Cell Biology: Nuclear Envelope, Nucleolus, Chromatin, and Chromosome PDF

Nuclear Envelope Cell Biology Nucleolus Chromatin Chromosome Lokender Kumar Ph.D.  Nuclear Envelope The rough ER, + ribosomes, is involved with the production, folding, quality control and dispatch of pro...

Nuclear Envelope Cell Biology Nucleolus Chromatin Chromosome Lokender Kumar Ph.D.  Nuclear Envelope The rough ER, + ribosomes, is involved with the production, folding, quality control and dispatch of proteins. The nucleolus : producing and assembling the cell's ribosomes. Chromatin is a complex of DNA and proteins that forms chromosomes within the nucleus of eukaryotic cells. The nucleoplasm is a gel-like substance inside the nucleus of a cell. Chromatin, protein fibers called fibrils, and water. Cell biology Lokender Kumar Ph.D.  The following are the different roles of the nucleus Regulating the heredity traits of an entity Protein synthesis, growth, cell division, and differentiation DNA strands that also store RNA and proteins in the nucleolus Process of transcription wherein mRNA is produced to generate proteins Exchange of RNA and DNA between the cell and the nucleus The nucleolus generates ribosomes that are referred to as protein factories It controls the integrity of gene expression and genes Cell biology Lokender Kumar Ph.D.  Nuclear Envelope Cell biology Lokender Kumar Ph.D.  Nuclear Envelope The nuclear membrane encloses the cell nucleus and consists of the following parts Outer Membrane It is a lipid bilayer containing two layers of molecules of lipid. The outer layer is made up of lipids which have ribosomes on the surface that are linked to the endoplasmic reticulum. Cell biology Lokender Kumar Ph.D.  Nuclear Envelope Inner Membrane: It contains proteins that → rearrange the nucleus and chain the genetic material in position. Proteins and fibers that are linked to the inner membrane. It provides structural support to the nucleus, assists in DNA repair, controls cell cycle events such as cell division and also on DNA replication. Cell biology Lokender Kumar Ph.D.  Nuclear Envelope Nuclear Pores: They move through both the inner and outer membranes of the nuclear membrane and are composed of → large complex proteins which allow a few molecules to permeate by the nuclear envelope. Each of the nuclear pores consists of 30 distinct proteins which operate together to transfer materials. Also, they link the inner and outer membranes. Cell biology Lokender Kumar Ph.D.  Nuclear Envelope Cell biology Lokender Kumar Ph.D. Proposed steps in nuclear protein import. Proteins bearing a nuclear localization signal (NLS) bind to the heterodimeric receptor (importin α / β ) (step 1) forming a complex that associates with a cytoplasmic filament (step 2). The receptor‐cargo complex moves through the nuclear pore (step 3) and into the nucleoplasm where it interacts with Ran‐GTP and dissociates (step 4). The importin β subunit, in association with Ran‐GTP, is transported back to the cytoplasm, where the Ran‐GTP is hydrolyzed (step 5). Ran‐GDP is subsequently transported back to the nucleus, where it is converted to Ran‐GTP. Conversely, importin α is transported back to the cytoplasm. Cell biology Lokender Kumar Ph.D.  Nucleolus These are tiny spherical bodies that are situated in the nucleus as they are usually present in a centralized site but are typically found closer to the nuclear membrane. What sets them apart from other nuclear material is that they are built by the (NOR) nucleolus organizing region of chromosomes, which is known to store the genes that are necessary for full Electron micrograph of part of a HeLa ribosomal production. They encode cell. ribosomal RNA subunits. Cell biology Lokender Kumar Ph.D.  Nucleolus Three major components of the nucleolus are recognized: the fibrillar center (FC), the dense fibrillar component (DFC), and the granular component (GC). Transcription of the rDNA occurs in the FC. The DFC contains the protein fibrillarin, which is important in rRNA processing. The GC contains the protein nucleophosmin Malfunction of nucleoli can be the cause of several human conditions called "nucleolopathies" and the nucleolus is being investigated as a target for cancer chemotherapy Cell biology Lokender Kumar Ph.D.  Nucleoplasm Nucleoplasm is a remarkably viscous liquid that contains the nuclear hyaloplasm which is the more soluble and liquid portion of the nucleoplasm. It is a type of protoplasm that is similar to the cytoplasm, which is present throughout the cell body to the exterior of the nucleus. As specific functions are carried out inside the nucleus, a different type of protoplasm is required. The constituents of the nucleoplasm are water, dissolved ions, and a blend of other substances. This element is completely confined in the nuclear envelope containing nucleotides and crucial enzymes that promote replication. Cell biology Lokender Kumar Ph.D.  Chromatin and Chromosomes To understand chromatin, it is helpful to first consider chromosomes. Chromosomes are structures within the nucleus that are made up of DNA, the hereditary material. In prokaryotes, DNA is organized into a single circular chromosome. In eukaryotes, chromosomes are linear structures. Every eukaryotic species has a specific number of chromosomes in the nuclei of its body’s cells. For example, in humans, the chromosome number is 46, while in fruit flies, it is 8. Cell biology Lokender Kumar Ph.D.  Chromatin and Chromosomes Chromosomes are only visible and distinguishable from one another when the cell is getting ready to divide. When the cell is in the growth and maintenance phases of its life cycle, proteins are attached to chromosomes, and they resemble an unwound, jumbled bunch of threads. These unwound protein-chromosome complexes are called chromatin Chromatin describes the material that makes up the chromosomes both when condensed and decondensed. Cell biology Lokender Kumar Ph.D.  Chromatin and Chromosomes This image shows various levels of the organization of chromatin (DNA and protein). Cell biology Lokender Kumar Ph.D. Chromatin and Chromosomes Levels of organization of chromatin Naked DNA molecules are wrapped around histones to form nucleosomes, which represent the lowest level of chromatin organization. Nucleosomes are organized into 30‐nm fibers, which in turn are organized into looped domains. When cells prepare for division, the loops become further compacted into mitotic chromosomes Cell biology Lokender Kumar Ph.D.  Chromatin and Chromosomes X‐ray crystallographic structure of a nucleosome core particle viewed down the central axis of the DNA superhelix, showing the position of each of the eight histone molecules of the core octamer. The histones are organized into four dimeric complexes. Each histone dimer binds 27 to 28 base pairs of DNA, with contacts occurring where the minor groove of the DNA faces the histone core. Schematic representation of a nucleosome core particle with its histone octamer composed of four histone heterodimers (two H3/H4 dimers and two H2A/H2B dimers). Cell biology Lokender Kumar Ph.D.  Chromatin and Chromosomes Karyotype showing a normal male chromosomal constitution. (Courtesy: Cytogenetic Lab Genetic Unit, All India Institute of Medical Sciences (AIIMS), New Delhi, India.) Cell biology Lokender Kumar Ph.D.