cleavage

(noun)

In embryology, this is the division of cells in the early embryo.

Related Terms

Examples of cleavage in the following topics:

  • Cleavage of the Zygote

    • The different cells derived from cleavage up to the blastula stage are called blastomeres.
    • Holoblastic cleavage occurs in animals with little yolk in their eggs.
    • Since cleavage is impeded by the vegetal pole, there is a very uneven distribution and size of cells.
    • In holoblastic eggs, the first cleavage always occurs along the vegetal–animal axis of the egg, and the second cleavage is perpendicular to the first.
    • From here, the spatial arrangement of blastomeres can follow various patterns, due to different planes of cleavage in various organisms.The end of cleavage is known as the midblastula transition and coincides with the onset of zygotic transcription.

  • Cleavage, the Blastula Stage, and Gastrulation

    • A zygote undergoes rapid cell divisions (cleavage) to form a spherical ball of cells: the blastula; this will further develop into a blastocyst.
    • The rapid, multiple rounds of cell division are termed cleavage.
    • After the cleavage has produced over 100 cells, the embryo is called a blastula.
    • Cleavage can take place in two ways: holoblastic (total) cleavage or meroblastic (partial) cleavage.
    • The type of cleavage depends on the amount of yolk in the eggs.

  • Lines of Cleavage and Surgery

    • Cleavage lines are topological lines drawn on a map of the human body and correspond to the orientation of collagen fibers in the dermis.
    • Langer's lines, sometimes called cleavage lines, are topological lines drawn on a map of the human body .

  • DNA Protection Analysis

    • DNA protection or footprinting is a technique from molecular biology/biochemistry that detects DNA-protein interaction using the fact that a protein bound to DNA will often protect that DNA from enzymatic cleavage.
    • The method uses an enzyme, deoxyribonuclease (DNase, for short) to cut the radioactively end-labeled DNA, followed by gel electrophoresis to detect the resulting cleavage pattern.
    • Cleavage by DNase will produce fragments, the smaller of which will move further on the electrophoretic gel.
    • The cleavage pattern of the DNA in the absence of a DNA binding protein, typically referred to as free DNA, is compared to the cleavage pattern of DNA in the presence of a DNA binding protein.
    • If the protein binds DNA, the binding site is protected from enzymatic cleavage.

  • Reactions of Epoxides

    • Because of the large angle strain in this small ring, epoxides undergo acid and base-catalyzed C–O bond cleavage more easily than do larger ring ethers.
    • Among the following examples, the first is unexceptional except for the fact that it occurs under milder conditions and more rapidly than other ether cleavages.
    • The aqueous acid used to work up the third reaction, following the Grignard reagent cleavage of the ethylene oxide, simply neutralizes the magnesium salt of the alcohol product.

  • Animal Characterization Based on Features of Embryological Development

    • Animals may be characterized by the presence of a coelom, formation of the mouth, and type of cell cleavage during embryonic development.
    • This spiral cleavage is due to the oblique angle of the cleavage.
    • Protostomes also undergo determinate cleavage: the developmental fate of each embryonic cell is pre-determined.
    • Deuterostomes undergo radial cleavage where the cleavage axes are either parallel or perpendicular to the polar axis, resulting in the alignment of the cells between the two poles.
    • Unlike protostomes, deuterostomes undergo indeterminate cleavage: cells remain undifferentiated until a later developmental stage.

  • Reactions of Ethers

    • The most common reaction of ethers is cleavage of the C–O bond by strong acids.
    • The last example shows the cleavage of a 3º-alkyl group by a strong acid.

  • Carbonyl Compounds

    • The ratio of type II cleavage and Yang cyclization products from a given substrate depends on several factors.
    • If R = H, type II cleavage is the only product; however this changes to exclusive stereoselective cyclization if R = CH3.
    • The top reaction in the following diagram illustrates this point; the quantum yield for type II cleavage being only 25%.
    • The two examples at the bottom are cases in which cyclobutanol formation exceeds type II cleavage.
    • The diastereomers undergoes singlet type II cleavage with almost complete stereospecificity, suggesting a very short lifetime for the singlet biradical or a nearly concerted sequence of bond making and breaking in the cleavage, as drawn in the gray-shaded box.

  • The Primary Structure of Peptides

    • Enzymatic C-terminal amino acid cleavage by one of several carboxypeptidase enzymes is a fast and convenient method of analysis.
    • Because the shortened peptide product is also subject to enzymatic cleavage, care must be taken to control the conditions of reaction so that the products of successive cleavages are properly monitored.
    • Three selective cleavage methods are outlined in the table below.
    • A plausible mechanism for the cyanogen bromide cleavage is outlined below.
    • Other enzymatic cleavages have been developed, but the two listed here will serve to illustrate their application.

  • The Favorskii Rearrangement

    • In the case of unsymmetrical cyclopropanones the ring cleavage takes place on the side that yields the more stable carbanion or leads to elimination of a stable anion (second example).
    • In this case cleavage of the cyclopropanol at the more substituted α-carbon probably reflects the inductive effect of the THPO substituent.