Which organelle controls the activities of the cell

The boss of a company is tasked with determining which employees fill certain positions and when specific actions are taken. Each of your cells has a boss, too: the nucleus. This control center runs the show, instructing the cell to carry out basic functions, such as growth, development and division. Most of your body’s genetic material -- its deoxyribonucleic acid, or DNA -- is located inside the nucleus. This organelle has only a few types of components, but it has major responsibilities.

Cell Structure

The cells of eukaryotes -- plants, animals, fungi and protists -- contain nuclei. Most of these cells have one nucleus each, but slime mold and certain algae cells have multiples. The parts of the nucleus reflect its functions. Most of the time, the entire nucleus is separated from the rest of the cell by a double-layered nuclear envelope. This membrane is covered with pores that regulate the movement of molecules in and out of the nucleus. Inside the nucleus, the nucleolus produces ribosomes, which make proteins for the cell. Hereditary material is found within the semi-fluid nucleoplasm.

Running the Show

The nucleus holds all the cell’s directions, which come in the form of genes. Genes are made of DNA and are organized into structures called chromosomes. The DNA for each gene is arranged in a specific order that determines the gene’s function. Some genes instruct cells to manufacture specific proteins required to carry out certain functions. Genes can also control the amount of proteins produced. Not all genes work around the clock. While some function continuously, overseeing the production of essential proteins, other genes are turned off until they are needed.

Chromosome Home

Although human cells are microscopic, each has about 6 feet of DNA inside its nucleus. To accommodate this tight squeeze, proteins fold DNA into tiny packages. This combination of DNA and protein is “chromatin.” Sections of chromatin form chromosomes. Rather than spreading randomly, chromosomes seem to settle in specific sections of the nucleus, which are called “chromosome territories.” This appears to be connected to gene expression; certain genes always seem to be neighbors. Each nuclei has a different, though internally consistent, arrangement of genes.

Divide and Conquer

As if the nucleus does not have enough to do while controlling cell functions, it also undergoes a complex process during cell division, or mitosis. In most cells, the nucleus breaks up, then rebuilds. Mitosis is essential, because genetic information in the nucleus is passed along to daughter cells. To make this possible, chromosomes replicate before cell division begins. During mitosis, the nucleolus is not visible. In most cases, the nuclear envelope comes apart. Most of the contents of the nucleus spill into the cell’s cytoplasm. The chromosomes separate into two equivalent groups, and a new envelope encircles each set. Finally, the entire cell separates into two identical cells.

References

• NLM: Genetics Home Reference -- Cells and DNA
• Florida State University: Molecular Expressions -- The Cell Nucleus
• American Cancer Society: How Do Cells Know What to Do?
• Nature: Scitable -- Chromosomes
• National Center for Biotechnology Information: The Cell -- The Nucleus During Mitosis
• Nature: Scitable -- Replication and Distribution of DNA During Mitosis

Resources

• University of California, Berkeley: Molecular and Cell Biology -- Scientists Find Signals That Make Cell Nucleus Blow up Like a Balloon

Writer Bio

Living in upstate New York, Susan Sherwood is a researcher who has been writing within educational settings for more than 10 years. She has co-authored papers for Horizons Research, Inc. and the Capital Region Science Education Partnership. Sherwood has a Ph.D. in curriculum and instruction from the University at Albany.

Complete answer:
We all have come across different organelles but the one that does multi-tasking is Nucleus. It is a double-membrane, specialized structure that bounds genetic material known as DNA.
The credit for this discovery goes to Robert Brown in 1831. The role of nucleus in heredity was established by the grafting experiments of Hammerling in 1953 with the unicellular algae Acetabularia.
In general, there is only its own nucleus in each cell, but this may vary in different types of cells. Some with more than one nucleus are binucleate like in paramecium while some with many nuclei are multinucleate like in Ascaris. However, some cells lack nucleus known as anucleate at maturity such as mammalian RBCs and sieve tube cells. A typical interphase nucleus is 5-25 mm in diameter.
The outer layer of nucleus is covered with ribosomes and continuous with the endoplasmic reticulum while the inner layer contains lamins that form a structure called nuclear membrane and give structural support to the nucleus. Between these two layers is a perinuclear space about 20 nm. From the above discussion it is clear to all of us that ‘nucleus’ controls most of the activities of the cell.

Note-
It will be interesting to know for you all that the nucleus was the first organelle to be discovered by the scientist.
Nucleus is the largest among the organelle and uses around 10 percent of the cells volume.
As the nucleus controls most of the activities of cells and also contains genetic material, it is known as the command center of cells.