Genes and DNA - Simple and Complex Cells, Chromosomes, DNA, and Genes
Chromosomes carry genetic information in a molecule called DNA. A type of cell division called mitosis ensures that when a cell divides each new cell produced. Alleles are different forms of same gene. Genes are linearly arranged on chromosomes. Chromosomes contain genetic material of cell i.e. DNA. Get an answer for 'Describe the relationship between cells, chromosomes, genes , and DNA.' and find homework help for other Science questions at eNotes.
How are DNA chromosomes and genes related? | Socratic
Genes influence what we look like on the outside and how we work on the inside. They contain the information our bodies need to make chemicals called proteins. Proteins form the structure of our bodies, as well playing an important role in the processes that keep us alive. Genes are made of a chemical called DNA, which is short for 'deoxyribonucleic acid'.
The DNA molecule is a double helix: The DNA double helix showing base pairs The sides are sugar and phosphate molecules. The rungs are pairs of chemicals called 'nitrogenous bases', or 'bases' for short. There are four types of base: These bases link in a very specific way: A always pairs with T, and C always pairs with G. The DNA molecule has two important properties. It can make copies of itself.
If you pull the two strands apart, each can be used to make the other one and a new DNA molecule. It can carry information. The order of the bases along a strand is a code - a code for making proteins. Genes A gene is a length of DNA that codes for a specific protein. So, for example, one gene will code for the protein insulin, which is important role in helping your body to control the amount of sugar in your blood.
Genes are the basic unit of genetics. Cells are the building blocks of life, and all living things—from bacteria to human beings—are composed of them. The number of cells varies greatly from organism to organism: A bacterium has just one cell; an average-sized adult human has between 60 trillion and trillion. Most cells are too small to be seen with the naked eye and must be viewed under a microscope.
Other cells are larger. A hen's egg, for example, is a single cell, and the largest cell of any organism on Earth is the ostrich egg, which weighs about a pound. Even the smallest cell contains a complete copy of the genetic information that gives an individual organism the traits that make it what it is and not some other thing. Cells have what are called life cycles. They are created, live, reproduce, and die. It is during the process of reproduction, or cell division, that genetic information is passed along from generation to generation.
Simple and Complex Cells There are two types of cells, prokaryotes and eukaryotes. The words are pronounced "pro-carry-oats" and "you-carry-oats. More complex forms of life, including plants and animals, are made of many eukaryotes. The two types of cells are distinguished from each other by their internal structure. Both are enclosed within an external membrane that separates them from their environment. All the internal components of a prokaryote float within this membrane.
Eukaryotes, on the other hand, have a number of additional internal membranes that divide them into compartments. The principal compartments of a eukaryotic cell are the nucleus and the cytoplasm. To use an analogy from the world of business, the nucleus is the cell's executive office and the cytoplasm is its factory. The nucleus generates instructions for a number of cellular processes that are, in turn, carried out in the cytoplasm.
The nucleus of a eukaryotic cell is itself a complex structure. It is composed of DNA deoxyribonucleic acidwhich contains genetic information and Single-celled bacteria infect a host. These organisms are far simpler creatures than their multicelled counterparts. However, when the nucleus is about to divide, the chromatin condenses and coils tightly to form a precise number of readily visible objects called chromosomes.
Each chromosome contains one long molecule of DNA. The chromosomes are the bearers of hereditary instructions; their DNA carries the information required to perform the functions of the cell and endow the cell's descendants with the same instructions. Human beings have 23 pairs of chromosomes for a total of Chimpanzees, humanity's closest relative in the animal kingdom, have 24 pairs; dogs have 39; cats, 17; ferns, Thus, in humans, the genetic information contained in DNA is divided among 23 pairs of homologous matching chromosomes in such a way that the nucleus of each individual cell contains a complete copy of the organism's entire genetic code.
Each chromosome is a long molecule which is further divided into subsections of genetic information. These subsections are the factors that Mendel discovered—what today we call genes. Chromosomes, DNA, and Genes Although the chromosomes contain a copy of an individual's genetic makeup—all the genes necessary to produce all the individual's traits—the two members of each matching set of chromosomes are not exactly identical to each other.
This is because one set of chromosomes is inherited from the maternal parent and its matching partner from the paternal parent.
Thus, it is possible for homologous chromosomes to contain different alleles for the same gene. In Mendel's experiments with peas, with respect to height some of his plants contained two dominant alleles for tallness, some contained two recessive alleles for shortness, and some contained both a dominant and recessive allele. This fact is crucial for an understanding of genetic inheritance. It explains why children are not identical to one or the other of their parents.
It also explains why parents can pass on the genes for recessive traits, traits that they do not themselves exhibit, to their progeny and why a specific trait may lie dormant for generations before making its appearance in a family tree. That matching homologous chromosomes can contain different alleles for the same gene accounts for the pervasive fact of genetic diversity—how from a relatively limited number of genes a virtually unlimited number of unique individuals can be produced.
Science writer Laura Gould sums up the role of the cell nucleus and its contents in the production of the traits that distinguish one individual from another: Chromosomes are thread-like structures in the nucleus of almost every cell [some red blood cells don't have a nucleus]; they are made in part of DNA.
How are DNA chromosomes and genes related?
They come in matching pairs, one member of the pair providing genetic information from the mother, the other from the father. Genes are just little pieces of chromosomes: Each gene has a fixed location on its chromosome and helps to specify a trait. The cytoplasm is found outside the cell's nucleus. A computer analogy is useful: The DNA contained in genes performs like software, telling the hardware in the cytoplasm what to do. Specifically, it sends a message through the membrane that encloses the nucleus to entities called ribosomes in the cytoplasm to manufacture one or several of a wide range of proteins.
It is these proteins that actually do the work of making peas tall or short, or humans brown-eyed or blue-eyed. He found it while studying pus that had accumulated on the bandages of wounded soldiers. Miescher, along with other scientists, learned that DNA was a large molecule composed mostly of a type of sugar called deoxyribose, which is related to table sugar. They also found traces of phosphate, a chemical derived from the element phosphorous.
But the most important discovery was that DNA also contained four substances called nucleotide bases. These bases are adenosine, cytosine, guanine, and thymine, and they are abbreviated A, C, G, and T. Miescher suspected that these bases combined to form chemical messages, and in so doing he came close to discovering the genetic code that governs all life. In fact, later research has shown that the bases that compose DNA function exactly like an alphabet that encodes meaningful expressions.
In the same way that the twenty-six letters of the English alphabet can be combined to form an enormous number of intelligible words, phrases, and sentences, the four letters of the genetic alphabet—A, C, G, and T—combine with each other to create chemical messages that are then transmitted to the ribosomes and other parts of the cell.
However, for a language to work as a method of communication, the various letters have to be associated with each other according to a set of rules. In human languages, these rules are called grammar and syntax. The genetic code also has a set of rules, but it took scientists a long time to discover exactly what it was. The first clue came in the early part of the twentieth century when they found that in any DNA molecule the number of As must equal the number of Ts and the number of Cs must equal the number of Gs, but the number of A-T, C-G combinations does not have to be equal.
The importance of this piece of information, however, was not understood for almost fifty years until scientists developed a complete description of how the various components of a DNA molecule fit together. This feat was accomplished by a process called X-ray crystallography, in which a substance is combined with salt and allowed to form crystals.
When these crystals are viewed under a powerful electron microscope, the structure of molecules becomes apparent. However, electron microscopes do not produce precise visual images of what they are focused on. Instead, they generate data that have to be interpreted. Two other scientists, American geneticist James Watson and British biophysicist Francis Crick, became aware of their work and began to construct a physical model of the DNA molecule. The paper in which Watson and Crick published the results of their painstaking research has been recognized as one of the most revolutionary and influential documents in the history of science.
How are DNA, chromosomes, genes, and alleles related?
Watson, Crick, and Wilkins each received a Nobel Prize for their work. Unfortunately, Franklin died before her invaluable contribution could be recognized in this way. Recently, historians of science have finally begun to recognize that without Franklin's groundbreaking work, the discovery of the structure of the DNA molecule would have been delayed by years, if not decades. Watson and Crick concluded that the DNA molecule was shaped like a double helix, two strands spiraling around each other.
A helix is the shape of a corkscrew. A double helix is the shape of two corkscrews, one intertwined with the other and curving parallel to it, like the railings of a spiral staircase. Another way to think of the double helix is to imagine a twisted rope ladder with rigid rungs, each rope forming a helix. The easiest way to think about DNA is to start by splitting the two helices [the plural form of the word helix ] apart.
Think of it as sawing down through the middles of the wooden rungs of a rope ladder. The result is two single ropes with half-rungs hanging off each rope. They serve as the four letters of the genetic alphabet. Opposite every T would be an A and vice versa and opposite every G would be a C and vice versa.