Name: animal mitochondrial dna and inheritance
Uploaded: 2020-11-23T11:47:35.000Z
Duration: 2 min 59 s
Channel: JoVE

Les mitochondries produisent des molécules ATP riches en énergie et sont les seules organites dans la cellule animale à avoir leur propre système génétique. Le modèle actuel de la mitochondrie dit qu'elle a évolué d'une bactérie aérobie, qui a formé une association mutuellement bénéfique, ou symbiotique, avec son prédateur. Au fil du temps, de nombreux gènes de cette bactérie ont été transférés à l'ADN nucléaire de la cellule hôte, et d'autres gènes ont été perdus, laissant derrière eux un ADN mitochondrial petit mais indépendant.Certaines cellules, comme les cellules musculaires, peuvent contenir des centaines de mitochondries. Tandis que d'autres, comme les globules rouges, n'en contiennent pas. Chaque mitochondrie peut contenir jusqu'à 10 copies de l'ADN mitochondrial.L'ADN mitochondrial est une molécule circulaire fermée dont la longueur varie de 14 000 à 20 000 paires de bases dans les cellules animales comparé aux millions de paires de bases présentes dans l'ADN nucléaire. Cet ADN mitochondrial code seulement un petit nombre de biomolécules les ARN ribosomiques 16S et 12S, jusqu'à 25 ARN de transfert et 13 protéines de la chaîne respiratoire. L'ADN nucléaire code pour les protéines restantes requises pour une fonction mitochondriale.Environ 93 d'ADN mitochondrial code pour des protéines, contrairement à l'ADN nucléaire, où seulement 1 sont des régions codantes. C'est en partie parce que les introns, qui sont une caractéristique régulière de l'ADN eucaryote, sont absents dans l'ADN mitochondrial. Plusieurs séquences du code génétique sont traduites différemment, selon le type d'ADN.Par exemple, le codon UGA code pour le tryptophane dans l'ADN mitochondrial. Alors qu'il s'agit d'un codon stop dans l'ADN nucléaire. L'ADN mitochondrial a un taux d'évolution plus rapide que celui de l'ADN nucléaire en raison du taux de mutation de l'ADN mitochondrial qui est dix fois plus élevé.En effet, l'ADN mitochondrial n'est pas protégé par des histones comme l'ADN nucléaire et est exposé à des espèces réactives de l'oxygène générées lors de réactions mitochondriales. De plus, il a également des machines de réparation de l'ADN moins efficaces. Le transfert de l'ADN mitochondrial se produit toujours de la mère vers la progéniture.C'est ce que l'on appelle l'héritage maternel. L'héritage maternel se produit car, après la fécondation, les quelques mitochondries présentes dans le sperme sont dégradées. Alors que les nombreuses mitochondries de l'ovule restent présentes dans l'embryon et sont transmises à toutes les cellules de la progéniture.

<ol>
	<li>Chinnery, Patrick Francis et Gavin Hudson. « Génétique mitochondriale. » British Medical Bulletin 106, n° 1 (2013) : 135-159. </li>
	<li>DiMauro, Salvatore et Guido Davidzon. « ADN mitochondrial et maladie. » Annales de médecine 37, n° 3 (2005) : 222-232.</li>
	<li>Zhang, Xiaoxue et Si Wang. « De la première édition de gènes humains à la naissance d’un bébé à trois parents. » Science China Life Sciences 59, n° 12 (2016) : 1341-1342.</li>
</ol>

génétique mitochondriale animale

Animal Mitochondrial Genetics

Parmi tous les organites d’une cellule animale, seules les mitochondries possèdent leur propre génome indépendant. L’ADN mitochondrial animal est une molécule double brin à cercle fermé contenant environ 20 000 paires de bases. L'ADN mitochondrial est unique en ce sens que l'un de ses deux brins, le brin lourd ou H, est riche en guanine, tandis que le brin complémentaire est riche en cytosine et est appelé brin léger, ou L. Comparé à l’ADN nucléaire, l’ADN mitochondrial possède un très faible pourcentage de régions non codantes et se caractérise par l’absence totale d’introns. De plus, leurs gènes sont très rapprochés et certains d’entre eux ont même des régions qui se chevauchent. La boucle D est la région régulatrice non codante la plus importante de l’ADN mitochondrial, qui contient également l’origine de la réplication du brin H. Le code génétique mitochondrial diffère du code ADN nucléaire par quelques codons. Par exemple, les codons UGA, AUA et AGA/AGG codent respectivement pour le codon STOP, l'isoleucine et l'arginine dans l'ADN nucléaire, tandis que les mêmes codons codent respectivement pour le tryptophane, la méthionine et le codon STOP dans l'ADN mitochondrial animal.

La réplication de l'ADN nucléaire est coordonnée avec le cycle cellulaire et doit être terminée avant que la division cellulaire ne se produise. Une autre caractéristique du génome mitochondrial est sa réplication détendue de l'ADN, où contrairement à l'ADN nucléaire, la réplication est indépendante du cycle cellulaire et peut se poursuivre dans les cellules filles même après la division cellulaire.

Héritage maternel

Chez les mammifères, l’ADN mitochondrial est hérité uniquement de l’ovocyte de la mère, car les mitochondries présentes dans le sperme sont dégradées de manière sélective par une voie médiée par l’ubiquitine dans le zygote. Les mutations des gènes mitochondriaux peuvent entraîner des maladies telles que la neuropathie optique héréditaire de Leber ou le syndrome de Leigh ; par conséquent, si la mère est porteuse de telles mutations, sa progéniture peut hériter de ces maladies. Récemment, de nouvelles thérapies telles que le remplacement mitochondrial peuvent permettre la naissance d'un enfant non affecté d'une mère affectée. Le noyau de l’ovocyte de la mère est transféré dans un ovocyte énucléé d’un donneur sain présentant des mitochondries normales avant la fécondation. Cette technique a conduit à la naissance de ce qu’on appelle le « bébé à trois parents », qui n’a pas hérité de la maladie mitochondriale de sa mère.

Génétique mitochondriale animale

Parmi tous les organites d’une cellule animale, seules les mitochondries ont leur propre génome indépendant. L’ADN mitochondrial animal est un double brin, ...

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JoVE Core

Molecular Biology

Biologie moléculaire

Unit 1

Unité 1

DNA Replication

Réplication de l'ADN

KEY TERMS AND CONCEPTS

TERMES ET CONCEPTS CLÉS

animal mitochondrial dna and inheritance

Animal mitochondrial DNA has its own genome, separate from nuclear DNA. It is a double-stranded, closed circular molecule with about 20,000 base pairs. One strand is the heavy, or H-strand, because it is rich in guanine. The other is the light, or L-strand, because it is rich in cytosine.

Compared with nuclear DNA, mitochondrial DNA has very little non-coding sequence. It also has no introns. Its genes are packed closely together, and some even overlap. The D-loop is the main non-coding control region, and it also contains the origin of replication for the H-strand.

Animal mitochondrial genes also use a genetic code that differs from the nuclear code in a few codons. In nuclear DNA, UGA is a stop codon, AUA codes for isoleucine, and AGA/AGG codes for arginine. In animal mitochondrial DNA, UGA codes for tryptophan, AUA codes for methionine, and AGA/AGG codes for stop.

Mitochondrial DNA replication is relaxed. Unlike nuclear DNA replication, it does not depend on the cell cycle. It can continue in daughter cells even after cell division. In mammals, mitochondrial DNA is inherited from the mother’s oocyte because the mitochondria from sperm are selectively broken down in the zygote by a ubiquitin-mediated pathway.

Changes in mitochondrial genes can cause disease. Examples include Leber’s hereditary optic neuropathy and Leigh syndrome. If the mother carries such mutations, her offspring can inherit them. Mitochondrial replacement therapy may help affected mothers have unaffected children. In this method, the mother’s oocyte nucleus is moved into a donor oocyte with healthy mitochondria before fertilization. This has led to the birth of a child who did not inherit the mother’s mitochondrial disease.

Animal Mitochondrial DNA and Inheritance

replication in prokaryotes

Prokaryotic DNA Replication Steps

Prokaryotic DNA replication copies the chromosome before a cell divides. In bacteria, this process starts at a specific DNA site called the origin of replication. From there, the cell builds new DNA strands using enzymes that match each base with its partner. The DNA double helix first opens so replication can begin. As the strands separate, each original strand serves as a template. New nucleotides are added in a set order, which helps the cell make an accurate copy of its genetic material. <br...

replication in eukaryotes

Eukaryotic DNA Replication Steps

Eukaryotic DNA replication copies the genome before a cell divides. In eukaryotes, this process happens in a controlled sequence so each new cell can receive genetic information. Replication begins at specific sites on the DNA called origins. The DNA is opened, and each original strand serves as a template, meaning it guides the building of a new complementary strand. This sets up two DNA molecules from one original molecule. The process then continues as enzymes add matching nucleotides to...

dna base pairing

DNA Base Pair Rules

DNA base pairing follows specific rules that help DNA carry genetic information. In DNA, the bases pair in a regular way, with adenine matching thymine and cytosine matching guanine. These pairs fit together because of their chemical shapes and bonding patterns. These base pairs also support accurate DNA replication. When DNA copies itself, each strand can guide the formation of a new partner strand using the pairing rules. Understanding base pairing helps explain how DNA stays organized and...

the dna replication fork

DNA Replication Stress and Fork Stalling

DNA replication stress and fork stalling can disrupt the copying of a cell’s genome. The replication fork is the Y-shaped site where DNA strands separate and new complementary strands are made at the same time. This linked unwinding and synthesis helps cells duplicate DNA efficiently and with fewer errors. In organisms with small circular DNA, such as E. coli, replication often begins at a single origin. That setup creates two replication forks that move in opposite directions from the opening...

proofreading

Proofreading in DNA Replication

Proofreading in DNA replication helps keep DNA copying accurate. It is a built-in check that reduces mistakes as new DNA is made. DNA polymerase is the enzyme that carries out this checking during replication. When it adds a wrong nucleotide, it can remove the error and replace it with the correct one. This correction step helps maintain the correct DNA sequence. Proofreading is an important part of DNA replication because it supports genetic accuracy. By catching mistakes as they happen, the...

dna helicases

Helicase Motor Proteins in DNA Unwinding

Helicase motor proteins help unwind DNA during key cell processes. They use energy from ATP hydrolysis, which is the breakdown of ATP to release usable energy. This movement lets helicases separate DNA strands when the cell needs access to the genetic code. These enzymes are involved in DNA replication, repair, recombination, and transcription. Helicases are found in all living organisms, but their structure, function, and movement can differ. In prokaryotes, the DnaB helicase moves along the...

the replisome

DNA Replication Teams in the Replisome

DNA replication depends on the replisome, a coordinated complex of proteins that copies DNA with high accuracy. This DNA replication machinery brings many parts together so the leading and lagging strands can be made at the same time. A key idea in this process is the trombone model, proposed by Bruce Alberts in 1980. In this model, a loop forms on the lagging strand when a primer is made. The loop grows as an Okazaki fragment is synthesized, then falls apart when that fragment is finished.

lagging strand synthesis

Okazaki Fragments in DNA Replication

DNA replication uses a leading strand and a lagging strand, and they are made at different rates. The leading strand starts first. The lagging strand starts later, moves more slowly, and is made in pieces. The two strands also differ in direction and starting steps. Leading strand synthesis follows the opening replication fork. Lagging strand synthesis goes in the opposite direction. The leading strand needs one RNA primer, while the lagging strand needs multiple RNA primers. After priming,...

mismatch repair

Fixing DNA Copying Errors

Mismatch repair helps fix DNA copying errors after replication. When DNA is copied, small mistakes can slip through. This repair system finds those mismatches and corrects them before they become permanent changes. The process depends on a group of mutator proteins. These proteins work together to detect the error, remove the incorrect section, and help replace it with the proper DNA sequence. In this way, mismatch repair supports the accuracy of genetic information. If the repair system does...

dna topoisomerases

How Topoisomerases Untwist DNA

DNA topoisomerases are enzymes that untwist DNA when it becomes overcoiled during cell processes such as DNA replication and transcription. They help regulate positive and negative DNA supercoiling without changing the nucleotide sequence. Clockwise overwinding creates positively supercoiled DNA, while counterclockwise underwinding produces negatively supercoiled DNA. Topoisomerases are grouped into two main types. Type I topoisomerases act on one strand of double-stranded DNA, and they...

telomeres and telomerase

How Telomerase Protects Chromosome Ends

Telomerase helps protect chromosome ends during eukaryotic DNA replication. When the final primer is removed, a single-stranded DNA fragment can remain at the end of the chromosome. That piece cannot be copied in the same way as the rest of the strand because there is no 3' end for new DNA to attach to. If this end piece is not replaced, chromosomal DNA is gradually lost each time a cell divides. The exposed single-stranded DNA can also trigger a DNA damage response from enzymes that detect it.

non-nuclear inheritance

Cytoplasmic Inheritance in Cells

Cytoplasmic inheritance explains how some traits are passed through cell structures outside the nucleus. These traits come from organelles such as mitochondria and chloroplasts. They do not follow the usual nuclear pattern of inheritance. Mitochondria and chloroplasts each contain their own DNA. Because of this, they can carry genetic information that affects cell function and certain visible traits. In high school biology, this topic helps explain why not all inherited traits come from...

animal mitochondrial genetics

Animal mitochondrial DNA has its own genome, separate from nuclear DNA. It is a double-stranded, closed circular molecule with about 20,000 base pairs. One strand is the heavy, or H-strand, because it is rich in guanine. The other is the light, or L-strand, because it is rich in cytosine. Compared with nuclear DNA, mitochondrial DNA has very little non-coding sequence. It also has no introns. Its genes are packed closely together, and some even overlap. The D-loop is the main non-coding...

comparing mitochondrial, chloroplast, and prokaryotic genomes

comparing-mitochondrial-chloroplast-and-prokaryotic-genomes

How Organelle Genomes Resemble Bacteria

Mitochondrial and chloroplast genomes still keep several traits from their bacterial ancestors. They also show changes that happened after these organelles evolved inside eukaryotic cells. Eukaryotic cells are cells with a nucleus, while prokaryotes are cells without one. Like prokaryotic genomes, mitochondrial and chloroplast genomes do not bind with histone-like proteins. They also do not show the complex chromosome-like packaging seen in eukaryotes. Mitochondria and chloroplasts divide by...

export of mitochondrial and chloroplast genes

export-of-mitochondrial-and-chloroplast-genes

How Organelles Pass Genes to the Nucleus

Eukaryotic cells can carry three genetic systems: nuclear, mitochondrial, and chloroplast. Over time, many genes from mitochondria and chloroplasts have moved into the nucleus. In some plant species, this gene transfer is still happening. This movement has affected large parts of the genome in some organisms. About 18% of the Arabidopsis thaliana nuclear genome is thought to come from the chloroplast's cyanobacterial ancestor. In yeast, around 75% of the genome is derived from the...

single-strand dna binding proteins

How SSB Proteins Protect DNA Strands

Single-strand DNA-binding proteins, or SSB proteins, help protect DNA during replication. When double-stranded DNA is unwound, the two strands separate. SSB proteins bind to the exposed single strands and keep them stable. These proteins bind in a sequence-independent manner. That means the order of the nitrogenous bases does not have to follow a specific pattern for SSB proteins to attach. Their binding straightens single-stranded DNA and makes it more rigid. This support may help DNA...

key terms and concepts

Explore animal mitochondrial DNA, its unique genetic code, relaxed replication, maternal inheritance, and how mutations can lead to disease.

Animal Mitochondrial DNA and Inheritance | JoVE K12

molecular biology

JoVE Core Biologie Moléculaire illustre les processus moléculaires au sein de la cellule grâce à des leçons vidéos claires et concises. Les applications de ces concepts sont ensuite démontrées grâce à des expériences concrètes en laboratoire.

Animal Mitochondrial DNA and Inheritance

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