Genetics and biochemistry are two methodologies that are used in conjunction with one another to investigate the activities of genes. The first thing that is done in genetics is the study of mutants. First, we either find or construct an organism that has a gene that has been changed, and then we analyze how this change affects the structure and functionality of the organism. In the field of biochemistry, molecules are taken from living organisms and their chemical reactions are studied in order to gain a more in-depth understanding of the roles that molecules play. When genetics and biochemistry are combined, it is possible to find compounds the synthesis of which is controlled by a certain gene. This can be accomplished by studying chemical reactions. In addition, a comprehensive analysis of the functioning of the mutant organism indicates the role that those chemicals play in the organism as a whole in its ability to perform its functions. Combining genetics, biochemistry, and cell biology is therefore the most effective approach to linking the structure and function of an organism to the genes and chemicals that make up that creature.

Recent years have seen a rapid acceleration of development thanks to the discovery of DNA sequences and the powerful techniques of molecular biology. Comparisons of sequences frequently enable us to zero in on particular subregions of a gene that have, for the most part, stayed largely unchanged throughout the course of evolution. These conserved subregions of the gene are probably the parts of the gene that contribute the most to the function of the gene. We are able to determine how each gene contributes to the activity of the gene product by either engineering lab-made mutations at specific gene sites or by producing synthetic hybrid genes that include pieces of two different genes. Both of these methods involve the production of synthetic hybrid genes. Organisms can be engineered to create huge quantities of either the RNA or the protein that is indicated by the gene. This can be done with the intention of making biochemical analysis more straightforward. Experts in the field of molecular structure are able to determine the three-dimensional conformation of the gene product, which exposes the specific location of every atom that is included inside it. Biochemists are able to determine the contribution of each component to the chemical behavior of the genetically engineered molecule.

Cell scientists are able to see cells that have been altered such that they express a mutant form of the gene, and they can analyze the activity of these cells.

However, there is neither a single clear approach for determining what a gene is responsible for, nor is there a single straightforward standard uniform format for explaining it. For example, we might discover that the product of a given gene catalyzes a certain chemical process without comprehending how or why the reaction is relevant to the organism. In contrast to the explanation of the gene sequences, the functional characterization of each new family of gene products presents scientists with an entirely new set of challenges to work through. In addition, we will never be able to have a complete understanding of anything like a gene until we can know its function within the context of the organism as a whole. In light of this, it will be helpful for us to understand how genes function in the most fundamental sense if we examine entire species rather than merely molecules or cells.

Because of the complexity of living things, a particular species becomes more appealing as a subject of research the more we understand about it. This is because living things have a lot going on inside of them. Each discovery spawns new lines of inquiry and brings to light other sources of information that can be used to tackle broader problems pertaining to the organism that was chosen. As a direct consequence of this, numerous large communities of biologists have emerged, each of which is dedicated to conducting research on a specific aspect of the same model organism.

This rod-shaped bacterial cell is generally found in the digestive tracts of humans and other animals; nevertheless, it is not difficult to cultivate in a culture bottle by using nutritional broth as the medium. It is able to evolve at an astoundingly rapid rate through the processes of mutation and selection, and it is also able to quickly reproduce and adapt to a wide variety of chemical circumstances.

Eukaryotic cells, in general, are larger and more complicated than prokaryotic cells, and this is also true of their genomes. Prokaryotic cells, on the other hand, are simpler. Because of its enormous size, the cell's structure and function are very different from what they are in smaller cells. In addition, the combination of a wide variety of eukaryotic cell types results in the generation of multicellular organisms that achieve a level of complexity that is unmatched by prokaryotes.

Eukaryotic organisms are so complicated that they offer molecular biologists with a one-of-a-kind set of challenges, all of which will be covered in the next chapters of this book. Analysis and manipulation of the genetic information contained within cells and organisms is becoming an increasingly popular method for biologists to try to solve these problems. Because of this, having a solid foundational understanding of the specific attributes that make up the eukaryotic genome is essential.

The nucleus, which is an intracellular chamber, is where eukaryotic cells are required to store their DNA by definition. The term "nuclear envelope" refers to the bilayer membrane that encloses the nucleus on all sides and separates the cytoplasm from the DNA in the center of the cell. Both prokaryotes and eukaryotes are distinguished from one another in a variety of other respects.

The average volume of one of these cells is one thousand times greater, and its linear dimension is ten times more. They have a complex cytoskeleton, which is a network of protein filaments that crisscross the cytoplasm and create, along with the numerous proteins attached to them, a network of girders, ropes, and motors that gives the cell mechanical strength, regulates its shape, and powers and directs its movements. They have a cytoplasm that is filled with a fluid called cytosol.

In addition, the nuclear envelope is just one of multiple internal membranes that enclose different cell compartments; the majority of these cell compartments are responsible for digestion and secretion of various substances. All of these internal membranes, including the plasma membrane, have structural similarities to one another. Because they do not have the thick cell wall that most bacteria do, animal cells and the free-living eukaryotic cells known as protozoa can rapidly change their structure and absorb other cells and tiny objects through a process called phagocytosis.

It is still not completely understood how all of the specific properties of eukaryotic cells developed or in what order they did so. On the other hand, a plausible theory is that they are all relics of an ancient predator cell that maintained its existence by seizing and consuming the bodies of other cells. For such a form of existence, you need a large cell that has a plasma membrane that is both flexible and pliable, as well as a complicated cytoskeleton that can maintain and move this membrane. It is possible that in order to protect the genome from damage brought on by the movements of the cytoskeleton, it will be required to isolate the lengthy and fragile DNA molecules of the cell in a separate nuclear compartment. This will allow the genome to remain undamaged.