Nucleus ppt

nucleus - structure and function
structure and organization of chromatin

1. Nucleus -By zoomania

2. Definition: What is a nucleus? The nucleus is a membrane-bound organelle that contains genetic material (DNA) of eukaryotic organisms. As such, it serves to maintain the integrity of the cell by facilitating transcription and replication processes. It's the largest organelle inside the cell taking up about a tenth of the entire cell volume. This makes it one of the easiest organelles to identify under the microscope.

3. S ome of the other main components of a nucleus include: A phospholipid bilayer membrane Nucleoplasm Nucleolus Chromatic    Some eukaryotic cells lack a nucleus and are referred to as enucleate cells (e.g. erythrocytes) while others may have more than one nucleus (e.g. slime molds).

4. Diagrammatic Representation of a Nucleus

5. Structure of nucleus contain: The Nuclear Membrane Nucleoplasm Nucleolus Chromosomes

6. The Nuclear Membrane The nuclear membrane is one of the aspects that distinguish eukaryotic cells from prokaryotic cells. As with the other cell organelles of eukaryotic organisms, the nucleus is a membrane-bound organelle. The nuclear membrane, like the cell membrane, is a double-layered structure that consists of phospholipids (forming the lipid bilayer nucleus envelope). Present on the nuclear membrane are nuclear pores (made up of proteins) through which substances enter or leave the cell (RNA, proteins, etc).

7. Fibrous lamina  - The fibrous lamina is part of the nuclear cytoskeleton that is attached to the inner layer of the nuclear membrane. It consists of fine protein filaments and serves to provide mechanical reinforcement to the bilayer membrane. Some of the other functions of the nuclear lamina include: It can play a role in regulating gene expression Serves as anchor sites for the pore complexes of the nuclear It regulates material entering or exiting the cell

8. Nucleoplasm karyoplasm/nucleus sap, the nucleoplasm is a type of protoplasm composed of enzymes, dissolved salts, and several organic molecules. In addition, the nucleoplasm helps cushion and thus protect the nucleolus and chromosomes while also helping maintain the general shape of the nucleus.

9. Nucleolus In the same way that the nucleus is the most prominent organelle of the cell, the nucleolus is the most prominent structure of the nucleus. Unlike the nucleus, however, this dense structure lacks its own membrane. During cell division (mitosis), the nucleolus breaks up only to reform from specific sections of the chromosomes after mitosis.

10. Chromosomes In the nucleus, chromosomes are thread-like structures made up of strands of DNA and the histone proteins. Main parts of the chromosome include: Kinetochores Telomeres Chromatids (each of which consists of the p and q arm) Chromosomes in the nucleus are tightly packed which makes it possible for very large amounts of the genetic material (DNA) to be contained in such a small space (about 3 billion pairs are contained in each cell) * Stretched, DNA in a single cell would be about 2 meters long. * Histones are alkaline proteins on which the DNA strands are packed.

11. S ome of the main functions of the nucleus include: Protein synthesis, cell division, and differentiation  Control the synthesis of enzymes involved in cellular metabolism  Controlling hereditary traits of the organism  Store DNA strands, proteins, and RNA  Site of RNA transcription - e.g. mRNA required for protein synthesis

12. Chromatin : In eukaryotic cells the genetic material is organized into a complex structure composed of DNA and proteins and localized in a specialized compartment, the nucleus. This structure was called chromatin (from the Greek "khroma" meaning coloured and "soma" meaning body). Close to two meters of DNA in each cell must be assembled into a small nucleus of some  n m in diameter. Despite this enormous degree of compaction, DNA must be rapidly accessible to permit its interaction with protein machineries that regulate the functions of chromatin:

13. Despite this enormous degree of compaction, DNA must be rapidly accessible to permit its interaction with protein machineries that regulate the functions of chromatin: replication, repair and recombination. The dynamic organization of chromatin structure thereby influences, potentially, all functions of the genome

14. Strucure of chromatin: The fundamental unit of chromatin, termed the nucleosome, is composed of DNA and histone proteins. This structure provides the first level of compaction of DNA into the nucleus. Nucleosomes are regularly spaced along the genome to form a nucleofilament which can adopt higher levels of compaction ultimately resulting in the highly condensed metaphase chromosome. Within an interphase nucleus chromatin is organized into functional territories.

15. Chromatin has been divided into : euchromatin and heterochromatin. Heterochromatin was defined as a structure that does not alter in its condensation throughout the cell cycle whereas euchromatin is decondensed during interphase. Heterochromatin is localized principally on the periphery of the nucleus and euchromatin in the interior of the nucleoplasm. We can distinguish: constitutive heterochromatin , containing few genes and formed principally of repetitive sequences located in large regions coincident with centromeres and telomeres, from facultative heterochromatin  composed of transcriptionally active regions that can adopt the structural and functional characteristics of heterochromatin, such as the inactive X chromosome of mammals.

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