He summarized his observations into three conclusions about cells:. We know today that the first two tenets are correct, but the third is clearly wrong. It became possible to maintain, grow, and manipulate cells outside of living organisms. The first continuous cell line to be so cultured was in by George Otto Gey and coworkers, derived from cervical cancer cells taken from Henrietta Lacks, who died from her cancer in The cell line, which was eventually referred to as HeLa cells , have been the watershed in studying cell biology in the way that the structure of DNA was the significant breakthrough of molecular biology.
In an avalanche of progress in the study of cells, the coming decade included the characterization of the minimal media requirements for cells and development of sterile cell culture techniques. It was also aided by the prior advances in electron microscopy, and later advances such as the development of transfection methods, the discovery of green fluorescent protein in jellyfish, and discovery of small interfering RNA siRNA , among others.
The study of the structure and function of cells continues today, in a branch of biology known as cytology. Advances in equipment, including cytology microscopes and reagents, have allowed this field to progress, particularly in the clinical setting.
Today, scientists are working on personalized medicine, which would allow us to grow stem cells from our very own cells and then use them to understand disease processes. All of this and more grew from a single observation of the cell in a cork. Robert Hook refined the design of the compound microscope around and published a book titled Micrographia which illustrated his findings using the instrument.
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You cannot download interactives. A cell is the smallest unit that is typically considered alive and is a fundamental unit of life. All living organisms are composed of cells, from just one unicellular to many trillions multicellular. Cell biology is the study of cells, their physiology, structure, and life cycle.
Contact Us. The Galleries:. Photo Gallery. Silicon Zoo. Chip Shots. DNA Gallery. Amino Acids. Religion Collection. Cocktail Collection. Screen Savers. Win Wallpaper. Mac Wallpaper. Movie Gallery. The envelope is riddled with holes called nuclear pores that allow specific types and sizes of molecules to pass back and forth between the nucleus and the cytoplasm.
It is also attached to a network of tubules, called the endoplasmic reticulum, where protein synthesis occurs. These tubules extend throughout the cell and manufacture the biochemical products that a particular cell type is genetically coded to produce.
Packing all this material into a microscopic cell nucleus is an extraordinary feat of packaging. For DNA to function, it can't be crammed into the nucleus like a ball of string. Instead, it is combined with proteins and organized into a precise, compact structure, a dense string-like fiber called chromatin. Each DNA strand wraps around groups of small protein molecules called histones, forming a series of bead-like structures, called nucleosomes, connected by the DNA strand.
Under the microscope, uncondensed chromatin has a "beads on a string" appearance. The string of nucleosomes, already compacted by a factor of six, is then coiled into an even denser structure, compacting the DNA by a factor of This compression and structuring of DNA serves several functions.
The overall negative charge of the DNA is neutralized by the positive charge of the histone molecules, the DNA takes up much less space, and inactive DNA can be folded into inaccessible locations until it is needed. There are two types of chromatin. Euchromatin is the genetically active portion and is involved in transcribing RNA to produce proteins used in cell function and growth. Heterochromatin contains inactive DNA and is the portion of chromatin that is most condensed, since it not being used.
Throughout the life of a cell, chromatin fibers take on different forms inside the nucleus. During interphase, when the cell is carrying out its normal functions, the chromatin is dispersed throughout the nucleus in what appears to be a tangle of fibers.
This exposes the euchromatin and makes it available for the transcription process. When the cell enters metaphase and prepares to divide, the chromatin changes dramatically.
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