve: Æ watching where, when, and how different kinds of cells form, Æ discovering which signals trigger and coordinate developmental events, and Æ understanding the differential gene action that underlies differentiation..

(104) Choosing the Right Experimental Organism for the Job Viruses have small genomes amenable to genetic dissection..

(105) Bacteria have several advantages as experimental organisms: Æ grow rapidly Æ possess elegant mechanisms for controlling gene activity Æ have powerful genetics.

(106) The yeast has the cellular organization of a eukaryote but is a relatively simple single-celled organism that is easy to grow and to manipulate genetically..

(107) In the nematode worm, which has a small number of cells arranged in a nearly identical way in every worm, the formation of each individual cell can be traced..

(108) The fruit fly, first used to discover the properties of chromosomes, has been especially valuable in identifying genes that control embryonic development..

(109) The zebrafish is used for rapid genetic screens to identify genes that control development and organogenesis..

(110) Mice are evolutionarily the closest to humans and have provided models for studying numerous human genetic and infectious diseases..

(111) The mustard-family weed has been used for genetic screens to identify genes involved in nearly every aspect of plant life..

(112) ~~~See you next week~~~.

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Life Begins with Cells 授課老師：王啟仲 基礎醫學研究所 E-mail: [email protected]

Life Begins with Cells 授課老師：王啟仲基礎醫學研究所 E-mail: [email protected]