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

ミトコンドリアは、エネルギーが豊富なATP分子を産生し、動物細胞内で独自の遺伝子システムを持つ唯一のオルガネラです。 
現在のミトコンドリアは、好気性細菌から進化したと考えられており、好気性細菌は捕食者と相互に有益な、または共生的な関係を形成しました。 
時間の経過とともに、この細菌からの多くの遺伝子が宿主細胞の核DNAに移され、他の遺伝子は失われ、小さいながらも独立したミトコンドリアDNAが残りました。
筋肉細胞のように、数百個のミトコンドリアを含む細胞もあれば、赤血球のようにミトコンドリアを含まない細胞もあります。各ミトコンドリアには、ミトコンドリアDNAの最大10コピーを含めることができます。
ミトコンドリアDNAは、核DNAに存在する数百万の塩基対と比較して、動物細胞では14,000〜20,000 bpsの長さが異なる閉鎖した環状分子です。 
このミトコンドリアDNAは、16Sおよび12S rRNA、最大25のtRNA、および13の呼吸鎖タンパク質という少数の生体分子のみをコードしています。核DNAは、ミトコンドリアの機能に必要な残りのタンパク質をコードしています。
ミトコンドリアDNAの約93%はタンパク質をコードしていますが、核DNAは約1%しかコードしていない領域です。これは、真核生物のDNAの規則的な特徴であるイントロンがミトコンドリアDNAに存在しないことが一因です。 
遺伝暗号のいくつかの配列は、DNAの種類によって翻訳が異なります。例えば、コドンUGAはミトコンドリアDNAのトリプトファンをコードしているのに対し、核DNAの終止コドンです。
ミトコンドリアDNAは、ミトコンドリアDNAの突然変異率が10倍以上高いため、核DNAよりも進化速度が速いです。 
これは、ミトコンドリアDNAが核DNAのようなヒストンに守られておらず、ミトコンドリア反応で発生する活性酸素種にさらされているためです。さらに、DNA修復機械の効率も劣ります。
ミトコンドリアDNAの移行は、常に母親から子孫に行われます。これは母方の相続として知られています。 
母系遺伝は、受精後、精子に存在する少数のミトコンドリアが分解される一方で、卵子の多くのミトコンドリアが胚に残り、子孫のすべての細胞に受け継がれるために発生します。

<ol>
	<li>チネリー、パトリック・フランシス、ギャビン・ハドソン「ミトコンドリア遺伝学」 British Medical Bulletin 106、no. 1 (2013): 135-159. </li>
	<li>「ミトコンドリアDNAと病気」 Annals of Medicine 37, no. 3 (2005): 222-232.</li>
	<li>「最初のヒト遺伝子編集から3人の親の赤ちゃんの誕生まで」 Science China Life Sciences 59, no. 12 (2016): 1341-1342.</li>
</ol>

動物のミトコンドリア遺伝学

Animal Mitochondrial Genetics

動物細胞内のすべての細胞小器官の中で、独自の独立したゲノムを持っているのはミトコンドリアだけです。 動物のミトコンドリアDNAは、約20,000塩基対を持つ二本鎖の閉環状分子です。ミトコンドリアDNAは、その2つの鎖のうちの1つである重鎖(H鎖)がグアニンに富んでいるのに対し、相補鎖はシトシンに富み、軽鎖(L鎖)と呼ばれるという点で独特です。核DNAと比較して、ミトコンドリアDNAには非コード領域の割合が非常に低く、イントロンが完全に存在しないことが特徴です。 また、それらの遺伝子は非常に狭い間隔で配置されており、一部の遺伝子には重複領域さえあります。DループはミトコンドリアDNAの最も重要な調節非コード領域であり、H鎖の複製起点も含まれています。ミトコンドリアの遺伝コードは、いくつかのコドンに関して核DNAコードとは異なります。たとえば、コドンUGA、AUA、およびAGA/AGG は、核DNAではそれぞれ停止コドン、イソロイシン、およびアルギニンをコードしますが、同じコドンは動物のミトコンドリアDNAではそれぞれトリプトファン、メチオニン、および停止コドンをコードします。

核DNAの複製は細胞周期と調整されており、細胞分裂が起こる前に完了する必要があります。 ミトコンドリアゲノムのもう1つの特徴は、そのリラックスしたDNA複製です。核DNAとは異なり、複製は細胞周期とは独立しており、細胞分裂後も娘細胞内で続行できます。

母系遺伝

哺乳類では、精子内に存在するミトコンドリアが受精卵内のユビキチン媒介経路によって選択的に分解されるため、ミトコンドリアDNAは母親の卵母細胞からのみ受け継がれます。ミトコンドリア遺伝子の変異は、レバー遺伝性視神経症やリー症候群などの病気を引き起こす可能性があります。 したがって、母親がそのような突然変異を持っている場合、その子供はこれらの病気を受け継ぐ可能性があります。最近、ミトコンドリア置換などの新しい治療法により、罹患した母親から罹患していない子供を出産できるようになりました。母親の卵母細胞の核は、受精前に正常なミトコンドリアを持つ健康なドナーの除核卵母細胞に移植されます。この技術は、母親のミトコンドリア病を受け継がなかった、いわゆる「三親の赤ちゃん」の誕生につながりました。

動物細胞内のすべての細胞小器官の中で、ミトコンドリアだけが独自の独立したゲノムを持っています。動物のミトコンドリアDNAは二本鎖です...

Education

JoVE Core

Molecular Biology

分子生物学

Unit 1

ユニット1

DNA Replication

DNA複製

KEY TERMS AND CONCEPTS

主要用語と概念

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 分子生物学は、明確で簡潔なアニメーション ビデオ レッスンを通じて細胞の分子プロセスを紹介します。さらに、科学者の実際のビデオでは、これらの概念の応用が現代の研究室での実際の実験を通じて実証されています。

Animal Mitochondrial DNA and Inheritance

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