The function of the nucleus is to store a cell’s hereditary material, or DNA, which helps with and controls a cell’s growth, function, and reproduction. The nucleus is an organelle found in eukaryotic cells and functions as the holder of a cell’s blueprint.
The nucleus often referred to as the “brain” of the cell, is the largest and most prominent organelle in the cell. The reason the nucleus is referred to as the brain of the cell is that it controls the growth and reproduction of the cell. In order to do this, the nucleus of the cell must contain all the hereditary information, as well as possess smaller organelles inside it, which help it regulate and manipulate this information.
Though there is usually only one nucleus in a eukaryotic cell, certain cells can have more than one nucleus or no nuclei at all. For example, red blood cells don’t have a nucleus. Meanwhile, the muscle cells of humans have multiple nuclei.
Parts Of The Nucleus:
- Nuclear Envelope
- Nuclear Pores
The Structure Of The Nucleus:
Before delving too deeply into all the different functions and parts of the nucleus, let’s go over its general structure. To begin with, the outer membrane of the nucleus is referred to as the nuclear envelope. The nuclear envelope is a double-layered membrane that contains all the parts of the nucleus and separates it from the cytoplasm of the cell. The nuclear envelope is full of holes called nuclear pores, which allow molecules to move in and out of the nucleus.
The nucleoplasm is a jelly-like substance that is found within the nuclear envelope, and its function is similar to the cytoplasm found in the main cell, supporting the nucleus and protecting its contents. Also found within the nucleus is a substance known as chromatin, a macromolecule that composes the genetic material of a cell. Finally, the nucleolus is the largest structure found in the nucleus. It is very dense, has no membrane, and is composed of chunks of protein and RNA.
The Function Of The Nucleus And Its Parts:
The job of the nucleus is to control the activity of the cell, regulate gene expression, and maintain the integrity of the cell’s genetic information. The various parts of the nucleus all have different roles in achieving these objectives.
Function Of The Nuclear Envelope
The nuclear envelope must protect the DNA of the cell, and ensure that it maintains its integrity. Damage to the DNA of a cell can cause a wide variety of health problems, so the DNA must be shielded from the chemical interactions that are happening in the other areas of the cell.
The outer membrane of the nucleus is a phospholipid bi-layer, much like the cell membrane, and it has ribosomes on the surface of it. The inner membrane of the nuclear envelope contains many different proteins that help keep genetic materials grouped together and in place. Fibers called nuclear lamina repair any damage to DNA and regulate events like cell division. Nuclear lamina are only found in the cells of animals, though plant cells seem to have equivalent proteins.
The nuclear envelope is semi-permeable, which allows it to manage which kind of materials can exit and enter the nucleus. Only select proteins that conform to a specific molecular structure can pass through the double-layer of the nuclear membrane, entering at spots called nuclear pores.
The Nuclear Pores
The nuclear pores are what allow substances to pass through both the inner and outer membranes of the nucleus. They are a collection of proteins, about 30 different ones, which only allow certain molecules to pass through them, rebuffing others. They also connect the inner and outer membranes.
The Function Of The Nucleoplasm
Much like the interior of the main cell, the interior of the nucleus has a gelatin-esque substance in it. This nucleoplasm, sometimes called karyoplasm, is mainly made out of water, dissolved ions, and various other molecules. The nucleoplasm helps to maintain the shape of the nucleus, and it supports the nucleoli and the chromosomes that are found within it.
The fluid component of the nucleoplasm is referred to as nuclear hyaloplasm, and it assists in the transportation of materials that the cell needs to function and metabolize substances. Enzymes and nucleotides are often dissolved into the nucleoplasm when they are no longer needed.
The chromatin found in the nucleus is a mass of DNA and proteins which are bundled together to create chromosomes during eukaryotic cell division. Chromatin is composed of small proteins known as histones and DNA, and it is responsible for compressing DNA into packages that are small enough to fit within the nucleus. Chromatin fibers are coiled up to create sister chromatids, which are joined together at a centromere to create chromosomes.
Another structure comes into play when organizing the DNA and preparing it for cell division. The centrosome helps position chromosomes, through the use of microtubules, when the cell is getting ready to divide. Only animal cells have centrosomes, and plant cells seem to rely solely on the force of the nuclear membrane to organize parts during cell division.
The nucleolus is a dense collection of proteins, RNA, and DNA. These components are gathered around nucleolar organizing regions. In addition to organizing DNA and RNA, ribosome biogenesis happens here.
“The nucleus has to take care of the inheritance of the heritable characters, while the surrounding cytoplasm is concerned with accommodation or adaptation to the environment.” — Ernst Haeckel
The Nucleus During Cell Division
Mitosis, the process of cell division, is responsible for creating two cells out of one. To do this, the cell must replicate all of its parts. Mitosis sees the nucleus actually disassemble and then reform itself once the division process is over. During mitosis, the nuclear envelope breaks down, which releases all of the contents of the nucleus of the cytoplasm of the cell. Before this happens, the nucleus readies itself for division. The chromosomes condense and ready themselves for replication and the nucleolus also disappears. This process reverses itself when mitosis is complete.
Note that while many cells dissolve the nucleus while reproducing, not all do. Some unicellular eukaryotes go through a process known as closed mitosis, where the nuclear envelope remains intact. In this instance, the chromosomes in the nucleus migrate to opposite ends of the nucleus, and then the nucleus itself divides into two, along with the rest of the cell.
The nucleus of the cell is critical for the cell’s functioning and reproduction. Without the nucleus, the cell wouldn’t be able to reproduce or grow.