prokaryotic and eukaryotic

TUGAS BIOLOGI SEL

MACAM-MACAM FOSFOLIPID

OLEH

NAMA           : TRIYATMI BUDIARSIH

NIM                : E1A015060

PRODI           : PENDIDIKAN BIOLOGI

FAKULTAS KEGURUAN DAN ILMU PENDIDIKAN

UNIVERSITAS MATARAM

TAHUN 2015/2016

Prokaryotes and Eukaryotes

On a very fundamental level, eukaryotes and prokaryotes are similar. They share many aspects of their basic  chemistry, physiology, and metabolism. Both cell types are constructed of and use similar kinds of molecules and macromoleculs to accomplish their cellular work. In both, for example, membranes are constructed mainly of fatty substances called lipids, and molecules that perform the cell’s biological and mechanical work are called proteins.

            Eukaryotes and prokaryotes both use the same chemical relay system to  make protein. A permanent record of the code for all of the proteins the cell will require is stored in the form of DNA. Because DNA is the master copy of the cell’s ( or organism’s) genetic make-up, the information it contains is absolutely crucial to the maintenance and perpetuation of the cell. As if to safeguard this archive, the cell does not use the DNA directly in protein synthesis but instead copies the information onto a temporary template of RNA, a chemical relative of DNA. Both the DNA and the RNA constitute a “recipe” for the cell’s proteins. The recipe specifies the order in which amino acids, the chemical subunits of protein,   should be strung together to make the functional protein. Protein synthesis both in eukaryotes and prokaryotes takes place on structures called ribosomes, which are composed of RNA and protein. This illustrates one way in which prokaryote and eukaryotes  are similar and highlights the idea that differences between these organisms are often architectural. In other words, both cell types use the same bricks with these materials vary dramatically.

Figure 1. Giardia lamblia, a single-celled intestinal parasite, occupies a privotal place in the progression from primitive cells to the more complex cells found in higher, multicelular organisms. Giardia belongs to the categoryof cells called eukaryotes, but in many respects it is not distant from more primitive prokaryotes. Thus Giardia may represent a missing link in the transition from prokaryote to eukaryote. Prokaryotes are single-celled organisms, and it is the emergence of eukaryotes that ultimately led to the evolution of complex multicellular life forms. Shown in a phase-contrast micrograph  and in two drawings are trophozoites, the form Giardia takes in the upper intestine of infected animals and the form on which many studies have been conducted. The structures that resemble large eyes are nuclei, membrane-bounded compartments, that house the genetic material DNA. The presence of nuclei distinguished the eukaryotes from more primitive, prokaryotic, cells. Yet Giardia trophozoites are unusual, even for eukaryotes, in that they have two equal-sized nuclei. The side view (lower right) reveals the disk used by the parasite to attach to cells in the upper intestine. The tail like structures are flagella, which Giardia uses to propel it self through its watery environment. Micrograph from Kabnick and Pealtie 1990. Reproduced with permission from The Company of Biologists, Ltd.

Figure 2. prokaryotes are a primitive cell type from which more complex cells, the eukaryotes, probably evolved. Today prokaryotes live on in the two major divisions of bacteria-eubacteria and archebacteria. A prokaryotic cell, schematized here, can be compared to a studio apartment in which all activities take place in a single chamber. The DNA of the prokaryote is attached to the inner cess membrane but is otherwise free-floating in the internal compartment. Ribosomes, the structures on which proteins are synthesized, are also in this compartment. When the organism breaks down nutrients, it releases digestive enzymes into the same space. The prokaryote gains structural support from an external cell wall, but the wall also limits the prokaryotes movement and its ability to communicate with other cells. These limitations restrict the size of most prokaryotic organisms to a single cell. According to one theory, the pivotal event in the evolution of complex cells and multicellular organisms was the loss of the cell wall.

The prokaryotes cell can be compared to a studio apertement : a one-room living space that has a kitchen area abutting the living room, which converts into a bedroom at night. All necessary items fit into their own locations in the one room. There is an everyday, washable rug. Room temperature is comfortable not too hot, not too cold. Conditions are adequate for everything that must occur in the apartement, but not optimal for any specific activity.

In a similar way, all of the prokaryote’s functions fit into a single compartment. The DNA is attached to the cell’s membrane. Ribosomes float freely in the single compartment.  Cellular respiration- the process by which nutrients are metabolized to release energy- is carried out at the cell membrane;  there is not dedicated  compartment for respiration.

A eukaryotes  cell can be compared to a mansion, where specific  rooms are designed for particular activities. The mansion is more diverse in the activities it support than the studio apartement. It can accommodate overnight guests comfortably and support social activities for adults in the living room or dining room, for children in the platroom. The baby’s room is warm and frnished with bright colors and soft, thick carpet. The kitchen has a stove, a refrigerator and a tile floor. Items are kept in the room thet is most appropriate for them, under conditions ideal for the activities in that specific room.

A eukaryotic cell resembles a mansion in that it is subdivided  into many compartmens. each compartment is furnished with items and conditions suitable for a specific function, yet the compartmens work together to allow the cell to maintain it self, to replicate and to perform more specialized activities. Taking a closer lokk, we find three main structural aspects that differentiate prokaryotes from eukaryotes. The definitive difference is the presence of a true (eu) nucleus (karyon) in the eukaryotic cell. The nucleus, a double membrane casing, sequesters the DNA in its own compartment ang keeps it separate from the rest of the cell. In contrast, no such housing is provided for the DNA of prokaryote. Instead the genetic material is tethered to the cell membrane and is otherwise allowed to float freely in the cell’s interior. It is interesting to note that the DNA of eukaryotes is attached to the nuclear membrane, in a manner reminiscent of the attachment of prokaryotic DNA to the cell’s outer membrane.

Although DNA performs the same critical function in both cell types, the presence or absence of a nucleus has some profound implications for the form that the molecule takes and the way that he DNA template ultimately becomes translated into protein. In prokaryotes almost all of the organism’s genetic information is carried on a single circular piece of DNA. The genetic material of the eukaryotic cell, on the other hand, consists of several liner pieces of DNA. The exact number of linear DNA segments varies from species to species. Generally, the DNA in a eukaryotes cell looks like a loose tangle of yarn, except during cell division, when the DNA becomes tightly wrapped into the structures called chromosomes. The membrane surrounding the eukaryotic cell’s nucleus breaks apart during cell division and reappears intact in the daughter cells, one nucleus in each daughter.

Not only is the physical configuration of the DNA different in the two cell types, but they also differ in the number of sets of genetic instructions they contain. A prokaryotic cell contains only a single representation of the genetic information the organism recuires, in this condition the cell is set to be haploid. In contrast, most eukaryotes have two sets of genetic information during some stage of theire live. Cells containing two set of genetic information are referred  to as diploid. Some simple eukaryotes past through only a fleeting diploid stages, but higher eukaryotes spend most of theire lives as diploid cells. Multicellular organism can include both diploid and haploid eukaryotic cells. Most of the cells of the organisms body are diploid. The gametes-eggs and sperm-are haploid eukaryotes. During fertilization two haploid gametes fuse, thus restosing the diploid condition two the resulting embryo. Having two sets of genetic information offers the eukaryotes certain advantages over prokaryotes, and the emergence of the diploid state was an important milestone in evolution.

The nucleus is one several specialized compartments in the eukaryotic cell. Other compartments, called organelles, accommodate several other cellular activities. Prokaryotes do not have subcellular compartments, and this constitutes the second major distinction between the two cell types.

 Figure 3. Eukaryotes are often larger and more complex than prokaryotes. The eukaryotic cell can be up to 100 times that size of a prokaryote. It is also more highly compartmentalized. The cells of all fungi, plants and animals are eukaryotes. The definitive difference between prokaryote and eukaryote is the presence of a membrane-delimited nucleus in the eukaryote. The organisms DNA is inside the nucleus, attached to the nuclear membrane. Ribosomes are outside the nucleus in the sitoplasm, and so that is where protein  sythesis occurs. Digestive enzyms are kept appart from other cellular components in membrane-defined lysosomes. In animals cells like the one schematized, cellular respiration takes place in special compartments called mitochondria. Eukaryotes have no cell wall. Instead, theire structural integrity is maintained by a system of protein tubules, called the cytoskeleton. Thin microfilaments form a meshwork underlying the cell membrane, while thicker  microtubules radiate from the nucleus toward the periphery of the cell. Because the cell structure is internally supported, the outer membrane can remain somewhat fluid.

The organelles of eukaryotes include membrane-bounded compartment such as the lysosome, a highly acidic compartment in which digestive enzymes break down food. The endoplasmic reticulum is an interconnected system of membranes in which lypid are syntesized and some proteins are chemically modified. The endoplasmic  reticulum communicates with another membrane system called golgi apparatus, where proteins are futrher procced and marked for transport to various sites inside or outhside the cells. Eukaryotic cells contain special energy centers. In animal cells, these are the mitochondria , organic compounds are broken down to generate the energy rich molecule adenosine triphosphate (ATP). ATP is short of moleculer fuel, which when degraded provides energy for many of the cells biochemical reaction. ATP is also generated in the chloroplasts of plants cells, but the enrgy for its shynthesis is derived from sunlight, in a procces that also builds up carbohydrates and liberates oxygen.

The third distinguishing feature between the two cell types is the way in which the cells maintain it shap cells, like most animals. Have skeletons and as in many animals. The cellular skeleton can be either internal or eksternal. Prokaryotes have an eksternal skeleton, a strong wall of cross-linked sugar  and protein molecules surround the cell membrane and is make rigid by the turgor pressure of the cell. The wall landes structural support it is also impermeabele to many macromolecules and those haves thus helps to maintain a barrier between substances inside and outside the cell. Such an external skeleton limits the  ability of the prokaryotic cell to move. It also limits communication between cells, a condition that probably accounts for the vastly  decreased ability of prokaryotes to form multicellular organisms.

COMPARISON OF PROKARYOTES AND EUKARYOTES

No	Comparison	Prokaryotes	Eukaryotes
1.	Organism	Bacteria	Protists, fungi, plants, and animals
2.	Cell size	Generally 1 t0 10 mm measured lengthwise	Generally 10 to 100 mm
3.	Metabolism	Anaerobic or aerobic	Anaerobic or aerobic
4.	Organelles	None	Nucleus, mitochondria, chloroplasts, endoplasmic reticulum, golgi apparatus, lysosomes, etc.
5.	Cell support	External cell wall	Internal cytoskeleton
6.	DNA	Circular DNA in single celular compartement	Very long linear DNA containedwithin a membrane-bounded nucleus
7.	RNA and protein	RNA and protein synthesized in the single compartement	RNA synthesized and processed in nucleus; proteins synthesized in cytoplasm
8.	Transmembrane movement	No endocytosis or exocytosis	Endocytosis and exocytosis
9.	Cell division	Chromosomes pulled apart by attachments to inner membrane	Chromosomes pulled apart by attachments to cytoskeletal components
10.	Celular organization	Mainly unicellular	Unicellular or multicellular, with many differentiated cell types.

( Prokaryotes and eukaryotes share many metabolic and biochemical features, even thought the architecture of the cells differs dramatically. Outlined here are somes of the different between the cell types).

Some Common Features and Some Distinguishing Features of Eukaryotic and Prokaryotic Cells and Organisms

	Prokaryotes	Eukaryotes
Basic  Structural   and  Fungtional  Features  of  Cell
Is cell enclosed by a cell membrane ?	Yes	Yes
Is DNA the hereditary material ?	Yes	Yes
Do proteins control all chemical reactions ?	Yes	Yes
Does RNA carry instructions from DNA for making proteins ?	Yes	Yes
Are proteins made on ribosomes ?	Yes	Yes
Is ATP the immediate source of energy for many reactions ?	Yes	Yes
Organization and Function of Genetic System
Is DNA attached to cell membrane ?	Yes	No
Is DNA enclosed by nuclear membrane ?	No	Yes
How many DNA molecules per cell ?	One	Multiple
Are DNA molecules circular ?	Yes	No
Is DNA organized into chromosomes containing proteins called histones ?	No	Yes
Are chromosomes separated by mitotic spindle during cell division ?	No	Yes
Is recombination of genetic material possible ?	Yes	Yes
Does sexual reproduction with meiosis and syngamy occur ?	No	Yes
Secondary Features of Cell Organization
Are cells divided by membranes into functional compartments ?	No	Yes
Smallest units capable of using oxygen to make ATP	Intact cells	Mitochondria
Smallest units capable of using light to make ATP	Intact cells	Chloroplasts
Is cell surrounded by a cell wall outside the membrane ?	Usually	Sometimes
Do cell walls contain peptidoglycan ?	Yes	No
Are microtubules regularly present ?	No	Yes
Does flagellum enclosed by cell membrane ?	No	Yes
Are microfilaments regularly present ?	No	Yes
Does streaming of contents occur within cells ?	No	Yes
Are cells capable of endocytosis ?	No	Often
Relative size of cells	Generally small	Generally large

The skeleton of the eukaryotic cell is internal, it is formed by a compleks of protein tubules called the cytoskeleton. The internal placement of the cytoskeleton means the surface exposed to the environment is a pliable membrane rather than a rigid cell wall. The combination of an internal framework and a non rigid outer membrane expands the repertory of motion and activity of the eukaryotic cell. For example, the cell can contract, as does a muscle cell. (the cells of most higher plants have a wall event more rigid than the prokaryotic wall. Plants cell walls are chemically and structurally very different from prokaryotic walls, presumably they are later, independent adaptation.

The Way It Was

Two billion years ago, before the emergence of the first eukaryotes, life on earth was very different from whatb it is today. The organisms populating the earth were prokaryotes, similar to modern bacteria. But unlike the vast majorityof modern organisms, even modern prokaryotes, these primordial organisms did not use oxygen. Free oxygen was scarce on the primordial earth, and the earliest organisms evolved a metabolism based on sulfur and hydrogen sulfide(H2S).rather than oxygen and water(H2O). Many of these organisms were obligate anaerobs; not only did they faile to make us of oxygen, but they could not survive in its presence.

How did eukaryotic cells as well as modern aerobic prokaryotes, evolve from these anaerobic forerunnerrs because of the improtance of the eukaryotic cell in the evolution of complex living organisms, the question is of intense interest. Two theories offer competing explanations. Although the theories differ dramatically, they are no mutually exclusive. We can envisage a scenario in which both mechanism contribute to the evolution of the evolution of the eukaryotes.

Figure 5. subcellular compartements of eukaryotes may have evolved from previously free- living organism,  according to the theory of serial endosymbiosis. The first step toward the evolution of eukaryotes occurred when a primitive prokaryote-like cell, which could not use oxygen,ingested, but did not digest, a free-living oxygen-using organism. This mutually beneficial arrangement allowed the host to cope with the dramatic rise in concentrations of oxygen on the earth. The oxygen-using organism that resulted from the union went on to ingest another free-living creature and formed a symbiotic relationship with it. Here the oxygen user is shown ingesting a spiral-shaped organism that functions in the symbiote as a flagellum. Serial endosymbiosis would predict that many of the eukaryote’s compartements were derived from the mutually beneficial union of a host and smaller, free-living organism.

 Figure 6. transport of material into and out of the cell is accomplished using membrane-bounded vesicles in the processes of endocytosis and exocytosis, respectively. In endocytosis, materials dissolved in the external aqueous environment gain entry to the cell when a small portion of the cell membrane surrounds them. The membrane invaginates and forms a pocket that completely surrounds the material. Eventually, the pocket seals itself up, breaks away from the membrane, and floats freely within the cytoplasm. Exocytosis works in the opposite direction to expel the same or different membrane-bounded materials from the cytoplasm into the external medium. Meterial is exocytosed when its membranous casing first fuses with the cell’s outer membrane; this causes the vesicle to open and empty its contents into the extracellular medium. The flexibility of the membrane and its ability to pinch off,feld and seal may underlie the evolution of membrane-defined compartements in eukaryotes.

Figur 7. Loss of the cell wall and the resulting fluidity of the outer cell membrane is akey event in the evolution of eukaryotes, according to one theory of eukaryotic evolution. Without a wall, the resulting cell lacks structural support, risks losing its contens and is vulnerable to external assaults. As shown in the diagram, cells that survived this situation adopted one of two solutions. Some acquired a new type of cell wall, these cells are now known as archebacteria to distinguish them from the older type of bacteria, the eubacteria. Other cells developed an internal skeleton, called the cytoskeleton, made from a network of proteinaceus fibers. The thicker microtubules are diagrammed here radiating from the cell’s nucleus, which may have formed at about the same time as the cytoskeleton, thinner microfilaments form a flexible meshwork underlying the cell membrane. This protein skeleton provides support, so that the outer membrane can remain relatively fluid without jeopardizing the cell’s structural integrity. With the cytoskeleton in place, the cell can develop the processes of endocytosis and exocytosis. The infoldings of the membrane led to the formation of the various subcellur compartments and membrane system of the modern eukaryote. This theory predicts that the first eukaryotes were anaerobic, that is they were unable to use oxygen. Later, possibly by endosymbiosis, anaerobic eukaryotes ingested a forerunner of the mitochondrion and gained the ability to use oxygen in generating energy. Recent evidence suggests that Giardia lamblia may represent the anaerobic eukaryote before it gained mitochondria.

Figure 8. Comparisons of the sequences of macromolecules are useful in inferring evolutinary distances between organisms. Shown here is the sequence and proposed secondarystructure of one of the RNAs making up the Giardia ribosome. This sequence has been compared with analogous eubacterial and archebacterial RNAs, and the positions where giardia shares its sequence with such RNAs are shown in reverse type. This analysis has led investigators to believe that giardia may represent the earliest lineage of cells to diverge from prokaryotes.

Figure 9. Phylogenetic trees show the order in which organisms diverged through evolution. The above tree, which shows the placement of Giardia lamblia, was constructed by comparing analogous ribosomal RNA sequences from  each organism. The horizontal component of separation represents evolutionary distance between organisms.

REFERENCES

Slatkin, Montgomery. 1995 . Exploring Evolutionary Biology. Sunderland: Sinauer Associates, Inc.

David, L. Kirk.1980. Biology Today. Random House, Inc: Washington.