CELLBIO Preview of Cell Biology

• Robert Hooke built a microscope and examined thin slices of cork. He observed compartments that reminded him of honeycomb and called them cells from the word cellula, meaning "litte room".
• Hooke's observations were limited by the magnification power of his microscope, which enlarged objects to only 30x their size.
• Antonie van Leeuwenhoek produced small lenses that could magnify objects to almost 300x their size.
• Antonie van Leeuwenhoek became the first to observe living cells, blood cells, sperm cells, bacteria, and single-celled organisms found in pond water.
• Two factors restricted further understanding of the nature of cells.

  1. The microscopes had limited resolution (resolving power).
  2. The descriptive nature of seventeenth-century biology.
• By the 1830s, important optical improvements were made in lens quality and in the compound microscope. Wherein one lens (eyepiece) magnifies the image created by a second lens (objective).
• Robert Hooke found that every plant cell contained a rounded structure, called the nucleus from the latin word for kernel.
• In 1838, Matthias Schleiden concluded that all plant tissues are composed of cells. A year later, Theodor Schwann reported the same thing concerning animal tissue.
• In 1839, Scwhann 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.
  3. All cells arise only from preexisting cells.
• By 1855, Rudolf Virchow encapsulated the Latin phrase omnis celllula e cellula meaning all cells arise only from preexisting cells.
• The cell is not only the basic unit of structure for all organisms but also the basic unit of reproduction.
• Modern cell biology results from the weaving together of three different strands of biological inquiry:

  1. Cytology - cellular structure
  2. Biochemistry - cellular structure and function
  3. Genetics - variety of proteins and RNA
• Cytology primarily deals with cellular structure, mainly through the use of optical techniques.
• Microscopy: most important technique within the cytological strand.
• Light microscope: earliest tool of cytologists, identifies membrane-bounded structures such as nuclei, mitochondria, and chloroplasts
• Types of Microscopy

  • brightfield microscopy
  • phase-contrast and differential interference contrast microscopy
  • fluorescence microscopy
  • confocal microscopy
  • digital microscopy
  • electron microscope
• Friedrich Wohler demonstrated that urea, could be synthesized in the laboratory from an inorganic starting material called ammonium cyanate.
• Wohler dispelled the notion that biochemical processes are somehow exempt from the laws of chemistry and physics.
• • Louis Pasteur showed that living cells were responsible for the fermentation of sugar into alcohol.
  • In 1897, Eduard and Hans Buchner found that fermentation could take place with isolated extracts from yeast cells.
  • The active agents were found to be biological catalysts called enzymes.
• In the 1920s and 1930s,

  • Gustav Embden, Otto Meyerhof, Otto Warburg, and Hands Krebs described the enzymatic steps in the Embden-Meyerhof pathway for glycolysis and Krebs cycle.
  • Fritz Lipmann showed that ATP is the principal energy storage compound in most cells.
  • Melvin Calvin traced the fate of 14CO2 which led to the elucidation of the Calvin cycle in the 1940s/1950s.
• Biochemistry Methods

  • Centrifugation: separating and isolating subcellular structures and macromolecules based on size, shape, and/or density called subcellular fractionation.
  • Chromatography: variety of techniques by which a mixture of molecules in solution is separated into individual components based on size, charge, or affinity for specific molecules or functional groups.
  • Electrophoresis: uses an electrical field to separate macromolecules based on their mobility through a semisolid gel.
  • After, mass spectrometry is used to determine the size and composition.
• • Genetics strand began with Gregor Mendel, who discovered hereditary factors known today as genes.
  • In 1880, Walther Flemming identified chromosomes, and called its division process mitosis.
  • As early as 1883, Wilhelm Roux and August Weissman suggested that chromosomes themselves might be the actual bearer of genetic information.
• • Walter Sutton and Theodor Boveri came up with the Chromosome Theory of Heredity, which proposed that the hereditary factors responsible for Mendelian inheritance are located on the chromosomes within the nucleus.
  • This hypothesis received strong confirmation from Thomas Hunt Morgan, Calvin Bridges, and Alfred Sturtevant using Drosophila melanogaster.
• In 1869, Johann Friedrich Miescher isolated and described nuclein.
• By 1930, DNA was known to be composed of only four different nucleotides.
• In 1953, James Watson and Francis Crick with the help of Rosaline Franklin proposed the double helix model for the structure of DNA.
• In the 1960s, polymerase enzymes that synthesize DNA/RNA and the cracking of the genetic code was discovered.

  
  

  Genetic code = relationship between the order of nucleotides in a DNA/RNA molecule and the order of amino acids in a protein
• In 1953, Francis Crick articulated a molecularly based model of genetic information flow, called the central dogma of molecular biology.

  • replication of DNA to produce two copies
  • transcription of information carried by DNA into the form of RNA
  • translation of this information from RNA to protein
• • messenger RNA (mRNA) = RNA that is translated into protein, carries genetic message from DNA to macromolecular complexes known as ribosomes, where protein synthesis takes place
  • ribosomal RNA (rRNA) = integral components of the ribosome itself
  • transfer RNA (tRNA) = intermediaries that recognize the coded base sequence of an mRNA and bring the appripriate amino acids to the ribosome for protein synthesis
• • Recombinant DNA technology = made possible by the discovery of restriction enzymes, which cleave DNA molecules at specific sequences to create recombinant DNA molecules containing DNA sequences from two different sources.
  • DNA cloning = process used to generate many copies of specific DNA sequences.
  • DNA transformation = process of introducing DNA into cells.
• • DNA sequencing methods were devised for rapidly determining the base sequences of DNA molecules
  • Genome sequencing were initially applied to bacterial genomes since they are relatively small.
  • Now, genome sequencing can now be used in larger genomes such as roundworms, plants, and animals.
• • The Human Genome Project = sequence of the entire human genome, containing about 3.2 billion bases that began in 1990 and ended in 2003.
• Bioinformatics

  • The challenge of analyzing the vast amount of data generated by DNA sequencing, merging computer science and biology as a means of making sense of sequence data.
  • Led to the recognition that the human genome contains approximately 20,000 protein-coding genes, half of which are not characterized before genome sequencing.
• Genomics

  • Study of all the genes of an organism, providing remarkable insights into cell biology and human health.
  • Using modern techniques and bioinformatics, scientists can also study the proteome (proteomics) which is the total protein content of a cell.
  • Proteomic studies aim to understand the structure and properties of every protein produced by a genome and to learn how these proteins interact with each other to regulate cellular functions.
• • Transcriptomics = advanced methods of RNA sequencing allows to determine the complete set of genes transcribed in a cell.
  • Metabolomics = analysis of all metabolic reactions happening at a given time in a cell
  • Lipidomics = study of all the lipids in a cell
  • Ionomics = global study of all the ions in a cell
• CRISPR Genome Editing

  • Clustered Regularly Interspace Short Palindromic Repeats
  • First discovered as a prokaryotic defense mechanism against viral infection.
• How is a system designed to protect bacteria from invading viruses useful for editing genomes?

  • Generation of a double-stranded break at a precise location in the genome, to be targeted by a short nucleotide called a guide RNA (gRNA).
  • Double-stranded breaks are difficult for the cell to repair, with errors often occurring in this repair process.
  • Also possible to provide a piece of DNA with an alternative sequence that the cell can use to repair the break using a process known as a repair template.
• Cell biology is rich with examples of "facts" that were once widely held but have since been altered or discarded.
• How do we know what we know?

  • Experiments test specific hypotheses
  • Model organisms play a key role in modern cell biology research
  • Cells and tissue cultures: cell cultures are used as model systems
  • Model organisms: species widely studied, well characterized, and easy to manipulate and has particular advantages