Heavy strand

Overview of the heavy strand in mitochondrial DNA

Overview

The heavy strand is one of the two strands of mitochondrial DNA (mtDNA), the other being the light strand. The terms "heavy" and "light" refer to the buoyant density of the strands when separated by density gradient centrifugation, which is a result of the differing nucleotide composition of the two strands. The heavy strand is rich in guanine nucleotides, while the light strand is rich in cytosine nucleotides.

Structure and Composition

Mitochondrial DNA is a circular DNA molecule found in the mitochondria of eukaryotic cells. It is distinct from the nuclear DNA and is inherited maternally. The heavy strand contains a higher proportion of purines, particularly guanine, which contributes to its higher density compared to the light strand.

The heavy strand encodes for 28 of the 37 genes found in human mitochondrial DNA. These include 12 of the 13 protein-coding genes, 14 of the 22 transfer RNA (tRNA) genes, and 2 of the 2 ribosomal RNA (rRNA) genes. The remaining genes are encoded by the light strand.

Function

The genes encoded by the heavy strand are crucial for the function of the mitochondria, particularly in the process of oxidative phosphorylation, which is the primary method by which cells generate adenosine triphosphate (ATP). The proteins encoded by the heavy strand are components of the electron transport chain, which is essential for ATP production.

Replication and Transcription

Replication of mitochondrial DNA is initiated at the origin of replication on the heavy strand, known as the OH (origin of heavy strand replication). Transcription of the heavy strand is initiated at the heavy strand promoter (HSP), which leads to the production of a polycistronic transcript that is subsequently processed into individual mRNAs, tRNAs, and rRNAs.

Clinical Significance

Mutations in the heavy strand of mitochondrial DNA can lead to a variety of mitochondrial diseases, which are often characterized by defects in energy production. These diseases can affect multiple organ systems, particularly those with high energy demands such as the nervous system, muscles, and heart.

Also see

• Mitochondrial DNA
• Light strand
• Oxidative phosphorylation
• Electron transport chain
• Mitochondrial diseases