cell biology cell biology cell biology (also cellular biology or cytology) is a branch of biology that studies the structure, function, and behavior of cells. all living organisms are made of cells. a cell is the basic unit of life that is responsible for the living and functioning of organisms. cell biology is the study of structural and functional units of cells. 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, molecular biology, medical microbiology, immunology, and cytochemistry. part of a series onbiologyscience of life index outline glossary history (timeline) key components cell theory ecosystem evolution phylogeny properties of life adaptation energy processing growth order regulation reproduction response to environment domains and kingdoms of life archaea bacteria eukarya (animals, fungi, plants, protists) branches anatomy biotechnology botany cell biology ecology evolutionary biology genetics marine biology microbiology molecular biology mycology neuroscience paleontology phycology physiology protistology virology zoology research biologist (list) list of biology awards list of journals list of research methods list of unsolved problems applications agricultural science biomedical sciences health technology pharming biology portal category history 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" (published in micrographia) after looking at a piece of cork and observing a cell-like structure, 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 1838, who viewed live cells in plant and animal tissue, respectively. 19 years later, rudolf virchow further contributed to the cell theory, adding that all cells come from the division of pre-existing cells. viruses are not considered in cell biology – they lack the characteristics of a living cell, and instead are studied in the microbiology subclass of virology. techniques 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 scientists to hold a better understanding of the structure and function of cells. many techniques commonly used to study cell biology are listed below: 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. 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). 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. phase-contrast microscopy: uses the optical aspect of light to represent the solid, liquid, and gas-phase changes as brightness differences. confocal microscopy: combines fluorescence microscopy with imaging by focusing light and snap shooting instances to form a 3-d image. 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. 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. 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. cell types 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. prokaryotic cells are much smaller than eukaryotic cells, making them the smallest form of life. prokaryotic cells include bacteria and archaea, and lack an enclosed cell nucleus. eukaryotic cells are found in plants, animals, fungi, and protists. they range from 10 to 100 μm in diameter, and their dna is contained within a membrane-bound nucleus. eukaryotes are organisms containing eukaryotic cells. the four eukaryotic kingdoms are animalia, plantae, fungi, and protista. they both reproduce through binary fission. bacteria, the most prominent type, have several different shapes, although most are spherical or rod-shaped. bacteria can be classed as either gram-positive or gram-negative depending on the cell wall composition. gram-positive bacteria have a thicker peptidoglycan layer than gram-negative bacteria. bacterial structural features include a flagellum that helps the cell to move, ribosomes for the translation of rna to protein, and a nucleoid that holds all the genetic material in a circular structure. there are many processes that occur in prokaryotic cells that allow them to survive. in prokaryotes, mrna synthesis is initiated at a promoter sequence on the dna template comprising two consensus sequences that recruit rna polymerase. the prokaryotic polymerase consists of a core enzyme of four protein subunits and a σ protein that assists only with initiation. for instance, in a process termed conjugation, the 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. structure and function structure of eukaryotic cells a diagram of an animal cell eukaryotic cells are composed of the following organelles: nucleus: the nucleus of the cell 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 the transportation of proteins between the inside and outside of the nucleus. 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. 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. 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. mitochondria: commonly known as the powerhouse of the cell is a double membrane bound cell organelle. 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. golgi apparatus: this functions to further process, package, and secrete the proteins to their destination. the proteins contain a signal sequence that allows the golgi apparatus to recognize and direct it to the correct place. golgi apparatus also produce glycoproteins and glycolipids. 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. ribosomes: functions to translate rna to protein. it serves as a site of protein synthesis. cytoskeleton: cytoskeleton is a structure that helps to maintain the shape and general organization of the cytoplasm. it anchors organelles within the cells and makes 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. cell membrane: the cell membrane can be described as a phospholipid bilayer and is also consisted of lipids and proteins. 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 the cell via osmotic pressure, diffusion, concentration gradients, and membrane channels. 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. 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. metabolism in plant cells includes photosynthesis which is simply the exact opposite of respiration as it ultimately produces molecules of glucose. cell signaling 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 seven 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. receptor tyrosine