Sapakhova Zagipa Beisenovna, PhD Shakarim State University of Semey LECTURE 6: Nucleus & Nucleolus Sapakhova Zagipa Beisenovna, PhD

History -Discovered in 1831 by Scottish botanist Robert Brown -Suggested the nucleus played a key role in fertilization and development of the embryo in plants -Name (nucleus) derived from the Latin word for kernel/nut Robert Brown 1773-1858

Main Characteristics Membrane-enclosed organelle found in eukaryotic cells Generally found in the central region of the cell (in animal cells) Roughly spherically shaped Largest and most easily seen organelle

General Definition The nucleus is the genetic control center of a eukaryotic cell. In most cells, there is only one nucleus. It is spherical, and the most prominent part of the cell, making up 10% of the cell’s volume. It has a unique structure and function that is essential the cell.

Primary Functions within the Cell Repository of genetic information (DNA & RNA) Enables the synthesis of nearly all proteins Houses the nucleolus Responsible for production of ribosomes Selective transportation of regulatory factors and energy molecules through nuclear pores

Structure of the Nucleus ] the nuclear envelope nucleoplasm chromatin the nucleolus the two major types of materials The Nucleus

Structure

Nuclear Envelope The nuclear envelope is a double-layered membrane perforated with pores, which control the flow of material going in and out of the nucleus. The outer layer is connected to the endoplasmic reticulum, communicating with the cytoplasm of the cell. The exchange of the large molecules (protein and RNA) between the nucleus and cytoplasm happens here.

Nuclear Envelope Phospholipid bi- layer membrane Nuclear Pores Consists of: Phospholipid bi- layer membrane Nuclear Pores Ribosomes

Nuclear Pores Allow small molecules to diffuse easily between nucleoplasm & cytoplasm Control passage of proteins & RNA protein complexes Import: proteins moving in to be incorporated into nuclear structure or to catalyze nuclear activities Export: RNA / RNA-protein complexes to the cytoplasm

Nucleolus Largest structure present inside the boundaries of the nucleus Dark staining zone in center of nucleus Where intensive synthesis of ribosomal RNA takes place Main components are ribonucleic acid (RNA), deoxyribonucleic acid (DNA) and proteins

Nucleoplasm A jelly-like (made mostly of water) matrix within the nucleus All the other materials “float” inside Helps the nucleus keep its shape and serves as the median for the transportation of important molecules within the nucleus

Chromatin & Chromosomes Chromosomes contain DNA in a condensed form attached to a histone protein. Chromatin is comprised of DNA. There are two types based on function. Heterochromatin: highly condensed, transcriptionally inactive mostly located adjacent to the nuclear membrane Eurochromatin: delicate, less condensed organization of chromatin, located in a transcribing cell * Transcribing means equivalent RNA copies are being made from the DNA to create proteins.

Functions The nucleus is often compared to the “command center,” as it controls all functions of the cell. It is important in regulating the actions of the cells. It plays an important part in creating the cell’s proteins. It is involved in important processes dealing with DNA and other genetic molecules.

DNA DNA, or deoxyribonucleic acid, contains the information needed for the creation of proteins (which include enzymes and hormones) and is stored in the nucleus, as already said, in the form of chromatin or chromosomes. The nucleus is the site of DNA duplication, which is needed for cell division (mitosis) and organism reproduction and growth.

Proteins and Cell Regulation The nucleus oversees cells’ functions and regulatory mechanisms for keeping the cell healthy and alive. The nucleus controls growth of the cell through the synthesis of structural proteins, energy and nutrient metabolism. The nucleus regulates the secretion of ribosomes, which are made in the nucleolus and are the sites of gene transcription.

Sources http://www.biologie.uni-hamburg.de/b-online/library/onlinebio/nucleus_1.gif http://kentsimmons.uwinnipeg.ca/cm1504/nucleus.htm http://www.cellsalive.com/cells/nucleus.htm http://www.buzzle.com/articles/nucleus-function.html http://www.buzzle.com/articles/cell-nucleus-structure-and-functions.html http://www.wisegeek.com/what-is-nucleoplasm.htm Campbell, Neil A., Lawrence G. Mitchell, and Jane B. Reece. Biology: Concepts and Connections. San Francisco: Benjamin/Cummings, 2000.

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