Receptor de estrógenoPor ello, los receptores nucleares juegan un papel crucial tanto en el desarrollo embrionario como en la homeostasis en el individuo adulto. Los receptores nucleares presentan una estructura modular y contienen los siguientes dominios: Estas secuencias HREs consisten en dos repeticiones invertidas separadas por una las hormonas esteroides tienen receptores nucleares porque de ADN de longitud variable. Estos ligandos son referidos como antagonistas. It is concerned particularly hormonws the forms of biological molecules and is predominantly que es proteina anabolica and structural—which does not mean, nuxleares and it must at the same time inquire into genesis and function. Researchers in molecular biology use specific techniques native to molecular biology but increasingly combine these techniques and ideas from genetics. There is not a line between these disciplines.
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Por ello, los receptores nucleares juegan un papel crucial tanto en el desarrollo embrionario como en la homeostasis en el individuo adulto. Los receptores nucleares presentan una estructura modular y contienen los siguientes dominios: Estas secuencias HREs consisten en dos repeticiones invertidas separadas por una secuencia de ADN de longitud variable.
Estos ligandos son referidos como antagonistas. It is concerned particularly with the forms of biological molecules and is predominantly three-dimensional and structural—which does not mean, however and it must at the same time inquire into genesis and function.
Researchers in molecular biology use specific techniques native to molecular biology but increasingly combine these techniques and ideas from genetics. There is not a line between these disciplines. Biochemists focus heavily on the role, function, and structure of biomolecules, the study of the chemistry behind biological processes and the synthesis of biologically active molecules are examples of biochemistry.
Genetics is the study of the effect of differences on organisms. This can often be inferred by the absence of a normal component, the study of mutants — organisms which lack one or more functional components with respect to the so-called wild type or normal phenotype.
Genetic interactions can often confound simple interpretations of such knockout studies, molecular biology is the study of molecular underpinnings of the processes of replication, transcription, translation, and cell function. This picture, however, is undergoing revision in light of emerging novel roles for RNA, much of molecular biology is quantitative, and recently much work has been done at its interface with computer science in bioinformatics and computational biology.
In the early s, the study of structure and function. There is also a tradition of studying biomolecules from the ground up in biophysics. This plasmid can be inserted into either bacterial or animal cells, introducing DNA into bacterial cells can be done by transformation via uptake of naked DNA, conjugation via cell-cell contact or by transduction via viral vector.
Introducing DNA into eukaryotic cells, such as cells, by physical or chemical means is called transfection. Several different transfection techniques are available, such as calcium phosphate transfection, electroporation, microinjection, the plasmid may be integrated into the genome, resulting in a stable transfection, or may remain independent of the genome, called transient transfection. DNA coding for a protein of interest is now inside a cell, a variety of systems, such as inducible promoters and specific cell-signaling factors, are available to help express the protein of interest at high levels.
Large quantities of a protein can then be extracted from the bacterial or eukaryotic cell, polymerase chain reaction is an extremely versatile technique for copying DNA. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, responding to stimuli, a linear chain of amino acid residues is called a polypeptide.
A protein contains at least one long polypeptide, short polypeptides, containing less than 20—30 residues, are rarely considered to be proteins and are commonly called peptides, or sometimes oligopeptides.
The individual amino acid residues are bonded together by peptide bonds, the sequence of amino acid residues in a protein is defined by the sequence of a gene, which is encoded in the genetic code. In general, the code specifies 20 standard amino acids, however. Sometimes proteins have non-peptide groups attached, which can be called prosthetic groups or cofactors, proteins can also work together to achieve a particular function, and they often associate to form stable protein complexes.
Once formed, proteins only exist for a period of time and are then degraded and recycled by the cells machinery through the process of protein turnover. A proteins lifespan is measured in terms of its half-life and covers a wide range and they can exist for minutes or years with an average lifespan of 1—2 days in mammalian cells. Abnormal and or misfolded proteins are degraded more rapidly due to being targeted for destruction or due to being unstable.
Like other biological macromolecules such as polysaccharides and nucleic acids, proteins are essential parts of organisms, many proteins are enzymes that catalyse biochemical reactions and are vital to metabolism.
Proteins also have structural or mechanical functions, such as actin and myosin in muscle and the proteins in the cytoskeleton, other proteins are important in cell signaling, immune responses, cell adhesion, and the cell cycle. In animals, proteins are needed in the diet to provide the essential amino acids that cannot be synthesized, digestion breaks the proteins down for use in the metabolism. Methods commonly used to study structure and function include immunohistochemistry, site-directed mutagenesis, X-ray crystallography, nuclear magnetic resonance.
Only proline differs from this structure as it contains an unusual ring to the N-end amine group. The amino acids in a chain are linked by peptide bonds. Once linked in the chain, an individual amino acid is called a residue, and the linked series of carbon, nitrogen.
The peptide bond has two forms that contribute some double-bond character and inhibit rotation around its axis, so that the alpha carbons are roughly coplanar. A cell is the smallest unit of life that can replicate independently, the study of cells is called cell biology. Cells consist of cytoplasm enclosed within a membrane, which contains many such as proteins.
Organisms can be classified as unicellular or multicellular, while the number of cells in plants and animals varies from species to species, humans contain more than 10 trillion cells.
Most plant and animal cells are only under a microscope. The cell was discovered by Robert Hooke in , who named the unit for its resemblance to cells inhabited by Christian monks in a monastery.
Cells emerged on Earth at least 3. Prokaryotes are single-celled organisms, while eukaryotes can be either single-celled or multicellular, prokaryotic cells were the first form of life on Earth, characterised by having vital biological processes including cell signaling and being self-sustaining. They are simpler and smaller than eukaryotic cells, and lack membrane-bound organelles such as the nucleus, prokaryotes include two of the domains of life, bacteria and archaea.
The DNA of a prokaryotic cell consists of a chromosome that is in direct contact with the cytoplasm. The nuclear region in the cytoplasm is called the nucleoid, most prokaryotes are the smallest of all organisms ranging from 0. Though most prokaryotes have both a cell membrane and a wall, there are exceptions such as Mycoplasma and Thermoplasma which only possess the cell membrane layer. The envelope gives rigidity to the cell and separates the interior of the cell from its environment, the cell wall consists of peptidoglycan in bacteria, and acts as an additional barrier against exterior forces.
It also prevents the cell from expanding and bursting from osmotic pressure due to a hypotonic environment, some eukaryotic cells also have a cell wall. Inside the cell is the region that contains the genome, ribosomes. The genetic material is found in the cytoplasm. Prokaryotes can carry extrachromosomal DNA elements called plasmids, which are usually circular, linear bacterial plasmids have been identified in several species of spirochete bacteria, including members of the genus Borrelia notably Borrelia burgdorferi, which causes Lyme disease.
Though not forming a nucleus, the DNA is condensed in a nucleoid, plasmids encode additional genes, such as antibiotic resistance genes.
Hormona tiroidea — The thyroid hormones, triiodothyronine and its prohormone, thyroxine, are tyrosine-based hormones produced by the thyroid gland that are primarily responsible for regulation of metabolism.
T3 and T4 are partially composed of iodine, a deficiency of iodine leads to decreased production of T3 and T4, enlarges the thyroid tissue and will cause the disease known as simple goitre.
The major form of hormone in the blood is thyroxine. In humans, the ratio of T4 to T3 released into the blood is between 14,1 and 20,1, T4 is converted to the active T3 within cells by deiodinases.
These are further processed by decarboxylation and deiodination to produce iodothyronamine and thyronamine, all three isoforms of the deiodinases are selenium-containing enzymes, thus dietary selenium is essential for T3 production. Edward Calvin Kendall was responsible for the isolation of thyroxine in They act to increase the metabolic rate, affect protein synthesis, help regulate long bone growth and neural maturation.
The thyroid hormones are essential to development and differentiation of all cells of the human body. These hormones also regulate protein, fat, and carbohydrate metabolism, numerous physiological and pathological stimuli influence thyroid hormone synthesis.
Thyroid hormone leads to generation in humans. However, the function via some unknown mechanism to inhibit neuronal activity, this plays an important role in the hibernation cycles of mammals. One effect of administering the thyronamines is a drop in body temperature. Thyroid hormones are produced by the cells of the thyroid gland and are regulated by TSH made by the thyrotropes of the anterior pituitary gland.
The effects of T4 in vivo are mediated via T3, T3 is 3- to 5- fold more active than T4. Thyroxine is produced by cells of the thyroid gland.
The process of gene expression is used by all known life—eukaryotes, prokaryotes, several steps in the gene expression process may be modulated, including the transcription, RNA splicing, translation, and post-translational modification of a protein. Gene regulation gives the cell control over structure and function, and is the basis for differentiation, morphogenesis.
In genetics, gene expression is the most fundamental level at which the genotype gives rise to the phenotype, the genetic code stored in DNA is interpreted by gene expression, and the properties of the expression give rise to the organisms phenotype. Such phenotypes are expressed by the synthesis of proteins that control the organisms shape. Regulation of gene expression is critical to an organisms development. A gene is a stretch of DNA that encodes information, genomic DNA consists of two antiparallel and reverse complementary strands, each having 5 and 3 ends.
Pol II includes a C-terminal domain that is rich in serine residues, when these residues are phosphorylated, the CTD binds to various protein factors that promote transcript maturation and modification. These include 5 capping, which is set of reactions that add 7-methylguanosine to the 5 end of pre-mRNA. The m7G cap is then bound by cap binding complex heterodimer, another modification is 3 cleavage and polyadenylation. The majority of eukaryotic pre-mRNAs consist of alternating segments called exons and introns, in certain cases, some introns or exons can be either removed or retained in mature mRNA.
Gen — A gene is a locus of DNA which is made up of nucleotides and is the molecular unit of heredity. The transmission of genes to an offspring is the basis of the inheritance of phenotypic traits. These genes make up different DNA sequences called genotypes, genotypes along with environmental and developmental factors determine what the phenotypes will be.
Most biological traits are under the influence of polygenes as well as gene—environment interactions, genes can acquire mutations in their sequence, leading to different variants, known as alleles, in the population. These alleles encode slightly different versions of a protein, which cause different phenotypical traits, usage of the term having a gene typically refers to containing a different allele of the same, shared gene.
Genes evolve due to natural selection or survival of the fittest of the alleles, the concept of a gene continues to be refined as new phenomena are discovered. For example, regulatory regions of a gene can be far removed from its coding regions, some viruses store their genome in RNA instead of DNA and some gene products are functional non-coding RNAs.
The existence of discrete inheritable units was first suggested by Gregor Mendel, from to , in Brno, he studied inheritance patterns in common edible pea plants, tracking distinct traits from parent to offspring.
He described these mathematically as 2n combinations where n is the number of differing characteristics in the original peas, although he did not use the term gene, he explained his results in terms of discrete inherited units that give rise to observable physical characteristics. Darwin used the term gemmule to describe hypothetical particles that would mix during reproduction, de Vries called these units pangenes, after Darwins pangenesis theory.
In the Danish botanist Wilhelm Johannsen shortened the name to gene, advances in understanding genes and inheritance continued throughout the 20th century. Deoxyribonucleic acid was shown to be the repository of genetic information by experiments in the s to s. In the early s the prevailing view was that the genes in a chromosome acted like discrete entities, indivisible by recombination, collectively, this body of research established the central dogma of molecular biology, which states that proteins are translated from RNA, which is transcribed from DNA.
This dogma has since shown to have exceptions, such as reverse transcription in retroviruses. The modern study of genetics at the level of DNA is known as molecular genetics, in , Walter Fiers and his team at the University of Ghent were the first to determine the sequence of a gene, the gene for Bacteriophage MS2 coat protein. The subsequent development of chain-termination DNA sequencing in by Frederick Sanger improved the efficiency of sequencing, an automated version of the Sanger method was used in early phases of the Human Genome Project.
The theories developed in the s and s to integrate molecular genetics with Darwinian evolution are called the evolutionary synthesis. The concept was described by French physiologist Claude Bernard in , the term cybernetics is applied to technological control systems such as thermostats, which function as homeostats, but is often defined much more broadly than the biological term homeostasis.
The conceptual origins of homeostasis reach back to the ancient Greek concepts of balance, harmony, equilibrium, following these hypotheses, Hippocrates compared health to the harmonious balance of the elements, and illness and disease to the systematic disharmony of these elements.
Cannon published an extrapolation from Bernards work naming his theory homeostasis, Cannon further posited that threats to homeostasis might originate from the external environment or the internal environment, and could be physical or psychological, as in emotional distress. Cannon identified these negative feedback systems and emphasized that, regardless of the nature of the threat to homeostasis, the metabolic processes of all living organisms can only take place in very specific physical and chemical environments.
The conditions vary with each organism, and with whether the chemical processes take place inside the cell or in the bathing the cells in multicellular creatures.