The cell is the functional basic unit of life. It was discovered by Robert Hooke Robert Hooke FRS was an English natural philosopher, architect and polymath who played an important role in the scientific revolution, through both experimental and theoretical work and is the functional unit of all known living organisms In biology, an organism is any contiguous living system . In at least some form, all organisms are capable of response to stimuli, reproduction, growth and development, and maintenance of homoeostasis as a stable whole. An organism may either be unicellular (single-celled) or be composed of, as in humans, many trillions of cells grouped into. It is the smallest unit of life that is classified as a living thing, and is often called the building block of life.[1] Some organisms, such as most bacteria The bacteria ( [bækˈtɪəriə] ; singular: bacterium)[α] are a large group of single-celled, prokaryote microorganisms. Typically a few micrometres in length, bacteria have a wide range of shapes, ranging from spheres to rods and spirals. Bacteria are ubiquitous in every habitat on Earth, growing in soil, acidic hot springs, radioactive waste,, are unicellular A microorganism or microbe is an organism that is microscopic (too small to be seen by the naked human eye). The study of microorganisms is called microbiology, a subject that began with Anton van Leeuwenhoek's discovery of microorganisms in 1675, using a microscope of his own design (consist of a single cell). Other organisms, such as humans Humans are a species of animal known taxonomically as Homo sapiens , and are the only extant member of the Homo genus of bipedal primates in Hominidae, the great ape family. However, in some cases "human" is used to refer to any member of the genus Homo, are multicellular Multicellular organisms are organisms that consist of more than one cell. Each cell is specialized to do a certain job for that organism. Most life that can be seen with the naked eye is multicellular, as are all members of the kingdoms Plantae and Animalia. (Humans have about 100 trillion or 1014 cells; a typical cell size is 10 µm A micrometre is one millionth of a metre, or equivalently one thousandth of a millimetre or one thousand nanometres. It can also be written in scientific notation as 1×10−6 m, meaning 1⁄1000000 m; a typical cell mass is 1 nanogram The kilogram is the base unit of mass in the International System of Units (SI, from the French Le Système International d’Unités),[Note 2] which is the modern standard governing the metric system. The kilogram is defined as being equal to the mass of the International Prototype Kilogram (IPK),[Note 3] which is almost exactly equal to the mass.) The largest known cells are unfertilised ostrich The ostrich, Struthio camelus, is a large flightless bird native to Africa. It is the only living species of its family, Struthionidae and its genus, Struthio. Ostriches share the order Struthioniformes with the kiwis, emus, and other ratites. It is distinctive in its appearance, with a long neck and legs and the ability to run at maximum speeds egg cells An ovum is a haploid female reproductive cell or gamete. Both animals and embryophytes have ova. The term ovule is used for the young ovum of an animal, as well as the plant structure that carries the female gametophyte and egg cell and develops into a seed after fertilization. In lower plants and algae, the ovum is also often called oosphere which weigh 3.3 pounds.[2][3]

In 1835, before the final cell theory was developed, Jan Evangelista Purkyně Jan Evangelista Purkyně (Czech pronunciation: [ˈjan ˈɛvaŋɡɛlɪsta ˈpurkɪɲɛ] ; also written Johannes Evangelists Purkinje) (17 December 1787 - 28 July 1869) was a Czech anatomist and physiologist observed small "granules" while looking at the plant tissue through a microscope. The cell theory Cell theory refers to the idea that cells are the basic unit of structure in every living thing. Development of this theory during the mid 1600s was made possible by advances in microscopy. This theory is one of the foundations of biology. The theory says that new cells are formed from other existing cells, and that the cell is a fundamental unit, first developed in 1839 by Matthias Jakob Schleiden Matthias Jakob Schleiden was a German botanist and co-founder of the cell theory, along with Theodor Schwann and Rudolf Virchow and Theodor Schwann Theodor Schwann was a German physiologist. His many contributions to biology include the development of cell theory, the discovery of Schwann cells in the peripheral nervous system, the discovery and study of pepsin, the discovery of the organic nature of yeast, and the invention of the term metabolism, states that all organisms are composed of one or more cells, that all cells come from preexisting cells, that vital functions of an organism occur within cells, and that all cells contain the hereditary information Genetics , a discipline of biology, is the science of heredity and variation in living organisms. The fact that living things inherit traits from their parents has been used since prehistoric times to improve crop plants and animals through selective breeding. However, the modern science of genetics, which seeks to understand the process of necessary for regulating cell functions and for transmitting information to the next generation of cells.[4]

The word cell comes from the Latin Latin or sometimes Roman is an Italic language originally spoken in Latium and Ancient Rome. Although often considered a dead language, in view of the fact that it has no native, fluent speakers, Latin continues to be taught in schools and has been, and currently is, used in the process of new word production in modern languages from many cellula, meaning, a small room. The descriptive term for the smallest living biological structure was coined by Robert Hooke Robert Hooke FRS was an English natural philosopher, architect and polymath who played an important role in the scientific revolution, through both experimental and theoretical work in a book he published in 1665 when he compared the cork Cork material is an impermeable, buoyant material, a prime-subset of generic cork tissue that is harvested for commercial use primarily from Quercus suber that is endemic to southwest Europe and northwest Africa. Cork is composed of suberin, a hydrophobic substance, and because of its impermeability, buoyancy, elasticity, and fire resistance, it cells he saw through his microscope to the small rooms monks lived in.[5]

Contents

Anatomy of cells

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

Prokaryotic cells

Main article: Prokaryote The prokaryotes are a group of organisms that lack a cell nucleus (= karyon), or any other membrane-bound organelles. They differ from the eukaryotes, which have a cell nucleus. Most are unicellular, but a few prokaryotes such as myxobacteria have multicellular stages in their life cycles. The word prokaryote comes from the Greek πρό- (pro-) & Diagram of a typical prokaryotic The prokaryotes are a group of organisms that lack a cell nucleus (= karyon), or any other membrane-bound organelles. They differ from the eukaryotes, which have a cell nucleus. Most are unicellular, but a few prokaryotes such as myxobacteria have multicellular stages in their life cycles. The word prokaryote comes from the Greek πρό- (pro-) & cell

The prokaryote The prokaryotes are a group of organisms that lack a cell nucleus (= karyon), or any other membrane-bound organelles. They differ from the eukaryotes, which have a cell nucleus. Most are unicellular, but a few prokaryotes such as myxobacteria have multicellular stages in their life cycles. The word prokaryote comes from the Greek πρό- (pro-) & cell is simpler, and therefore smaller, than a eukaryote cell, lacking a nucleus In cell biology, the nucleus , also sometimes referred to as the "control center", is a membrane-enclosed organelle found in eukaryotic cells. It contains most of the cell's genetic material, organized as multiple long linear DNA molecules in complex with a large variety of proteins, such as histones, to form chromosomes. The genes and most of the other organelles In cell biology, an organelle is a specialized subunit within a cell that has a specific function, and is usually separately enclosed within its own lipid bilayer of eukaryotes. There are two kinds of prokaryotes: bacteria The bacteria ( [bækˈtɪəriə] ; singular: bacterium)[α] are a large group of single-celled, prokaryote microorganisms. Typically a few micrometres in length, bacteria have a wide range of shapes, ranging from spheres to rods and spirals. Bacteria are ubiquitous in every habitat on Earth, growing in soil, acidic hot springs, radioactive waste, and archaea The Archaea (/ɑrˈkiːə/ ar-KEE-ə) are a group of single-celled microorganisms. A single individual or species from this domain is called an archaeon (sometimes spelled "archeon"). They have no cell nucleus or any other organelles within their cells. In the past they were viewed as an unusual group of bacteria and named archaebacteria; these share a similar structure.

A prokaryotic cell has three architectural regions:

Eukaryotic cells

Main article: Eukaryote A eukaryote is an organism whose cells contain complex structures enclosed within membranes. The defining membrane-bound structure that sets eukaryotic cells apart from prokaryotic cells is the nucleus, or nuclear envelope, within which the genetic material is carried. The presence of a nucleus gives eukaryotes their name, which comes from the Diagram of a typical animal Animals are a major group of mostly multicellular, eukaryotic organisms of the kingdom Animalia or Metazoa. Their body plan eventually becomes fixed as they develop, although some undergo a process of metamorphosis later on in their life. Most animals are motile, meaning they can move spontaneously and independently. All animals are also (eukaryotic A eukaryote is an organism whose cells contain complex structures enclosed within membranes. The defining membrane-bound structure that sets eukaryotic cells apart from prokaryotic cells is the nucleus, or nuclear envelope, within which the genetic material is carried. The presence of a nucleus gives eukaryotes their name, which comes from the) cell, showing subcellular components. Organelles In cell biology, an organelle is a specialized subunit within a cell that has a specific function, and is usually separately enclosed within its own lipid bilayer: (1) nucleolus The nucleolus is a non-membrane bound structure composed of proteins and nucleic acids found within the nucleus. Ribosomal RNA (rRNA) is transcribed and assembled within the nucleolus. The nucleolus ultrastructure can be visualized through an electron microscope, while the organization and dynamics can be studied through fluorescent protein (2) nucleus (3) ribosome (4) vesicle (5) rough endoplasmic reticulum (ER) (6) Golgi apparatus (7) Cytoskeleton (8) smooth endoplasmic reticulum (9) mitochondria (10) vacuole (11) cytoplasm (12) lysosome (13) centrioles within centrosome

Eukaryotic cells are about 15 times wider than 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 a cell nucleus, a membrane-delineated compartment that houses the eukaryotic cell's DNA. This nucleus gives the eukaryote its name, which means "true nucleus." Other differences include:

Table 1: Comparison of features of prokaryotic and eukaryotic cells
Prokaryotes Eukaryotes
Typical organisms bacteria, archaea protists, fungi, plants, animals
Typical size ~ 1–10 µm ~ 10–100 µm (sperm cells, apart from the tail, are smaller)
Type of nucleus nucleoid region; no real nucleus real nucleus with double membrane
DNA circular (usually) linear molecules (chromosomes) with histone proteins
RNA-/protein-synthesis coupled in cytoplasm RNA-synthesis inside the nucleus protein synthesis in cytoplasm
Ribosomes 50S+30S 60S+40S
Cytoplasmatic structure very few structures highly structured by endomembranes and a cytoskeleton
Cell movement flagella made of flagellin flagella and cilia containing microtubules; lamellipodia and filopodia containing actin
Mitochondria none one to several thousand (though some lack mitochondria)
Chloroplasts none in algae and plants
Organization usually single cells single cells, colonies, higher multicellular organisms with specialized cells
Cell division Binary fission (simple division) Mitosis (fission or budding) Meiosis
Table 2: Comparison of structures between animal and plant cells
Typical animal cell Typical plant cell
Organelles

Subcellular components

The cells of eukaryotes (left) and prokaryotes (right)

All cells, whether prokaryotic or eukaryotic, have a membrane that envelops the cell, separates its interior from its environment, regulates what moves in and out (selectively permeable), and maintains the electric potential of the cell. Inside the membrane, a salty cytoplasm takes up most of the cell volume. All cells possess DNA, the hereditary material of genes, and RNA, containing the information necessary to build various proteins such as enzymes, the cell's primary machinery. There are also other kinds of biomolecules in cells. This article will list these primary components of the cell, then briefly describe their function.

Cell membrane: A cell's defining boundary

Main article: Cell membrane

The cytoplasm of a cell is surrounded by a cell membrane or plasma membrane. The plasma membrane in plants and prokaryotes is usually covered by a cell wall. This membrane serves to separate and protect a cell from its surrounding environment and is made mostly from a double layer of lipids (hydrophobic fat-like molecules) and hydrophilic phosphorus molecules. Hence, the layer is called a phospholipid bilayer. It may also be called a fluid mosaic membrane. Embedded within this membrane is a variety of protein molecules that act as channels and pumps that move different molecules into and out of the cell. The membrane is said to be 'semi-permeable', in that it can either let a substance (molecule or ion) pass through freely, pass through to a limited extent or not pass through at all. Cell surface membranes also contain receptor proteins that allow cells to detect external signaling molecules such as hormones.

Cytoskeleton: A cell's scaffold

Main article: Cytoskeleton Bovine Pulmonary Artery Endothelial cell: nuclei stained blue, mitochondria stained red, and F-actin, an important component in microfilaments, stained green. Cell imaged on a fluorescent microscope.

The cytoskeleton acts to organize and maintain the cell's shape; anchors organelles in place; helps during endocytosis, the uptake of external materials by a cell, and cytokinesis, the separation of daughter cells after cell division; and moves parts of the cell in processes of growth and mobility. The eukaryotic cytoskeleton is composed of microfilaments, intermediate filaments and microtubules. There is a great number of proteins associated with them, each controlling a cell's structure by directing, bundling, and aligning filaments. The prokaryotic cytoskeleton is less well-studied but is involved in the maintenance of cell shape, polarity and cytokinesis.[7]

Genetic material

Two different kinds of genetic material exist: deoxyribonucleic acid (DNA) and ribonucleic acid (RNA). Most organisms use DNA for their long-term information storage, but some viruses (e.g., retroviruses) have RNA as their genetic material. The biological information contained in an organism is encoded in its DNA or RNA sequence. RNA is also used for information transport (e.g., mRNA) and enzymatic functions (e.g., ribosomal RNA) in organisms that use DNA for the genetic code itself. Transfer RNA (tRNA) molecules are used to add amino acids during protein translation.

Prokaryotic genetic material is organized in a simple circular DNA molecule (the bacterial chromosome) in the nucleoid region of the cytoplasm. Eukaryotic genetic material is divided into different, linear molecules called chromosomes inside a discrete nucleus, usually with additional genetic material in some organelles like mitochondria and chloroplasts (see endosymbiotic theory).

A human cell has genetic material contained in the cell nucleus (the nuclear genome) and in the mitochondria (the mitochondrial genome). In humans the nuclear genome is divided into 23 pairs of linear DNA molecules called chromosomes. The mitochondrial genome is a circular DNA molecule distinct from the nuclear DNA. Although the mitochondrial DNA is very small compared to nuclear chromosomes, it codes for 13 proteins involved in mitochondrial energy production and specific tRNAs.

Foreign genetic material (most commonly DNA) can also be artificially introduced into the cell by a process called transfection. This can be transient, if the DNA is not inserted into the cell's genome, or stable, if it is. Certain viruses also insert their genetic material into the genome.

Organelles

Main article: Organelle

The human body contains many different organs, such as the heart, lung, and kidney, with each organ performing a different function. Cells also have a set of "little organs," called organelles, that are adapted and/or specialized for carrying out one or more vital functions.

There are several types of organelles within an animal cell. Some (such as the nucleus and golgi apparatus) are typically solitary, while others (such as mitochondria, peroxisomes and lysosomes) can be numerous (hundreds to thousands). The cytosol is the gelatinous fluid that fills the cell and surrounds the organelles.

Mitochondria and Chloroplasts – the power generators
Mitochondria are self-replicating organelles that occur in various numbers, shapes, and sizes in the cytoplasm of all eukaryotic cells. Mitochondria play a critical role in generating energy in the eukaryotic cell. Mitochondria generate the cell's energy by oxidative phosphorylation, using oxygen to release energy stored in cellular nutrients (typically pertaining to glucose) to generate ATP. Mitochondria multiply by splitting in two. Respiration occurs in the cell mitochondria.
Organelles that are modified chloroplasts are broadly called plastids, and are involved in energy storage through photosynthesis, which uses solar energy to generate carbohydrates and oxygen from carbon dioxide and water.[citation needed]
Mitochondria and chloroplasts each contain their own genome, which is separate and distinct from the nuclear genome of a cell. Both organelles contain this DNA in circular plasmids, much like prokaryotic cells, strongly supporting the evolutionary theory of endosymbiosis; since these organelles contain their own genomes and have other similarities to prokaryotes, they are thought to have developed through a symbiotic relationship after being engulfed by a primitive cell.[citation needed]
Ribosomes
The ribosome is a large complex of RNA and protein molecules. They each consist of two subunits, and act as an assembly line where RNA from the nucleus is used to synthesise proteins from amino acids. Ribosomes can be found either floating freely or bound to a membrane (the rough endoplasmatic reticulum in eukaryotes, or the cell membrane in prokaryotes).[8]
Cell nucleus – a cell's information center
The cell nucleus is the most conspicuous organelle found in a eukaryotic cell. It houses the cell's chromosomes, and is the place where almost all DNA replication and RNA synthesis (transcription) occur. The nucleus is spherical and separated from the cytoplasm by a double membrane called the nuclear envelope. The nuclear envelope isolates and protects a cell's DNA from various molecules that could accidentally damage its structure or interfere with its processing. During processing, DNA is transcribed, or copied into a special RNA, called mRNA. This mRNA is then transported out of the nucleus, where it is translated into a specific protein molecule. The nucleolus is a specialized region within the nucleus where ribosome subunits are assembled. In prokaryotes, DNA processing takes place in the cytoplasm.
 Diagram of a cell nucleus
Endoplasmic reticulum – eukaryotes only
The endoplasmic reticulum (ER) is the transport network for molecules targeted for certain modifications and specific destinations, as compared to molecules that will float freely in the cytoplasm. The ER has two forms: the rough ER, which has ribosomes on its surface and secretes proteins into the cytoplasm, and the smooth ER, which lacks them. Smooth ER plays a role in calcium sequestration and release.
Golgi apparatus – eukaryotes only
The primary function of the Golgi apparatus is to process and package the macromolecules such as proteins and lipids that are synthesized by the cell. It is particularly important in the processing of proteins for secretion. The Golgi apparatus forms a part of the endomembrane system of eukaryotic cells. Vesicles that enter the Golgi apparatus are processed in a cis to trans direction, meaning they coalesce on the cis side of the apparatus and after processing pinch off on the opposite (trans) side to form a new vesicle in the animal cell.[citation needed]
 Diagram of an endomembrane system
Lysosomes and Peroxisomes – eukaryotes only
Lysosomes contain digestive enzymes (acid hydrolases). They digest excess or worn-out organelles, food particles, and engulfed viruses or bacteria. Peroxisomes have enzymes that rid the cell of toxic peroxides. The cell could not house these destructive enzymes if they were not contained in a membrane-bound system. These organelles are often called a "suicide bag" because of their ability to detonate and destroy the cell.[citation needed]
Centrosome – the cytoskeleton organiser
The centrosome produces the microtubules of a cell – a key component of the cytoskeleton. It directs the transport through the ER and the Golgi apparatus. Centrosomes are composed of two centrioles, which separate during cell division and help in the formation of the mitotic spindle. A single centrosome is present in the animal cells. They are also found in some fungi and algae cells.[citation needed]
Vacuoles
Vacuoles store food and waste. Some vacuoles store extra water. They are often described as liquid filled space and are surrounded by a membrane. Some cells, most notably Amoeba, have contractile vacuoles, which can pump water out of the cell if there is too much water. The vacuoles of eukaryotic cells are usually larger in those of plants than animals.

Structures outside the cell wall

Capsule

A gelatinous capsule is present in some bacteria outside the cell wall. The capsule may be polysaccharide as in pneumococci, meningococci or polypeptide as Bacillus anthracis or hyaluronic acid as in streptococci.[citation needed] Capsules are not marked by ordinary stain and can be detected by special stain. The capsule is antigenic. The capsule has antiphagocytic function so it determines the virulence of many bacteria. It also plays a role in attachment of the organism to mucous membranes.[citation needed]

Flagella

Flagella are the organelles of cellular mobility. They arise from cytoplasm and extrude through the cell wall. They are long and thick thread-like appendages, protein in nature. Are most commonly found in bacteria cells but are found in animal cells as well.

Fimbriae (pili)

They are short and thin hair like filaments, formed of protein called pilin (antigenic). Fimbriae are responsible for attachment of bacteria to specific receptors of human cell (adherence). There are special types of pili called (sex pili) involved in conjunction.[citation needed]

Cell functions

Cell growth and metabolism

Main articles: Cell growth and Metabolism

Between successive cell divisions, cells grow through the functioning of cellular metabolism. Cell metabolism is the process by which individual cells process nutrient molecules. Metabolism has two distinct divisions: catabolism, in which the cell breaks down complex molecules to produce energy and reducing power, and anabolism, in which the cell uses energy and reducing power to construct complex molecules and perform other biological functions. Complex sugars consumed by the organism can be broken down into a less chemically complex sugar molecule called glucose. Once inside the cell, glucose is broken down to make adenosine triphosphate (ATP), a form of energy, through two different pathways.

The first pathway, glycolysis, requires no oxygen and is referred to as anaerobic metabolism. Each reaction is designed to produce some hydrogen ions that can then be used to make energy packets (ATP). In prokaryotes, glycolysis is the only method used for converting energy.

The second pathway, called the Krebs cycle, or citric acid cycle, occurs inside the mitochondria and can generate enough ATP to run all the cell functions.

An overview of protein synthesis. Within the nucleus of the cell (light blue), genes (DNA, dark blue) are transcribed into RNA. This RNA is then subject to post-transcriptional modification and control, resulting in a mature mRNA (red) that is then transported out of the nucleus and into the cytoplasm (peach), where it undergoes translation into a protein. mRNA is translated by ribosomes (purple) that match the three-base codons of the mRNA to the three-base anti-codons of the appropriate tRNA. Newly synthesized proteins (black) are often further modified, such as by binding to an effector molecule (orange), to become fully active.

Creation of new cells

Main article: Cell division

Cell division involves a single cell (called a mother cell) dividing into two daughter cells. This leads to growth in multicellular organisms (the growth of tissue) and to procreation (vegetative reproduction) in unicellular organisms.

Prokaryotic cells divide by binary fission. Eukaryotic cells usually undergo a process of nuclear division, called mitosis, followed by division of the cell, called cytokinesis. A diploid cell may also undergo meiosis to produce haploid cells, usually four. Haploid cells serve as gametes in multicellular organisms, fusing to form new diploid cells.

DNA replication, or the process of duplicating a cell's genome, is required every time a cell divides. Replication, like all cellular activities, requires specialized proteins for carrying out the job.

Protein synthesis

Main article: Protein biosynthesis

Cells are capable of synthesizing new proteins, which are essential for the modulation and maintenance of cellular activities. This process involves the formation of new protein molecules from amino acid building blocks based on information encoded in DNA/RNA. Protein synthesis generally consists of two major steps: transcription and translation.

Transcription is the process where genetic information in DNA is used to produce a complementary RNA strand. This RNA strand is then processed to give messenger RNA (mRNA), which is free to migrate through the cell. mRNA molecules bind to protein-RNA complexes called ribosomes located in the cytosol, where they are translated into polypeptide sequences. The ribosome mediates the formation of a polypeptide sequence based on the mRNA sequence. The mRNA sequence directly relates to the polypeptide sequence by binding to transfer RNA (tRNA) adapter molecules in binding pockets within the ribosome. The new polypeptide then folds into a functional three-dimensional protein molecule.

Cell movement or motility

Cells can move during many processes: such as wound healing, the immune response and cancer metastasis. For wound healing to occur, white blood cells and cells that ingest bacteria move to the wound site to kill the microorganisms that cause infection. At the same time fibroblasts (connective tissue cells) move there to remodel damaged structures. In the case of tumor development, cells from a primary tumor move away and spread to other parts of the body. Cell motility involves many receptors, crosslinking, bundling, binding, adhesion, motor and other proteins.[9] The process is divided into three steps – protrusion of the leading edge of the cell, adhesion of the leading edge and de-adhesion at the cell body and rear, and cytoskeletal contraction to pull the cell forward. Each step is driven by physical forces generated by unique segments of the cytoskeleton.[10][11]

Evolution

Main article: Evolutionary history of life

The origin of cells has to do with the origin of life, which began the history of life on Earth.

Origin of the first cell

Further information: Abiogenesis

There are several theories about the origin of small molecules that could lead to life in an early Earth. One is that they came from meteorites (see Murchison meteorite). Another is that they were created at deep-sea vents. A third is that they were synthesized by lightning in a reducing atmosphere (see Miller–Urey experiment); althougyze chemical reactions (see RNA world hypothesis). But some other entity with the potential to self-replicate could have preceded RNA, like clay or peptide nucleic acid.[12]

Cells emerged at least 4.0–4.3 billion years ago. The current belief is that these cells were heterotrophs. An important characteristic of cells is the cell membrane, composed of a bilayer of lipids. The early cell membranes were probably more simple and permeable than modern ones, with only a single fatty acid chain per lipid. Lipids are known to spontaneously form bilayered vesicles in water, and could have preceded RNA. But the first cell membranes could also have been produced by catalytic RNA, or even have required structural proteins before they could form.[13]

Origin of eukaryotic cells

The eukaryotic cell seems to have evolved from a symbiotic community of prokaryotic cells. DNA-bearing organelles like the mitochondria and the chloroplasts are almost certainly what remains of ancient symbiotic oxygen-breathing proteobacteria and cyanobacteria, respectively, where the rest of the cell seems to be derived from an ancestral archaean prokaryote cell – a theory termed the endosymbiotic theory.

There is still considerable debate about whether organelles like the hydrogenosome predated the origin of mitochondria, or viceversa: see the hydrogen hypothesis for the origin of eukaryotic cells.

Sex, as the stereotyped choreography of meiosis and syngamy that persists in nearly all extant eukaryotes, may have played a role in the transition from prokaryotes to eukaryotes. An 'origin of sex as vaccination' theory suggests that the eukaryote genome accreted from prokaryan parasite genomes in numerous rounds of lateral gene transfer. Sex-as-syngamy (fusion sex) arose when infected hosts began swapping nuclearized genomes containing co-evolved, vertically transmitted symbionts that conveyed protection against horizontal infection by more virulent symbionts.[14]

History

See also

Wikimedia Commons has media related to: Cell biology
Main article: Topic outline of cell biology

References

  1. ^ Cell Movements and the Shaping of the Vertebrate Body in Chapter 21 of Molecular Biology of the Cell fourth edition, edited by Bruce Alberts (2002) published by Garland Science. The Alberts text discusses how the "cellular building blocks" move to shape developing embryos. It is also common to describe small molecules such as amino acids as "molecular building blocks".
  2. ^ Campbell, Neil A.; Brad Williamson; Robin J. Heyden (2006). Biology: Exploring Life. Boston, Massachusetts: Pearson Prentice Hall. ISBN 0-13-250882-6. http://www.phschool.com/el_marketing.html.
  3. ^ Mitzi Perdue. "Facts about Birds and Eggs". http://www.eggscape.com/birds.htm. Retrieved 2010-04-15.
  4. ^ Maton, Anthea; Hopkins, Jean Johnson, Susan LaHart, David Quon Warner, Maryanna Wright, Jill D (1997). Cells Building Blocks of Life. New Jersey: Prentice Hall. ISBN 0-13-423476-6.
  5. ^ a b "... I could exceedingly plainly perceive it to be all perforated and porous, much like a Honey-comb, but that the pores of it were not regular [..] these pores, or cells, [..] were indeed the first microscopical pores I ever saw, and perhaps, that were ever seen, for I had not met with any Writer or Person, that had made any mention of them before this. . ." – Hooke describing his observations on a thin slice of cork. Robert Hooke
  6. ^ Satir, P; Christensen, ST; Søren T. Christensen (2008-03-26). "Structure and function of mammalian cilia". Histochemistry and Cell Biology (Springer Berlin / Heidelberg) 129 (6): 687–693. doi:10.1007/s00418-008-0416-9. 1432-119X. PMID 18365235. http://www.springerlink.com/content/x5051hq648t3152q/. Retrieved 2009-09-12.
  7. ^ Michie K, Löwe J (2006). "Dynamic filaments of the bacterial cytoskeleton". Annu Rev Biochem 75: 467–92. doi:10.1146/annurev.biochem.75.103004.142452. PMID 16756499.
  8. ^ Ménétret JF, Schaletzky J, Clemons WM, et al. (December 2007). "Ribosome binding of a single copy of the SecY complex: implications for protein translocation". Mol. Cell 28 (6): 1083–92. doi:10.1016/j.molcel.2007.10.034. PMID 18158904.
  9. ^ Revathi Ananthakrishnan1 *, Allen Ehrlicher2 ✉. "The Forces Behind Cell Movement". Biolsci.org. http://www.biolsci.org/v03p0303.htm. Retrieved 2009-04-17.
  10. ^ Alberts B, Johnson A, Lewis J. et al. Molecular Biology of the Cell, 4e. Garland Science. 2002
  11. ^ Ananthakrishnan R, Ehrlicher A. The Forces Behind Cell Movement. Int J Biol Sci 2007; 3:303–317. http://www.biolsci.org/v03p0303.htm
  12. ^ Orgel LE (1998). "The or--a review of facts and speculations". Trends Biochem Sci 23 (12): 491–5. doi:10.1016/S0968-0004(98)01300-0. PMID 9868373.
  13. ^ Griffiths G (December 2007). "Cell evolution and the problem of membrane topology". Nature reviews. Molecular cell biology 8 (12): 1018–24. doi:10.1038/nrm2287. PMID 17971839.
  14. ^ Sterrer W (2002). "On the origin of sex as vaccination". Journal of Theoretical Biology 216: 387–396. doi:10.1006/jtbi.2002.3008. PMID 12151256.

External links

Textbooks

Structures of the cell
Endomembrane system

Cell membrane - Nucleus (and Nucleolus) - Endoplasmic reticulum - Golgi apparatus - Peroxisome - Parenthesome

Vesicles (Exosome - Lysosome - Endosome - Phagosome - Vacuole)

Cytoplasmic granules (Melanosome - Microbody - Glyoxysome - Weibel-Palade body)
Endosymbionts Mitochondrion - Plastids (Chloroplast - Chromoplast - Leucoplast)
Cytoskeleton Microfilaments - Intermediate filaments - Microtubules - Prokaryotic cytoskeleton
External Cell wall - Undulipodium (Cilium/Flagellum) - Acrosome
Other Cytoplasm - Ribosome - MTOCs (Centrosome/Centriole - Basal body - Spindle pole body) - Vault - Proteasome
Hierarchy of life
Biosphere > Ecosystem > Community (Biocoenosis) > Population > Organism > Organ system > Organ > Tissue > Cell > Organelle > Molecule (Macromolecule · Biomolecule) > Atom

Categories: Cell biology

 

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2008 Arizona Science Olympiad

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'Cell (Biology)' Blogs
Postdoc position in Molecular Biology 2010 DHHS NIMH NIH USA ...
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Postdoc position in Molecular Biology 2010 DHHS NIMH NIH USA ...

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Mon, 12 Jul 2010 17:13:34 GM

Postdoc position in Molecular Biology 2010 @ NIH, USA graduate degree (or foreign equivalent) in neuroscience, developmental biology or . cell biology. .

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'Cell (Biology)' Answers
Is Cell Biology a hard class?
Q. Did you think it was a hard class? How did you do in it? And did you find microbiology more or less difficult? I'm studying biology and starting my cell biology class next week.
Asked by Julianna - Tue Sep 22 23:26:17 2009 - - 2 Answers - 0 Comments

A. This is going to depend on your professor more than anything. At least at my school, celll is considered one of the hardest bio classes. Much harder than micro, but we also have a relatively easy micro professor so maybe that isn't the best comparison. My advice is to go into the class expecting it to be very difficult. If it ends up being easy, you get a nice suprise.
Answered by GrizzlyMint - Tue Sep 22 23:32:51 2009

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