What structural differences did you notice between prokaryotic and eukaryotic cells??

Question

Be specific

Answer 1

Eukaryotic cells are much larger and much more complex than prokaryotic cells.

Eukaryotic cells have a true nucleus, bound by a double membrane. Prokaryotic cells have no nucleus.

Eukaryotic DNA is linear; prokaryotic DNA is circular (it has no ends).

Eukaryotic DNA is complexed with proteins called "histones," and is organized into chromosomes; prokaryotic DNA is "naked," meaning that it has no histones associated with it, and it is not formed into chromosomes.

ribosomes of the eukaryotic cells are larger and more complex than those of the prokaryotic cell.

The cytoplasm of eukaryotic cells is filled with a large, complex collection of organelles, many of them enclosed in their own membranes; the prokaryotic cell contains no membrane-bound organelles which are independent of the plasma membrane.

All info is taken from http://www.cod.edu/people/faculty/fancher/ProkEuk.htm

Answer 2

Prokaryotic cells lack a nucleus, while eukaryotic cells have one. Also prokaryotic cells lack organelle but eukaryotates have organelles. Organelles are things such as smooth and rough edoplasmic reticulum, ribosomes, and the golgi apparatus.

Answer 3

Pro cells are for and Eukary cells are against.

Answer 4

The complexity.

Answer 5

i can't answer this question, i'm not you!

Answer 6

Animals, plants, fungi, and protists are eukaryotes (IPA: [juːˈkæɹɪɒt]), organisms whose cells are organized into complex structures by internal membranes and a cytoskeleton. The most characteristic membrane bound structure is the nucleus. This feature gives them their name, also spelled "eucaryote", which comes from the Greek ευ, meaning good/true, and κάρυον, meaning nut, referring to the nucleus. In the nucleus the genetic material, DNA, is arranged in chromosomes. Many eukaryotic cells also contain membrane-bound organelles such as mitochondria, chloroplasts and Golgi bodies. Eukaryotes often have unique flagella made of microtubules in a 9+2 arrangement.

Finally, cell division involves a complex way of separating the duplicated chromosomes, which is also mediated by complexly choreographed arrangements of microtubules. There are two methods. In mitosis one cell divides to produce two genetically identical cells. In meiosis, which is required in sexual reproduction, one diploid cell (having two copies of each chromosome, one from each parent) undergoes a process of recombination between each pair of parental chromosomes, and then two stages of cell division, resulting in four haploid cells (gametes) each of which has only a single complement of chromosomes, each one being a unique mix and match of the corresponding pair of parental chromosomes.

Eukaryotes appear to be monophyletic and thus make up one of the three domains of life. The two other domains: bacteria and archaea (prokaryotes (without a nucleus)) share none of the above features, though the eukaryotes do share some aspects of their biochemistry with the archaea, and as such, are grouped with the archaea in the clade Neomura.

[edit] Differences between eukaryotic cells
There are many different types of eukaryotic cells, though animals and plants are the most familiar eukaryotes, and thus provide an excellent starting point for understanding eukaryotic structure. Fungi and many protists have some substantial differences, however.


[edit] Animal cell

Structure of a typical animal cell.
Structure of a typical plant cell.An animal cell is a form of eukaryotic cell which make up many tissues in animals. The animal cell is distinct from other eukaryotes, most notably plant cells, as they lack cell walls and chloroplasts, and they have smaller vacuoles. Due to the lack of a rigid cell wall, animal cells can adopt a variety of shapes and a phagocytic cell can even engulf other structures.


[edit] Plant cell
Further information: Plant cell
Plant cells are quite different from the cells of the other eukaryotic organisms. Their distinctive features are:

A large central vacuole (enclosed by a membrane, the tonoplast), which maintains the cell's turgor and controls movement of molecules between the cytosol and sap.
A cell wall made up of cellulose and protein, and in many cases lignin, and deposited by the protoplast on the outside of the cell membrane. This contrasts with the cell walls of fungi, which are made of chitin, and prokaryotes, which are made of peptidoglycan.
The plasmodesmata, linking pores in the cell wall that allow each plant cell to communicate with other adjacent cells. This is different from the network of hyphae used by fungi.
Plastids, especially chloroplasts that contain chlorophyll, the pigment that gives plants their green color and allows them to perform photosynthesis.
Plant groups without flagella (including conifers and flowering plants) also lack centrioles that are present in animal cells.

[edit] Fungal cell
Fungal cells are most similar to animal cells, with the following exceptions.

A cell wall made of chitin.
Less definition between cells. Higher fungal cells have porous separations called septa which allow the passage of cytoplasm, organelles, and sometimes, nuclei. Primitive fungi have no such divisions, and each organism is essentially a giant supercell. These fungi are described as coenocytic.
Only the most primitive fungi, chytrids, have flagella.

[edit] Other eukaryotic cells
Eukaryotes are a very diverse group, and their cell structures are equally diverse. Many have cell walls, many do not. Many have chloroplasts, derived from primary, secondary, or even tertiary endosymbiosis, and many do not. Some groups have unique structures, such as the cyanelles of the glaucophytes, the haptonema of the haptophytes, or the ejectisomes of the cryptomonads. Other structures, such as pseudopods, are found in various eukaryote groups in different forms, such as the lobose amoebozoans or the reticulose foraminiferans.


[edit] Structure
Eukaryotic cells are generally much larger than prokaryotes. They have a variety of internal membranes and structures, called organelles, and a cytoskeleton composed of microtubules, microfilaments and intermediate filaments, which play an important role in defining the cell's organization and shape. Eukaryotic DNA is divided into several linear bundles called chromosomes, which are separated by a microtubular spindle during nuclear division. In addition to asexual cell division (mitosis), most eukaryotes have some process of sexual reproduction via cell fusion (meiosis), which is not found among prokaryotes.



Detail of the endomembrane system and its components
[edit] Internal membrane
Eukaryotic cells include a variety of membrane-bound structures, collectively referred to as the endomembrane system. Simple compartments, called vesicles or vacuoles, can form by budding off other membranes. Many cells ingest food and other materials through a process of endocytosis, where the outer membrane invaginates and then pinches off to form a vesicle. It is probable that most other membrane-bound organelles are ultimately derived from such vesicles.

The nucleus is surrounded by a double membrane (commonly referred to as a nuclear envelope), with pores that allow material to move in and out. Various tube- and sheet-like extensions of the nuclear membrane form what is called the endoplasmic reticulum or ER, which is involved in protein transport and maturation. It includes the Rough ER where ribosomes are attached, and the proteins they synthesize enter the interior space or lumen. Subsequently, they generally enter vesicles, which bud off from the Smooth ER. In most eukaryotes, this protein-carrying vesicles are released and further modified in stacks of flattened vesicles, called Golgi bodies or dictyosomes.

Vesicles may be specialized for various purposes. For instance, lysosomes contain enzymes that break down the contents of food vacuoles, and peroxisomes are used to break down peroxide which is toxic otherwise. Many protozoa have contractile vacuoles, which collect and expel excess water, and extrusomes, which expel material used to deflect predators or capture prey. In multicellular organisms, hormones are often produced in vesicles. In higher plants, most of a cell's volume is taken up by a central vacuole, which primarily maintains its osmotic pressure.


Mitochondria structure:
1) Inner membrane
2) Outer membrane
3) Crista
4) Matrix
[edit] Mitochondria and plastids
Mitochondria are organelles found in nearly all eukaryotes. They are surrounded by double membranes (known as the phospholipid bi-layer), the inner of which is folded into invaginations called cristae, where aerobic respiration takes place. They contain their own DNA and are only formed by the fission of other mitochondria. They are now generally held to have developed from endosymbiotic prokaryotes, probably proteobacteria. The few protozoa that lack mitochondria have been found to contain mitochondrion-derived organelles, such as hydrogenosomes and mitosomes.

Plants and various groups of algae also have plastids. Again, these have their own DNA and developed from endosymbiotes, in this case cyanobacteria. They usually take the form of chloroplasts, which like cyanobacteria contain chlorophyll and produce energy through photosynthesis. Others are involved in storing food. Although plastids likely had a single origin, not all plastid-containing groups are closely related. Instead, some eukaryotes have obtained them from others through secondary endosymbiosis or ingestion.

Endosymbiotic origins have also been proposed for the nucleus, for which see below, and for eukaryotic flagella, supposed to have developed from spirochaetes. This is not generally accepted, both from a lack of cytological evidence and difficulty in reconciling this with cellular reproduction.


[edit] Cytoskeletal structures
Many eukaryotes have long slender motile cytoplasmic projections, called flagella. These are composed mainly of tubulin and shorter cilia, both of which are variously involved in movement, feeding, and sensation. These are entirely distinct from prokaryotic flagella. They are supported by a bundle of microtubules arising from a basal body, also called a kinetosome or centriole, characteristically arranged as nine doublets surrounding two singlets. Flagella also may have hairs, or mastigonemes, and scales connecting membranes and internal rods. Their interior is continuous with the cell's cytoplasm. Microfilamental structures composed by actin and actin binding proteins e.g. α-actinin, fimbrin, filamin are present in submembraneous cortical layers and bundles as well. Motor proteins of microtubules e.g. dynein or kinesin and actin e.g. myosins provide dynamic character of the network.

Centrioles are often present even in cells and groups that do not have flagella. They generally occur in groups of one or two, called kinetids, that give rise to various microtubular roots. These form a primary component of the cytoskeletal structure, and are often assembled over the course of several cell divisions, with one flagellum retained from the parent and the other derived from it. Centrioles may also be associated in the formation of a spindle during nuclear division.

Significance of cytoskeletal structures is underlined in determination of shape of the cells as well as they are essential components of migratory responses like chemotaxis and chemokinesis. Some protists have various other microtubule-supported organelles. These include the radiolaria and heliozoa, which produce axopodia used in flotation or to capture prey, and the haptophytes, which have a peculiar flagellum-like organelle called the haptonema.


[edit] Plant cell wall
Further information: Cell wall
Plant cells contain a cell wall, which is a fairly rigid layer surrounding a cell, located external to the cell membrane, that provides the cell with structural support, protection, and a filtering mechanism. The cell wall also prevents over-expansion when water enters the cell. The major carbohydrates making up the primary cell wall are cellulose, hemicellulose and pectin. The cellulose microfibrils are linked via hemicellulosic tethers to form the cellulose-hemicellulose network, which is embedded in the pectin matrix. The most common hemicellulose in the primary cell wall is xyloglucan.


[edit] Reproduction
Nuclear division is often coordinated with cell division. This generally takes place by mitosis, a process which allows each daughter nucleus to receive one copy of each chromosome. In most eukaryotes there is also a process of sexual reproduction, typically involving an alternation between haploid generations, where only one copy of each chromosome is present, and diploid generations, where two are present, occurring through nuclear fusion (syngamy) and meiosis. There is considerable variation in this pattern, however.

Eukaryotes have a smaller surface to volume area ratio than prokaryotes, and thus have lower metabolic rates and longer generation times. In some multicellular organisms, cells specialized for metabolism will have enlarged surface areas, such as intestinal vili.


[edit] Origin and evolution

The original, now outdated, five-kingdom system.The origin of the eukaryotic cell was a milestone in the evolution of life, since they include all complex cells and almost all multi-cellular organisms. The timing of this series of events is hard to determine; Knoll (1992) suggests they developed approximately 1.6 - 2.1 billion years ago. Fossils that are clearly related to modern groups start appearing around 1.2 billion years ago, in the form of a red alga.

rRNA trees constructed during the 1980s and 1990s left most eukaryotes in an unresolved "crown" group (not technically a true crown), which was usually divided by the form of the mitochondrial cristae. The few groups that lack mitochondria branched separately and so the absence was believed to be primitive, but this is now considered an artifact of long branch attraction and they are known to have lost them secondarily.

Trees based on actin and other molecules have painted a different and more complete picture. Most eukaryotes are now included in several supergroups:

Opisthokonts Animals, fungi, choanoflagellates, etc.
Amoebozoa Most lobose amoebae and slime moulds
Rhizaria Foraminifera, Radiolaria, and various other amoeboid protozoa
Excavates Various flagellate protozoa
Archaeplastida (or Primoplantae) Land plants, green algae, red algae, and glaucophytes
Chromalveolates Heterokonts, Haptophytes, Cryptomonads, and Alveolates.

Eukarya Bikonta
Apusozoa



Corticata
Archaeplastida




Chromalveolata






Cabozoa
Rhizaria




Excavata









Unikonta
Amoebozoa



Opisthokonta
Metazoa




Choanozoa




Eumycota













Modern cladogram of Eukarya
Several authorities recognize two larger clades, the unikonts and the bikonts, the unikonts deriving from an ancestral uniflagellar organism, and the bikonts deriving from an ancestral biflagellate. In this system, the opisthokonts and amoebozoans are considered unikonts, and the rest are considered bikonts. The chromalveolates were originally thought to be two separate groups, the chromists and the alveolates, but the former was proved to be paraphyletic to the latter, and the two groups combined. Some small protist groups have not been related to any of these supergroups, in particular the centrohelids. Eukaryotes are closely related to Archaea, at least in terms of nuclear DNA and genetic machinery, and are placed by some, along with the Archaea, in the clade Neomura. In other respects, such as membrane composition, they are similar to eubacteria. Three main explanations for this have been proposed:

Eukaryotes resulted from the complete fusion of two or more cells, the cytoplasm forming from a eubacterium and the nucleus from an archaeon (alternatively a virus).
Eukaryotes developed from Archaea, and acquired their eubacterial characteristics from the proto-mitochondrion.
Eukaryotes and Archaea developed separately from a modified eubacterium.
The final hypothesis is currently the most accepted. The origin of the endomembrane system and mitochondria are also disputed. The phagotrophic hypothesis states the membranes originated with the development of endocytosis and later specialized; mitochondria were acquired by ingestion, like plastids. The syntrophic hypothesis states that the proto-eukaryote relied on the proto-mitochondrion for food, and so ultimately grew to surround it; the membranes originate later, in part thanks to mitochondrial genes (the hydrogen hypothesis is one particular version).

Prokaryotes (IPA: /prəʊˈkæriəʊtiz/) are a group of organisms that lack a cell nucleus (= karyon), or any other membrane-bound organelles. Most are unicellular, but some prokaryotes are multicellular organisms. The word prokaryotes comes from the Old Greek pro- before + karyon nut or kernel, referring to the cell nucleus, + suffix -otos, pl. -otes; it is also spelled "procaryotes"

The prokaryotes are divided into two domains: the bacteria and the archaea. Archaea or Archaebacteria are a newly appointed kingdom of life. These organisms were originally thought to live only in inhospitable conditions such as extremes of temperature, pH, and radiation, but have since been found in all types of habitats
[edit] Relationship to Eukaryotes
A distinction between prokaryotes and eukaryotes (meaning true kernel, also spelled "eucaryotes") is that eukaryotes do have "true" nuclei containing their DNA, whereas the genetic material in prokaryotes is not membrane-bound. Eukaryotic organisms, such as humans, may be unicellular or multicellular. The difference between the structure of prokaryotes and eukaryotes is so great that it is considered to be the most important distinction among groups of organisms. Most prokaryotes are bacteria, and the two terms are often treated as synonyms. In 1977, Carl Woese proposed dividing prokaryotes into the Bacteria and Archaea (originally Eubacteria and Archaebacteria) because of the significant genetic differences between the two. This arrangement of Eukaryota (also called "Eukarya"), Bacteria, and Archaea is called the three-domain system replacing the traditional two-empire system. A criticism of this classification is that the word "prokaryote" itself is based on what these organisms are not (they are not eukaryotic), rather than what they are (either archea or bacteria).

In light of the two-empire system, the cell structure of prokaryotes differs greatly from eukaryotes. Thus using the three-domain system, the cell structure of archea are to a great extent (and bacteria to some lesser extent) differ from the cell structure of eukaryotes. The defining characteristic is the absence of a nucleus or nuclear envelope. Prokaryotes were also previously considered to lack cytoskeletons and to lack membrane-bound cell compartments such as vacuoles, endoplasmic reticulum/endoplasmic reticula, Golgi apparatus, mitochondria and chloroplasts. In eukaryotes, the latter two perform various metabolic processes and are believed to have been derived from endosymbiotic bacteria. In prokaryotes similar processes occur across the cell membrane; endosymbionts are extremely rare. The cell walls of prokaryotes are generally formed of a different molecule (peptidoglycan) to those of eukaryotes (many eukaryotes do not have a cell wall at all). Both eukaryotes and prokaryotes have structures called ribosomes, which produce protein. Prokaryotes are usually much smaller than eukaryotic cells.

Prokaryotes also differ from eukaryotes in that they contain only a single loop of stable chromosomal DNA stored in an area named the nucleoid, while eukaryote DNA is found on tightly bound and organised chromosomes. Although some eukaryotes have satellite DNA structures called plasmids, these are generally regarded as a prokaryote feature and many important genes in prokaryotes are stored on plasmids.

Prokaryotes have a larger surface area to volume ratio giving them a higher metabolic rate, a higher growth rate and consequently a shorter generation time compared to Eukaryotes.


[edit] Genes
Nearly all prokaryotes have a single circular chromosome contained within a conglomeration of ribosomes and other proteins related to a transcription and translation region called the nucleoid, as opposed to the well defined, double membrane bound eukaryotic nucleus. Certain exceptions do apply, however. For example, Borrelia burgdorferi and the genus Streptomyces contain linear chromosomes, like the eukaryotes. Vibrio cholerae, the causative agent of cholera, has two circular chromosomes, the smaller of which contains most of the genes responsible for virulence. Mycoplasma genitalium, which has the smallest genome of any free-living organism, has a genome of 580,000 base pairs.

Most notable, however, are the plasmids, which are small (about 1 to 10 thousand base pairs), circular pieces of DNA that are replicated by the host's DNA replication machinery, but whose genes are not absolutely critical for general survival. In nature, they usually contain special genes that confer some type of selective advantage such as antibiotic resistance, virulence, or gene transfer mechanisms. In genetic engineering artificially introduced plasmids carry genes to be expressed and studied.

Prokaryotes also differ from eukaryotes in the structure, packing, density, and arrangement of their genes on the chromosome. Prokaryotes have incredibly compact genomes compared to eukaryotes, mostly because prokaryote genes lack introns and large non-coding regions between each gene. Whereas nearly 95% of the human genome does not code for proteins or RNAs or includes a gene promoter, nearly all of the prokaryote genome codes or controls something. Prokaryote genes are also expressed in groups, known as operons, instead of individually, as in eukaryotes. In a prokaryote cell, all genes in an operon(three in the case of the famous lac operon) are transcribed on the same piece of RNA and then made into separate proteins, whereas if these genes were native to eukaryotes, they each would have their own promoter and be transcribed on their own strand of mRNA. This lesser degree of control over gene expression contributes to the simplicity of the prokaryotes as compared to the eukaryotes. It is worth noting that one of the most convincing pieces of evidence for the endosymbiotic theory of the origin of mitochondria is that mitochondrial genomes look like prokaryotic genomes, replete with circular genomes, operons, and plasmids, while that of the host follows the eukaryotic model.

Reproduction is most often asexual, through binary fission, where the chromosome is duplicated and attaches to the cell membrane, and then the cell divides in two. However, they show a variety of parasexual processes where DNA is transferred between cells, such as transformation and transduction.


[edit] Colonies
While prokaryotes are nearly always unicellular, some are capable of forming groups of cells called colonies. Unlike many eukaryotic multicellular organisms, each member of the colony is undifferentiated and capable of free-living (but consider cyanobacteria, a very successful prokaryotic group which does exhibit definite cell differentiation). Individuals that make up such bacterial colonies most often still act independent of one another. Colonies are formed by organisms that remain attached following cell division, sometimes through the help of a secreted slimy layer.


[edit] Structure

The sizes of prokaryotes relative to other organisms and biomolecules.Recent research indicates that all prokaryotes actually do have cytoskeletons albeit more primitive than those of eukaryotes. Besides homologues of actin and tubulin (MreB and FtsZ) the helically arranged building block of flagellum, flagellin is one of the most significant cytoskeletal protein of bacteria as it provides structural backgrounds of chemotaxis, the basic cell physiological response of bacteria. At least some prokaryotes also contain intracellular structures which can be seen as primitive organelles. Membranous organelles (a. k .a. intracellular membranes) are known in some groups of prokaryotes, such as vacuoles or membrane systems devoted to special metabolic properties, e. g. photosynthesis or chemolithotrophy. Additionally, some species also contain protein-enclosed microcompartments mostly associated with special physiological properties (e. .g. carboxysomes or gas vacuoles).

Prokaryotic cell Structure
Flagellum
Cell membrane
Cell wall
Cytoplasm
Ribosome
Nucleoid
Glycocalyx
Inclusions


[edit] Morphology of Prokaryotic cells
Prokaroyotic cells have various shapes, the three basic shapes are.[1]

Cocci - spherical
Bacilli - rod shaped
Spiral - curve

[edit] Environment
Prokaryotes are found in nearly all environments on earth. Archaea in particular seem to thrive in harsh conditions, such as high temperatures, thermophiles, or salinity, halophiles. Organisms such as these are referred to as extremophiles. Many prokaryotes live in or on the bodies of other organisms, including humans.


[edit] Evolution of prokaryotes
It is generally accepted that the first living cells were some form of prokaryote and may have developed out of protobionts. Fossilized prokaryotes approximately 3.5 billion years old have been discovered (less than 1 billion years after the formation of the earth's crust), and prokaryotes are perhaps the most successful and abundant organism even today. Eukaryotes only formed later, from symbiosis of multiple prokaryote ancestors; their first evidence in the fossil record appears approximately 1.7 billion years ago, although genetic evidence suggests they could have formed as early as 3 billion years ago.[2]

While Earth is the only known place in the universe where life exist, some have suggested structures within a Martian meteorite should be interpreted as fossil prokaryotes; this is open to considerable debate and skepticism.

Prokaryotes diversified greatly throughout their long existence. The metabolism of prokaryotes is far more varied than that of eukaryotes, leading to many highly distinct types of prokaryotes. For example, in addition to using photosynthesis or organic compounds for energy like eukaryotes do, prokaryotes may obtain energy from inorganic chemicals such as hydrogen sulfide. This has enabled the bacteria to thrive and reproduce. Today, archaebacteria can be found in the cold of Antarctica and in the hot Yellowstone springs.