Lecture 5 - The Nucleus and Genetic Material

5. The Nucleus and Gene c material Introduc on Unques onably, nucleus is the largest and most vital organelle of eukaryo c cell that maintains the instruc ons for synchronizing the cell ac vi es (gene c informa on–DNA). Among others it is involved in processes such as gene regula on, cell prolifera on, cell cycle and cellular differen a on. The study of the nucleus and its role in the cell and in dividing is a fundamental step to grasp the mechanisms of the living organisms’ cells and the ways in which informa on is passed on from one genera on to the other. Structure of the Nucleus The smaller organelle is called nucleus which is covered by a double layer of membranes known as nuclear envelope which prevents other components of the cell, such as cytoplasm to enter the nucleus. • Nuclear Envelope: o The nuclear envelope consists of two lipid bilayers: an inner and an outer membrane A mitochondrion may be considered as a double-membraned organelle. The outer membrane is actually a con nua on of the endoplasmic re culum or the ER, for short. o Nuclear Pores: These are big protein structures that extend through the nuclear membrane, also termed as nuclear pore complexes responsible for the selec ve transport of ju ces between nucleus and cytoplasm, for example, RNA and subunits of ribosome. • Nucleoplasm: o Nucleoplasm is the semi-fluid material of the nucleus including chroma n and nucleolus. It is used in holding of nuclear or other components and also in moving of some of the materials. • Chroma n: o DNA: The DNA situated in the nucleus forms chroma n which is a combina on of DNA and histone proteins. Chroma n exists in two forms:Chroma n exists in two forms:  Euchroma n: Less condensed and transcrip onally ac ve like the Gene expression , where genes are actually being read and copied.  Heterochroma n: Chroma n condensed and gene cally uninforma ve, typically connec ve ssue or involved in the repression of gene expression. o Chromosomes: In general, during the cell cycle, the chroma n becomes condense forming chromosomes mainly for adequate segrega on of gene c material in the to be formed daughter cells. • Nucleolus: Nucleolus is large circular body in the nucleus where ribosomal RNA (rRNA) biosynthesis and the forma on of ribosome takes place. It is an intranuclear structure that does not have a membrane around it and is usually dis nguished by a black dot. Func ons of the Nucleus The nucleus performs several fundamental func ons, par cularly in the areas of storage, replica on, and expression of gene c informa on: • Gene c Repository: o The nucleus contains the cell’s DNA, which contains instruc ons for all cell func ons. These genes are organized into genes, which code for proteins and other molecules that are important for cellular func on. • Gene Expression and Produc on: o The nucleus regulates gene expression, determining which genes are turned on or off in response to signals. This regula on is cri cal for cellular differen a on and maintenance of cellular iden ty. o Transcrip on: The process of copying the DNA sequence of a gene into messenger RNA (mRNA) takes place in the nucleus. This mRNA is then transported from the nucleus by nuclear membranes to be translated into proteins in the cytoplasm. • DNA cloning: o Before a cell can divide, its DNA must be replicated to ensure that each daughter cell receives iden cal gene c informa on. DNA replica on occurs in the nucleus during the S phase of the cell cycle. • Ribosome Synthesis: o The nucleolus of the nucleus is composed of ribosomal RNA (rRNA) and assembles with proteins to form ribosomes subunits. These subunits are then transported to the cytoplasm, where they are assembled to form func onal ribosomes involved in protein synthesis. The Role of the Nucleus in Cell Division The nucleus plays an important role in cell division, ensuring that gene c material is properly transferred to daughter cells: • Mitosis: During mitosis, the nuclear envelope breaks apart, and chromosomes accumulate and align at the cell’s equator. Spindle fibers are a ached to the chromosomes, leading to opposite poles of the cell, •Meiosis: In meiosis, the nucleus undergoes two rounds of division, resul ng in four daughter cells, each with half the number of chromosomes as the original cell. This process is essen al for the produc on of gametes (sperm and egg cells) in sexually reproducing organisms.