Nucleoplasm, Biology

NUCLEOPLASM OR KARYOPLASM OR KARYOLYMPH OR NUCLEAR SAP

Nucleoplasm and cytoplasm name proposed by E. Strassburger. Chemical composition of nucleoplasm given by Kossel. Compositions of nucleoplasm is similar to cytoplasm but it contains high concentration of nucleotides in form of triphosphates. Nucleoplasm have enzymes for glycolysis. Thus nucleus obtains its own energy by glycolytic pathway.

Inside nucleoplasm, there is a net work of fine threads. These threads called chromatin fibers. Chormatin name proposed by Flemming. Chromatin threads composed of DNA, RNA, histone protein & nonhistone protein. Chromatic threads contain genetic information Alkaline stain (Acetocarmine, Haematoxylene, Feulgen) are used to stain chromatin. In stained preparation under light compound microscope chromatin net work appears differentiated in two parts :-

1. Euchromatin - Lightly stained thin and diffused part of chromatin. This part have less histone and more acidic proteins. Euchromatin is more active part of Chromatin and its DNA undergoes rapid transcription. During nuclear division euchromatin replicates in S-phase of cell cycle. It is affected by pH, temperature, poisons etc. It takes part in crossing over. It is formed by loose spiralisation of nucleosome strands.

2. Hetrochromatin - Darkly stained thick and condensed part of chromatin. This part have more histone and less acidic proteins Heterochromatin is genetically a less active part of chromatin. Heterochromatin forms stop points in transcription.

  • Large granular masses of heterochromatin are called false nucleoli/ karyosomes/ chromocentres.  False nucleolus stainable by basic dyes.
  • It is formed by solenoid type of coiling of nucleosome containing DNA strands. It does not take part in crossing over.
  • It is less affected by pH, temperature, poison etc. Replication occurs late in S or G - costitutive and facultative phase. It is of further two types
  • Constituting heterochromatine is present in all cells in all stages of life cycle whereas facultative heterochromatin develops secondarily.
  • In mammalian females one X chromosome becomes heterochromatin during embryogenesis but becomes normal in oocytes. It forms barr body, discovered by Barr and Bertman.
  • It presents indicates that sex of embryo is female. Higher number of barr bodies shows abnormal embryo. Barr body present as drumstick in neutrophils. Euchromatin and Heterochromatin discovered by Emil Heitz. Heteropycnosis - Differential staining of chromatin is called heteropycnosis
Posted Date: 10/5/2012 8:00:14 AM | Location : United States







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