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

Mitokondri, enerji bakımından zengin ATP molekülleri üretir ve hayvan hücresinde kendi genetik sistemine sahip tek organeldir. Günümüz mitokondrisinin, avcısıyla karşılıklı olarak yararlı veya simbiyotik bir ilişki kuran, aerobik bir bakteriden evrimleştiği düşünülmektedir. Zamanla, bu bakteriden birçok gen, konakçı hücrenin çekirdek DNA'sına aktarılmış ve diğer genler kaybedilerek, geride küçük ama bağımsız bir mitokondriyal DNA bırakmıştır.Kas hücreleri gibi bazı hücreler yüzlerce mitokondri içerebilir. Kırmızı kan hücreleri gibi bazı hücreler ise hiç mitokondri içermez. Her mitokondride, mitokondriyal DNA'nın en fazla 10 kopyası bulunabilir.Mitokondriyal DNA, kapalı ve dairesel bir moleküldür;çekirdek DNA'sında bulunan milyonlarca baz çiftine kıyasla hayvan hücrelerinde 14.000 ila 20.000 baz çifti arasında değişen uzunluğa sahiptir. Bu mitokondriyal DNA, oldukça az sayıda biyomolekül kodlar:16S ve 12S ribozomal RNA'ları, en fazla 25 adet transfer RNA ve 13 adet solunum zinciri proteini. Mitokondriyal işlev için gerekli olan proteinlerin kalanını, çekirdek DNA'sı kodlar.Mitokondriyal DNA'nın yaklaşık 93'ü proteinleri kodlar, çekirdek DNA'sının ise yalnızca 1'i kodlama bölgeleridir. Bunun nedeni kısmen, ökaryotik DNA'nın değişmez bir özelliği olan intronların mitokondriyal DNA'da bulunmamasıdır. Genetik kodun birçok dizisi, DNA tipine bağlı olarak farklı şekilde transle edilir Örneğin, mitokondriyal DNA'da kodon UGA, triptofan için kodlar.Çekirdek DNA'sında ise bir durma kodonudur. Mitokondriyal DNA'daki mutasyon oranının on kat daha yüksek olması nedeniyle, mitokondriyal DNA, çekirdek DNA'sından daha hızlı evrimleşir. Bunun nedeni, mitokondriyal DNA'nın çekirdek DNA'sı gibi histonlar tarafından korunmaması ve mitokondriyal reaksiyonlar sırasında üretilen reaktif oksijen türlerine maruz kalmasıdır.Ayrıca, DNA onarım mekanizmaları da daha az verimlidir. Mitokondriyal DNA'nın transferi her zaman anneden çocuğa gerçekleşir. Bu, anasal kalıtım olarak adlandırılır.Döllenmeden sonra spermde bulunan az sayıdaki mitokondrinin parçalanması nedeniyle anasal kalıtım oluşur. Yumurtadaki birçok mitokondri ise, embriyoda varlığını korur ve yavrudaki tüm hücrelere aktarılır.

<ol>
	<li>Chinnery, Patrick Francis ve Gavin Hudson. "Mitokondriyal genetik." İngiliz Tıp Bülteni 106, no. 1 (2013): 135-159. </li>
	<li>DiMauro, Salvatore ve Guido Davidzon. "Mitokondriyal DNA ve hastalık." Tıp Yıllıkları 37, hayır. 3 (2005): 222-232.</li>
	<li>Zhang, Xiaoxue ve Si Wang. "İlk insan gen düzenlemesinden üç ebeveynli bebeğin doğumuna kadar." Science China Yaşam Bilimleri 59, no. 12 (2016): 1341-1342.</li>
</ol>

hayvan mitokondriyal genetiği

Animal Mitochondrial Genetics

Bir hayvan hücresindeki tüm organeller arasında yalnızca mitokondrinin kendi bağımsız genomu vardır. Hayvan mitokondriyal DNA'sı, yaklaşık 20.000 baz çiftine sahip, çift sarmallı, kapalı dairesel bir moleküldür. Mitokondriyal DNA, iki iplikçiğinden biri olan ağır iplikçik veya H, guanin bakımından zengindir; tamamlayıcı iplikçik ise sitozin bakımından zengindir ve hafif veya L iplikçik olarak adlandırılır. Nükleer DNA ile karşılaştırıldığında, mitokondriyal DNA'da kodlamayan bölgelerin yüzdesi çok düşüktür ve intronların tamamen yokluğuyla belirgindir. Ayrıca genleri çok yakın aralıklıdır ve hatta bazılarının örtüşen bölgeleri bile vardır. D döngüsü, mitokondriyal DNA'nın en önemli düzenleyici kodlamayan bölgesidir ve aynı zamanda H iplikçiğinin replikasyonunun kökenini de içerir. Mitokondriyal genetik kod, birkaç kodon(dizgi) bakımından nükleer DNA kodundan farklılık gösterir. Örneğin, UGA, AUA ve AGA/AGG kodonu nükleer DNA'da sırasıyla STOP kodonunu, izolösin ve arginini kodlarken, aynı kodonlar hayvan mitokondriyal DNA'sında sırasıyla triptofan, metiyonin ve STOP kodonunu kodlar. Nükleer DNA'nın replikasyonu hücre döngüsü ile koordine edilir ve hücre bölünmesi gerçekleşmeden önce tamamlanması gerekir. Mitokondriyal genomun bir diğer karakteristik özelliği, nükleer DNA'nın aksine, replikasyonun hücre döngüsünden bağımsız olduğu ve hücre bölünmesinden sonra bile yavru hücrelerde devam edebildiği gevşemiş (relaxed) DNA replikasyonudur. Anneden Miras Memelilerde mitokondriyal DNA yalnızca annenin ovositinden miras alınır, çünkü spermde bulunan mitokondri zigottaki ubikuitin aracılı bir yol tarafından seçici olarak parçalanır. Mitokondriyal genlerdeki mutasyonlar, Leber'in Herediter Optik Nöropatisi veya Leigh sendromu gibi hastalıklara yol açabilir; dolayısıyla eğer anne bu tür mutasyonları taşıyorsa, çocuğuna da bu hastalıklar kalıtsal olarak aktarılabilir. Son zamanlarda, mitokondriyal replasman gibi yeni tedaviler, etkilenmiş bir anneden etkilenmemiş bir çocuğun, doğmasına olanak tanıyabilmektedir. Annenin ovositinin çekirdeği, döllenmeden önce normal mitokondriye sahip sağlıklı bir donörün enükleasyonlu ovositine aktarılır. Bu teknik, annesinin mitokondriyal hastalığını miras almayan sözde "üç ebeveynli bebeğin" doğmasına yol açtı.

Hayvan Mitokondriyal Genetiği

Bir hayvan hücresindeki tüm organeller arasında sadece mitokondrinin kendi bağımsız genomları vardır. Hayvan mitokondriyal DNA'sı çift sarmallıdır, ...

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Molecular Biology

Moleküler Biyoloji

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DNA Replication

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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 Moleküler Biyoloji, hücrenin moleküler süreçlerini açık ve özlü animasyonlu video dersleriyle sergiler. Buna ek olarak, bilim insanı-eylem videolarında, bu kavramların uygulaması modern laboratuvarlarda gerçek deneylerle gösterilmektedir.

Animal Mitochondrial DNA and Inheritance

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