Medical Genetics · MU Plovdiv

18. Mitochondrial genome. Mitochondrial type of inheritance – essence, examples, clinical-genetic characteristics. MGC.

Inside: 14 sections · 16 labelled pictures · 31 flashcards · 9 min

Topic 18 of 33 in the MU Plovdiv syllabus for Medical Genetics (Medicine, Year 4). The free AceMed note covers it in 14 sections, about 1,308 words (9 min of reading), with 31 flashcards.

In this note

  1. Introduction
  2. I. Introduction
  3. II. General Features of the Human Mitochondrial Genome
  4. III. Gene Content
  5. IV. Replication, Transcription and Translation
  6. V. Mitochondrial Type of Inheritance and Mutation
  7. VI. Clinical Relevance and General Characteristics of Mitochondrial Diseases
  8. VII. Leigh Syndrome
  9. VIII. NARP Syndrome
  10. IX. Leber Hereditary Optic Neuropathy (LHON)
  11. X. MERRF Syndrome
  12. XI. MELAS Syndrome
  13. XII. Kearns–Sayre Syndrome (KSS)
  14. Key Points

Introduction

This topic covers the human mitochondrial genome (its size, gene content, replication, transcription and translation), the mitochondrial type of inheritance with its genetic peculiarities, and the clinical-genetic characteristics of the main mitochondrial diseases: Leigh syndrome, NARP, LHON, MERRF, MELAS and Kearns–Sayre syndrome.

I. Introduction

Mitochondria are known as the powerhouses of the cell because they generate most of the ATP through oxidative phosphorylation.

Unlike other organelles, they are semi-autonomous: they contain their own DNA, transcription, and translation machinery. This makes them similar to bacteria, supporting the endosymbiotic theory (mitochondria originated from prokaryotes that entered ancestral eukaryotic cells).

The mitochondrial genome is much smaller than the nuclear genome, but it is essential for energy metabolism. Without it, cells cannot sustain high energy-demanding processes like muscle contraction or neuronal signaling.

II. General Features of the Human Mitochondrial Genome

  • Shape and size: a closed circular double-stranded DNA molecule, about 16,569 base pairs in humans. This is tiny compared to the nuclear genome (~3.2 billion base pairs).
  • Copy number: each mitochondrion contains several copies of mtDNA, and a typical cell may have hundreds to thousands of mitochondria, giving a very high total copy number of mtDNA per cell. This high redundancy is important for function and resilience.
  • No introns: unlike nuclear DNA, mtDNA is extremely compact. Almost every base is part of a gene or a control sequence. This means no “junk DNA” and no introns interrupting genes.

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