Cell biology

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Not to be confused with Cell (biology).

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Cell biology (also cellular biology or cytology) is a branch of biology that studies the structure, function and behavior of cells.[1][2] Cell biology encompasses both prokaryotic and eukaryotic cells and has many subtopics which may include the study of cell metabolism, cell communication, cell cycle, biochemistry, and cell composition. The study of cells is performed using several microscopy techniques, cell culture, 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.

History[edit]

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,[3][4] 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[4] and animal scientist Theodor Schwann in 1838, who viewed live cells in plant and animal tissue, respectively.[5] 19 years later, Rudolf Virchow further contributed to the cell theory, adding that all cells come from the division of pre-existing cells.[5] 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.[6] The cell was first discovered and named by Robert Hooke in 1665 who had remarked that it looked strangely similar to the cells or small rooms which monks inhabited, thus deriving the name. However what Hooke actually saw was the dead cell walls of plant cells (cork) as it appeared under the microscope. Hooke’s description of these cells was published in Micrography.[7]Scientists have struggled to decide whether viruses are alive or not and whether they are in agreement with the cell theory.

Techniques[edit]

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:[8]

  • Cell culture: Utilizes rapidly growing cells on media which allows for a large amount of a specific cell type and an efficient way to study cells.[9]Cell culture is one of the major tools used in cellular and molecular biology, providing excellent model systems for studying the normal physiology and biochemistry of cells (e.g., metabolic studies, aging), the effects of drugs and toxic compounds on the cells, and mutagenesis and carcinogenesis. It is also used in drug screening and development, and large scale manufacturing of biological compounds (e.g., vaccines, therapeutic proteins). The major advantage of using cell culture for any of these applications is the consistency and reproducibility of results that can be obtained from using a batch of clonal cells.[10]
  • Fluorescence microscopy: Fluorescent markers such as GFP, are used to label a specific component of the cell. Afterwards, a certain light wavelength is used to excite the fluorescent marker which can then be visualized.[9]
  • Phase-contrast microscopy: Uses the optical aspect of light to represent the solid, liquid, and gas phase changes as brightness differences.[9]
  • Confocal microscopy: Combines fluorescence microscopy with imaging by focusing light and snap shooting instances to form a 3-D image.[9]
  • Transmission electron microscopy: Involves metal staining and the passing of electrons through the cells, which will be deflected upon interaction with metal. This ultimately forms an image of the components being studied.[9]
  • Cytometry: The cells are placed in the machine which uses a beam to scatter the cells based on different aspects and can therefore separate them based on size and content. Cells may also be tagged with GFP-fluorescence and can be separated that way as well.[11]Cytometry involves a wide range of cutting-edge techniques, most of which measure the molecular properties of cells by employing fluorescent labeling to detect specific antigens using antibodies.
  • Cell fractionation: This process requires breaking up the cell using high temperature or sonification followed by centrifugation to separate the parts of the cell allowing for them to be studied separately.[9]

Cell types[edit]

A drawing of a prokaryotic cell.

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.[12] Prokaryotic cells are much smaller than eukaryotic cells, making them the smallest form of life.[13] 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. Gram positive bacteria have a thick peptidoglycan layer, and no outer lipid membrane Bacterial structural features include a flagellum that helps the cell to move,[14] ribosomes for the translation of RNA to protein,[14] and a nucleoid that holds all the genetic material in a circular structure.[14] 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.[15]

Structure and function[edit]

Structure of eukaryotic cells[edit]

A diagram of an animal cell.

Eukaryotic cells are composed of the following organelles:

  • Nucleus: This functions as the genome and genetic information storage for the cell, containing all the DNA organized in the form of chromosomes. It is surrounded by a nuclear envelope, which includes nuclear pores allowing for transportation of proteins between the inside and outside of the nucleus.[16] This is also the site for replication of DNA as well as transcription of DNA to RNA. Afterwards, the RNA is modified and transported out to the cytosol to be translated to protein. So this is really an important part of cell to protect. Sometimes things like RNA need to traffic between the nucleus and the cytoplasm, and so there are pores in this nuclear membrane that allow molecules to go in and out of the nucleus. It used to be thought that the nuclear membrane only allowed molecules to go out, but now it's realized that there is an active process also for bringing molecules into the nucleus.[17]
  • Nucleolus: This structure is within the nucleus, usually dense and spherical in shape. It is the site of ribosomal RNA (rRNA) synthesis, which is needed for ribosomal assembly.
  • Endoplasmic reticulum (ER): This functions to synthesize, store, and secrete proteins to the Golgi apparatus.[18]Structurally, the endoplasmic reticulum is a network of membranes found throughout the cell and connected to the nucleus. The membranes are slightly different from cell to cell and a cell’s function determines the size and structure of the ER.[19]
  • Mitochondria: Commonly known as powerhouse of the cell. [20]This functions for the production of energy or ATP within the cell. Specifically, this is the place where the Krebs cycle or TCA cycle for the production of NADH and FADH occurs. Afterwards, these products are used within the electron transport chain (ETC) and oxidative phosphorylation for the final production of ATP.[21]
  • Golgi apparatus: This functions to further process, package, and secrete the proteins to their destination. The proteins contain a signal sequence which allows the golgi apparatus to recognize and direct it to the correct place.[22]
  • Lysosome: The lysosome functions to degrade material brought in from the outside of the cell or old organelles. This contains many acid hydrolases, proteases, nucleases, and lipases, which break down the various molecules. Autophagy is the process of degradation through lysosomes which occurs when a vesicle buds off from the ER and engulfs the material, then, attaches and fuses with the lysosome to allow the material to be degraded.[23]
  • Ribosomes: Functions to translate RNA to protein. it serves as a site of protein synthesis.[24]
  • Cytoskeleton: Cytoskeleton is a structure that helps maintain their shape and general organization of cytoplasm. functions to anchor organelles within the cells and make up the structure and stability of the cell. The cytoskeleton is composed of three principal types of protein filaments: actin filaments, intermediate filaments, and microtubules, which are held together and linked to subcellular organelles and the plasma membrane by a variety of accessory proteins.[25]
  • Cell membrane: The cell membrane can be described as a phospholipid bilayer and is also consisted of lipids and proteins.[14] Because the inside of the bilayer is hydrophobic and in order for molecules to participate in reactions within the cell, they need to be able to cross this membrane layer to get into cell via osmotic pressure, diffusion, concentration gradients, and membrane channels.[26]
  • Centrioles: Function to produce spindle fibers which are used to separate chromosomes during cell division.

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

  • Chromatin: This makes up chromosomes and is a mixture of DNA with various proteins.
  • Cilia: They help to propel substances and can also be used for sensory purposes.[27]

Cell metabolism[edit]

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.[28] Metabolism in plant cells includes photosynthesis which is simply the exact opposite of respiration as it ultimately produces molecules of glucose.

Cell signaling[edit]

Further information: Cell signaling

Cell signaling or cell communication is important for cell regulation and for cells to process information from the environment and respond accordingly. Signaling 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:

  • Ion channels: Can be of different types such as voltage or ligand gated ion channels. They allow for the outflow and inflow of molecules and ions.
  • G-protein coupled receptor (GPCR): Is widely recognized to contain 7 transmembrane domains. The ligand binds on the extracellular domain and once the ligand binds, this signals a guanine exchange factor to convert GDP to GTP and activate the G-α subunit. G-α can target other proteins such as adenyl cyclase or phospholipase C, which ultimately produce secondary messengers such as cAMP, Ip3, DAG, and calcium. These secondary messengers function to amplify signals and can target ion channels or other enzymes. One example for amplification of a signal is cAMP binding to and activating PKA by removing the regulatory subunits and releasing the catalytic subunit. The catalytic subunit has a nuclear localization sequence which prompts it to go into the nucleus and phosphorylate other proteins to either repress or activate gene activity.[28]
  • Receptor tyrosine kinases: Bind growth factors, further promoting the tyrosine on the intracellular portion of the protein to cross phosphorylate. The phosphorylated tyrosine becomes a landing pad for proteins containing an SH2 domain allowing for the activation of Ras and the involvement of the MAP kinase pathway.[29]

Growth and development[edit]

Cell cycle[edit]

Main article: Cell cycle
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 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.[30]

Cell mortality, cell lineage immortality[edit]

The ancestry of each present day cell presumably traces back, in an unbroken lineage for over 3 billion years to the origin of life. It is not actually cells that are immortal but multi-generational cell lineages.[31] The immortality of a cell lineage depends on the maintenance of cell division potential. This potential may be lost in any particular lineage because of cell damage, terminal differentiation as occurs in nerve cells, or programmed cell death (apoptosis) during development. Maintenance of cell division potential over successive generations depends on the avoidance and the accurate repair of cellular damage, particularly DNA damage. In sexual organisms, continuity of the germline depends on the effectiveness of processes for avoiding DNA damage and repairing those DNA damages that do occur. Sexual processes in eukaryotes, as well as in prokaryotes, provide an opportunity for effective repair of DNA damages in the germ line by homologous recombination.[31][32]

Cell cycle phases[edit]

The cell cycle is a four-stage process that a cell goes through as it develops and divides. It includes Gap 1 (G1), synthesis (S), Gap 2 (G2), and mitosis (M).The cell either restarts the cycle from G1 or leaves the cycle through G0 after completing the cycle. The cell can progress from G0 through terminal differentiation.

The interphase refers to the phases of the cell cycle that occur between one mitosis and the next, and includes G1, S, and G2.

G1 phase[edit]

The size of the cell grows.

The contents of cells are replicated.

S phase[edit]

Replication of DNA

The cell replicates each of the 46 chromosomes (23 pairs).

G2 phase[edit]

The cell multiplies.

In preparation for cell division, organelles and proteins form.

M phase[edit]

After mitosis, cytokinesis occurs (cell separation)

Formation of two daughter cells that are identical

G0 phase[edit]

These cells leave G1 and enter G0, a resting stage. A cell in G0 is doing its job without actively preparing to divide. [33]

Pathology[edit]

Main article: Cytopathology

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.[34]

Notable cell biologists[edit]

See also[edit]

Notes[edit]

  1. ^ Alberts, Bruce; Johnson, Alexander D.; Morgan, David; Raff, Martin; Roberts, Keith; Walter, Peter (2015). "Cells and genomes". Molecular Biology of the Cell (6th ed.). New York, NY: Garland Science. pp. 1–42. ISBN 978-0815344322.
  2. ^ Bisceglia, Nick. "Cell Biology". Scitable. www.nature.com.
  3. ^ Hooke, Robert (September 1665). Micrographia.
  4. ^ a b Chubb, Gilbert Charles (1911). "Cytology" . In Chisholm, Hugh (ed.). Encyclopædia Britannica. 7 (11th ed.). Cambridge University Press. p. 710.
  5. ^ a b Gupta, P. (1 December 2005). Cell and Molecular Biology. Rastogi Publications. p. 11. ISBN 978-8171338177.
  6. ^ Kendrick, Karolyn (1 January 2010). Chemistry in Medicine. Benchmark Education Company. p. 26. ISBN 978-1450928526.
  7. ^ "History of Cell Biology". Retrieved 27 September 2021.
  8. ^ Lavanya, P. (1 December 2005). Cell and Molecular Biology. Rastogi Publications. p. 11. ISBN 978-8171338177.
  9. ^ a b c d e f Cooper, Geoffrey M. (2000). "Tools of Cell Biology". The Cell: A Molecular Approach. 2nd Edition.
  10. ^ "Introduction to Cell Culture - US". www.thermofisher.com. Retrieved 27 September 2021.
  11. ^ 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.
  12. ^ Doble, Mukesh; Gummadi, Sathyanarayana N. (5 August 2010). Biochemical Engineering. New Delhi: Prentice-Hall of India Pvt.Ltd. ISBN 978-8120330528.
  13. ^ Kaneshiro, Edna (2 May 2001). Cell Physiology Sourcebook: A Molecular Approach (3rd ed.). Academic Press. ISBN 978-0123877383.
  14. ^ a b c d Nelson, Daniel (22 June 2018). "The Difference Between Eukaryotic And Prokaryotic Cells". Science Trends. doi:10.31988/scitrends.20655.
  15. ^ Griffiths, Anthony J.F.; Miller, Jeffrey H.; Suzuki, David T.; Lewontin, Richard C.; Gelbart, William M. (2000). "Bacterial conjugation". An Introduction to Genetic Analysis. 7th Edition.
  16. ^ 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)
  17. ^ "Nucleus". Genome.gov. Retrieved 27 September 2021.
  18. ^ "Endoplasmic Reticulum (Rough and Smooth) | British Society for Cell Biology". Retrieved 6 October 2019.
  19. ^ Studios, Andrew Rader. "Biology4Kids.com: Cell Structure: Endoplasmic Reticulum". www.biology4kids.com. Retrieved 27 September 2021.
  20. ^ "Powerhouse of the cell has self-preservation mechanism". EurekAlert!. Retrieved 27 September 2021.
  21. ^ 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
  22. ^ Cooper, Geoffrey M. (2000). "The Golgi Apparatus". The Cell: A Molecular Approach. 2nd Edition.
  23. ^ Verity, M A. Lysosomes: some pathologic implications. OCLC 679070471.
  24. ^ "Ribosome | cytology". Encyclopedia Britannica. Retrieved 27 September 2021.
  25. ^ The CELL A MOLEQULAR APPROACH. Geoffrey M Cooper. 2000.
  26. ^ Cooper, Geoffrey M. (2000). "Transport of Small Molecules". The Cell: A Molecular Approach. 2nd Edition.
  27. ^ "What Are the Main Functions of Cilia & Flagella?". Sciencing. Retrieved 23 November 2020.
  28. ^ a b Ahmad, Maria; Kahwaji, Chadi I. (2019), "Biochemistry, Electron Transport Chain", StatPearls, StatPearls Publishing, PMID 30252361, retrieved 20 October 2019
  29. ^ 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. S2CID 11465988.
  30. ^ 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.
  31. ^ a b Bernstein C, Bernstein H, Payne C. Cell immortality: maintenance of cell division potential. Prog Mol Subcell Biol. 2000;24:23-50. doi: 10.1007/978-3-662-06227-2_2. PMID: 10547857.
  32. ^ Avise JC. Perspective: The evolutionary biology of aging, sexual reproduction, and DNA repair. Evolution. 1993 Oct;47(5):1293-1301. doi: 10.1111/j.1558-5646.1993.tb02155.x. PMID: 28564887.
  33. ^ "The Cell Cycle - Phases - Mitosis - Regulation". TeachMePhysiology. Retrieved 7 October 2021.
  34. ^ "What is Pathology?". News-Medical.net. 13 May 2010. Retrieved 21 September 2021.

References[edit]

External links[edit]

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Cell biology
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