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Thursday, February 19, 2009

Anatomy of Cell

There are two types of cells: eukaryotic and prokaryotic. Prokaryotic cells are usually independent, while eukaryotic cells are often found in multicellular organisms.

Eukaryotic cells

Eukaryotic cells are about 10 times the size of a typical prokaryote and can be as much as 1000 times greater in volume. The major difference between prokaryotes and eukaryotes is that eukaryotic cells contain membrane-bound compartments in which specific metabolic activities take place. Most important among these is the presence of a cell nucleus, a membrane-delineated compartment that houses the eukaryotic cell's DNA. It is this nucleus that gives the eukaryote its name, which means "true nucleus". Other differences include:

  • The plasma membrane resembles that of prokaryotes in function, with minor differences in the setup. Cell walls may or may not be present.
  • The eukaryotic DNA is organized in one or more linear molecules, called chromosomes, which are associated with histone proteins. All chromosomal DNA is stored in the cell nucleus, separated from the cytoplasm by a membrane. Some eukaryotic organelles also contain some DNA.
  • Eukaryotes can move using cilia or flagella. The flagella are more complex than those of prokaryotes.

Prokaryotic cells

Prokaryotes differ from eukaryotes since they lack of a nuclear membrane and a cell nucleus. Prokaryotes also lack most of the intracellular organelles and structures that are seen in eukaryotic cells. There are

two kinds of prokaryotes, bacteria and archaea, but these are similar in the overall structures of their cells. Most functions of organelles, such as mitochondria, chloroplasts, and the Golgi apparatus, are taken over by the prokaryotic cell's plasma membrane. Prokaryotic cells have three architectural regions: appendages called flagella — proteins attached to the cell surface; a and pilicell envelope - consisting of a capsule, a cell wall, and a plasma membrane; and a cytoplasmic region that contains the cell genome (DNA) and ribosomes and various sorts of inclusions. Other differences include:
  • The plasma membrane (a phospholipid bilayer) separates the interior of the cell from its environment and serves as a filter and communications beacon.
  • Most prokaryotes have a cell wall (some exceptions are Mycoplasma (bacteria) and Thermoplasma (archaea)). This wall consists of peptidoglycan in bacteria, and acts as an additional barrier against exterior forces. It also prevents the cell from "exploding" (cytolysis) from osmotic pressure against a hypotonic environment. A cell wall is also present in some eukaryotes like plants (cellulose) and fungi, but has a different chemical composition.
  • A prokaryotic chromosome is usually a circular molecule (an exception is that of the bacterium Borrelia burgdorferi, which causes Lyme disease). Even without a real nucleus, the DNA is condensed in a nucleoid. Prokaryotes can carry extrachromosomal DNA elements called plasmids, which are usually circular. Plasmids can carry additional functions, such as antibiotic resistance.
Souce : wikipedia

Saturday, June 28, 2008

Human genetic engineering

Human genetic engineering

Human genetic engineering is the genetic engineering of humans by modifying the genotype of the unborn individual to control what traits it will possess when born.[1]

Healthy humans do not need gene therapy to survive, though it may prove helpful to treat certain diseases. Special gene modification research has been carried out on groups such as the 'bubble children' - those whose immune systems do not protect them from the bacteria and irritants all around them. The first clinical trial of human gene therapy began in 1990, but (as of 2006) is still experimental. Other forms of human genetic engineering are still theoretical, or restricted to fiction stories. Recombinant DNA research is usually performed to study gene expression and various human diseases. Some drastic demonstrations of gene modification have been made with mice and other animals, however; testing on humans is generally considered off-limits. In some instances changes are usually brought about by removing genetic material from one organism and transferring them into another species.

There are two main types of genetic engineering. Somatic modifications involve adding genes to cells other than egg or sperm cells. For example, if a person had a disease caused by a defective gene, a healthy gene could be added to the affected cells to treat the disorder. The distinguishing characteristic of somatic engineering is that it is non-inheritable, e.g. the new gene would not be passed to the recipient’s offspring.

Germline engineering would change genes in eggs, sperm, or very early embryos. This type of engineering is inheritable, meaning that the modified genes would appear not only in any children that resulted from the procedure, but in all succeeding generations. This application is by far the more consequential as it could open the door to the perpetual and irreversible alteration of the human species.

There are two techniques researchers are currently experimenting with:

  • Viruses are good at injecting their DNA payload into human cells and reproducing it. By adding the desired DNA to the DNA of non-pathogenic virus, a small amount of virus will reproduce the desired DNA and spread it all over the body.
  • Manufacture large quantities of DNA, and somehow package it to induce the target cells to accept it, either as an addition to one of the original 23 chromosomes, or as an independent 24th human artificial chromosome.

Human genetic engineering means that some part of the genes or DNA of a person are changed. It is possible that through engineering, people could be given more arms, bigger brains or other structural alterations if desired. A more common type of change would be finding the genes of extraordinary people, such as those for intelligence, stamina, longevity, and incorporating those in embryos. Human genetic engineering holds the promise of being able to cure diseases and increasing the immunity of people to viruses. An example of such a disease is cystic fibrosis, a genetic disease that affects lungs and other organs.

Researchers are currently trying to map out and assign genes to different body functions or disease. When the genes or DNA sequence responsible for a disease is found, theoretically gene therapy should be able to fix the disease and eliminate it permanently. However, with the complexity of interaction between genes and gene triggers, gene research is currently in its infancy. Computer modeling and expression technology could be used in the future to create people from scratch. This would work by taking existing DNA knowledge and inserting DNA of "superior" body expressions from people, such as a bigger heart, stronger muscles, etc and implanting this within an egg to be inserted into a female womb. The visual modeling of this process may be very much like the videogame Spore, where people are able to manipulate the physical attributes of creatures and then "release them" in the digital world.

The possibilities of physical changes are endless. Strength, speed, endurance and so on can be enhanced. The baby can be made taller, more beautiful, the changes possible are really up to the imagination, and the ability of the techniques employed by future gene manipulators. Certain people have been identified with extraordinary physical abilities, (such as athletes, geniuses, physical and mental event record holders) and their genes could be identified and replaced into the target embryo. There is also the possibility that science will advance so much that people will create genes not identified in nature or people and implant those in the human body.

Corresponding gene function to intelligence or mental aptitude in various fields is much harder because while researchers are finding out which sections of the brain light up when used through MRI imaging, corresponding genes to manipulate and/or expand intelligence are harder to map. The brain seems to be the last great medical mystery because unlike a muscle, it transfers information and handles complex processes like a computer, but without any logical process discernible to researchers. However, in certain individuals that have a higher aptitude at certain tasks, the history of their family having done the same work seems to show that either through practice, teaching, or gene expressions these individuals find tasks such as composing music or mathematics much easier than the average member of the population.

Souce : wikipedia
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