Cell Biology Preview PDF

Course Materials: Copyright © 2022 Pearson Education Ltd. All Rights Reserved.  A Preview of Cell Biology Fluorescence Microscopy of Fibroblast Cells. This image Copyright shows...

Course Materials: Copyright © 2022 Pearson Education Ltd. All Rights Reserved.  A Preview of Cell Biology Fluorescence Microscopy of Fibroblast Cells. This image Copyright shows © 2022 fluorescently Pearson labeled Education cell Ltd. All nuclei Rights (red), Reserved. microtubules (green), and cell-cell contacts (blue).  The cell is the basic unit of biology. Cells are constantly changing. The convergence of cytology, genetics, and biochemistry has made modern cell biology one of the most exciting and dynamic disciplines in biology. Copyright © 2022 Pearson Education Ltd. All Rights Reserved. The Cell Theory: A Brief History Robert Hooke (1665) observed compartments in cork, under a microscope, and first named them cells. He had observed the compartments formed by cell walls of dead plant tissue. Copyright © 2022 Pearson Education Ltd. All Rights Reserved. The Birth of Microscopy Robert Hooke's drawings of the cellular structure of cork cells of the plant. Thin slices of cork have microscopic, honeycomb-like cavities. Copyright © 2022 Pearson Education Ltd. All Rights Reserved. Advances in Microscopy Allowed Detailed Studies of Cells Two factors restricted progress in early cell biology – Microscopes had limited resolution, or resolving power (ability to see fine detail) – The descriptive nature of cell biology: the focus was on observation, with little emphasis on explanation Copyright © 2022 Pearson Education Ltd. All Rights Reserved. Compound Microscopes By the 1830s, compound microscopes were used – These had two lenses – Both magnification and resolution were improved – Structures only 1 µm in size could be seen clearly Copyright © 2022 Pearson Education Ltd. All Rights Reserved. The Cell Theory Applies to All Organisms Using a compound microscope, Robert Brown identified the nucleus, a structure inside plant cells. Matthias Schleiden concluded that all plant tissues are composed of cells. Thomas Schwann made the same conclusion for animals. Copyright © 2022 Pearson Education Ltd. All Rights Reserved. The Cell Theory In 1839, Schwann postulated the cell theory: 1. All organisms consist of one or more cells. 2. The cell is the basic unit of structure for all organisms. Later, Virchow (1855) added: 3. All cells arise only from preexisting cells. Copyright © 2022 Pearson Education Ltd. All Rights Reserved. The Cells of the World Copyright © 2022 Pearson Education Ltd. All Rights Reserved.  The Emergence of Modern Cell Biology Three strands of biological inquiry weave into modern cell biology: – Cytology focuses mainly on cellular structure and emphasizes optical techniques. – Biochemistry focuses on cellular structure and function. – Genetics focuses on information flow and heredity and includes sequencing of the entire genome (all of the DNA) in numerous organisms. Copyright © 2022 Pearson Education Ltd. All Rights Reserved. The Cell Biology Timeline Copyright © 2022 Pearson Education Ltd. All Rights Reserved. The Cytological Strand Deals with Cellular Structure Historically, cytology deals primarily with cell structure and observation using optical techniques. Microscopy has been invaluable in helping cell biologists deal with the problem of small size of cells and their components. Copyright © 2022 Pearson Education Ltd. All Rights Reserved.  Cellular Dimensions The units used to measure cells and organelles may not be familiar. The micrometer (µm), also called the micron, is one millionth of a meter (10−6 m). Bacterial cells are a few micrometers in diameter, whereas the cells of plants and animals are 10–20 times larger. Organelles are comparable to bacterial cells in size. Copyright © 2022 Pearson Education Ltd. All Rights Reserved. The Worlds of Micrometer and Nanometer Copyright © 2022 Pearson Education Ltd. All Rights Reserved.  Measurements in Cell Biology The nanometer (nm) is used for molecules and subcellular structures that are too small to be seen using the light microscope. – The nanometer is one-billionth of a meter (10−9 m). The angstrom (Å), which is 0.1 nm, equals about the size of a hydrogen atom. – It is used in cell biology to measure dimensions within proteins and DNA molecules. Copyright © 2022 Pearson Education Ltd. All Rights Reserved. https://learn.genetics.utah.edu/content/cells/scale/ Copyright © 2022 Pearson Education Ltd. All Rights Reserved. The Light Microscope The light microscope was the earliest tool of cytologists. It allowed identification of nuclei, mitochondria, and chloroplasts within cells. Light microscopy is also called brightfield microscopy because white light is passed directly through a specimen. Brightfield microscopy samples are dead, fixed, and stained. The preparation process can introduce distortions not typical to living cells. Copyright © 2022 Pearson Education Ltd. All Rights Reserved. Relative Resolving Power of the Human Eye, the Light Microscope, and the Electron Microscope The scale shows the size of different objects from 10 meters to 0.1 nanometers for human to atoms. The size and the corresponding object and seen by are listed as follows: 2 meters; human height; unaided eye 800 millimeters; length of some nerve and muscle cells; unaided eye 80 millimeters; chicken egg; unaided eye 1.3 millimeters; frog egg; unaided eye, light microscope 10 to 100 micrometers; eukaryotic cells; light microscope, electron microscope 1 to 10 micrometers; most bacteria; light microscope, electron microscope 9 micrometers; nucleus; light microscope, electron microscope 2 micrometers; mitochondrion; light microscope, electron microscope 60 to 110 nanometers; viruses; electron microscope 30 nanometers; ribosome; electron microscope 2 to 10 nanometers; proteins, D N A, lipids; electron microscope 0.6 to 1.0 nanometers; small molecules; electron microscope 0.2 nanometers; atoms; electron microscope. Copyright © 2022 Pearson Education Ltd. All Rights Reserved. Specialized Light Microscopes A variety of special optical techniques have been developed for observing living cells directly. These include: – Phase-contrast microscopy – Differential interference contrast (DIC) microscopy – Fluorescence microscopy – Confocal microscopy Copyright © 2022 Pearson Education Ltd. All Rights Reserved. Enhancements to Microscopy Phase contrast and differential interference contrast microscopy make it possible to see living cells clearly. The phase of transmitted light changes as it passes through a structure with a different density from the surrounding medium. These types of microscopy enhance and amplify these slight changes. Copyright © 2022 Pearson Education Ltd. All Rights Reserved. An example for phase contrast microscopy Copyright © 2022 Pearson Education Ltd. All Rights Reserved.  Fluorescence Microscopy (1 of 2) Fluorescence microscopy allows detection of proteins, DNA sequences, or molecules that have been made fluorescent by binding to antibodies. An antibody is a protein that binds a particular target molecule, called an antigen. The antibody can be coupled to a fluorescent molecule, which emits fluorescence wherever the target molecule is bound by the antibody. Copyright © 2022 Pearson Education Ltd. All Rights Reserved. https://ruo.mbl.co.jp/bio/e/support/method/conjugated.html  Fluorescence Microscopy (2 of 2) Green fluorescent protein (GFP) can also be used to study the temporal and spatial distribution of proteins in a living cell. Confocal microscopy uses a laser beam to illuminate a single plane of a fluorescently labeled specimen. Digital video microscopy uses video cameras to collect digital images. Copyright © 2022 Pearson Education Ltd. All Rights Reserved. Labeling Cells Using Two Different Colors. HeLa cells were stained using indirect immunofluorescence for microtubules (green) and a dye to label DNA (purple). Copyright © 2022 Pearson Education Ltd. All Rights Reserved.  Limits of Resolution The limit of resolution refers to how far apart objects must be to appear as distinct. The smaller the microscope’s limit of resolution, the greater is its resolving power (ability to see fine details). The resolution for a light microscope is related to the physical nature of light. For visible light, the limit of resolution is about 200–350 nm. Copyright © 2022 Pearson Education Ltd. All Rights Reserved.  Electron Microscopy (1 of 2) The electron microscope, which uses a beam of electrons rather than light, was a major breakthrough for cell biology. The limit of resolution of electron microscopes is about 100 times better than light microscopes. The magnification is much higher than light microscopes—up to 100,000×. Copyright © 2022 Pearson Education Ltd. All Rights Reserved.  Electron Microscopy (2 of 2) In transmission electron microscopy (TEM), electrons are transmitted through the specimen. In scanning electron microscopy (SEM), the surface of a specimen is scanned by detecting electrons deflected from the outer surface. Specialized approaches in electron microscopy allow for visualization of specimens in three dimensions, and allow for the determination of protein macromolecular structures. Copyright © 2022 Pearson Education Ltd. All Rights Reserved. Electron Microscopy TEM images a&b SEM images c&d Copyright © 2022 Pearson Education Ltd. All Rights Reserved. The Biochemical Strand Studies the Chemistry of Biological Structure and Function Around the same time cytologists were studying cells microscopically, others began to explore cellular function. These scientists began to try to understand the structure and function of biological molecules. Copyright © 2022 Pearson Education Ltd. All Rights Reserved.  Biological Reactions and Pathways In 1828, Fredrich Wöhler showed that a compound made in a living organism could be synthesized in the lab. Prior to this work, it was thought that living organisms were unique and not governed by the laws of physics and chemistry. Copyright © 2022 Pearson Education Ltd. All Rights Reserved. Key Observations in Early Biochemistry Louis Pasteur (1860s) showed that yeasts could ferment sugar into alcohol. The Buchners (1897) showed that yeast extracts could do the same. This led to the discovery of enzymes, biological catalysts. Copyright © 2022 Pearson Education Ltd. All Rights Reserved.  Early Biochemistry Steps of the pathways of fermentation and other cellular processes were elucidated in the 1920s,1930s, and 1940s. Gustav Embden, Otto Meyerhof, Otto Warburg, and Hans Krebs described the steps of glycolysis (the Embden– Meyerhof pathway) and the Krebs cycle. Fritz Lipmann showed that adenosine triphosphate (ATP) is the principal energy storage compound in most cells. Melvin Calvin and colleagues elucidated the Calvin cycle. Copyright © 2022 Pearson Education Ltd. All Rights Reserved.  Biochemistry Methods (1 of 2) Subcellular fractionation—uses centrifugation to separate/isolate different structures and macromolecules Ultracentrifuges—are capable of very high speeds (over 100,000 revolutions per minute) Copyright © 2022 Pearson Education Ltd. All Rights Reserved.  Biochemistry Methods (2 of 2) Chromatography—techniques to separate molecules from a solution based on size, charge, or chemical affinity Electrophoresis—uses an electrical field to move proteins, DNA, or RNA molecules through a medium based on size/charge Mass spectrometry—is used to determine the size and composition of individual proteins Copyright © 2022 Pearson Education Ltd. All Rights Reserved. Separation of Molecules by Chromatography and Electrophoresis Separation of Molecules by Chromatography Technique used to separate molecules are as follows: The chromatogram shows different plant pigments separated on a filter paper. The bottom portion of the filter paper has a brownish green layer. The top portion of the filter paper has about seven layers of colors from top to bottom, as follows: Pale brown, gap, light green, very dark green, gap, dark green, light yellowish green, dark yellowish green, and pale yellowish green. Copyright © 2022 Pearson Education Ltd. All Rights Reserved. Separation of Molecules by Chromatography and Electrophoresis The electrophoresed agarose gel shows DNA molecules separated as illuminated bands of varying thickness. Bands that come out of the first well are that of a marker and the bands that come out of the other wells are that of the samples. Copyright © 2022 Pearson Education Ltd. All Rights Reserved.  The Genetic Strand Focuses on Information Flow The genetic strand is the study of the inheritance of characteristics from generation to generation. It was not until the nineteenth century that scientists discovered the nature of inherited physical entities, now called genes. Copyright © 2022 Pearson Education Ltd. All Rights Reserved. Classical Genetics Gregor Mendel’s experiments with peas (1866) laid the foundation for understanding the passage of ―hereditary factors‖ from parents to offspring. The hereditary factors are now known to be genes. Copyright © 2022 Pearson Education Ltd. All Rights Reserved. Chromosomes Walther Flemming (1880) saw threadlike bodies in the nucleus called chromosomes. He called the process of cell division mitosis. Wilhelm Roux (1883) and August Weisman (shortly after) suggested that chromosomes carried the genetic material. Copyright © 2022 Pearson Education Ltd. All Rights Reserved. Chromosome Theory Three geneticists formulated the chromosome theory of heredity, proposing that Mendel’s hereditary factors are located on chromosomes. Morgan, Bridges, and Sturtevant (1920s) were able to connect specific traits to specific chromosomes in the model organism, Drosophila melanogaster (the common fruit fly). Copyright © 2022 Pearson Education Ltd. All Rights Reserved. DNA Friedrich Miescher (1869) first isolated DNA, which he called ―nuclein.‖ Known to be a component of chromosomes by 1914 Known to be composed of only four different nucleotides by the 1930s Proteins, composed of 20 different amino acids, were thought more likely to be a genetic material. Copyright © 2022 Pearson Education Ltd. All Rights Reserved.  DNA is the Genetic Material Experiments with bacteria and viruses in the 1940s began to implicate DNA as the genetic material. Beadle and Tatum formulated the one gene–one enzyme concept (each gene is responsible for the production of a single protein). Copyright © 2022 Pearson Education Ltd. All Rights Reserved.  Molecular Genetics In 1953, Watson and Crick, with assistance from Rosalind Franklin, proposed the double helix model for DNA structure. In the 1960s, there were many advances toward understanding DNA replication, RNA production, and the genetic code Crick coined the central dogma of molecular biology, which can be summarized as: Copyright © 2022 Pearson Education Ltd. All Rights Reserved.  RNA Three important kinds of RNA molecules: – mRNAs (messenger RNAs)—translated to produce protein – rRNAs (ribosomal RNAs)—components of ribosomes – tRNAs (transfer RNAs)—bring the appropriate amino acid for protein synthesis Exceptions to the central dogma include viruses with RNA genomes Reverse transcriptase is an enzyme that uses viral RNA to synthesize complementary DNA. Copyright © 2022 Pearson Education Ltd. All Rights Reserved. Central Dogma: The Flow of Genetic Material in the Cell Copyright © 2022 Pearson Education Ltd. All Rights Reserved. Long Description: The illustration shows a cell with nucleus and cytoplasm, in which genetic information is carried from one stage to the other, as follows: 1.D N A replication: Nuclear D N A is fully copied one time each cell division. The illustration shows a looped arrow which points back to a double helical D N A molecule inside the nucleus. 2.Transcription: Nuclear D N A directs the synthesis of specific m R N A molecules. The illustration shows that a part of the D N A molecule is unwound and a single hyphen stranded m R N A is synthesized complementary to one of its strands. The newly synthesized m R N A is transported from the nucleus into the cytoplasm. 3.Translation: A ribosome synthesizes the specific protein encoded by the m R N A. The illustration shows some free amino acids and t R N A and also the translational complex in the cytoplasm. The translational complex consists of m R N A and t R N A bound to a ribosome and newly synthesized protein which appears as a chain of beads comes out of this complex. Copyright © 2022 Pearson Education Ltd. All Rights Reserved.  Working with DNA Recombinant DNA technology uses restriction enzymes to cut DNA at specific places, allowing scientists to create recombinant DNA molecules with DNA from different sources. DNA cloning is the generation of many copies of a specific DNA sequence. DNA transformation is the process of introducing DNA into cells. Copyright © 2022 Pearson Education Ltd. All Rights Reserved. Sequencing DNA DNA sequencing methods are used routinely for rapidly determining the base sequences of DNA molecules. It is now possible to sequence entire genomes (entire DNA content of a cell). Copyright © 2022 Pearson Education Ltd. All Rights Reserved.