Cell biology

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Cell biology is a branch of biology that studies the structure and function of the cell, also known as the basic unit of life. [1] Cell biology encompasses both prokaryotic and eukaryotic cells and can be divided into many sub-topics which may include the study of cell metabolism, cell communication, cell cycle , and cell composition. The study of cells is performed using several techniques such as cell culture, various types of microscopy, and cell fractionation. These have allowed for and are currently being used for discoveries and research pertaining to how cells function, ultimately giving insight into understanding larger organisms. Knowing the components of cells and how cells work is fundamental to all biological sciences while also being essential for research in biomedical fields such as cancer, and other diseases. Research in cell biology is interconnected to other fields such as genetics, molecular genetics, biochemistry, molecular biology, medical microbiology, immunology, and cytochemistry.



Cells were first seen in 17th century Europe with the invention of the compound microscope. In 1665, Robert Hooke termed the building block of all living organisms as "cells" after looking at a piece of cork and observing a cell-like structure, [2] however, the cells were dead and gave no indication to the actual overall components of a cell. A few years later, in 1674, Anton Van Leeuwenhoek was the first to analyze live cells in his examination of algae. All of this preceded the cell theory which states that all living things are made up of cells and that cells are the functional and structural unit of organisms. This was ultimately concluded by plant scientist, Matthias Schleiden and animal scientist, Theodor Schwann in 1839, who viewed live cells in plant and animal tissue, respectively. [3] 19 years later, Rudolf Virchow further contributed to the cell theory, adding that all cells come from the division of pre-existing cells. [3] Although widely accepted, there have been many studies that question the validity of the cell theory. Viruses, for example, lack common characteristics of a living cell, such as membranes, cell organelles, and the ability to reproduce by themselves. [4] Scientists have struggled to decide whether viruses are alive or not and whether they are in agreement with the cell theory.


Modern-day cell biology research looks at different ways to culture and manipulate cells outside of a living body to further research in human anatomy and physiology, and to derive medications. The techniques by which cells are studied have evolved. Due to advancements in microscopy, techniques and technology have allowed for scientists to hold a better understanding of the structure and function of cells. Many techniques commonly used to study cell biology are listed below: [5]

Cell classification and composition

There are two fundamental classifications of cells: prokaryotic and eukaryotic. Prokaryotic cells are distinguished from eukaryotic cells by the absence of a cell nucleus or other membrane bound organelle. [8] Prokaryotic cells are much smaller than eukaryotic cells, making them the smallest form of life. [9] The study of eukaryotic cells is typically the main focus of cytologists, whereas prokaryotic cells are the focus of microbiologists.

Prokaryotic cells

A typical prokaryote cell. Prokaryote cell.svg
A typical prokaryote cell.

Prokaryotic cells include Bacteria and Archaea, and lack an enclosed cell nucleus. They both reproduce through binary fission. Bacteria, the most prominent type, have several different shapes which include mainly spherical, and rod-shaped. Bacteria can be classed as either gram positive or gram negative depending on the cell wall composition. Bacterial structural features include:

There are many process that occur in prokaryotic cells that allow them to survive. For instance, in a process termed conjugation, fertility factor allows the bacteria to possess a pilus which allows it to transmit DNA to another bacteria which lacks the F factor, permitting the transmittance of resistance allowing it to survive in certain environments. [11]

Eukaryotic cells

A typical animal cell. Animal cell NIH.jpg
A typical animal cell.

Eukaryotic cells can either be unicellular or multicellular [10] and include animal, plant, fungi, and protozoa cells which all contain organelles with various shapes and sizes. [12] These cells are composed of the following organelles:

Eukaryotic cells may also be composed of the following molecular components:


Cell metabolism

Cell metabolism is necessary for the production of energy for the cell and therefore its survival and includes many pathways. For cellular respiration, once glucose is available, glycolysis occurs within the cytosol of the cell to produce pyruvate. Pyruvate undergoes decarboxylation using the multi-enzyme complex to form acetyl coA which can readily be used in the TCA cycle to produce NADH and FADH2. These products are involved in the electron transport chain to ultimately form a proton gradient across the inner mitochondrial membrane. This gradient can then drive the production of ATP and H2O during oxidative phosphorylation. [19] Metabolism in plant cells includes photosynthesis which is simply the exact opposite of respiration as it ultimately produces molecules of glucose.

Cell communication and signaling

Cell communication is important for cell regulation and for cells to process information from the environment and respond accordingly. Communication can occur through direct cell contact or endocrine, paracrine, and autocrine signaling. Direct cell-cell contact is when a receptor on a cell binds a molecule that is attached to the membrane of another cell. Endocrine signaling occurs through molecules secreted into the bloodstream. Paracrine signaling uses molecules diffusing between two cells to communicate. Autocrine is a cell sending a signal to itself by secreting a molecule that binds to a receptor on its surface. Forms of communication can be through:

Cell cycle

The process of cell division in the cell cycle. Animal cell cycle-en.svg
The process of cell division in the cell cycle.

The growth process of the cell does not refer to the size of the cell, but the density of the number of cells present in the organism at a given time. Cell growth pertains to the increase in the number of cells present in an organism as it grows and develops; as the organism gets larger so does the number of cells present. Cells are the foundation of all organisms and are the fundamental unit of life. The growth and development of cells are essential for the maintenance of the host and survival of the organism. For this process, the cell goes through the steps of the cell cycle and development which involves cell growth, DNA replication, cell division, regeneration, and cell death. The cell cycle is divided into four distinct phases: G1, S, G2, and M. The G phase – which is the cell growth phase – makes up approximately 95% of the cycle. The proliferation of cells is instigated by progenitors. All cells start out in an identical form and can essentially become any type of cells. Cell signaling such as induction can influence nearby cells to differentiate determinate the type of cell it will become. Moreover, this allows cells of the same type to aggregate and form tissues, then organs, and ultimately systems. The G1, G2, and S phase (DNA replication, damage and repair) are considered to be the interphase portion of the cycle, while the M phase (mitosis) is the cell division portion of the cycle. Mitosis is composed of many stages which include, prophase, metaphase, anaphase, telophase, and cytokinesis, respectively. The ultimate result of mitosis is the formation of two identical daughter cells.

The cell cycle is regulated by a series of signaling factors and complexes such as cyclins, cyclin-dependent kinase, and p53. When the cell has completed its growth process and if it is found to be damaged or altered, it undergoes cell death, either by apoptosis or necrosis, to eliminate the threat it can cause to the organism's survival. [21]


The scientific branch that studies and diagnoses diseases on the cellular level is called cytopathology. Cytopathology is generally used on samples of free cells or tissue fragments, in contrast to the pathology branch of histopathology, which studies whole tissues. Cytopathology is commonly used to investigate diseases involving a wide range of body sites, often to aid in the diagnosis of cancer but also in the diagnosis of some infectious diseases and other inflammatory conditions. For example, a common application of cytopathology is the Pap smear, a screening test used to detect cervical cancer, and precancerous cervical lesions that may lead to cervical cancer.

Notable cell biologists

See also


  1. "Cell Biology | Learn Science at Scitable". www.nature.com. Retrieved 10 June 2018.
  2. Hooke, Robert (September 1665). Micrographia.
  3. 1 2 Gupta, P. (1 December 2005). Cell and Molecular Biology. Rastogi Publications. p. 11. ISBN   978-8171338177.
  4. Kendrick, Karolyn (1 January 2010). Chemistry in Medicine. Benchmark Education Company. p. 26. ISBN   978-1450928526.
  5. Lavanya, P. (1 December 2005). Cell and Molecular Biology. Rastogi Publications. p. 11. ISBN   978-8171338177.
  6. 1 2 3 4 5 6 Cooper, Geoffrey M. (2000). "Tools of Cell Biology". The Cell: A Molecular Approach. 2nd Edition.
  7. McKinnon, Katherine M. (21 February 2018). "Flow Cytometry: An Overview". Current Protocols in Immunology. 120: 5.1.1–5.1.11. doi:10.1002/cpim.40. ISSN   1934-3671. PMC   5939936 . PMID   29512141.
  8. Doble, Mukesh; Gummadi, Sathyanarayana N. (5 August 2010). Biochemical Engineering. New Delhi: Prentice-Hall of India Pvt.Ltd. ISBN   978-8120330528.
  9. Kaneshiro, Edna (2 May 2001). Cell Physiology Sourcebook: A Molecular Approach (3rd ed.). Academic Press. ISBN   978-0123877383.
  10. 1 2 3 4 5 Nelson, Daniel (22 June 2018). "The Difference Between Eukaryotic And Prokaryotic Cells". Science Trends. doi:10.31988/scitrends.20655.
  11. Griffiths, Anthony JF; Miller, Jeffrey H.; Suzuki, David T.; Lewontin, Richard C.; Gelbart, William M. (2000). "Bacterial conjugation". An Introduction to Genetic Analysis. 7th Edition.
  12. "The Morphology of Eukaryotic Cells: Shape, Number and Size". YourArticleLibrary.com: The Next Generation Library. 19 March 2014. Retrieved 22 November 2015.
  13. De Rooij, Johan (25 June 2019). "F1000Prime recommendation of Force Triggers YAP Nuclear Entry by Regulating Transport across Nuclear Pores". doi:10.3410/f.732079699.793561846.Cite journal requires |journal= (help)
  14. "Endoplasmic Reticulum (Rough and Smooth) | British Society for Cell Biology" . Retrieved 6 October 2019.
  15. Pelley, John W. (2007), "Citric Acid Cycle, Electron Transport Chain, and Oxidative Phosphorylation", Elsevier's Integrated Biochemistry, Elsevier, pp. 55–63, doi:10.1016/b978-0-323-03410-4.50013-4, ISBN   9780323034104
  16. Cooper, Geoffrey M. (2000). "The Golgi Apparatus". The Cell: A Molecular Approach. 2nd Edition.
  17. Verity, M A. Lysosomes: some pathologic implications. OCLC   679070471.
  18. Cooper, Geoffrey M. (2000). "Transport of Small Molecules". The Cell: A Molecular Approach. 2nd Edition.
  19. 1 2 Ahmad, Maria; Kahwaji, Chadi I. (2019), "Biochemistry, Electron Transport Chain", StatPearls, StatPearls Publishing, PMID   30252361 , retrieved 20 October 2019
  20. Schlessinger, Joseph (October 2000). "Cell Signaling by Receptor Tyrosine Kinases". Cell. 103 (2): 211–225. doi:10.1016/s0092-8674(00)00114-8. ISSN   0092-8674. PMID   11057895.
  21. Shackelford, R E; Kaufmann, W K; Paules, R S (February 1999). "Cell cycle control, checkpoint mechanisms, and genotoxic stress". Environmental Health Perspectives. 107 (suppl 1): 5–24. doi:10.1289/ehp.99107s15. ISSN   0091-6765. PMC   1566366 . PMID   10229703.


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Cell (biology) Basic structural and functional unit of organisms

The cell is the basic structural, functional, and biological unit of all known organisms. A cell is the smallest unit of life. Cells are often called the "building blocks of life". The study of cells is called cell biology, cellular biology, or cytology.

Cell nucleus A membrane-bounded organelle of eukaryotic cells in which chromosomes are housed and replicated.

In cell biology, the nucleus is a membrane-bound organelle found in eukaryotic cells. Eukaryotes usually have a single nucleus, but a few cell types, such as mammalian red blood cells, have no nuclei, and a few others including osteoclasts have many.

Endoplasmic reticulum Irregular network of membranes coterminous with the outer nuclear membrane in eukaryote cytoplasm that form a meshwork of tubular channels, often expanded into cisternae

The endoplasmic reticulum (ER) is a type of organelle found in eukaryotic cells that forms an interconnected network of flattened, membrane-enclosed sacs or tube-like structures known as cisternae. The membranes of the ER are continuous with the outer nuclear membrane. The endoplasmic reticulum occurs in most eukaryotic cells, but is absent from red blood cells and spermatozoa.

Endomembrane system A collection of membranous structures involved in transport within the cell. The main components of the endomembrane system are endoplasmic reticulum, Golgi bodies, vesicles, cell membrane and nuclear envelope.

The endomembrane system is composed of the different membranes that are suspended in the cytoplasm within a eukaryotic cell. These membranes divide the cell into functional and structural compartments, or organelles. In eukaryotes the organelles of the endomembrane system include: the nuclear membrane, the endoplasmic reticulum, the Golgi apparatus, lysosomes, vesicles, endosomes, and plasma (cell) membrane among others. The system is defined more accurately as the set of membranes that form a single functional and developmental unit, either being connected directly, or exchanging material through vesicle transport. Importantly, the endomembrane system does not include the membranes of chloroplasts or mitochondria, but might have evolved from the latter.

Nuclear pore Any of the numerous similar discrete openings in the nuclear envelope of a eukaryotic cell, where the inner and outer nuclear membranes are joined.

A nuclear pore is a part of a large complex of proteins, known as a nuclear pore complex that spans the nuclear envelope, which is the double membrane surrounding the eukaryotic cell nucleus. There are approximately 1,000 nuclear pore complexes (NPCs) in the nuclear envelope of a vertebrate cell, but it varies depending on cell type and the stage in the life cycle. The human nuclear pore complex (hNPC) is a 110 MDa structure. The proteins that make up the nuclear pore complex are known as nucleoporins; each NPC contains at least 456 individual protein molecules and is composed of 34 distinct nucleoporin proteins.About half of the nucleoporins typically contain solenoid protein domains—either an alpha solenoid or a beta-propeller fold, or in some cases both as separate structural domains. The other half show structural characteristics typical of "natively unfolded" or intrinsically disordered proteins, i.e. they are highly flexible proteins that lack ordered tertiary structure. These disordered proteins are the FG nucleoporins, so called because their amino-acid sequence contains many phenylalanine—glycine repeats.

In cell biology, an organelle is a specialized subunit within a cell that has a specific function. Organelles are either separately enclosed within their own lipid bilayers or are spatially distinct functional units without a surrounding lipid bilayer.

Protein Biological molecule consisting of chains of amino acid residues

Proteins are large biomolecules, or macromolecules, consisting of one or more long chains of amino acid residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, responding to stimuli, providing structure to cells, and organisms, and transporting molecules from one location to another. Proteins differ from one another primarily in their sequence of amino acids, which is dictated by the nucleotide sequence of their genes, and which usually results in protein folding into a specific three-dimensional structure that determines its activity.

Vesicle (biology and chemistry) Any small, fluid-filled, spherical organelle enclosed by a membrane

In cell biology, a vesicle is a structure within or outside a cell, consisting of liquid or cytoplasm enclosed by a lipid bilayer. Vesicles form naturally during the processes of secretion (exocytosis), uptake (endocytosis) and transport of materials within the plasma membrane. Alternatively, they may be prepared artificially, in which case they are called liposomes. If there is only one phospholipid bilayer, they are called unilamellar liposome vesicles; otherwise they are called multilamellar. The membrane enclosing the vesicle is also a lamellar phase, similar to that of the plasma membrane, and intracellular vesicles can fuse with the plasma membrane to release their contents outside the cell. Vesicles can also fuse with other organelles within the cell. A vesicle released from the cell is known as an extracellular vesicle.

Symbiogenesis An evolutionary theory holding that eukaryotic organelles evolved through symbiosis with prokaryotes

Symbiogenesis, or endosymbiotic theory, is an evolutionary theory of the origin of eukaryotic cells from prokaryotic organisms, first articulated in 1905 and 1910 by the Russian botanist Konstantin Mereschkowski, and advanced and substantiated with microbiological evidence by Lynn Margulis in 1967. It holds that the organelles distinguishing eukaryote cells evolved through symbiosis of individual single-celled prokaryotes . The theory holds that mitochondria, plastids such as chloroplasts, and possibly other organelles of eukaryotic cells represent formerly free-living prokaryotes taken one inside the other in endosymbiosis. In more detail, mitochondria appear to be related to Rickettsiales proteobacteria, and chloroplasts to nitrogen-fixing filamentous cyanobacteria. Among the many lines of evidence supporting symbiogenesis are that new mitochondria and plastids are formed only through binary fission, and that cells cannot create new ones otherwise; that the transport proteins called porins are found in the outer membranes of mitochondria, chloroplasts and bacterial cell membranes; that cardiolipin is found only in the inner mitochondrial membrane and bacterial cell membranes; and that some mitochondria and plastids contain single circular DNA molecules similar to the chromosomes of bacteria.


Endoplasm generally refers to the inner, dense part of a cell's cytoplasm. This is opposed to the ectoplasm which is the outer (non-granulated) layer of the cytoplasm, which is typically watery and immediately adjacent to the plasma membrane. These two terms are mainly used to describe the cytoplasm of the amoeba, a protozoan, eukaryotic cell. The nucleus is separated from the endoplasm by the nuclear envelope. The different makeups/viscosities of the endoplasm and ectoplasm contribute to the amoeba's locomotion through the formation of a pseudopod. However, other types of cells have cytoplasm divided into endo- and ectoplasm. The endoplasm, along with its granules, contains water, nucleic acids amino acids, carbohydrates, inorganic ions, lipids, enzymes, and other molecular compounds. It is the site of most cellular processes as it houses the organelles that make up the endomembrane system, as well as those that stand alone. The endoplasm is necessary for most metabolic activities, including cell division.

Cellular compartments in cell biology comprise all of the closed parts within the cytosol of a eukaryotic cell, usually surrounded by a single or double lipid layer membrane. These compartments are often, but not always, defined as membrane enclosed regions. The formation of cellular compartments is called compartmentalization.

Cell physiology is the biological study of the activities that take place in a cell to keep it alive. The term physiology refers to normal functions in a living organism. Animal cells, plant cells and microorganism cells show similarities in their functions even though they vary in structure.

Outline of cell biology Overview of and topical guide to cell biology

The following outline is provided as an overview of and topical guide to cell biology:

Prokaryote Group of organisms whose cells lack a cell nucleus

A prokaryote is a unicellular organism that lacks a membrane-bound nucleus, mitochondria, or any other membrane-bound organelle. The word prokaryote comes from the Greek πρό and κάρυον. Prokaryotes are divided into two domains, Archaea and Bacteria. Species with nuclei and organelles are placed in the third domain, Eukaryota. Prokaryotes are asexual, reproducing without fusion of gametes. The first living organisms are thought to have been prokaryotes. The term prokaryote however is now used informally to refer to bacteria and archaea as in the late 1970s Carl Woese determined that bacteria and archaea were less closely related than previously thought.

The NAS Award in Molecular Biology is awarded by the U.S. National Academy of Sciences "for recent notable discovery in molecular biology by a young scientist who is a citizen of the United States." It has been awarded annually since its inception in 1962.

Cell membrane Biological membrane that separates the interior of a cell from its outside environment

The cell membrane is a biological membrane that separates the interior of all cells from the outside environment which protects the cell from its environment. Cell membrane consists of a lipid bilayer, including cholesterols that sit between phospholipids to maintain their fluidity under various temperature, in combination with membrane proteins such as integral proteins, and peripheral proteins that go across inside and outside of the membrane serving as membrane transporter, and loosely attached to the outer (peripheral) side of the cell membrane acting as several kinds of enzymes shaping the cell, respectively. The cell membrane controls the movement of substances in and out of cells and organelles. In this way, it is selectively permeable to ions and organic molecules. In addition, cell membranes are involved in a variety of cellular processes such as cell adhesion, ion conductivity and cell signalling and serve as the attachment surface for several extracellular structures, including the cell wall, the carbohydrate layer called the glycocalyx, and the intracellular network of protein fibers called the cytoskeleton. In the field of synthetic biology, cell membranes can be artificially reassembled.

This glossary of biology terms is a list of definitions of fundamental terms and concepts used in biology, the study of life and of living organisms. It is intended as introductory material for novices; for more specific and technical definitions from sub-disciplines and related fields, see Glossary of genetics, Glossary of ecology, Glossary of speciation, Glossary of botany, and Glossary of scientific naming.

Intracellular transport The directed movement of substances within a cell.

Intracellular transport is the movement of vesicles and substances within the cell. Eukaryotic cells transport packets of components to particular intracellular locations by attaching them to molecular motors that haul them along microtubules and actin filaments. This method of transport is often confused with intercellular transport, which deals solely with the movement of cargo between cells not the net movement within a cell. Since intracellular transport heavily relies on microtubules for movement, the components of the cytoskeleton play a vital role in trafficking vesicles between organelles and the plasma membrane.

A plastid is a membrane-bound organelle found in plants, algae and other eukaryotic organisms that contribute to the production of pigment molecules. Most plastids are photosynthetic, thus leading to color production and energy storage or production. There are many types of plastids in plants alone, but all plastids can be separated based on the number of times they have undergone endosymbiotic events. Currently there are three types of plastids; primary, secondary and tertiary. Endosymbiosis is reputed to have led to the evolution of eukaryotic organisms today, although the timeline is highly debated.