Cell physiology
Encyclopedia
Cell physiology
(including cellular electrophysiology
) is the biological study of the cell
's mechanism and interaction in its environment. The term "physiology" refers to all the normal functions that take place in a living organism. Absorption of water by roots, production of food in the leaves, and growth of shoots towards light are examples of plant physiology. The heterotrophic metabolism of food derived from plants and animals and the use of movement to obtain nutrients (even if the organism itself remains in a relatively stationary position) are characteristic of animal physiology.
In the context of human physiology
, cell physiology is often the term used to describe the physiology of membrane
transport, neuron
transmission, and (less frequently) muscle
contraction. In general these cover the digestion of food, circulation of blood and contraction of muscles and, therefore, are important aspects of human physiology. For a more complete description of the general physiological function of human cells (as well as the cells of other life forms), see the article on cell biology
s and Eukaryote
s.
Prokaryotes first came into existence and contain no self-contained nucleus, therefore making their mechanisms much simpler compared to the later-evolved Eukaryotes, which do contain a nucleus
enveloping the cell's DNA
and nuclear organelles. Because virus
es, viroid
s, prion
s and such (see Acytota/Aphanobionta) depend entirely on the physiology of other cells (i.e., cells containing their own physiology), the former entities are often not considered to be "living" by the biologists who study them.
All living cells, whether prokaryotes or eukaryotes, contain the following distinguishing characteristics:
Based on the properties shared by all independently living organisms on Earth,
The earliest ancestor of all life that is hypothesized to contain these attributes is known as the last common ancestor.
Physiology
Physiology is the science of the function of living systems. This includes how organisms, organ systems, organs, cells, and bio-molecules carry out the chemical or physical functions that exist in a living system. The highest honor awarded in physiology is the Nobel Prize in Physiology or...
(including cellular electrophysiology
Electrophysiology
Electrophysiology is the study of the electrical properties of biological cells and tissues. It involves measurements of voltage change or electric current on a wide variety of scales from single ion channel proteins to whole organs like the heart...
) is the biological study of the cell
Cell (biology)
The cell is the basic structural and functional unit of all known living organisms. It is the smallest unit of life that is classified as a living thing, and is often called the building block of life. The Alberts text discusses how the "cellular building blocks" move to shape developing embryos....
's mechanism and interaction in its environment. The term "physiology" refers to all the normal functions that take place in a living organism. Absorption of water by roots, production of food in the leaves, and growth of shoots towards light are examples of plant physiology. The heterotrophic metabolism of food derived from plants and animals and the use of movement to obtain nutrients (even if the organism itself remains in a relatively stationary position) are characteristic of animal physiology.
In the context of human physiology
Human physiology
Human physiology is the science of the mechanical, physical, bioelectrical, and biochemical functions of humans in good health, their organs, and the cells of which they are composed. Physiology focuses principally at the level of organs and systems...
, cell physiology is often the term used to describe the physiology of membrane
Cell membrane
The cell membrane or plasma membrane is a biological membrane that separates the interior of all cells from the outside environment. The cell membrane is selectively permeable to ions and organic molecules and controls the movement of substances in and out of cells. It basically protects the cell...
transport, neuron
Neuron
A neuron is an electrically excitable cell that processes and transmits information by electrical and chemical signaling. Chemical signaling occurs via synapses, specialized connections with other cells. Neurons connect to each other to form networks. Neurons are the core components of the nervous...
transmission, and (less frequently) muscle
Muscle
Muscle is a contractile tissue of animals and is derived from the mesodermal layer of embryonic germ cells. Muscle cells contain contractile filaments that move past each other and change the size of the cell. They are classified as skeletal, cardiac, or smooth muscles. Their function is to...
contraction. In general these cover the digestion of food, circulation of blood and contraction of muscles and, therefore, are important aspects of human physiology. For a more complete description of the general physiological function of human cells (as well as the cells of other life forms), see the article on cell biology
Cell biology
Cell biology is a scientific discipline that studies cells – their physiological properties, their structure, the organelles they contain, interactions with their environment, their life cycle, division and death. This is done both on a microscopic and molecular level...
General characteristics of cell physiology
There are two types of cells, ProkaryoteProkaryote
The prokaryotes are a group of organisms that lack a cell nucleus , or any other membrane-bound organelles. The organisms that have a cell nucleus are called eukaryotes. Most prokaryotes are unicellular, but a few such as myxobacteria have multicellular stages in their life cycles...
s and Eukaryote
Eukaryote
A eukaryote is an organism whose cells contain complex structures enclosed within membranes. Eukaryotes may more formally be referred to as the taxon Eukarya or Eukaryota. The defining membrane-bound structure that sets eukaryotic cells apart from prokaryotic cells is the nucleus, or nuclear...
s.
Prokaryotes first came into existence and contain no self-contained nucleus, therefore making their mechanisms much simpler compared to the later-evolved Eukaryotes, which do contain a nucleus
Cell nucleus
In cell biology, the nucleus 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 within these...
enveloping the cell's DNA
DNA
Deoxyribonucleic acid is a nucleic acid that contains the genetic instructions used in the development and functioning of all known living organisms . The DNA segments that carry this genetic information are called genes, but other DNA sequences have structural purposes, or are involved in...
and nuclear organelles. Because virus
Virus
A virus is a small infectious agent that can replicate only inside the living cells of organisms. Viruses infect all types of organisms, from animals and plants to bacteria and archaea...
es, viroid
Viroid
Viroids are plant pathogens that consist of a short stretch of highly complementary, circular, single-stranded RNA without the protein coat that is typical for viruses. The smallest discovered is a 220 nucleobase scRNA associated with the rice yellow mottle sobemovirus...
s, prion
Prion
A prion is an infectious agent composed of protein in a misfolded form. This is in contrast to all other known infectious agents which must contain nucleic acids . The word prion, coined in 1982 by Stanley B. Prusiner, is a portmanteau derived from the words protein and infection...
s and such (see Acytota/Aphanobionta) depend entirely on the physiology of other cells (i.e., cells containing their own physiology), the former entities are often not considered to be "living" by the biologists who study them.
All living cells, whether prokaryotes or eukaryotes, contain the following distinguishing characteristics:
Based on the properties shared by all independently living organisms on Earth,
- The genetic codeGenetic codeThe genetic code is the set of rules by which information encoded in genetic material is translated into proteins by living cells....
is based on DNADNADeoxyribonucleic acid is a nucleic acid that contains the genetic instructions used in the development and functioning of all known living organisms . The DNA segments that carry this genetic information are called genes, but other DNA sequences have structural purposes, or are involved in...
.- The DNA is composed of four nucleotideNucleotideNucleotides are molecules that, when joined together, make up the structural units of RNA and DNA. In addition, nucleotides participate in cellular signaling , and are incorporated into important cofactors of enzymatic reactions...
s (deoxyadenosineDeoxyadenosineDeoxyadenosine is a deoxyribonucleoside. It is a derivative of the nucleoside adenosine, differing from the latter by the replacement of a hydroxyl group by hydrogen at the 2' position of its ribose sugar moiety. Deoxyadenosine is the DNA nucleoside A, which pairs with deoxythymidine in...
, deoxycytidineDeoxycytidineDeoxycytidine is a deoxyribonucleoside. It is like cytidine, but with one oxygen atom removed....
, deoxythymidine and deoxyguanosineDeoxyguanosineDeoxyguanosine is composed of the purine nucleoside guanine linked by its N9 nitrogen to the C1 carbon of deoxyribose. It is similar to guanosine, but with one hydroxyl group removed from the 2' position of the ribose sugar . If a phosphate group is attached at the 5' position, it becomes...
), to the exclusion of other possible deoxynucleotides. - The genetic code is composed of three-nucleotide codons, thus producing 64 different codons. Since only 20 amino acids are used, multiple codons code for the same amino acids. This structure is arbitrary and shared by all eukaryotes and prokaryotes. ArchaeaArchaeaThe Archaea are a group of single-celled microorganisms. A single individual or species from this domain is called an archaeon...
and mitochondria use a similar code with minor differences. - The DNA is kept double-stranded by a template-dependent DNA polymeraseDNA polymeraseA DNA polymerase is an enzyme that helps catalyze in the polymerization of deoxyribonucleotides into a DNA strand. DNA polymerases are best known for their feedback role in DNA replication, in which the polymerase "reads" an intact DNA strand as a template and uses it to synthesize the new strand....
. - The integrity of the DNA is maintained by a group of maintenance enzymes, including DNA topoisomerase, DNA ligaseDNA ligaseIn molecular biology, DNA ligase is a specific type of enzyme, a ligase, that repairs single-stranded discontinuities in double stranded DNA molecules, in simple words strands that have double-strand break . Purified DNA ligase is used in gene cloning to join DNA molecules together...
and other DNA repairDNA repairDNA repair refers to a collection of processes by which a cell identifies and corrects damage to the DNA molecules that encode its genome. In human cells, both normal metabolic activities and environmental factors such as UV light and radiation can cause DNA damage, resulting in as many as 1...
enzymes. The DNA is also protected by DNA-binding proteins like histones.
- The DNA is composed of four nucleotide
- The genetic code is expressed via RNARNARibonucleic acid , or RNA, is one of the three major macromolecules that are essential for all known forms of life....
intermediates, which are single-stranded.- RNA is produced by a DNA-dependent RNA polymeraseRNA polymeraseRNA polymerase is an enzyme that produces RNA. In cells, RNAP is needed for constructing RNA chains from DNA genes as templates, a process called transcription. RNA polymerase enzymes are essential to life and are found in all organisms and many viruses...
using nucleotides similar to those of DNA with the exception of Thymidine in DNA, replaced by Uridine in RNA.
- RNA is produced by a DNA-dependent RNA polymerase
- The genetic code is expressed into proteins. All other properties of the organism (e.g. synthesis of lipids or carbohydrates) are the result of protein enzymes.
- Proteins are assembled from free amino acids by translationTranslation (genetics)In molecular biology and genetics, translation is the third stage of protein biosynthesis . In translation, messenger RNA produced by transcription is decoded by the ribosome to produce a specific amino acid chain, or polypeptide, that will later fold into an active protein...
of an mRNA by ribosomes, tRNA and a group of related proteins.- Ribosomes are composed of two subunits, one big and one small.
- Each ribosomal subunit is composed of a core of ribosomal RNARibosomal RNARibosomal ribonucleic acid is the RNA component of the ribosome, the enzyme that is the site of protein synthesis in all living cells. Ribosomal RNA provides a mechanism for decoding mRNA into amino acids and interacts with tRNAs during translation by providing peptidyl transferase activity...
surrounded by ribosomal proteins. - The RNA molecules (rRNA and tRNA) play an important role in the catalytic activity of the ribosomes
- Only 20 amino acids are used, to the exclusion of countless non-standard amino acids; only the L-isomerIsomerIn chemistry, isomers are compounds with the same molecular formula but different structural formulas. Isomers do not necessarily share similar properties, unless they also have the same functional groups. There are many different classes of isomers, like stereoisomers, enantiomers, geometrical...
s are used.- Amino acids must be synthesized from glucose by a group of specialized enzymes; the synthesis pathways are arbitrary and conserved.
- GlucoseGlucoseGlucose is a simple sugar and an important carbohydrate in biology. Cells use it as the primary source of energy and a metabolic intermediate...
can be used as a source of energy and carbonCarbonCarbon is the chemical element with symbol C and atomic number 6. As a member of group 14 on the periodic table, it is nonmetallic and tetravalent—making four electrons available to form covalent chemical bonds...
; only the D-isomerIsomerIn chemistry, isomers are compounds with the same molecular formula but different structural formulas. Isomers do not necessarily share similar properties, unless they also have the same functional groups. There are many different classes of isomers, like stereoisomers, enantiomers, geometrical...
is used.- GlycolysisGlycolysisGlycolysis is the metabolic pathway that converts glucose C6H12O6, into pyruvate, CH3COCOO− + H+...
goes through an arbitrary degradation pathway.
- Glycolysis
- ATPAdenosine triphosphateAdenosine-5'-triphosphate is a multifunctional nucleoside triphosphate used in cells as a coenzyme. It is often called the "molecular unit of currency" of intracellular energy transfer. ATP transports chemical energy within cells for metabolism...
is used as an energy intermediate. - The cell is surrounded by a cellular membrane composed of a lipid bilayerLipid bilayerThe lipid bilayer is a thin membrane made of two layers of lipid molecules. These membranes are flat sheets that form a continuous barrier around cells. The cell membrane of almost all living organisms and many viruses are made of a lipid bilayer, as are the membranes surrounding the cell nucleus...
. - Inside the cell, the concentration of sodiumSodiumSodium is a chemical element with the symbol Na and atomic number 11. It is a soft, silvery-white, highly reactive metal and is a member of the alkali metals; its only stable isotope is 23Na. It is an abundant element that exists in numerous minerals, most commonly as sodium chloride...
is lower, and potassiumPotassiumPotassium is the chemical element with the symbol K and atomic number 19. Elemental potassium is a soft silvery-white alkali metal that oxidizes rapidly in air and is very reactive with water, generating sufficient heat to ignite the hydrogen emitted in the reaction.Potassium and sodium are...
is higher, than outside. This gradient is maintained by specific ion pumps. - The cell multiplies by duplicating all its contents followed by cellular division.
The earliest ancestor of all life that is hypothesized to contain these attributes is known as the last common ancestor.
Physiological processes
- Movement of proteins — The movement of proteins about the cell for use in structure and in enzymatic processes.
- Active transportActive transportActive transport is the movement of a substance against its concentration gradient . In all cells, this is usually concerned with accumulating high concentrations of molecules that the cell needs, such as ions, glucose, and amino acids. If the process uses chemical energy, such as from adenosine...
and Passive transportPassive transportPassive transport means moving biochemicals and other atomic or molecular substances across membranes. Unlike active transport, this process does not involve chemical energy, because, unlike in an active transport, the transport across membrane is always coupled with the growth of entropy of the...
— The processes facilitating the movement of molecules into and out of cells. - AutophagyAutophagyIn cell biology, autophagy, or autophagocytosis, is a catabolic process involving the degradation of a cell's own components through the lysosomal machinery. It is a tightly regulated process that plays a normal part in cell growth, development, and homeostasis, helping to maintain a balance...
— The process whereby cells "eat" their own internal components or microbial invaders. - AdhesionCell adhesionCellular adhesion is the binding of a cell to a surface, extracellular matrix or another cell using cell adhesion molecules such as selectins, integrins, and cadherins. Correct cellular adhesion is essential in maintaining multicellular structure...
— The chemical processes whereby cells and other tissues are held together. - Cell divisionCell divisionCell division is the process by which a parent cell divides into two or more daughter cells . Cell division is usually a small segment of a larger cell cycle. This type of cell division in eukaryotes is known as mitosis, and leaves the daughter cell capable of dividing again. The corresponding sort...
— a eukaryotic cell process resulting in the formation of daughter cells; there are two major types: that of mitosisMitosisMitosis is the process by which a eukaryotic cell separates the chromosomes in its cell nucleus into two identical sets, in two separate nuclei. It is generally followed immediately by cytokinesis, which divides the nuclei, cytoplasm, organelles and cell membrane into two cells containing roughly...
(asexual reproductionAsexual reproductionAsexual reproduction is a mode of reproduction by which offspring arise from a single parent, and inherit the genes of that parent only, it is reproduction which does not involve meiosis, ploidy reduction, or fertilization. A more stringent definition is agamogenesis which is reproduction without...
) and meiosisMeiosisMeiosis is a special type of cell division necessary for sexual reproduction. The cells produced by meiosis are gametes or spores. The animals' gametes are called sperm and egg cells....
(sexual reproductionSexual reproductionSexual reproduction is the creation of a new organism by combining the genetic material of two organisms. There are two main processes during sexual reproduction; they are: meiosis, involving the halving of the number of chromosomes; and fertilization, involving the fusion of two gametes and the...
). - Cell movement: ChemotaxisChemotaxisChemotaxis is the phenomenon in which somatic cells, bacteria, and other single-cell or multicellular organisms direct their movements according to certain chemicals in their environment. This is important for bacteria to find food by swimming towards the highest concentration of food molecules,...
, ContractionMuscle contractionMuscle fiber generates tension through the action of actin and myosin cross-bridge cycling. While under tension, the muscle may lengthen, shorten, or remain the same...
, Cilia and FlagellaFlagellumA flagellum is a tail-like projection that protrudes from the cell body of certain prokaryotic and eukaryotic cells, and plays the dual role of locomotion and sense organ, being sensitive to chemicals and temperatures outside the cell. There are some notable differences between prokaryotic and...
. - Cell signalingCell signalingCell signaling is part of a complex system of communication that governs basic cellular activities and coordinates cell actions. The ability of cells to perceive and correctly respond to their microenvironment is the basis of development, tissue repair, and immunity as well as normal tissue...
— Regulation of cell behavior by signals from outside, such as the use of hormones or neurotransmitters. - DNA repairDNA repairDNA repair refers to a collection of processes by which a cell identifies and corrects damage to the DNA molecules that encode its genome. In human cells, both normal metabolic activities and environmental factors such as UV light and radiation can cause DNA damage, resulting in as many as 1...
and Cell death - MetabolismMetabolismMetabolism is the set of chemical reactions that happen in the cells of living organisms to sustain life. These processes allow organisms to grow and reproduce, maintain their structures, and respond to their environments. Metabolism is usually divided into two categories...
: GlycolysisGlycolysisGlycolysis is the metabolic pathway that converts glucose C6H12O6, into pyruvate, CH3COCOO− + H+...
, RespirationCellular respirationCellular respiration is the set of the metabolic reactions and processes that take place in the cells of organisms to convert biochemical energy from nutrients into adenosine triphosphate , and then release waste products. The reactions involved in respiration are catabolic reactions that involve...
, PhotosynthesisPhotosynthesisPhotosynthesis is a chemical process that converts carbon dioxide into organic compounds, especially sugars, using the energy from sunlight. Photosynthesis occurs in plants, algae, and many species of bacteria, but not in archaea. Photosynthetic organisms are called photoautotrophs, since they can...
— Processes whereby energyEnergyIn physics, energy is an indirectly observed quantity. It is often understood as the ability a physical system has to do work on other physical systems...
is stored and/or liberated for use by the cell. - TranscriptionTranscription (genetics)Transcription is the process of creating a complementary RNA copy of a sequence of DNA. Both RNA and DNA are nucleic acids, which use base pairs of nucleotides as a complementary language that can be converted back and forth from DNA to RNA by the action of the correct enzymes...
and mRNA splicingSplicing (genetics)In molecular biology and genetics, splicing is a modification of an RNA after transcription, in which introns are removed and exons are joined. This is needed for the typical eukaryotic messenger RNA before it can be used to produce a correct protein through translation...
— Processes by which genes express themselves, primarily by way of RNARNARibonucleic acid , or RNA, is one of the three major macromolecules that are essential for all known forms of life....
and protein transcription.
External links
- Overview at Medical College of GeorgiaMedical College of GeorgiaGeorgia Health Sciences University formerly known as, and now home of the, Medical College of Georgia , is a public academic health center, with its main campus located in the Medical District of Augusta, Georgia. It is the smallest of four research universities in the University System of Georgia...