Name: genes, introns, and regulatory dna
Uploaded: 2026-08-26T08:20:12.834Z
Duration: 2 min 39 s
Channel: JoVE

K12 Standards

Pennsylvania State Academic Standards

9-12

Life Science

Structure and Function

3.1.9-12.A

Organization of Genes

- [Instructeur] Avec l&#x27;agencement complexedu mat&#xE9;riel g&#xE9;n&#xE9;tique dans le noyau d&#x27;une cellule,les g&#xE8;nes humains &#xE9;tablissent aussi leur organisation. 
Plus de 20 000 g&#xE8;nes distribu&#xE9;s entre les chromosomesparfois s&#xE9;par&#xE9;s par de vastes &#xE9;tendues d&#x27;ADN non codant. 
Ou qui ne s&#x27;encode pas avec les prot&#xE9;ines. 
La cl&#xE9; de l&#x27;organisation d&#x27;un g&#xE8;ne individuelest son promoteur auquel des rouages,en particulier l&#x27;ARN polym&#xE9;rase, peuvent se fixer. 
Lorsque cette enzyme reconna&#xEE;t&#xE0; proximit&#xE9; un site d&#x27;initiation de la transcription,elle commence &#xE0; g&#xE9;n&#xE9;rer un brin d&#x27;ARNen utilisant l&#x27;ADN comme matrice. 
La polym&#xE9;rase traverse ensuite le mat&#xE9;riel g&#xE9;n&#xE9;tiqueet continue &#xE0; produire de l&#x27;ARNjusqu&#x27;&#xE0; ce qu&#x27;elle identifiela s&#xE9;quence de terminaison de la transcription d&#x27;un g&#xE8;nequi arr&#xEA;te le processus. 
Il faut noter qu&#x27;entrent ces points de d&#xE9;part et d&#x27;arriv&#xE9;ese trouvent des zones appel&#xE9;es introns et exons,qui sont toutes deux refl&#xE9;t&#xE9;es dans le produit ARN. 
Cependant, les processus ult&#xE9;rieurs suppriment les intronsde cette transcription. 
Puisque cet ARN sera utilis&#xE9; pour g&#xE9;n&#xE9;rer des prot&#xE9;ines,les exons sont d&#xE9;sign&#xE9;s comme r&#xE9;gions codantes,o&#xF9; les introns sont un autre exemple de mat&#xE9;riel non codant. 
Fait int&#xE9;ressant, d&#x27;autres types d&#x27;ADN non codant,tels que les silencers, s&#x27;associent &#xE9;galement &#xE0; des g&#xE8;nes. 
Les prot&#xE9;ines appel&#xE9;es r&#xE9;presseurs se lient &#xE0; ces r&#xE9;gions,emp&#xEA;chant ainsi la transcription par l&#x27;associationdu promoteur de la polym&#xE9;rase. 
En cons&#xE9;quence, les silencers aident &#xE0; r&#xE9;gulerl&#x27;expression des g&#xE8;nes. 
Ainsi, un g&#xE8;ne est constitu&#xE9; de divers composants. 
Parmi eux, un promoteur, des exons, des intronset des &#xE9;l&#xE9;ments r&#xE9;gulateurs. 
Qui tous ensemble aident&#xE0; d&#xE9;terminer l&#x27;expression de la prot&#xE9;ine dans une cellule.

1. William Roy, Scott et Walter Gilbert. « L’évolution des introns splicéosomaux : motifs, énigmes et progrès », Nature Reviews Genetics 7, n° 3 (mars 2006) : 211-21. <a href="https://doi.org/10.1038/nrg1807">https://doi.org/10.1038/nrg1807</a>.

organisation des gènes

<h4>Aper&#xE7;u</h4>
 
 Les g&#xE9;nomes des eucaryotes peuvent &#xEA;tre structur&#xE9;s en plusieurs cat&#xE9;gories fonctionnelles. Un brin d&#x2019;ADN est compos&#xE9; de g&#xE8;nes et de r&#xE9;gions interg&#xE9;niques. Les g&#xE8;nes eux-m&#xEA;mes sont constitu&#xE9;s d&#x2019;exons codant des prot&#xE9;ines et d&#x2019;introns non codants. Les introns sont excis&#xE9;s une fois que la s&#xE9;quence est transcrite en ARNm, ne laissant que des exons pour coder des prot&#xE9;ines.
 
 <h4>Les g&#xE8;nes d&#x2019;eucaryotes sont s&#xE9;par&#xE9;s par des r&#xE9;gions interg&#xE9;niques</h4>
 
 Dans les g&#xE9;nomes eucaryotes, les g&#xE8;nes sont s&#xE9;par&#xE9;s par de grandes &#xE9;tendues d&#x2019;ADN qui ne codent pas de prot&#xE9;ines. Cependant, ces r&#xE9;gions interg&#xE9;niques portent des &#xE9;l&#xE9;ments importants qui r&#xE9;gulent l&#x27;activit&#xE9; des g&#xE8;nes, par exemple, le promoteur o&#xF9; la transcription commence, ainsi que les amplificateurs et les inactivateurs qui r&#xE8;glent avec pr&#xE9;cision l&#x27;expression des g&#xE8;nes. Parfois, ces sites de liaison peuvent &#xEA;tre situ&#xE9;s loin du g&#xE8;ne associ&#xE9;.
 
 <h4>Les exons codant des prot&#xE9;ines sont entrecoup&#xE9;s d&#x2019;introns</h4>
 
 En &#xE9;tudiant le m&#xE9;canisme de la transcription des g&#xE8;nes chez les eucaryotes, les chercheurs ont r&#xE9;alis&#xE9; que l&#x2019;ARNm final qui code une prot&#xE9;ine est plus court que l&#x2019;ADN dont il est d&#xE9;riv&#xE9;. Cette diff&#xE9;rence de longueur est due &#xE0; un processus nomm&#xE9; &#xE9;pissage. Une fois que le pr&#xE9;-ARNm a &#xE9;t&#xE9; transcrit &#xE0; partir de l&#x2019;ADN dans le noyau, l&#x2019;&#xE9;pissage enl&#xE8;ve imm&#xE9;diatement les introns et r&#xE9;uni les exons. Le r&#xE9;sultat est de l&#x2019;ARNm codant des prot&#xE9;ines qui se d&#xE9;place vers le cytoplasme et qui est traduit en prot&#xE9;ines.
 
 <h4>Le nombre d&#x2019;introns par g&#xE8;ne peut varier consid&#xE9;rablement</h4>
 
 L&#x2019;un des plus grands g&#xE8;nes humains, DMD, est long de plus de deux millions de paires de bases. Ce g&#xE8;ne code la prot&#xE9;ine du muscle dystrophine. Les mutations dans le DMD causent la dystrophie musculaire, un trouble caract&#xE9;ris&#xE9; par la d&#xE9;t&#xE9;rioration progressive du muscle. Ce g&#xE8;ne contient 79 exons et 103 introns. &#xC0; l&#x2019;autre extr&#xE9;mit&#xE9; du spectre se trouve le g&#xE8;ne de l&#x2019;histone H1A &#x2014; c&#x2019;est l&#x2019;un des plus petits g&#xE8;nes dans le g&#xE9;nome humain &#xE0; seulement 781 paires de bases de long avec un exon mais aucun intron.
 
 <h4>Les introns ont des fonctions importantes</h4>
 
 Est-ce que les introns sont des d&#xE9;chets de l&#x2019;ADN qui doivent &#xEA;tre enlev&#xE9;s ? Fait int&#xE9;ressant, les introns peuvent transporter des &#xE9;l&#xE9;ments qui sont importants pour la r&#xE9;gulation des g&#xE8;nes. De plus, la coupure de la transcription initiale et le r&#xE9;assemblage des exons permettent de m&#xE9;langer les s&#xE9;quences d&#x2019;ADN. Ce processus de m&#xE9;lange et d&#x2019;appariement des exons est connu sous le nom d&#x2019;&#xE9;pissage alternatif. Il permet de produire plusieurs variantes prot&#xE9;iques &#xE0; partir d&#x2019;une seule s&#xE9;quence codante.
 
 <h4>La grande majorit&#xE9; du g&#xE9;nome humain ne code pas des prot&#xE9;ines</h4>
 
 Saviez-vous que 99 % de votre g&#xE9;nome ne code pas des prot&#xE9;ines ? Au d&#xE9;but de la recherche sur le g&#xE9;nome, les biologistes ont invent&#xE9; le terme accrocheur &#x201C; ADN poubelle &#x201D; pour ces s&#xE9;quences apparemment non fonctionnelles. Pendant ce temps, nous avons appris qu&#x2019;une grande partie de l&#x2019;ADN non codant comporte des fonctions importantes. Au moins 9 % du g&#xE9;nome humain est impliqu&#xE9; dans la r&#xE9;gulation des g&#xE8;nes, soit neuf fois plus que les s&#xE9;quences codant des prot&#xE9;ines.

Organisation des gènes

Overview

The genomes of eukaryotes can be structured in several functional categories. A strand of DNA is comprised of genes and intergenic regions. ...

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genes, introns, and regulatory dna

Eukaryotic genes are arranged within DNA along with non-coding regions that help control gene activity. A DNA strand includes genes and intergenic regions, which are the stretches between genes. These regions do not code for proteins, but they can contain important regulatory elements such as promoters, enhancers, and silencers.

A gene itself is not a single continuous coding block. It usually contains protein-coding exons and non-coding introns. After DNA is transcribed into pre-mRNA in the nucleus, splicing removes the introns and joins the exons together. The shorter mRNA then moves to the cytoplasm, where it is translated into protein.

The number of introns in a gene can vary a lot. The human DMD gene is more than two million base pairs long and encodes dystrophin, a muscle protein. Mutations in DMD can cause muscular dystrophy, a disease that leads to progressive muscle deterioration. This gene has 79 exons and 103 introns. In contrast, the histone H1A gene is only 781 base pairs long and has one exon and no introns.

Introns are not always useless DNA. Some introns contain elements that help regulate genes. They also support alternative splicing, a process that mixes and matches exons after transcription. This lets one coding sequence produce several protein variants.

Most of the human genome does not code for proteins. Early genome research called many of these sequences junk DNA, but scientists now know that much of this non-coding DNA has important roles. At least 9% of the human genome is involved in gene regulation, which is far more than the protein-coding portion.

Genes, Introns, and Regulatory DNA

the dna helix

How DNA Stores Genetic Information

DNA stores genetic information that is passed from one generation to the next in organisms and most viruses. It is built from two strands of nucleotides that twist together into a double helix. The story of how scientists uncovered this structure developed step by step over nearly a century. Each DNA strand is made of nucleotides. A nucleotide contains the sugar deoxyribose, a phosphate group, and one of four nitrogen bases: adenine (A), guanine (G), cytosine (C), or thymine (T). Adenine and...

dna packaging

Chromatin and Histones in DNA Packing

Eukaryotic cells must pack long DNA molecules into the nucleus, and chromatin makes that possible. DNA wraps around proteins called histones to form nucleosomes, which are the main unit of DNA packaging. Nucleosomes then coil into compact chromatin fibers. The amount of DNA in a cell is much larger than it first seems. A single human skin cell has about 3 billion base pairs of DNA, and if that DNA were stretched out in a line, it would be about 2 meters long. With about 50 trillion cells in...

organization of genes

Eukaryotic genes are arranged within DNA along with non-coding regions that help control gene activity. A DNA strand includes genes and intergenic regions, which are the stretches between genes. These regions do not code for proteins, but they can contain important regulatory elements such as promoters, enhancers, and silencers. A gene itself is not a single continuous coding block. It usually contains protein-coding exons and non-coding introns. After DNA is transcribed into pre-mRNA in the...

karyotyping

Chromosome Stains for Detecting Disorders

Chromosome staining helps scientists find genetic disorders by showing the number and physical features of chromosomes. These features appear after DNA condenses into chromosomes during mitosis. Cytogeneticists then stop mitosis and stain the chromosomes to study their banding pattern. The pattern reveals details such as chromosome number, shape, and type. A chromosome description like this is called a karyotype. To create one, scientists take an image of the stained chromosomes and identify...

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How Prokaryotic DNA Is Copied

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replication in eukaryotes

Eukaryotic DNA Copying and Telomeres

Eukaryotic DNA copying is tightly regulated and must duplicate many linear chromosomes before cell division. The process is highly conserved and uses many proteins with specialized roles. It moves through initiation, elongation, and termination, and it ends with two complete sets of chromosomes in the nucleus. Eukaryotic replication shares basic steps with prokaryotic DNA replication, but the larger genome and linear chromosomes require more proteins. Replication begins at multiple origins of...

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DNA Polymerase Fixes Replication Errors

DNA polymerase helps copy DNA and fix mistakes during replication. It adds nucleotides in a sequence that matches the template DNA strand. The enzyme also has a higher affinity for the correct base, which helps keep DNA replication accurate. As new genomic DNA is made, it is synthesized in the 5’ to 3’ direction. In many cells, DNA polymerases have different jobs in this process. DNA polymerase delta and DNA polymerase epsilon can proofread when nuclear DNA is being copied. These polymerases...

mismatch repair

DNA Mismatch Repair in Replication

DNA mismatch repair fixes copying errors that happen during DNA replication. When DNA polymerase makes a mistake, the cell can detect a wrong base pair, such as A with G or T with C, and replace it with the correct nucleotide. This repair system works in both prokaryotes and eukaryotes and depends on several proteins. The Mutator protein family plays a central role in this process. In bacteria such as Escherichia coli, MutS first binds the mismatch. MutL then helps identify which strand is the...

nucleotide excision repair

DNA Damage Repair by Excision

DNA damage repair by excision protects cells from mutagens that can change DNA. Exposure to environmental mutagens can create bulky lesions that bend the double helix or block transcription. If these changes are not repaired, they can lead to mutations and may contribute to cancer or disease, depending on which DNA sequences are affected. Nucleotide excision repair, or NER, is the process that detects and removes this kind of damage. Specialized proteins scan the DNA for a damaged region, then...

mutations

DNA Changes From Point Mutations to UV Damage

Mutations are changes in the DNA sequence. They can happen by chance during DNA copying, or they can be caused by environmental factors such as radiation and chemicals. Scientists also describe mutations by how much DNA they affect, how they change a protein, and whether they happen in body cells or germline cells. Some mutations affect only one nucleotide, which is a point mutation. When a point mutation falls inside a gene, the outcome depends on how the amino acid sequence changes. A silent...

transcription

Transcription and Gene Control

Transcription and gene control explain how cells make RNA from DNA and decide which genes are active. RNA polymerase copies a DNA sequence into RNA, and this is the first step in making a protein from a gene. Many other proteins and control sequences help make messenger RNA, or mRNA, correctly. In eukaryotes, the DNA is first copied into a primary RNA, also called pre-mRNA. This RNA can then be processed into mature mRNA, which serves as the template for protein synthesis. In prokaryotes such...

translation

Protein Synthesis and mRNA Decoding

Protein synthesis begins when ribosomes decode messenger RNA (mRNA) and build a chain of amino acids. This final step of gene expression is called translation. The finished chain is a polypeptide, which can later become a functional protein. Proteins are often called the building blocks of life because they make up much of the body, from muscle fibers to hairs and immune system parts. The instructions for each protein are encoded in genes found in the DNA of every cell. In biology, the central...

bacterial transformation

Griffith’s Mouse Experiment and DNA

Bacterial transformation explains how DNA can move into bacteria and change their traits. Frederick Griffith first noticed this in 1928 while studying pneumonia-causing Streptococcus pneumoniae in mice. He compared one pathogenic strain with one non-pathogenic strain and found that only the pathogenic strain killed the host mice. Griffith made an unexpected discovery when he killed the pathogenic bacteria and mixed their remains with live, non-pathogenic bacteria. The mixture killed the mice,...

key terms and concepts

Explore how eukaryotic genes are organized with exons, introns, intergenic regions, and regulatory DNA, plus how splicing and alternative splicing work.

Genes, Introns, and Regulatory DNA | JoVE K12

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Genes, Introns, and Regulatory DNA

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