Cell NucleusStephen Stahr, Grace Tam and Alex Keklak

General Definition

The nucleus is the genetic control The nucleus is the genetic control center of a eukaryotic cell.center of a eukaryotic cell.

In most cells, there is only one In most cells, there is only one nucleus. It is spherical, and the most nucleus. It is spherical, and the most prominent part of the cell, making up prominent part of the cell, making up 10% of the cell’s volume.10% of the cell’s volume.

It has a unique structure and It has a unique structure and function that is essential the cell.function that is essential the cell.

Structure of the Nucleus

the nuclear the nuclear envelopeenvelope

nucleoplasmnucleoplasm

chromatinchromatin

the nucleolusthe nucleolus

]the two major

types of materials

The Nucleus

Nuclear Envelope

The nuclear envelope is a double-The nuclear envelope is a double-layered membrane perforated with layered membrane perforated with pores, which control the flow of pores, which control the flow of material going in and out of the material going in and out of the nucleus.nucleus.

The outer layer is connected to the The outer layer is connected to the endoplasmic reticulum, communicating endoplasmic reticulum, communicating with the cytoplasm of the cell. The with the cytoplasm of the cell. The exchange of the large molecules exchange of the large molecules (protein and RNA) between the nucleus (protein and RNA) between the nucleus and cytoplasm happens here. and cytoplasm happens here.

Nucleoplasm

A jelly-like (made mostly of water) A jelly-like (made mostly of water) matrix within the nucleusmatrix within the nucleus

All the other materials “float” insideAll the other materials “float” inside

Helps the nucleus keep its shape and Helps the nucleus keep its shape and serves as the median for the serves as the median for the transportation of important molecules transportation of important molecules within the nucleuswithin the nucleus

Chromatin & Chromosomes

Chromosomes contain DNA in a condensed Chromosomes contain DNA in a condensed form attached to a histone protein.form attached to a histone protein.

Chromatin is comprised of DNA. There are Chromatin is comprised of DNA. There are two types based on function.two types based on function.

Heterochromatin: highly condensed, Heterochromatin: highly condensed, transcriptionally inactive mostly transcriptionally inactive mostly located adjacent to the nuclear located adjacent to the nuclear membranemembrane

Eurochromatin: delicate, less Eurochromatin: delicate, less condensed organization of chromatin, condensed organization of chromatin, located in a transcribing celllocated in a transcribing cell

* Transcribing means equivalent RNA copies are being made from the DNA to create proteins.

FunctionsThe nucleus is often compared to the The nucleus is often compared to the “command center,” as it controls all “command center,” as it controls all functions of the cell. functions of the cell.

It is important in regulating the It is important in regulating the actions of the cells.actions of the cells.

It plays an important part in creating It plays an important part in creating the cell’s proteins.the cell’s proteins.

It is involved in important processes It is involved in important processes dealing with DNA and other genetic dealing with DNA and other genetic molecules. molecules.

DNA

DNA, or deoxyribonucleic acid, DNA, or deoxyribonucleic acid, contains the information needed for contains the information needed for the creation of proteins (which include the creation of proteins (which include enzymes and hormones) and is stored enzymes and hormones) and is stored in the nucleus, as already said, in the in the nucleus, as already said, in the form of chromatin or chromosomes. form of chromatin or chromosomes.

The nucleus is the site of DNA The nucleus is the site of DNA duplication, which is needed for cell duplication, which is needed for cell division (mitosis) and organism division (mitosis) and organism reproduction and growthreproduction and growth.

Proteins and Cell Regulation

The nucleus oversees cells’ functions The nucleus oversees cells’ functions and regulatory mechanisms for keeping and regulatory mechanisms for keeping the cell healthy and alive. the cell healthy and alive.

The nucleus controls growth of the cell The nucleus controls growth of the cell through the synthesis of structural through the synthesis of structural proteins, energy and nutrient proteins, energy and nutrient metabolism.metabolism.

The nucleus regulates the secretion of The nucleus regulates the secretion of ribosomes, which are made in the ribosomes, which are made in the nucleolus and are the sites of gene nucleolus and are the sites of gene transcription.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.biologie.uni-hamburg.de/b-online/library/onlinebio/

nucleus_1.gif 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.