Name: operons in bacterial gene control
Uploaded: 2020-11-23T11:47:37.000Z
Duration: 2 min 9 s
Channel: JoVE

在原核细胞中，操纵子 是一组基因序列， 其中含有调控元件和 几个蛋白质编码基因， 这些基因是转录在一起的结构基因。
 最好的研究案例之一 是细菌中的lac操纵子， 它包含三个基因， lac-Z，lac-Y和lac-A， 它们是乳糖代谢 所需要的酶， 以及启动子、操纵子 和调节lac基因 呈现的终止子序列。
 通常，当葡萄糖浓度较丰富时， lac阻遏蛋白与操作子 紧密结合并通过 阻断RNA聚合酶与 启动子的结合 来阻止lac基因的转化。
 lac阻遏蛋白是组成型呈现的， 意味着含有它的基因 默认开启。
 当葡萄糖浓度非常低时， 细胞将使用乳糖作为能量来源。
 一旦存在于细胞内， 一些乳糖被转化为 改良形式，称为allolactose， 它被称为lac操纵子的诱导物， 因为它结合并抑制阻遏物， 引发lac基因的显现。
 另外，在低葡萄糖水平的情况下， 信号分子环 AMP的量增加并与 分解代谢物活化蛋白或CAP结合。
 它们一起结合 大约在启动子上游的调节序列， 并帮助募集RNA聚合酶 以显着增加转变。
 在转化期间，当聚合酶 到达终止子序列时， 产生并释放单个mRNA链。
 从这个mRNA中，转变处理了 乳糖所必需的三种蛋白质。

Osbourn、Anne E. 和 Ben Field。"纵子。细胞和分子生命科学 66，第 23 期（2009 年）:3755-3775。[<a href="https://doi.org/10.1007/s00018-009-0114-3">来源</a>]

操纵子

Operons

原核生物可通过操纵子控制基因表达。它们由调控元件和成簇的，功能相关的蛋白质编码基因组成的DNA序列。操纵子使用单个启动子序列来启动基因簇（即一组结构基因）转录成单个mRNA分子。终止子序列结束转录。位于启动子和结构基因之间的操纵基因序列，如果被阻遏蛋白结合，则禁止操纵子的转录活性。总而言之，启动子、操纵子、结构基因和终止子构成了操纵子的核心。
操纵子通常是可诱导的或可抑制的。可诱导的操纵子，如细菌 lac 操纵子，通常是“关闭”的，但在一种称为诱导剂的小分子（如乳糖）存在下会“打开”。当葡萄糖不存在，但乳糖存在时，异乳糖结合并灭活 lac 操纵子阻遏物，允许操纵子产生负责乳糖代谢的酶。
可抑制的操作，如细菌的trp操作，通常是“开”的，但在一种叫做共加压素的小分子（如色氨酸）存在下会“关”的。当必需氨基酸色氨酸含量丰富时，色氨酸结合并激活抑制因子，阻止操纵子产生合成所需的酶。
操纵子也可以是构成性的（即持续的）活跃的。例如，细菌核糖体RNA（rRNA）的操作总是“开”的，因为翻译经常需要rRNA。
其它调控因素也有助于操纵子的协调基因表达。调控基因编码转录激活物或阻遏蛋白。例如， lacI 和 trpR基因为其各自的操纵子抑制子编码。其它调控序列，如 lac操纵子的分解代谢激活蛋白（CAP）结合位点，为其它激活物或抑制物提供结合位点。例如，当葡萄糖含量较低时，信号分子（即环腺苷酸）激活CAP，使其结合CAP位点， 吸收RNA聚合酶，并启动lac操纵子转录。

原核生物可通过操纵子控制基因表达——操纵子是一段包含调控元件以及成簇且功能相关的基因的DNA序列……

Education

教育

JoVE Core

Molecular Biology

分子生物学

Unit 1

第一单元

Gene Expression

基因表达

KEY TERMS AND CONCEPTS

关键术语与概念

纵子

operons in bacterial gene control

Operons help bacteria control groups of genes at the same time. An operon is a set of genes that are regulated together and can be turned on or off as a unit. This shared control helps bacteria respond quickly to changes in their environment.

In many operons, a promoter gives RNA polymerase a place to bind and start transcription. The operon also includes a regulatory region that helps control whether the genes are expressed. When conditions change, the cell can use this setup to manage gene activity efficiently.

Operons are a key example of gene regulation in prokaryotes. The transcript highlights the lac operon as a model for this process. Studying operons shows how bacteria coordinate gene expression without separating the genes into different control systems.

Operons in Bacterial Gene Control

cell specific gene expression

How Cells Switch Genes On and Off

Cells switch genes on and off to make different proteins for different jobs. In multicellular organisms, many cell types are built from the same DNA, but they do not use the same genes in the same way. This difference in gene expression helps explain why cells can look and act so differently. Liver cells are a clear example. They help detoxify blood, make bile to help digest fats, and produce proteins needed for metabolism. To do these jobs, liver cells must express a specific set of genes.

regulation of expression occurs at multiple steps

regulation-of-expression-occurs-at-multiple-steps

How Cells Control Gene Expression

Cells control gene expression at several points between DNA and protein. The most common control point is transcription. At this stage, proteins bind to short regulatory DNA sequences and can either increase or reduce transcription of the linked gene. After transcription, a precursor mRNA is made. This pre-mRNA contains exons, which code for protein, and introns, which do not. It must be processed before translation, and splicing removes the introns and joins the exons. Cells can also regulate...

cis-regulatory sequences

How Cis-Regulatory DNA Controls Transcription

Cis-regulatory sequences are short, non-coding DNA segments that control gene transcription. They sit on the same chromosome as the genes they regulate and act as binding sites for transcriptional regulators. In eukaryotes, these proteins help control gene expression patterns in different cell types. These DNA sequences can be close to a gene or thousands of bases away. When they are far from the gene in the DNA sequence, they are often brought close together in space because chromosomes are...

cooperative binding of transcription regulators

cooperative-binding-of-transcription-regulators

How Transcription Factors Bind DNA

Transcriptional regulators bind to cis-regulatory DNA sequences to control gene transcription. These DNA sequences are very short, usually fewer than ten nucleotide pairs long. Because they are so short, the same sequence can appear by chance in many places across the genome. Some regulators can also bind to groups of similar sequences. That raises the chance of random binding even more. To lower this risk, transcription regulators often form dimers, which are pairs of proteins that bind a DNA...

prokaryotic transcriptional activators and repressors

prokaryotic-transcriptional-activators-and-repressors

Operon Control by Activators and Repressors

Operon control in prokaryotes depends on activators and repressors. Prokaryotic genes are often arranged in groups, not one by one like in eukaryotes. Genes that help carry out the same biochemical process are placed together with their regulatory elements. This group is called an operon, and it is transcribed into a single polycistronic mRNA strand. Activators and repressors are DNA-binding proteins that control transcription in an operon. Activators bind near the promoter, which is the site...

operons

Operons help bacteria control groups of genes at the same time. An operon is a set of genes that are regulated together and can be turned on or off as a unit. This shared control helps bacteria respond quickly to changes in their environment. In many operons, a promoter gives RNA polymerase a place to bind and start transcription. The operon also includes a regulatory region that helps control whether the genes are expressed. When conditions change, the cell can use this setup to manage gene...

the eukaryotic promoter region

Eukaryotic Promoter Motifs and Gene Control

The eukaryotic promoter region is a stretch of DNA located upstream of a gene. It includes an RNA polymerase binding site, a transcription start site, and several cis-regulatory sequences. These DNA signals help control when transcription begins. The promoter can be divided into proximal and distal regions. The proximal promoter lies close to the gene and includes cis-regulatory sequences and the core promoter. The core promoter is the RNA polymerase binding site, and it is usually found...

co-activators and co-repressors

Chromatin Control in Gene Transcription

Chromatin control plays a major role in gene transcription in eukaryotes. Gene expression is regulated by several proteins that work together at a gene regulatory site. Some of these proteins bind directly to specific DNA sequences, while co-regulators attach to those regulators but do not bind DNA on their own. Co-regulators can act as co-activators or co-repressors, depending on the complex they join. One co-regulator may even switch roles in different settings. For example, the...

eukaryotic transcription activators

How Transcription Activators Turn Genes On

Transcription activators are proteins that help turn genes on by promoting transcription from DNA to RNA. They often have two parts. One part binds to DNA, and the other part activates transcription. In some proteins, such as the glucocorticoid receptor and MyoD, one domain can do both jobs. The DNA-binding part recognizes specific regulatory sequences on the DNA. These binding domains are grouped into families based on their structure. Common examples include the leucine zipper, zinc finger,...

eukaryotic transcription inhibitors

How Eukaryotic Gene Repressors Work

Eukaryotic gene repressors help turn specific genes off when the cell needs to control growth, development, or other biochemical processes. These DNA-binding proteins regulate gene expression in eukaryotes. Their presence at the right time and place can be triggered by hormones and signals from other cells. Most transcription inhibitors have two main parts. One part binds DNA, and the other is a repressor domain, which helps shut down transcription. Repressor domains can connect with basal...

combinatorial gene control

Gene Expression by Transcription Factor Combinations

Gene expression can depend on combinations of transcription factors working together. In combinatorial gene control, several transcription factors act in a coordinated way to regulate a single gene. If one or more of these factors are missing, the level of gene expression or repression can change a lot. This kind of control helps explain how a relatively small number of transcription factors can regulate a very large number of genes. More than 30,000 genes are controlled by about 2,000 to...

induced pluripotent stem cells

Reprogramming Cells into Stem Cells

Induced pluripotent stem cells are created by reprogramming mature cells back into a stem-cell state. This process shows that specialized cells can be changed into cells with broader developmental potential. The topic is important in biology because it links cell identity, gene control, and stem cell research. These cells begin as ordinary body cells and are pushed to de-differentiate, or lose their specialized features. After reprogramming, they behave like pluripotent stem cells, which means...

master transcription regulators

MEF2C and Gene Control Cascades

MEF2C is a master transcription regulator that controls gene expression in coordinated cascades. These regulators are proteins that manage the activity of multiple genes that often work together to produce a complex outcome. When a master transcription regulator is activated, it can start a chain of transcriptional activation that supports that outcome. Master transcription regulators can act in two main ways. They may bind directly to the regulatory sequences of several genes involved in a...

epigenetic regulation

DNA Methylation and Histone Changes

Epigenetic regulation controls gene activity without changing the DNA sequence. It helps determine when genes are turned on or off in a cell. Two major epigenetic mechanisms are DNA methylation and histone modification. DNA methylation adds chemical groups to DNA, while histone changes affect how tightly DNA is packed around histone proteins. These changes can make genes easier or harder to use. In high school biology, epigenetic regulation is important for understanding how cells with the...

genomic imprinting and inheritance

Genomic Imprinting in Human Disease

Genomic imprinting affects how some inherited genes are turned on or off in human cells. Diploid organisms inherit chromosomes from both parents, and each gene usually has two alleles. In most cases, both alleles are expressed. If one allele is missing or mutated, the other can often compensate, but some genes do not work that way. In genomic imprinting, a gene or its regulatory sequence carries chemical tags, such as methyl groups, on the copy inherited from only one parent. These tags are...

key terms and concepts

Learn how operons let bacteria regulate groups of genes together, with a focus on promoters, regulatory regions, and the lac operon model.

Operons in Bacterial Gene Control | JoVE K12

molecular biology

JoVE Core 分子生物学通过清晰简洁的动画视频课程展示了细胞的分子过程。此外，在科学家在行动的视频中，这些概念的应用是通过现代实验室中的真实实验演示的。

myJoVE Corporation

Operons in Bacterial Gene Control

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