分子生物学名词解释

IsoacceptingtRNA：同工受体tRNA，能解读同工密码子的不同tRNA。
inducer;（诱导物）凡能诱导操纵子开启的效应物称为诱导物。
Insulater（绝缘子）：真核生物基因组的调控元件之一，亦为一种边界元件。
Pr omoter（启动子）：指DNA分子上被RNApol调节因子等识别并结合形成转
录起始复合体的 区域，是控制转录起始的序列。
Gene（基因）：书
Enhancer (增强子)：是 一个顺式作用序列，能够提高一些真核生物启动子的利
用，并能够在启动子任何方向以及任何位置(上游 或者下游)作用。
Gene ciston(基因顺反子)：指能产生一条多肽链的DNA片段。包括 编码区和
其上下游区域(引导区和尾)，以及在编码片段间(外显子)的割裂序列(内含子)。
Gene family (基因家族)：一系列外显子相关联的基因，其成员是由一个祖先基
因复制或趋异产生
Induction (诱导)：指细菌或者酵母只有当底物存在时才会合成某种酶的能力。
当 用在基因表达中，指诱导物与调控蛋白结合造成的转录转换。
Initiation factors (起始因子，原核中IF，真核中eIF)：在蛋白质合成起始阶段
特异性作用于核糖体小亚基的蛋白质 。
Intron (内含子)：一段DNA片段，它转录但通过将其两端的序列(外显子)剪接
在一起而被移出转录本。
IsoacceptingtRNAs(同工tRNA)：携带相同的氨基酸的tRNA。
Molecular chaperone (分子伴侣)：协助一些蛋白质装配或者恰当折叠所需的蛋
白质，但这种蛋白质并不是靶复合物的成分。
Operator(操纵基因)：DNA 上的一个位点，阻遏蛋白能与之结合抑制相邻启动
子从而抑制转录。
Primosome ( 引发体)：指在非连续DNA复制中，每个岗崎片段合成引发反应中
涉及的蛋白质复合体。引发体能沿着 DNA 移动，参与连续的引发反应。
Promoter (启动子)：结合RNA 聚合酶并起始转录的DNA 区域-10 sequence
(-10区)：位于细菌基因起始位点上 游10bp的一段保守序列TATAATG。在RNA
聚合酶诱导DNA 溶解起始时起作用。-35 sequence (-35区)：细菌基因起始位点
上游35bp处的保守序列，在RNA聚合酶起始识别中作用。
Pseudogenes (假基因)：由原始活性基因突变引起的基因组中稳定但不活泼的成
分。
Pseudogenes are segments of DNA that are related to real genes. Pseudogenes
have lost at least some functionality, relative to the complete gene, in cellular
gene expression or protein-coding ability.
snRNPs：核小核糖体蛋白质(snRNA与蛋白质结合)颗粒。
negative r egulation(负调节):当细胞中存在的调节蛋白处于激活状态时,会使目
的基因的表达活性受 到抑制,我们称这种抑制基因表达活性的调节类型为负调节。
顺式作用元件(cis-acting element)存在于基因旁侧序列中能影响基因表达的序
列。顺式作用元件包括启动子、增强子、调 控序列和可诱导元件等，它们的作用
是参与基因表达的调控。顺式作用元件本身不编码任何蛋白质，仅仅 提供一个作
用位点，要与反式作用因子相互作用而起作用。Cis-Acting Element Download
PDF (6,857 KB)
The Cis-acting element must be located in the same DNA strand as its target to
act upon it during transcription. Genes that are conserved across species will also

display conservation at the level of their transcriptional regulation and this will
be reflected in the organization of cis-elements mediating this regulation. Using a
computational approach, clusters of transcription factor binding sites that are
absolutely conserved in order and in spacing across human, rat, and mouse
genomes were identified.
mutation hot spot(突变热点):突变机率较高的碱基序列。
trans-acting element反式 作用因子：是指能直接或间接地识别或结合在各类顺式
作用元件核心序列上参与调控靶基因转录效率的蛋 白质。多为转录因子。大多数
真核转录调节因子由某一基因表达后，可通过另一基因的特异的顺式作用元 件相
互作用，从而激活另一基因的转录。这种调节蛋白称反式作用因子。
转录因子: 真核基因的转录调节蛋白又称转录调节因子或转录因子。
Transcription factor
In molecular biology, a transcription factor (or sequence-specific DNA-binding
factor) is a protein that controls the rate of transcription of genetic information
from DNA to messenger RNA, by binding to a specific DNA sequence.[1][2] In
turn, this helps to regulate the expression of genes near that sequence. This is
essential in embryogenesis.

Transcription factors work alone or with other proteins in a complex, by
promoting (as an activator), or blocking (as a repressor) the recruitment of RNA
polymerase (the enzyme that performs the transcription of genetic information
from DNA to RNA) to specific genes.[3][4][5]

A defining feature of transcription factors is that they contain at least one
DNA-binding domain (DBD), which attaches to a specific sequence of DNA
adjacent to the genes that they regulate.[6][7] Transcription factors are usually
classified into different families based on their DBDs.[8][9] Other proteins such
as coactivators, chromatin remodelers, histone acetyltransferases, histone
deacetylases, kinases, and methylases, while also essential to gene regulation,
lack DNA-binding domains, and, therefore, are not transcription factors.[10]
终止密码子：在mPNA翻译过程中，起蛋白质合成终止信号作用的密码子，即
UAA， UAG和UGA
multi gene family（多基因家族）是指由某一祖先基因经过重复和变异所产生的
一组基因。
A methyltransferase is a type of transferase enzyme that transfers a methyl group
from a donor to an acceptor.
Methylation often occurs on nucleic bases in DNA or amino acids in protein
structures. Methytransferases use a reactive methyl group bound to sulfur in
S-adenosyl methionine (SAM) as the methyl donor.
DNA methylation is often utilized to silence and regulate genes without changing
the original DNA sequence, an example of epigenetic modification. This
methylation occurs on cytosine residues. DNA methylation may be necessary for
normal growth from embryonic stages in mammals. When mutant embryonic
stem cells lacking the murine DNA methyltransferase gene were introduced to a

germline of mice, they caused a recessive lethal phenotype.[1] Methylation may
also be linked to cancer development, as methylation of tumor suppressor genes
promotes tumorgenesis and metastasis.[2]
Site-specific methyltransferases have the same DNA target sequences as certain
restriction enzymes. Methylation can also serve to protect DNA from enzymatic
cleavage, since restriction enzymes are unable to bind and recognize externally
modified sequences. This is especially useful in bacterial restriction modification
systems that use restriction enzymes to cleave foreign DNA while keeping their
own DNA protected by methylation.
Methylation of amino acids in the formation of proteins leads to more diversity of
possible amino acids and, therefore, more diversity of function. The methylation
reaction occurs on nitrogen atoms either on the N terminus or on the side-chain
position of the protein and are usually irreversible.
翻译起始因子：翻译起始所必需的特异蛋白因子。与核 糖体、信使核糖核酸、起
始转移核糖核酸等组成动态翻译起始复合体。真核和原核生物翻译起始因子分别
有eIF 1～6和IF 1～3等。
Initiation factors起始因子（英 语：）是指翻译起始阶段端结合到核糖体小亚基
上的一些蛋白质，翻译是蛋白质生物合成中的一部分。
house-keeping genes持家基因()：又称管家基因，是指所有细胞中均要稳定表< br>达的一类基因，其产物是对维持细胞基本生命活动所必需的。如微管蛋白基因、
糖酵解酶系基因与 核糖体蛋白基因等。
HSP：英文全称为：heat shock protein，中文名为：热休克蛋白，属于应激反应
性蛋白，高温应激可诱导该蛋白质形成。 HSP是分子伴侣的一种，在蛋白质翻译后修饰过程中，起到促进需要折叠的多肽
链折叠为天然空间 构象的蛋白质。
genetic mapping遗传作图（）是指应用遗传学技术构建能显示基因以 及其他序
列特征在基因组上位置的图。遗传学技术包括杂交育种实验，对人类则是检查家
族史或 系谱。与任何一种图一样，一个遗传图必须显示出显著特征的位置，在地
理图中，标记是图中可以识别的 部分，如河流、道路以及建筑物。
Gene mapping describes the methods used to identify the locus of a gene and
the distances between genes.
Genome，基因组，一个 细胞或者生物体所携带的一套完整的单倍体序列，包括
全套基因和间隔序列。
operon操 纵子（）：指启动基因、操纵基因和一系列紧密连锁的结构基因的总称。
转录的功能单位。很多功能上相 关的基因前后相连成串，由一个共同的控制区进
行转录的控制，包括结构基因以及调节基因的整个DNA 序列。主要见于原核生
物的转录调控，如乳糖操纵子、阿拉伯糖操纵子、组氨酸操纵子、色氨酸操纵子< br>等
gene expression基因表达()是指细胞在生命过程中，把储存在DNA顺序 中遗传
信息经过转录和翻译，转变成具有生物活性的蛋白质分子。
Gene expression is the process by which information from a gene is used in the
synthesis of a functional gene product. These products are often proteins, but in
non-protein coding genes such as transfer RNA (tRNA) or small nuclear RNA
(snRNA) genes, the product is a functional RNA.

效应物_百度百科是指能引起生理效应的物质。
In biochemistry, an effector molecule is usually a small molecule that selectively
binds to a protein and regulates its biological activity. In this manner, effector
molecules act as ligands that can increase or decrease enzyme activity, gene
expression, or cell signalling. Effector molecules can also directly regulate the
activity of some mRNA molecules (riboswitches).
In some cases, proteins can be considered to function as effector molecules,
especially in cellular signal transduction cascades.
The term effector is used in other fields of biology. For instance, the effector end
of a neuron is the terminus where an axon makes contact with the muscle or
organ that it stimulates or suppresses.
跳跃基因或转座子:一段可以从原位上单独复 制或断裂下来，环化后插入另一位
点，并对其后的基因起调控作用的DNA序列。
Denaturation (biochemistry)
Denaturation is a process in which proteins or nucleic acids lose the quaternary
structure, tertiary structure and secondary structure which is present in their
native state, by application of some external stress or compound such as a strong
acid or base, a concentrated inorganic salt, an organic solvent (e.g., alcohol or
chloroform), radiation or heat.[3] If proteins in a living cell are denatured, this
results in disruption of cell activity and possibly cell death. Protein denaturation
is also a consequence of cell death.[4][5] Denatured proteins can exhibit a wide
range of characteristics, from conformational change and loss of solubility to
aggregation due to the exposure of hydrophobic groups.
乳糖操纵子：大肠杆菌中与乳糖 代谢功能相关的基因成镞的串联在一起共同组成
一个转录单位即乳糖操纵子，包括：Z 、Y 及A三个结构基因，一个操纵序列O ,
一个启动序列P及一个调节基因I。
增强子：增强子 是能够结合特异基因调节蛋白，促进邻近或远处特定基因表达的
DNA序列。增强子距转录起始点的距离 变化很大，但总是作用于最近的启动子。
前导序列：存在于原核生物，为编码区之前的不翻译的mRNA区段，是mRNA
区段类型。
在原核生物中，一条mRNA分子常常编码数种不同的多肽链。这种多顺反子
mRNA的头一条 多肽链合成的起点，同RNA分子的5’—P末端间的距离可达数
百个核苷酸，这段编码区之前的不翻译 的mRNA区段，叫做前导序列。
Klenow片段：又名DNA聚合酶I（DNA pol 1）大片段（克列诺片段，Klenow
fragment，或称克列诺酶，Klenow enzyme）： DNA聚合酶Ⅰ经胰蛋白酶或
枯草杆菌蛋白酶部分水解生成的C末端605个氨基酸 残基片段。该片段保留了
DNA聚合酶I的5ˊ-3ˊ聚合酶和3ˊ-5ˊ外切酶活性，但缺少完整酶的 5ˊ-3ˊ外切酶活
性。DNA聚合酶 I（DNA-pol I）断开后的存在另一个323个氨基酸残基片段，
保留5‘-3’外切酶活性。
termi nator终止子(T)是给予RNA聚合酶转录终止信号的DNA序列。在一个操
纵元中至少在构基因 群最后一个基因的后面有一个终止子。
In genetics, a transcription terminator is a section of nucleic acid sequence that
marks the end of a gene or operon in genomic DNA during transcription. This
sequence mediates transcriptional termination by providing signals in the newly

synthesized mRNA that trigger processes which release the mRNA from the
transcriptional complex. These processes include the direct interaction of the
mRNA secondary structure with the complex andor the indirect activities of
recruited termination factors. Release of the transcriptional complex frees RNA
polymerase and related transcriptional machinery to begin transcription of new
mRNAs.
作为起始信号的密码子称为起始密码子。
silen cer沉默子（）也称为沉默子元件，是真核基因中的一种特殊的序列，与增
强子有许多类似之处。按功 能特性，真核基因顺式作用元件可以分为启动子，增
强子和沉默子。沉默子能够同反式因子结合从而阻断 增强子及反式激活因子的作
用，并最终抑制该基因的转录活性。
弱化子
atten uator，是指原核生物的操纵子中可以明显衰减乃至终止转录作用的一段核
苷酸序列，位于操纵子的 上游。
An insulator is a genetic boundary element that blocks the interaction between
enhancers and promoters.
It is thought that an insulator must reside between the enhancer and promoter to
inhibit their subsequent interactions. Insulators therefore determine the set of
genes an enhancer can influence. The need for insulators arises where two
adjacent genes on a chromosome have very different transcription patterns; it is
critical that the inducing or repressing mechanisms of one do not interfere with
the neighbouring gene.[1] Insulators have also been found to cluster at the
boundaries of topologically associating domains (TADs) and may have a role in
partitioning the genome into neighborhoods- genomic regions
within which regulation occurs.[2][3]
Insulator activity is thought to
occur primarily through the 3D
structure of DNA mediated by
proteins including CTCF.[4]
Insulated neighborhoods formed
by physical interaction between two CTCF-bound DNA loci contain the
interactions between enhancers and their target genes.[5]
顺 式作用元件.遗传学：一种长约数百个核苷酸对,通常位于启动子正调控元件或
负调控元件之间的一种调 控序列.
primosome引发体（）是DNA复制过程中的一种负责专一性引发的多酶复合物，< br>位于复制叉的前端，能够生成后随链冈崎片段合成必需的RNA引物，主要成分
为引物酶（如Dn aG）以及DNA解旋酶（如DnaB）等。
editosome编辑体；英文名称：；定义1：进行 RNA转录物编辑的一个复杂系统。
除了有许多酶之外，还有一个指导RNA。
splice osome剪接体（英文：）是指进行RNA剪接时形成的多组分复合物，其大
小为60S，主要是由小 分子的核RNA和蛋白质组成。
A spliceosome is a large and complex molecular machine
found primarily within the splicing speckles of the cell
nucleus of eukaryotic cells. The spliceosome is assembled

from snRNAs and protein complexes. The spliceosome removes introns from a
transcribed pre-mRNA, a type of primary transcript. This process is generally
referred to as splicing.[1] Only eukaryotes have spliceosomes and some
organisms have a second spliceosome, the minor spliceosome.[2] An analogy is a
film editor, who selectively cuts out irrelevant or incorrect material (equivalent to
the introns) from the dailies and sends the cleaned-up version to be screened for
the producer.
HTH；最早在原核基因的激活蛋白和阻遏蛋白中发现的调控蛋白, 是一种同型二
聚体。
In proteins, the helix-turn- helix (HTH) is a major structural motif capable of
binding DNA. It is composed of two α helices joined by a short strand of amino
acids and is found in many proteins that regulate gene expression. It should not
be confused with the helix-loop-helix domain.[1]
basic helix-loop- helix
DNA-binding domain
Basic helix-loop- helix structural
motif ofARNT.
Two α-helices (blue) are
connected by a
short loop (red).
[1]

Stringent response严紧反应： 当细菌在缺乏合成蛋白质所必须的氨基酸时，停
止合成核糖体RNA的反应。
From Wikipedia, the free encyclopedia
The stringent response, also called stringent control, is a stress response of
bacteria and plant chloroplasts in reaction to amino-acid starvation,[1] fatty acid
limitation,[2] iron limitation,[3] heat shock[4] and other stress conditions. The
stringent response is signaled by the alarmone (p)ppGpp, and modulates
transcription of up to 13 of all genes in the cell. This in turn causes the cell to
divert resources away from growth and division and toward amino acid synthesis
in order to promote survival until nutrient conditions improve.

In Escherichia coli, (p)ppGpp production is mediated by the ribosomal protein

L11 (rplK resp. relC) and the ribosome-associated (p)ppGppsynthetase I, RelA;
deacylatedtRNA bound in the ribosomal A-site is the primary induction signal.[1]
RelA converts GTP and ATP into pppGpp by adding the pyrophosphate from ATP
onto the 3' carbon of the ribose in GTP, releasing AMP. pppGpp is converted to
ppGpp by the gpp gene product, releasing Pi. ppGpp is converted to GDP by the
spoT gene product, releasing pyrophosphate (PPi). GDP is converted to GTP by
the ndk gene product. Nucleoside triphosphate (NTP) provides the Pi, and is
converted to Nucleoside diphosphate (NDP).

In other bacteria, the stringent response is mediated by a variety of RelASpoT
Homologue (RSH) proteins,[5] with some having only synthetic, or hydrolytic or
both (Rel) activities.[6]

During the stringent response, (p)ppGpp accumulation affects the
resource-consuming cell processes replication, transcription, and translation.
(p)ppGpp is thought to bind RNA polymerase and alter the transcriptional profile,
decreasing the synthesis of translational machinery (such as rRNA and tRNA),
and increasing the transcription of biosynthetic genes.[7] Additionally, the
initiation of new rounds of replication is inhibited and the cell cycle arrests until
nutrient conditions improve.[8] Translational GTPases involved in protein
biosynthesis are also affected by ppGpp, with Initiation Factor 2 (IF2) being the
main target.[9]

Chemical reaction catalyzed by RelA:

ATP + GTP → AMP + pppGpp

Chemical reaction catalyzed by SpoT:

ppGpp → GDP + PPi or pppGpp -> GTP + PPi

Extensive Mendeley collection of scientific papers covering stringent response is
available here.




Molecular biology
Molecular biology m??l?kj?l?r concerns the molecular basis of biological activity between biomolecules in
the various systems of a cell, including the interactions between DNA, RNA, and proteins and their
biosynthesis, as well as the regulation of these interactions.[1] Writing in Nature in 1961, William Astbury
described molecular biology as:

with the leading idea of searching below the large-scale manifestations of classical biology for the
corresponding molecular plan. It is concerned particularly with the forms of biological molecules and [...] is
predominantly three- dimensional and structural—which does not mean, however, that it is merely a
refinement of morphology. It must at the same time inquire into genesis and function.


Life is a characteristic distinguishing physical entities having biological processes, such as signaling and
self-sustaining processes, from those that do not, either because such functions have ceased, or because they
never had such functions and are classified as inanimate. Various forms of life exist, such as plants, animals,
fungi, protists, archaea, and bacteria. The criteria can at times be ambiguous and may or may not define
viruses, viroids, or potential artificial life as
of life, although many other sciences are involved.

The definition of life is controversial. The current definition is that organisms maintain homeostasis, are
composed of cells, undergo metabolism, can grow, adapt to their environment, respond to stimuli, and
reproduce. However, many other biological definitions have been proposed, and there are some borderline
cases of life, such as viruses. Throughout history, there have been many attempts to define what is meant by

that everything is made out of matter and that life is merely a complex form of it; hylomorphism, the belief
that all things are a combination of matter and form, and the form of a living thing is its soul; spontaneous
generation, the belief that life repeatedly emerges from non-life; and vitalism, a now largely discredited
hypothesis that living organisms possess a
with input from a diversity of scientific disciplines. Biophysicists have proposed many definitions based on
chemical systems; there are also some living systems theories, such as the Gaia hypothesis, the idea that the
Earth itself is alive. Another theory is that life is the property of ecological systems, and yet another is
elaborated in complex systems biology, a branch or subfield of mathematical biology. Abiogenesis describes
the natural process of life arising from non-living matter, such as simple organic compounds. Properties
common to all organisms include the need for certain core chemical elements to sustain biochemical
functions.

Life on Earth first appeared as early as 4.28 billion years ago, soon after ocean formation 4.41 billion years
ago, and not long after the formation of the Earth 4.54 billion years ago.[1][2][3][4] Earth's current life may
have descended from an RNA world, although RNA-based life may not have been the first. The mechanism by
which life began on Earth is unknown, though many hypotheses have been formulated and are often based
on the Miller–Urey experiment. The earliest known life forms are microfossils of bacteria. In July 2016,
scientists reported identifying a set of 355 genes believed to be present in the last universal common
ancestor (LUCA) of all living organisms.[5]

Since its primordial beginnings, life on Earth has changed its environment on a geologic time scale. To
survive in most ecosystems, life must often adapt to a wide range of conditions. Some microorganisms,
called extremophiles, thrive in physically or geochemically extreme environments that are detrimental to
most other life on Earth. Aristotle was the first person to classify organisms. Later, Carl Linnaeus introduced
his system of binomial nomenclature for the classification of species. Eventually new groups and categories
of life were discovered, such as cells and microorganisms, forcing dramatic revisions of the structure of

relationships between living organisms. Cells are sometimes considered the smallest units and
blocks
enclosed within a membrane and contain many biomolecules such as proteins and nucleic acids. Cells
reproduce through a process of cell division, in which the parent cell divides into two or more daughter cells.

Though currently only known on Earth, life need not be restricted to it, and many scientists believe in the
existence of extraterrestrial life. Artificial life is a computer simulation or man-made reconstruction of any
aspect of life, which is often used to examine systems related to natural life. Death is the permanent
termination of all biological functions which sustain an organism, and as such, is the end of its life. Extinction
is the process by which an entire group or taxon, normally a species, dies out. Fossils are the preserved
remains or traces of organisms.

Love is a variety of different feelings, states, and attitudes that ranges from interpersonal affection (
my mother
attachment.[1] Love can also be a virtue representing human kindness, compassion, and affection—
unselfish loyal and benevolent concern for the good of another
affectionate actions towards other humans, one's self or animals.[3]
Ancient Greek philosophers identified four forms of love: kinship or familiarity (in Greek, storge), friendship
(philia), romantic desire (eros), and self- emptying or unconditional love (agape). Modern authors have
distinguished further varieties of love: limerence, amour de soi, and courtly love. Non-Western traditions
have also distinguished variants or symbioses of these states.[4][5] Love has additional religious or spiritual
meaning—notably in Abrahamic religions. This diversity of uses and meanings combined with the
complexity of the feelings involved makes love unusually difficult to consistently define, compared to other
emotional states.
Love in its various forms acts as a major facilitator of interpersonal relationships and, owing to its central
psychological importance, is one of the most common themes in the creative arts.[6]
Love may be understood as a function to keep human beings together against menaces and to facilitate the
continuation of the species.[7]
The word can have a variety of related but distinct meanings in different contexts. Many other
languages use multiple words to express some of the different concepts that in English are denoted as
one example is the plurality of Greek words for
in conceptualizing love thus doubly impede the establishment of a universal definition.[9]

Although the nature or essence of love is a subject of frequent debate, different aspects of the word can be
clarified by determining what isn't love (antonyms of Love as a general expression of positive
sentiment (a stronger form of like) is commonly contrasted with hate (or neutral apathy); as a less sexual
and more emotionally intimate form of romantic attachment, love is commonly contrasted with lust; and as
an interpersonal relationship with romantic overtones, love is sometimes contrasted with friendship,
although the word love is often applied to close friendships. (Further possible ambiguities come with usages



Fraternal love (Prehispanic sculpture from 250–900 AD, of Huastec origin). Museum of Anthropology in
Xalapa, Veracruz, Mexico

Abstractly discussed love usually refers to an experience one person feels for another. Love often involves
caring for, or identifying with, a person or thing (cf. vulnerability and care theory of love), including oneself
(cf. narcissism). In addition to cross-cultural differences in understanding love, ideas about love have also
changed greatly over time. Some historians date modern conceptions of romantic love to courtly Europe
during or after the Middle Ages, although the prior existence of romantic attachments is attested by ancient
love poetry.[10]

The complex and abstract nature of love often reduces discourse of love to a thought-terminating cliché.
Several common proverbs regard love, from Virgil's conquers allto The Beatles' All You Need Is
LoveSt. Thomas Aquinas, following Aristotle, defines love as will the good of nd
Russell describes love as a condition of value,as opposed to relative value.[citation needed]
Philosopher Gottfried Leibniz said that love is
stated that in love there is a
of love.

Impersonal love
People can be said to love an object, principle, or goal to which they are deeply committed and greatly value.
For example, compassionate outreach and volunteer workers'
not of interpersonal love but impersonal love, altruism, and strong spiritual or political convictions.[15]
People can also material objects, animals, or activities if they invest themselves in bonding or
otherwise identifying with those things. If sexual passion is also involved, then this feeling is called
paraphilia.[16] A common principle that people say they love is life itself.

Interpersonal love
Interpersonal love refers to love between human beings. It is a much more potent sentiment than a simple
liking for a person. Unrequited love refers to those feelings of love that are not reciprocated. Interpersonal
love is most closely associated with interpersonal relationships.[15] Such love might exist between family
members, friends, and couples. There are also a number of psychological disorders related to love, such as
erotomania.


Pair of Lovers. 1480–1485
Throughout history, philosophy and religion have done the most speculation on the phenomenon of love. In
the 20th century, the science of psychology has written a great deal on the subject. In recent years, the
sciences of psychology, anthropology, neuroscience, and biology have added to the understanding the
concept of love.

Biological basis
Main article: Biological basis of love
Biological models of sex tend to view love as a mammalian drive, much like hunger or thirst.[17] Helen
Fisher, a leading expert in the topic of love, divides the experience of love into three partly overlapping
stages: lust, attraction, and attachment. Lust is the feeling of sexual desire; romantic attraction determines
what partners mates find attractive and pursue, conserving time and energy by choosing; and attachment
involves sharing a home, parental duties, mutual defense, and in humans involves feelings of safety and

security.[18] Three distinct neural circuitries, including neurotransmitters, and three behavioral patterns,
are associated with these three romantic styles.[18]

Lust is the initial passionate sexual desire that promotes mating, and involves the increased release of
chemicals such as testosterone and estrogen. These effects rarely last more than a few weeks or months.
Attraction is the more individualized and romantic desire for a specific candidate for mating, which develops
out of lust as commitment to an individual mate forms. Recent studies in neuroscience have indicated that as
people fall in love, the brain consistently releases a certain set of chemicals, including the neurotransmitter
hormones, dopamine, norepinephrine, and serotonin, the same compounds released by amphetamine,
stimulating the brain's pleasure center and leading to side effects such as increased heart rate, loss of
appetite and sleep, and an intense feeling of excitement. Research has indicated that this stage generally
lasts from one and a half to three years.[19]

Since the lust and attraction stages are both considered temporary, a third stage is needed to account for
long-term relationships. Attachment is the bonding that promotes relationships lasting for many years and
even decades. Attachment is generally based on commitments such as marriage and children, or on mutual
friendship based on things like shared interests. It has been linked to higher levels of the chemicals oxytocin
and vasopressin to a greater degree than short-term relationships have.[19] EnzoEmanuele and coworkers
reported the protein molecule known as the nerve growth factor (NGF) has high levels when people first fall
in love, but these return to previous levels after one year.[20]

Psychological basis

Grandmother and grandchild in Sri Lanka
Further information: Human bonding
Psychology depicts love as a cognitive and social phenomenon. Psychologist Robert Sternberg formulated a
triangular theory of love and argued that love has three different components: intimacy, commitment, and
passion. Intimacy is a form in which two people share confidences and various details of their personal lives,
and is usually shown in friendships and romantic love affairs. Commitment, on the other hand, is the
expectation that the relationship is permanent. The last form of love is sexual attraction and passion.
Passionate love is shown in infatuation as well as romantic love. All forms of love are viewed as varying
combinations of these three components. Non- love does not include any of these components. Liking only
includes intimacy. Infatuated love only includes passion. Empty love only includes commitment. Romantic
love includes both intimacy and passion. Companionate love includes intimacy and commitment. Fatuous
love includes passion and commitment. Lastly, consummate love includes all three.[21] American
psychologist Zick Rubin sought to define love by psychometrics in the 1970s. His work states that three
factors constitute love: attachment, caring, and intimacy.[22][23]

Following developments in electrical theories such as Coulomb's law, which showed that positive and
negative charges attract, analogs in human life were developed, such as attractOver the last
century, research on the nature of human mating has generally found this not to be true when it comes to
character and personality—people tend to like people similar to themselves. However, in a few unusual and
specific domains, such as immune systems, it seems that humans prefer others who are unlike themselves
(e.g., with an orthogonal immune system), since this will lead to a baby that has the best of both worlds.[24]

In recent years, various human bonding theories have been developed, described in terms of attachments,
ties, bonds, and affinities. Some Western authorities disaggregate into two main components, the altruistic
and the narcissistic. This view is represented in the works of Scott Peck, whose work in the field of applied
psychology explored the definitions of love and evil. Peck maintains that love is a combination of the

not simply a feeling.

Psychologist Erich Fromm maintained in his book The Art of Loving that love is not merely a feeling but is
also actions, and that in fact, the
via a series of loving actions over time.[15] In this sense, Fromm held that love is ultimately not a feeling at
all, but rather is a commitment to, and adherence to, loving actions towards another, oneself, or many others,
over a sustained duration.[15] Fromm also described love as a conscious choice that in its early stages might
originate as an involuntary feeling, but which then later no longer depends on those feelings, but rather
depends only on conscious commitment.[15]

Evolutionary basis
Evolutionary psychology has attempted to provide various reasons for love as a survival tool. Humans are
dependent on parental help for a large portion of their lifespans compared to other mammals. Love has
therefore been seen as a mechanism to promote parental support of children for this extended time period.
Another factor may be that sexually transmitted diseases can cause, among other effects, permanently
reduced fertility, injury to the fetus, and increase complications during childbirth. This would favor
monogamous relationships over polygamy.[26]

Comparison of scientific models
Biological models of love tend to see it as a mammalian drive, similar to hunger or thirst.[17] Psychology
sees love as more of a social and cultural phenomenon. Certainly love is influenced by hormones (such as
oxytocin), neurotrophins (such as NGF), and pheromones, and how people think and behave in love is
influenced by their conceptions of love. The conventional view in biology is that there are two major drives
in love: sexual attraction and attachment. Attachment between adults is presumed to work on the same
principles that lead an infant to become attached to its mother. The traditional psychological view sees love
as being a combination of companionate love and passionate love. Passionate love is intense longing, and is
often accompanied by physiological arousal (shortness of breath, rapid heart rate); companionate love is
affection and a feeling of intimacy not accompanied by physiological arousal.