cells

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
prot...

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.

A diploid cell may also undergo meiosis to produce haploid cells, usually four.

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.

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.

It also prevents the cell from expanding and finally bursting (cytolysis) from osmotic pressure against a hypotonic environment.

Organelles:
(1) nucleolus
(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 centrosomeEukaryotic cells are about 15 times wider than a typical prokaryote and can be as much as 1000 times greater in volume.

Anatomy
There are two types of cells: eukaryotic and prokaryotic.

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.

These are structures (not present in all prokaryotes) made of proteins that facilitate movement and communication between cells;
Enclosing the cell is the cell envelope – generally consisting of a cell wall covering a plasma membrane though some bacteria also have a further covering layer called a capsule.

The cytosol is the gelatinous fluid that fills the cell and surrounds the organelles.

Organelles:
(1) nucleolus
(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 centrosomeEukaryotic cells are about 15 times wider than a typical prokaryote and can be as much as 1000 times greater in volume.

It also prevents the cell from expanding and finally bursting (cytolysis) from osmotic pressure against a hypotonic environment.

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
prot...

Anatomy
There are two types of cells: eukaryotic and prokaryotic.

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.

Organelles:
(1) nucleolus
(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 centrosomeEukaryotic cells are about 15 times wider than a typical prokaryote and can be as much as 1000 times greater in volume.

A diploid cell may also undergo meiosis to produce haploid cells, usually four.

Transfer RNA (tRNA) molecules are used to add amino acids during protein translation.

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.

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."

Organelles:
(1) nucleolus
(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 centrosomeEukaryotic cells are about 15 times wider than a typical prokaryote and can be as much as 1000 times greater in volume.

The eukaryotic DNA is organized in one or more linear molecules, called chromosomes, which are associated with histone proteins.

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
prot...

Protein synthesis
Main article: Protein biosynthesis
Cells are capable of synthesizing new proteins, which are essential for the modulation and maintenance of cellular activities.

Centrosomes are composed of two centrioles, which separate during cell division and help in the formation of the mitotic spindle.

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.

Transfer RNA (tRNA) molecules are used to add amino acids during protein translation.

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.

These are structures (not present in all prokaryotes) made of proteins that facilitate movement and communication between cells;
Enclosing the cell is the cell envelope – generally consisting of a cell wall covering a plasma membrane though some bacteria also have a further covering layer called a capsule.

Other organisms, such as humans, are multicellular.

A prokaryotic chromosome is usually a circular molecule (an exception is that of the bacterium Borrelia burgdorferi, which causes Lyme disease).

A prokaryotic chromosome is usually a circular molecule (an exception is that of the bacterium Borrelia burgdorferi, which causes Lyme disease).

The capsule is antigenic.

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.

Hence, the layer is called a phospholipid bilayer.

In 1835, before the final cell theory was developed, Jan Evangelista Purkyně observed small "granules" while looking at the plant tissue through a microscope.

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.

The cell theory, first developed in 1839 by Matthias Jakob Schleiden and Theodor Schwann, 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 necessary for regulating cell functions and for transmitting information to the next generation of cells.[5]

Once inside the cell, glucose is broken down to make adenosine triphosphate (ATP), a form of energy, through two different pathways.

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.

Cilia may thus be "viewed as sensory cellular antennae that coordinate a large number of cellular signaling pathways, sometimes coupling the signaling to ciliary motility or alternatively to cell division and differentiation."[7]

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
prot...

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.

During processing, DNA is transcribed, or copied into a special RNA, called messenger RNA (mRNA).

It also prevents the cell from expanding and finally bursting (cytolysis) from osmotic pressure against a hypotonic environment.

Some eukaryote cells (plant cells and fungi cells) also have a cell wall;
Inside the cell is the cytoplasmic region that contains the cell genome (DNA) and ribosomes and various sorts of inclusions.

Prokaryotes can carry extrachromosomal DNA elements called plasmids, which are usually circular.

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.

The largest cells are about 135 µm in the anterior horn in the spinal cord while granule cells in the cerebellum, the smallest, can be some 4 µm and the longest cell can reach from the toe to the lower brain stem (Pseudounipolar cells).[2]

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 nucleu...

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.

Some eukaryote cells (plant cells and fungi cells) also have a cell wall;
Inside the cell is the cytoplasmic region that contains the cell genome (DNA) and ribosomes and various sorts of inclusions.

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 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 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.

Newly synthesized proteins (black) are often further modified, such as by binding to an effector molecule (orange), to become fully active.Creation

Some eukaryotic organelles such as mitochondria also contain some DNA.
Many eukaryotic cells are ciliated with primary cilia.

An 'origin of sex as vaccination' theory suggests that the eukaryote genome accreted from prokaryan parasite genomes in numerous rounds of lateral gene transfer.

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.

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
prot...

Organelles:
(1) nucleolus
(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 centrosomeEukaryotic cells are about 15 times wider than a typical prokaryote and can be as much as 1000 times greater in volume.

Though most prokaryotes have a cell wall, there are exceptions such as Mycoplasma (bacteria) and Thermoplasma (archaea).

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.

Once inside the cell, glucose is broken down to make adenosine triphosphate (ATP), a form of energy, through two different pathways.

RNA is generally assumed to be the earliest self-replicating molecule, as it is capable of both storing genetic information and catalyzing chemical reactions (see RNA world hypothesis).

Genetic material
Two different kinds of genetic material exist: deoxyribonucleic acid (DNA) and ribonucleic acid (RNA).

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.

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.

Each reaction is designed to produce some hydrogen ions that can then be used to make energy packets (ATP).

Drawing of the structure of cork as it appeared under the microscope to Robert Hooke from Micrographia which is the origin of the word "cell" being used to describe the smallest unit of a living organism
Cells in culture, stained for keratin (red) and DNA (green)The cell is the functional basic unit of life.

Transfer RNA (tRNA) molecules are used to add amino acids during protein translation.

At the same time fibroblasts (connective tissue cells) move there to remodel damaged structures.

But some other entity with the potential to self-replicate could have preceded RNA, like clay or peptide nucleic acid.[13]

Fimbriae (pili)
They are short and thin hair like filaments, formed of protein called pilin (antigenic).

Transfer RNA (tRNA) molecules are used to add amino acids during protein translation.

Cilia may thus be "viewed as sensory cellular antennae that coordinate a large number of cellular signaling pathways, sometimes coupling the signaling to ciliary motility or alternatively to cell division and differentiation."[7]

Cell surface membranes also contain receptor proteins that allow cells to detect external signaling molecules such as hormones.

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.

Genetic material
Two different kinds of genetic material exist: deoxyribonucleic acid (DNA) and ribonucleic acid (RNA).

The largest cells are about 135 µm in the anterior horn in the spinal cord while granule cells in the cerebellum, the smallest, can be some 4 µm and the longest cell can reach from the toe to the lower brain stem (Pseudounipolar cells).[2]

All chromosomal DNA is stored in the cell nucleus, separated from the cytoplasm by a membrane.

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.

Main article: Cell division
Cell division involves a single cell (called a mother cell) dividing into two daughter cells.

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.

Most organisms use DNA for their long-term information storage, but some viruses (e.g., retroviruses) have RNA as their genetic material.

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.

Cilia may thus be "viewed as sensory cellular antennae that coordinate a large number of cellular signaling pathways, sometimes coupling the signaling to ciliary motility or alternatively to cell division and differentiation."[7]

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.

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
prot...

Movement or motility
Cells can move during many processes: such as wound healing, the immune response and cancer metastasis.

But some other entity with the potential to self-replicate could have preceded RNA, like clay or peptide nucleic acid.[13]

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 nucleu...

A prokaryotic chromosome is usually a circular molecule (an exception is that of the bacterium Borrelia burgdorferi, which causes Lyme disease).

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.

Movement or motility
Cells can move during many processes: such as wound healing, the immune response and cancer metastasis.

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.

The cell theory, first developed in 1839 by Matthias Jakob Schleiden and Theodor Schwann, 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 necessary for regulating cell functions and for transmitting information to the next generation of cells.[5]

The largest known cells are unfertilised ostrich egg cells which weigh 3.3 pounds.[3][4]

Some cells, most notably Amoeba, have contractile vacuoles, which can pump water out of the cell if there is too much water.

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.[14]

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.

Cytoskeleton
Main article: Cytoskeleton

Bovine Pulmonary Artery Endothelial cell: nuclei stained blue, mitochondria stained red, and F-actin, an important component in microfilaments, stained green.

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.

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.

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.

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.

RNA is generally assumed to be the earliest self-replicating molecule, as it is capable of both storing genetic information and catalyzing chemical reactions (see RNA world hypothesis).

The major difference between prokaryotes and eukaryotes is that eukaryotic cells contain membrane-bound compartments in which specific metabolic activities take place.

Smooth ER plays a role in calcium sequestration and release.

The early cell membranes were probably more simple and permeable than modern ones, with only a single fatty acid chain per lipid.

At the same time fibroblasts (connective tissue cells) move there to remodel damaged structures.

Other organisms, such as humans, are multicellular.

Peroxisomes have enzymes that rid the cell of toxic peroxides.

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.

This leads to growth in multicellular organisms (the growth of tissue) and to procreation (vegetative reproduction) in unicellular organisms.

At the same time fibroblasts (connective tissue cells) move there to remodel damaged structures.

Cilia may thus be "viewed as sensory cellular antennae that coordinate a large number of cellular signaling pathways, sometimes coupling the signaling to ciliary motility or alternatively to cell division and differentiation."[7]

Complex sugars consumed by the organism can be broken down into a less chemically complex sugar molecule called glucose.

It also plays a role in attachment of the organism to mucous membranes.[citation needed]

Flagella
Flagella are the organelles of cellular mobility.

The largest cells are about 135 µm in the anterior horn in the spinal cord while granule cells in the cerebellum, the smallest, can be some 4 µm and the longest cell can reach from the toe to the lower brain stem (Pseudounipolar cells).[2]

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.

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.

It also plays a role in attachment of the organism to mucous membranes.[citation needed]

Flagella
Flagella are the organelles of cellular mobility.

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 nucleu...

Smooth ER plays a role in calcium sequestration and release.

The early cell membranes were probably more simple and permeable than modern ones, with only a single fatty acid chain per lipid.

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.

The largest cells are about 135 µm in the anterior horn in the spinal cord while granule cells in the cerebellum, the smallest, can be some 4 µm and the longest cell can reach from the toe to the lower brain stem (Pseudounipolar cells).[2]

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.

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

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.

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.

Movement or motility
Cells can move during many processes: such as wound healing, the immune response and cancer metastasis.