Las estructuras moleculares y las secuencias son generalmente ms reveladoras en las Relaciones evolutivas que en los Fenotipos clsicos especialmente en los microorganismos. Por lo tanto, la definicin bsica de taxones poco a poco ha cambiado de lo orgsmico a lo celular y de lo celular a los niveles moleculares. Las comparaciones moleculares muestran que la vida en este planeta se divide en tres grupos principales, comnmente conocidos como la eubacterias, las arqueobacterias y los eucariotas. Los tres son muy diferentes, las diferencias que los separan son de natularezas ms profundas que las diferencias que separan.
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You should now be able to explain how genetic information maintains the continuity of a species from one generation to the next. But how is the genetic information in DNA used by each organism that possesses it? How do your cells use the information in the sequence of nucleotides in your DNA to build and maintain the physical being that is you?
In this Explain activity, Expression of Genetic Information , you will develop your own explanation of the relationship between genetic information and physical characteristics. You will do this by tracing the series of events that lead to sickle cell disease. As you and your partner work through this activity, you will create a poster that illustrates the molecular basis of sickle cell disease.
La figura Each year, about 1 in African American children is born with sickle cell disease. Although the disease may affect other populations, African Americans are the most commonly affected population. This disease is caused by an abnormality in the protein hemoglobin. Hemoglobin is present in red blood cells and carries oxygen to body cells. When the oxygen supply in the blood is low, these abnormal hemoglobin molecules stack to form long polymers.
Typical hemoglobin molecules remain separate. Figure In a person with sickle cell disease, the stacking of the hemoglobin molecules at low oxygen levels causes the red blood cells to become long and rigid like a sickle instead of remaining round and flexible figure That change in cell shape causes a variety of problems in the body.
For example, as cells become sickled, they tend to block small blood vessels figure The blockage causes pain and damage to the areas that do not receive an adequate blood supply. This includes the heart, lungs, kidneys, brain, and liver. For some people, the damage is so severe that they die in childhood. With good medical care, however, many people with sickle cell disease can live reasonably normal lives.
Think back to the information you learned about the circulatory system in unit 2, Homeostasis: Maintaining Dynamic Equilibrium in Living Systems. On your poster, include pictures and words that you think would be appropriate and helpful. Add a descriptive label to each area so that a viewer will understand what each section is displaying. Refer to the essay, Replication Errors and Mutation , in the previous Explore-Explain activity if you need more information about types of mutations.
Las regiones particulares del ADN se llaman genes. Se estima que los seres humanos poseen entre 20, y 25, genes. Las diferentes versiones de un gen se denominan alelos. Debido a esto, el ARN tiene una cadena sencilla. En cambio hay una base relacionada denominada uracilo U en las posiciones complementarias a la adenina A. El ARN se produce de igual forma para todos los genes.
Como lo muestra la figura En cambio, como lo muestra la figura El diagrama de la figura When an error in replication takes place, the nucleotide sequence of a DNA molecule is altered. The resulting mutations may be passed on during the next round of DNA replication. Knowing how a change in DNA sequence can be preserved and passed to new cells, however, does not tell us what effect the altered DNA structure has on the organism.
In other words, we must see whether the mutation caused a change in a region of DNA that is used to control some characteristic of the organism.
In order to understand this, we need to know how DNA is organized. You already saw that DNA uses four nucleotides. Particular regions of DNA are called genes. A gene is a segment of DNA that will code for a specific product in cells.
Genes are the basic units of heredity. Humans are estimated to have 20,—25, genes. Humans have two copies of each gene. One copy is on a chromosome from our mother and one copy is on a chromosome from our father. This means that our two copies of the gene may not be identical. The different versions of a gene are called alleles. For example, a person might have one allele that specifies sickle cell disease and one allele that does not have the mutation for that disease.
The process by which a cell uses the genetic information in genes is called gene expression. Genes contain information that is required to build proteins. Proteins carry out critical biochemical and structural activities inside cells. These activities include a number of housekeeping functions that almost all cells must continuously perform to remain alive. Think about how you must replace burned-out lightbulbs, take out the trash, and grocery shop to maintain a healthy household.
Cells must also replace and repair worn-out parts, eliminate wastes, and break down glucose for energy to stay healthy. In addition to those basic chores, however, most cells also conduct very specialized types of activities.
These are all types of proteins. However, in a living organism, proteins are much more than that. For example, enzymes are proteins that help reactions take place. Some enzymes in your stomach help break down the food you eat. Replication enzymes help DNA to replicate. Insulin is another protein. It is a type of hormone that aids in controlling the level of sugar in your body. Other proteins produce pigments that determine the color of your eyes and hair.
Collagen is a protein that helps make your skin and bones strong. Proteins such as hemoglobin help move oxygen around your body. Antibody proteins help your body fight off illness. Proteins help give cells their structure and shape. Those are just a few examples of the variety of proteins and what they do.
DNA contains the original instructions to make all of the different types of proteins in your body. The first step in expressing the information in DNA is to construct another nucleic acid. This nucleic acid is called ribonucleic acid RNA. RNA contains a ribose sugar instead of a deoxyribose sugar. These sugars are similar, but slight differences in them make DNA able to easily form a double helix while RNA cannot.
Although there can be areas where RNA pairs with other bases on the same strand, it does not form true double helices with two strands.
Because of this, RNA is single stranded. Instead, a related base, uracil U , is found at positions complementary to adenine A. As with the sugars, thymine and uracil are similar in structure.
The small difference in structure, though, helps protect DNA from enzymes that might break it down in the cell. Why do you think it is important that DNA be protected?
RNA is produced in the same way for all genes. As figure This is where the proteins will be made. The name messenger RNA comes from the idea that this type of RNA carries the information, or message, from the nucleus to the cytoplasm of the cell. These types of RNA function in the actual process of assembling proteins. These two forms of RNA are transcribed from genes that are not expressed as proteins.
Instead, as figure During gene expression, the sequence of an mRNA directs the synthesis of a protein through a process called translation. A protein consists of a chain of subunits called amino acids. The diagram in figure Notice that a set of three nucleotides codes for one amino acid. Then the mRNA is read to find the set of nucleotides for an amino acid. Amino acids are first put together in a long, linear molecule. Proteins fold into particular shapes based on the order of amino acids.
Proteins will function properly only when they have folded into a very specific shape. Think about complementary base pairing and the characteristics of RNA as you do this. Estudia cuidadosamente la tabla de la figura Estudia la tabla nuevamente. Luego un componente celular llamado ribosoma se liga al ARNm.
Trabajo Academico de Microbiologia Ambiental
You should now be able to explain how genetic information maintains the continuity of a species from one generation to the next. But how is the genetic information in DNA used by each organism that possesses it? How do your cells use the information in the sequence of nucleotides in your DNA to build and maintain the physical being that is you? In this Explain activity, Expression of Genetic Information , you will develop your own explanation of the relationship between genetic information and physical characteristics. You will do this by tracing the series of events that lead to sickle cell disease.
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