fragmentation

Examples of fragmentation in the following topics:

• Characteristics of Mass Spectra

  • Also, the structure of most fragment ions is seldom known with certainty.
  • A less common fragmentation, in which an even-electron neutral fragment is lost, produces an odd-electron radical cation fragment ion.
  • Fragment ions themselves may fragment further.
  • As a rule, odd-electron ions may fragment either to odd or even-electron ions, but even-electron ions fragment only to other even-electron ions.
  • Spectrum diagrams are followed by the fragmentations leading to the chief fragment ions.

• Grob Fragmentation

  • An interesting and generally useful skeletal transformation, involving specific carbon-carbon bond cleavage with accompanying conversion of certain sigma-bonds to pi-bonds, is known as the Grob fragmentation.
  • Here a simple nucleophilic fragmentation at M is converted to an ethylagous analog by the insertion of a two carbon (ethyl) segment between the reacting moieties.
  • A Grob fragmentation takes place in the top example, because the orbitals of the bonding and non-bonding electron pairs participating in the reaction are aligned properly.
  • Other examples of Grob fragmentations will be shown above in the second diagram.
  • The third diagram above displays a Grob-like fragmentation, favored by the relief of ring strain in the four-membered ring.

• Fragmentation Patterns

  • The fragmentation of molecular ions into an assortment of fragment ions is a mixed blessing.
  • Alcohols, ethers and highly branched alkanes generally show the greatest tendency toward fragmentation.
  • All of the significant fragment ions in this spectrum are even-electron ions.
  • By localizing the reactive moiety, certain fragmentation processes will be favored.
  • Odd-electron fragment ions are often formed by characteristic rearrangements in which stable neutral fragments are lost.

• DNA Sequencing Techniques

  • They can only be sequenced in tiny fragments and the tiny fragments have to put in the correct order to generate the uninterrupted genome sequence.
  • As a result, each copy of the same chromosome is fragmented at different locations and the fragments from the same part of the chromosome will overlap each other.
  • Each fragment is sequenced and sophisticated computer algorithms compare all the different fragments to find which overlaps with which.
  • From the order of fragments formed, the DNA sequence can be read.
  • When the complete collection of fragments has been sequenced, comparing the sequences of all the fragments will reveal which fragments have ends that overlap with other fragments.

• Strategies Used in Sequencing Projects

  • Then, with the help of a computer, the fragments are analyzed to see where their sequences overlap.
  • By matching overlapping sequences at the end of each fragment, the entire DNA sequence can be reformed.
  • A third fragment shows only the lake, but it reveals that there is a cabin on the shore of the lake.
  • Originally, shotgun sequencing only analyzed one end of each fragment for overlaps.
  • In pairwise-end sequencing, both ends of each fragment are analyzed for overlap.

• Diphtheria

  • Diphtheria toxin is a single, 60,000 dalton molecular weight protein composed of two peptide chains, fragment A and fragment B, held together by a disulfide bond.
  • Fragment B is a recognition subunit that gains the toxin entry into the host cell by binding to the EGF-like domain of heparin-binding EGF-like growth factor (HB-EGF) on the cell surface.
  • Inside the endosome, the toxin is split by a trypsin-like protease into its individual A and B fragments.
  • The acidity of the endosome causes fragment B to create pores in the endosome membrane, thereby catalyzing the release of fragment A into the cell's cytoplasm.
  • Fragment A inhibits the synthesis of new proteins in the affected cell.

• Fungi Reproduction

  • Fungi can reproduce asexually by fragmentation, budding, or producing spores, or sexually with homothallic or heterothallic mycelia.
  • Fungi reproduce asexually by fragmentation, budding, or producing spores.
  • Fragments of hyphae can grow new colonies.
  • Mycelial fragmentation occurs when a fungal mycelium separates into pieces with each component growing into a separate mycelium.
  • Other asexual spores originate in the fragmentation of a hypha to form single cells that are released as spores; some of these have a thick wall surrounding the fragment.

• Platelets

  • Platelets, also called thrombocytes, are membrane-bound cell fragments that are essential for clot formation during wound healing.
  • Platelets, also called thrombocytes, are membrane-bound cell fragments derived from the fragmentation of larger precursor cells called megakaryocytes, which are derived from stem cells in the bone marrow.
  • Platelets are not true cells, but are instead classified as cell fragments produced by megakaryocytes.
  • However, they do contain mitochondria and mitochondrial DNA, as well as endoplasmic reticulum fragments and granules from the megakaryocyte parent cells.
  • The platelets are the small, bright purple fragments.

• Molecular and Cellular Cloning

  • Molecular cloning reproduces the desired regions or fragments of a genome, enabling the manipulation and study of genes.
  • Cloning small fragments of the genome allows for the manipulation and study of specific genes (and their protein products) or noncoding regions in isolation.
  • In cloning, the plasmid molecules can be used to provide a "folder" in which to insert a desired DNA fragment.
  • An important feature of plasmid vectors is the ease with which a foreign DNA fragment can be introduced via the multiple cloning site (MCS).
  • Addition of an enzyme called DNA ligase permanently joins the DNA fragments via phosphodiester bonds.

• Types of Sexual and Asexual Reproduction

  • Animals may reproduce asexually through fission, budding, fragmentation, or parthenogenesis.
  • Fragmentation is the breaking of the body into two parts with subsequent regeneration.
  • Many sea stars reproduce asexually by fragmentation.
  • Fragmentation also occurs in annelid worms, turbellarians, and poriferans.
  • Sea stars can reproduce through fragmentation.