The difference between prokaryote and eukaryote cells is the presence of absence of a nucleus. Prokaryote cells lack a nucleus and eukaryote cells. Their chromosomes are loosely grouped together in the center of the cell. In Eukaryote cells the chromosomes are contained within a membrane bound organelle called the nucleus.
The nucleus is composed of a nuclear membrane, pores, lamina, nucleolus, chromatin and chromosomes. As we will be discussing some of these structures in more detail later on in this series, we will only provide a brief description and function of the components that make up the nucleus.
The nuclear membrane is a double membrane also known as the nuclear envelope. One of the main functions of the nuclear membrane is to compartment off the nucleus from the rest of cell.
Unlike the double membrane of the cell, the nuclear membrane has pores that pass through both the outer and inner membrane layers. These pores allow for communication pathways between the nucleus and the rest of the cell.
The nuclear lamina provides the skeletal structure and integrity of the nucleus. It consists of a lattice of intermediate filaments that extend from the nuclear pores throughout the nucleus much like the cellular skeleton we discussed in Things Just Don’t Float Around – Simple Cell Part 3.
The nucleolus is a tightly packed concentration of chromatin which is generally located near the center of the nucleus. It contains ribosomal DNA (rDNA) that controls the synthesis of ribosomes. After the ribosomes have been created, it is transported from the nucleolus through the nuclear pores and into the cytoplasm of the cell.
The chromatin is composed of the components that make up the chromosomes. Those components include DNA, histone and a variety of necessary proteins. Chromatin prepares DNA for cell division, controls DNA replication and gene expression, and the packaging of the DNA into a form that allows it to fit into a smaller area.
The chromosomes contain the genetic code that provides all of the information necessary for the development and maintenance for the cell, organ and body of the organism. We will be discussing chromosomes in greater detail later in this series.
Functions of the nucleus include:
Division of cellular compartments. The nuclear membrane separates the nuclear contents from the rest of the cellular contents. One of the byproducts of mRNA splicing is the formation of strands of unspliced mRNA. The compartmentalization of the nucleus helps prevent any of these unspliced mRNA strands from being translated.
Nuclear Transport. A number of different molecules must be imported into the nucleus and others exported out into the cytoplasm of the cell. The transportation of these molecules is controlled by a number of control proteins that monitor what passes in and out through the pores in the nuclear membrane.
Biochemical processing. There are thousands of biochemical processes that take place in the cell and throughout the body. The vast majority of these processes are controlled by the genes contained in the nucleus.
Gene expression. The thousands of genes contained in the chromosomes carry out their functions in the nucleus. We will discuss gene expression in a later issue of this series.
Synthesis of ribosomes. The synthesis of ribosomes is synthesized in the nucleolus. For more information on ribosomes and their function refer to FedEx of the Cell – Simple Cell – Part 5
mRNA pre-processing. Once mRNA is synthesized, they undergo further modification in the nucleus before they are exported out of the nucleus and into the cytoplasm. The modification process involves 3′ poly adenylation, 5’capping and RNA splicing.
Chromosomal replication. Part of the process of cell division involves the replication of chromosomes in preparation for cell division. We will discuss this in more detail in a later issue of this series.
Cell division. The nucleus is an integral part of cell division. It undergoes a complete disintegration and reformation during and after cell division. We will discuss this in more detail is a later issue of this series.
In eukaryote cells, the nucleus is the brain or central processing unit of the cell. It contains the vital information that governs everything else that takes place in the living cell. Today, we have only scratched the surface of the nucleus and its many complex systems and functions. Over the next several weeks, we will take closer looks at some of these systems. With each additional part of this series, it will add to the evidence that we have been amassing for the existence and necessity of an infinitely intelligent Creator that designed it all from the very beginning.