changes

Y chromosome

...omosome Y The following conditions are caused by changes in the structure or number of copies of chromosome...tra copies of the sex chromosomes or by structural changes in the chromosomes. Rarely, males may have more than one extra copy of the Y chromosome in every ce...

X-ray crystallography

...ials (thanks to the JCPDS pattern database), and changes in peak width or position can be used to determine crystal size, purity, and texture . Organic Structures The first protein crystal structure was of sperm whale myoglobin , as determined by Max Perutz and Sir John Cowdery Kendrew in 1958, ...

X chromosome

...tra copies of the sex chromosomes or by structural changes in the chromosomes. Other conditions Many diseases are due to mutations on the X chromosome. These are characteristic as they occur much more often in men than in women. Moreover, they inherit in a characteristic manner: fathers do not transmit...

Virus evolution

...times. As a consequence, many viruses can adapt to changes in their environment within months. Virus evolution is an important aspect of the epidemiology of viral diseases such as influenza , HIV , hepatitis , and many others. It also causes problems in the development of successful antiviral drugs ...

Unsolved problems in biology

...he brain ? Humanity : Why are there drastic changes in hominid morphology ? Why are there giant hominid skeletons and very small hominid skeletons? Is hominid evolution static? Is hominid devolution possible? Are there Human- Neandertal hybrids? What explain the differences between Human and Nean...

Transmembrane receptor

...rmone (although certain receptors respond also to changes in transmembrane potential ), and in many receptors these ligands bind to the extracellular domain. The transmembrane domain In the majority of receptors for which structural evidence exists, transmembrane alpha helices make up most of the t...

Thermoregulation

... temperature of the environment, thermoconformer changes its body temperature according to the temperature .... Also a certain amount of heat is produced by the changes which the food undergoes in the alimentary canal before it really enters the body. But heat while ...

Mitosis

...aphase, and telophase. Diagram showing the changes which occur in the centrosomes and nucleus of a cell in the process of mitotic division. (Schfer.) I to III, prophase; IV, metaphase; V and VI, anaphase; VII and VIII, telophase. The whole procedure is very similar among most eukaryotes, with only...

Symbiosis

...the lifetime of the symbionts due to developmental changes as well as changes in the biotic/abiotic environment in which the interaction occurs. See also Commensalism ...

Speciation

...olated populations, each of which then accumulates changes from sexual reproduction and/or random mutation ...e species .) If a single population of a species changes enough over time to be designated a new species while the old species dies out, we have a process ca...

Signal transduction

...nsduction of transmembrane receptors by structural changes 3.1.3 Signal transduction of transmembrane recep...nsduction of transmembrane receptors by structural changes Signal transduction across the plasma membrane is possible only by many components working togethe...

Rudolf Steiner

...ner characterized history as essentially shaped by changes formed through a progressive development of human consciousness. The activity of individualised human thinking was seen as a relatively recent advance which led to the dramatic developments of the Renaissance and the Industrial Revolution . In his...

Quaternary structure

...in quaternary structure are called conformational changes . It is through such changes, which underlie cooperativity and allostery in "multimeric" enzymes, that many proteins undergo regulation and perform their physiological function. The above definition follows a classical approach to biochemistry...

Punctuated equilibrium

...ria , is a theory of evolution which states that changes such as speciation can occur relatively quickly,...rm of gradualism. This is because even though the changes are considered to be occurring relatively quickly, they are still occurring gradually, with no great...

Population dynamics

...n dynamics is the study of marginal and long-term changes in the numbers, individual weights and age composition of individuals in one or several populations , and biological and environmental processes influencing those changes. Population dynamics is the dominant branch of mathematical biology , wh...

Cell membrane

...o maintain the fluidity of their membranes despite changes in temperature. Cholesterol molecules (in case of eukaryotes) or hopanoids (in case of prokaryotes) in the bilayer assist in regulating fluidity. Detailed Structure In fact, not all lipid molecules in the cell membrane are "fluid," in the sen...

Polymerase chain reaction

... Mutagenesis Mutagenesis is a way of making changes to the sequence of nucleotides in the DNA. There a...ers have used traditional PCR as a way to estimate changes in the amount of a gene's expression . Ribonucleic acid (RNA) is the molecule into which DNA is t...

Parthenogenesis

...pe in each individual. Similar arguments apply to changes in the physical environment. Some species alternate between the sexual and assexual strategies, an ability known as heterogamy , depending on conditions. For example, the freshwater crustacean Daphnia reproduces by parthenogenesis in the spring ...

Paleontology

...n its contexts, by studying how long-term physical changes of global geography (" paleogeography ") and clima...n of life, how ecosystems have responded to these changes and have changed the planetary environment in turn, and how these mutual responses have affected tod...

Nutrition

... prevent much disease... To get really significant changes in disease rates, it will be necessary to shift the American diet from its heavy reliance on animal-based foods to one that relies far more on plant-based foods" (Cornell Chronicle 10/1/94) (See also: Walter C. Willett and Meir J. Stampfer, Rebuild...

Neutral theory of molecular evolution

...e). Consequently, many potential single-nucleotide changes are in effect "silent" or "unexpressed" (see synonymous or silent substitution ). Such changes are presumed to have little or no biological effect. A second assertion or hypothesis of the neutr...

Natural selection

...c conditions of life. We see nothing of these slow changes in progress, until the hand of time has marked the long lapses of ages, and then so imperfect is our view into long past geological ages, that we only see that the forms of life are now different from what they formerly were. Darwin ends his book w...

Mutagen

...n , literally origin of change ) is an agent that changes the genetic information (usually DNA ) of an organism and thus increases the number of mutations above the natural background level. Mutagens are usually chemical compounds or radiation . The Ames test is one method to determine how muta...

Magnetic resonance imaging

...y the most sensitive way to evaluate the brain for changes of multiple sclerosis . The typical MRI examinat... computed tomography , which often does not detect changes of acute infarct for up to 4-6 hours) and remains for up to two weeks. As such, DWI sequences are e...

Modern evolutionary synthesis

...uring meiosis ). Evolution consists primarily of changes in the frequencies of alleles between one generation and another as a result of genetic drift , gene flow and natural selection . Speciation occurs gradually when populations are reproductively isolated by geographic barriers. Further ad...

Molecular evolution

...n each individual organism. Because most heritable changes in visible traits are a result of changes in the DNA, molecular evolution must be seen as part of general evolution . The boundary between ...

Mitosis

...aphase, and telophase. Diagram showing the changes which occur in the centrosomes and nucleus of a cell in the process of mitotic division. (Schfer.) I to III, prophase; IV, metaphase; V and VI, anaphase; VII and VIII, telophase. The whole procedure is very similar among most eukaryotes, with only...

Mitochondrion

... them to be dynamic organelles capable of dramatic changes in shape. Finally, mitochondria can fuse with one another, or split in two. The outer boundary of a mitochondrion contains two functionally distinct membranes: the outer mitochondrial membrane and the inner mitochondrial membrane . The outer mit...

Mitochondrion

... them to be dynamic organelles capable of dramatic changes in shape. Finally, mitochondria can fuse with one another, or split in two. The outer boundary of a mitochondrion contains two functionally distinct membranes: the outer mitochondrial membrane and the inner mitochondrial membrane . The outer mit...

Microevolution

Microevolution is the occurrence of small-scale changes in gene frequencies in a population over a few gen...own as change at or below the species level. These changes may be due to several processes: mutation , gene flow , genetic drift , as well as natural selec...

Memory

...e that short-term memory is supported by transient changes in neuronal communication, whereas long-term memories are maintained by more stable and permanent changes in neural structure that are dependent on protein synthesis. Some psychologists, however, argue that...

Long-term potentiation

...vity (or "trace") tends to induce lasting cellular changes that add to its stability.... When an axon of cell A is near enough to excite a cell B and repeatedly or persistently takes part in firing it, some growth process or metabolic change takes place in one or both cells such that A's efficiency, as one o...

Lac repressor

... present the lac repressor hooks up to lactose and changes shape and detaches from the DNA. The technical term for this shape-shifting is " allosteric signal transduction ". See also Lac operon...

Jean-Baptiste Lamarck

...ce of arousing attention to the probability of all changes in the organic, as well as in the inorganic world, being the result of law, and not of miraculous interposition." Lamarck's own theory of evolution was in fact based on the idea that individuals adapt during their own lifetimes and transmit trait...

Ion channel

...variety of biological processes that involve rapid changes in cells. In the search for any drug, ion channels are a favorite target. Diversity and activation Voltage-gated channels sense the transmembrane potential and open or close in response to depolarization or hyperpolarization , respect...

Immune system

...tive immunity , in which the response to pathogens changes during the lifetime of an individual, appeared somewhat abruptly in evolutionary time with the appearance of cartilaginous (jawed) fish . Organisms that possess an adaptive immunity also possess an innate immunity and many of the mechanisms betwee...

Hermaphrodite

...rodite : The organism is born as one sex and later changes into the other sex. Protandry : When the organism starts as a male, and changes sex to a female later in life. Example: The seabasses (Family Serranidae ). These are a highly so...

Genetics

... containing linear arranged genes 1927 Physical changes in genes are called mutations 1928 Frederick...of inherited features not strictly associated with changes in the DNA sequence is called epigenetics . Some take the view that life can be defined, in m...

Genetic code

... However, the genetic code is not perfect as minor changes such as the single-base substitution in sickle cell anaemia is disasterous. The hydrophilic glutamate (Glu) is substituted by the hydrophobic valine (Val) which reduces the solubility of -globin. This causes haemoglobin to form linear polymers ...

Genetic drift

...ost strongly in small populations and results in changes that need not be adaptive . Contents showTo...ective effects may not be seen at all as the small changes in frequency they would produce are overshadowed by drift. Genetic drift in populations Drift ca...

Gene

...silenced through DNA methylation or by chemical changes to the protein components of chromosomes (see histone ). This is a permanent form of regulation of the transcription. The RNA is often edited before its translation into a protein. Eukaryotic cells splice the transcripts of a gene, by keepin...

Fungus

... the various fungal taxa has undergone substantial changes in the last several decades, especially as techniques for comparing biochemical characteristics (such as ribosomal RNA and DNA) have become increasingly more sophisticated. The phylogeny presented here is after Bruns et al. (1991, 1993) for the Eumy...

Cell membrane

...o maintain the fluidity of their membranes despite changes in temperature. Cholesterol molecules (in case of eukaryotes) or hopanoids (in case of prokaryotes) in the bilayer assist in regulating fluidity. Detailed Structure In fact, not all lipid molecules in the cell membrane are "fluid," in the sen...

Fick's law of diffusion

...when the concentration within the diffusion volume changes with respect to time. Where c is the concentration in dimensions of [parts length -3 ] t is time D is the diffusion coefficient in dimensions of [length 2 time -1 ] x is the position A Biological Perspective The firs...

Facilitated diffusion

...ansported. After binding the molecule, the protein changes shape and carries the molecule across the membrane, where it is released. The protein then returns to its original shape, to wait for more molecules to transport. In contrast to active transport , facilitated diffusion does not require energy and c...

Evolutionary developmental biology

...locus free to fulfill a new function. In contrast, changes in gene regulation , is a "second-order" effect o...ariation for natural selection to act upon, than changes in the gene product alone. References Sean B. Carroll, 2000 , "Endless forms: the evolution of...

Evolution

...echanisms: natural selection , genetic drift or changes in population structure ( gene flow ). Content...information about the history of the Earth and the changes produced by life. A great deal of information about the early Earth has been destroyed by geological...

Bacterium

..., either using flagella , bacterial gliding , or changes of buoyancy. A unique group of bacteria, the spirochaetes , have structures similar to flagella, called axial filaments , between two membranes in the periplasmic space. They have a distinctive helical body that twists about as it moves. Bacteri...

Epigenetics

...ng within an organism. The study of heritable changes in gene function that occur without a change in ...ronmental factors affecting a parent can result in changes in the way genes are expressed in the offspring (see Waterland citation). In both cases, the objec...

Enzyme

...on EC 5 Isomerases : catalyze isomerization changes within a single molecule EC 6 Ligases : join two molecules with covalent bonds The complete nomenclature can be browsed at http://www.chem.qmul.ac.uk/iubmb/enzyme/ Enzymes and classes of enzyme Adenylate cyclase : participate in s...

Warm-blooded

...rom muscle contractions), blanching (circulatory changes to direct less heat to the skin), flushing (circulatory changes to radiate more heat from the skin), panting or sweating (to increase heat loss through evaporati...

Electrophysiology

...ble the measurement of this flow and the potential changes related to them. At the cellular level, these in...ectrode and is typically used to detect and record changes in the chemical composition of the oxidized components inside of biological solution being studied. ...

Digital organism

...em. He introduced mutations, in the form of random changes in the instructions of the programs inhabiting t... similar to core world. However, Ray made some key changes to the programming language such that mutations were much less likely to destroy a program. With the...

Dialysis

...e, and weight are all measured again. Temperature changes may indicate infection. BP discussed above. Weighing is to confirm the removal of the desired amount of fluid. Care staff verifies that the patient is in condition suitable for leaving. The patient must be able to stand (if previously able), main...

Digestion

...her decompose it chemically. As the acidic level changes in the stomach and later parts of the digestive tract, more enzymes are activated or deactivated to extract and process various nutrients. After being processed in the stomach, food is passed to the small intestine where it is further mixed with ...

Diabetes mellitus

...ses obesity. 12 Type 2 is initially treated by changes in diet and through weight loss . This can restor...ltered vision. Prolonged high blood glucose causes changes in the shape of the lens in the eye, leading to blurred vision and, perhaps, a visit to an optometr...

Culture

...ntary roles in many cultures. One sex might desire changes that affect the other, as happened in the second half of the 20th century in western cultures. Cultural change can be caused by the environment, inventions and other internal influences, and contact with other cultures. For example, the end of the l...

Computed axial tomography

... is excellent for detecting both acute and chronic changes in the lung parenchyma. For detection of airspace disease (such as pneumonia ) or cancer , ordinary non-contrast scans are adequate. For evaluation of chronic interstitial processes ( emphysema , fibrosis , and so forth), thin sections with hig...

Ion gradient

...ATP synthase to make the necessary conformational changes required to synthesize ATP. Proton gradients are also be made by bacteria by running ATP synthase in reverse, this is used to drive flagellas. The F 1 F O ATP synthase is a reversible enzyme. Large enough quantities of ATP cause it to create a t...

Bioinformatics

...searchers to trace evolution of species by tracing changes in their DNA. CEB research from the pre-genome era involved building computational models of populations and watching their behavior over time. The field of genetic algorithms might be described as the rough inverse of CEB --- rather than investi...