condensation nucleus, tiny suspended particle, either solid or liquid, upon which water vapour condensation begins in the atmosphere. Nuclei that have diameters of several microns and are composed of a hygroscopic, or moisture-attracting, substance (e.g., sea salt) are called giant condensation nuclei.
What is the difference between heterochromatic and Euchromatic nuclei?
Heterochromatin is darkly stained under nuclear stains. Euchromatin is lightly stained under nuclear stains. In heterochromatin, the DNA is tightly bound or condensed. In euchromatin, the DNA is lightly bound or compressed.
What is centromere telomere?
The centromere is a specialized chromosomal locus that directs kinetochore assembly and provides the site for microtubule attachment, allowing accurate chromosome segregation during cell division. Telomeres are specialized nucleoprotein complexes that protect the chromosome ends from degradation.
What is euchromatin made of?
Euchromatin is a lightly packed form of chromatin (DNA, RNA, and protein) that is enriched in genes, and is often (but not always) under active transcription. Euchromatin comprises the most active portion of the genome within the cell nucleus. 92% of the human genome is euchromatic.
What is heterochromatic state?
Heterochromatin is a tightly packed form of DNA or condensed DNA, which comes in multiple varieties. Facultative heterochromatin is the result of genes that are silenced through a mechanism such as histone deacetylation or Piwi-interacting RNA (piRNA) through RNAi.
What is heterochromatin in the nucleus?
Dark-staining areas of the nucleus are called “heterochromatin”. There is always a rim of heterochromatin under the real nuclear membrane. Abundant heterochromatin with only scanty euchromatin denotes an inactive cell. This is a section of the epidermis, the epithelial covering of the skin.
What is facultative heterochromatin?
Facultative heterochromatin, on the other hand, is reversible, i.e. its structure can change depending on the cell cycle, and is characterized by another kind of repeated DNA sequences known as LINE sequences.
How does constitutive heterochromatin affect gene expression?
Constitutive heterochromatin. All cells of a given species package the same regions of DNA in constitutive heterochromatin, and thus in all cells any genes contained within the constitutive heterochromatin, will be poorly expressed.
Is Saccharomyces cerevisiae heterochromatin or euchromatin?
Saccharomyces cerevisiae, or budding yeast, is a model eukaryote and its heterochromatin has been defined thoroughly. Although most of its genome can be characterized as euchromatin, S. cerevisiae has regions of DNA that are transcribed very poorly.
