Mitochondria - The Powerhouse for Cells

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Mitochondria - The Powerhouse for Cells

How mitochondria work used to be a mystery. In fact, they were named because the main mitochondria function was thought (by the scientists who discovered it) to be genetic information. So, why are the mitochondria of today known as the powerhouse of the cell?

Essentially, what mitochondria do is turn the food we eat into usable energy for the body. Many defects, diseases, and disorders in organisms can be traced back to deficiencies in this tiny organelle. This article explains everything you need to know -- from the first observed mitochondria to the most recent research on therapies and treatments for mitochondrial disease. 

Read on to learn all about your mitochondria and how the cell's powerhouse got its name.

What are Mitochondria?

What are Mitochondria?

Mitochondria are classically known as the "powerhouse of the cell" or the "energy factory" of the body. A mitochondrion (the singular form of mitochondria) is an organelle, like a tiny organ inside a living cell. It contains organized or specialized structures that help convert parts of the food we eat into chemical energy that powers every life process.

Why Mitochondria is Known as Powerhouse of the Cell

Why Mitochondria is Known as Powerhouse of the Cell

Mitochondria are the power generators of the cell. They work to convert oxygen and other nutrients into energy the body can use. That energy helps to power cell metabolism and, ultimately, overall body function.

In addition to producing energy, mitochondria also make chemicals for other cell purposes, such as:

  • Breaking down waste products
  • Recycling waste products to save energy
  • Apoptosis (cell death) 
  • Responding to infections and injury

From the birth to the death of a cell, mitochondria are involved. 

Are Mitochondria Found in Plant and Animal Cells?

Are Mitochondria Found in Plant and Animal Cells?

Mitochondria are found in many types of cells, including in the following:

  • Animals 
  • Body Cells 
  • Fungi
  • Plants
  • Protists (one-cell organisms)

Mitochondria are likely the reason higher animals can exist. Humans and higher animals are complex creatures who need large amounts of energy to survive and thrive each day. Without mitochondria, cells wouldn't be able to obtain energy very efficiently.

Who Observed Mitochondria First?

Who Observed Mitochondria First?

First seen with a light microscope in the 1800s, mitochondria were named after the Greek word for "thread" and "granule". The scientists that first discovered them named them after the way they looked, believing that they transmitted hereditary information.

During the mid-1950s, a method for isolating and studying organelles was developed. This method helped scientists to better understand how mitochondria function.

Mitochondria Function (How Mitochondria Work)

Mitochondria Function (How Mitochondria Work)

Understanding the structure of a mitochondrion is important to understanding exactly how it works. 

Mitochondria are oblong in shape, and commonly characterized as rod-shaped or oval. They can range from 1-10 micrometers long and are quite flexible. They are capable of changing shape rapidly and are known to move around the cell almost constantly.

The outer membrane and inner membrane house the intermembrane space. This space contains proteins that are highly specialized. 

The outer membrane functions like a sieve. It filters out molecules that are too big before they can make their way into the mitochondria. This happens with the help of a protein called porin that helps it accomplish this function.

The inner membrane twists and turns with large inner foldings called cristae. The cristae multiply the surface area available for the cell components to complete vital processes like cellular respiration. Similarly to the outer membrane, the inner membrane only allows certain molecules into the inner mitochondrial matrix -- which is where the magic of making energy happens.

Can Mitochondria Survive On Its Own?

Within the inner membrane, there are transport proteins. This group of transport proteins move the correct molecules wherever they need to go. They work in harmony with other components of the mitochondrion to complete a multi-step process and generate the energy the cell needs.

Can Mitochondria Survive On Its Own?

Can Mitochondria Survive On Its Own?

The number of mitochondria existing in a cell correlates directly with the cell's level of metabolic activity (metabolism).

Some organisms have a single, large mitochondrion. Others have thousands of mitochondria.

For example, here are some organs that contain higher amounts of mitochondria:

  • Muscle
  • Liver
  • Kidney
  • Brain 

Experts believe that these organelles appear to be linked in some sort of network of traveling chains based on the needs of the cell.

Can Mitochondria Survive Outside the Cell?

Can Mitochondria Survive Outside the Cell?

While mitochondria produce about 90% of the chemical energy that cells need to survive, mitochondria cannot survive outside of the cell.

Mitochondria move and function in the cell because of interactions in the cytoskeleton. The cytoskeleton is a dynamic, microscopic network inside all cells that helps give them internal organization, coherence, and  shape.

Essentially, the mitochondria and cell need the cytoplasm to help add mechanical support to their chemical functions. The cell also supplies the mitochondria with the oxygen it needs to produce energy.

Can Mitochondria Self Replicate

Can Mitochondria Self Replicate?

Mitochondria are different from other organelles because they have their own small chromosomes and DNA. They replicate (reproduce) independently of the cell in which they are found. Their genetic system is separate and distinct from the nucleus of the cell.

This means that the mitochondria don't rely on cell division to multiply. This came about by a process called endosymbiosis, and is thought to be a result of evolutionary adaptations that took place millions of years ago.

The DNA in mitochondria is localized, and is located in the matrix. It contains:

  • Enzymes
  • Ribosomes (protein synthesis)

However, the mitochondria cannot be created "from scratch". They need genetic material from both the mitochondria and the nucleus. They do reply to the needs of the cell -- if a muscle cell is stimulated by repeated movement, the mitochondria will multiply within the cell to respond to that energy need.

How Mitochondria Produce Energy

How Mitochondria Produce Energy

Energy is produced by mitochondria in the cell in the form of chemical energy. This energy is converted by going through the cell's pathways of metabolism.

Mitochondria generate chemical energy in a form called adenosine triphosphate (ATP). The phosphate in this form creates a high-energy bond that provides energy for other reactions that occur in the cell.

The production of energy happens by metabolizing the following components (from the food we eat) through cellular respiration with the assistance of molecular oxygen:

  • Carbohydrates (sugars)
  • Fats
  • Proteins
  • Chemical fuels
Mitochondrial Disease

Mitochondrial Disease

Sometimes defects occur in the pathways mitochondria uses to turn food and oxygen into energy. Since mitochondria exist in multiple places and produce the majority of energy each cell needs to survive, it's not uncommon to experience symptoms from cell injury and cell death to organ systems failing -- from the muscles to the brain to the kidneys.

Quality of life can seriously suffer and serious disease can result when the mitochondria are damaged. It's suggested that 3+ malfunctioning organ systems may be a red flag for mitochondrial disease.

Experts suspect that we aren't aware of all the different diseases

Experts suspect that we aren't aware of all the different diseases that mitochondrial dysfunction causes. This complex organelle may be involved in many conditions and can have long-term effects.

Research suggests mitochondria are linked to: 

  • Aging 
  • Cancer
  • Chronic disorders
  • Diabetes
  • Degenerative conditions (i.e. Alzheimer's disease, Parkinson's) 
  • Genetic disorders
  • Lou Gehrig's disease
  • Muscular dystrophy 
  • Obesity

In instances of a heart attack or stroke, for example, the mitochondria may not receive the oxygen it needs. When the mitochondria stop working, the cells of vital organs like the brain or heart can be damaged or die. Cell injury can overwhelm the mitochondria. 

Can Mitochondria Be Repaired?

Can Mitochondria Be Repaired?

The possibility for mitochondria to be repaired depends on the type of damage that was caused.

Mitochondrial damage can be divided into two main categories:

  1. Primary- Mitochondrial malfunction caused by an inherited condition.

This damage is caused by a genetic defect, either in mitochondrial DNA or the cell nucleus, that results in the improper assembly or function of the organelle.

These are often referred to as "mitochondrial diseases", and they usually show up in babies or children and affect organs that use lots of energy (i.e. brain, heart, essential organs). In adults, mitochondrial disease can manifest in a form that leads to blindness or diabetes.

  1. Secondary-  Mitochondrial malfunction caused by environmental factors.

This type of malfunction is often called "secondary mitochondrial dysfunction", and it's caused by damaging events during life (i.e. heart attack).

Sepsis, organ transplantation, and autoimmune diseases are just a few of the many disorders where mitochondrial dysfunction plays a role.

Typical testing to determine if mitochondrial disease is the suspect often include blood and urine tests, DNA testing, and muscle biopsy from the thigh. Since mitochondria are central to many diseases, they are often a target for therapies.

Therapies and Treatments for Mitochondrial Disease

Therapies and Treatments for Mitochondrial Disease

Mitochondrial medicine is relatively new, really only occurring within the last 30 years. The following timeline will give you an idea of a few important milestones in mapping mitochondrial disease:

  • 1962- First suspected case (large mitochondria, both in size and number); chemical staining is applied to mitochondria to identify and observe changes under a microscope
  • 1975- The first case of Mitochondrial Encephalopathy, Lactic Acidosis, and Stroke-like episodes syndrome (MELAS) is described 
  • 1981- The mitochondrial genome is mapped 
  • 1982- Scientific studies are published on two mitochondrial diseases,  Kearns-Sayre syndrome (KSS) and Myoclonic Epilepsy with Ragged-Red Fibers syndrome (MERRF)
  • 1984- First scientific paper on MELAS is published
  • 1991 - Tissue analysis becomes more available for testing 

While they may seem rare, mitochondrial diseases are more frequent than you might think. They typically present in children, and according to the United Mitochondrial Disease Foundation, "every 30 minutes a child is born who will develop a mitochondrial disease by age 10."

You can learn more about the different types of mitochondrial diseases by visiting the types of mitochondrial disease page on their website. 

It is said that one in 5,000 individuals has a mitochondrial disease. Since there are a number of symptoms and body systems involved in these conditions, it's important for research to find better treatments and tests to identify these diseases. 

Current Therapeutic Options
Current Therapeutic Options

For primary mitochondrial diseases, the main focus is in developing gene therapies. These therapies target the dysfunction by replacing the defective genes in the nucleus of the cell.

Another related approach is repairing or replacing the "on/off switch" of the damaged gene inside of the mitochondria. Other therapies aim to mitigate the symptoms caused by mitochondrial diseases.

The spectrum of symptoms that occur due to mitochondrial disease can include:

  • Brain
    • Atypical cerebral palsy
    • Autism or autism-like features
    • Dementia
    • Developmental delays
    • Learning disabilities
    • Mental retardation
    • Neurological problems 
    • Migraines
    • Seizure
    • Stroke
  • Ears- hearing loss or problems
  • Eyes
    • Ophthalmoplegia 
    • Optic atrophy 
    • Ptosis
    • Retinitis pigmentosa
    • Strabismus
    • Vision loss or problems
  • Gastrointestinal System
    • Constipation
    • Cramping
    • Diarrhea 
    • Reflux
    • Swallowing difficulties
    • Unexplained vomiting
  • Heart
    • Blockage 
    • Cardiomyopathy 
    • Defects 
    • Heart disease
  • Kidney
    • Kidney diseases
    • Renal tube failure
  • Liver
    • Liver failure or disease
    • Low blood sugar
  • Muscles
    • Constipation
    • Cramping
    • Diarrhea
    • Dysmotility 
    • Exercise intolerance
    • Hypotonia
    • Low tone
    • Movement disorders
    • Pain
    • Reflux
    • Vomiting  
    • Weakness
  • Nerves
    • Fainting 
    • Temperature intolerance
    • Pain
    • Zero reflexes
  • Pancreas
    • Diabetes
    • Pancreatic failure
    • Parathyroid failure
  • Systemic
    • Failure to gain weight
    • Fatigue
    • Increased risk of infection
    • Poor growth 
    • Respiratory problems
    • Short stature 
    • Thyroid problems
    • Unexplained vomiting 

Treatment plans and approaches depend on the specific diagnosis as well as the severity of symptoms.

Typical treatment may include:

  • Vitamins and supplements (i.e. Co-Q10, B complex vitamins)
  • Conserving ("budgeting") energy
  • Exercises (endurance, resistance/strength training)
  • Specialized treatment (i.e. speech, physical, respiratory, or occupational therapy)
Implications for the Future
Implications for the Future

New methods are searching for ways to measure mitochondrial efficiency. This way, damage can be diagnosed more quickly and easily. Currently, mitochondrial diseases share symptoms with other diseases, so they are commonly mistaken for other conditions. These methods may also be able to check whether new treatments are working the way they are intended to.

While current treatments are focused on managing symptoms, future therapies are aimed at correcting the defects related to biological mutations.

Recently, scientists in Japan found a new approach to mitochondrial disease. Using a chemical compound that penetrates mitochondrial proteins, they report being able to eliminate certain sequences in the mitochondria's mutant DNA. This approach is being referred to as targeted elimination.

Making Sense of Mitochondria

Making Sense of Mitochondria

Who knew a tiny organelle could be the key to making organs, organ systems, and organisms function? Usable energy is made by mitochondria at the cellular level, and that energy helps muscles (and more) to function and fuel us each day. Scientists are still just starting to scratch the surface when it comes to disease treatment and therapies -- but this powerhouse of the cell holds a lot of promise.

References

Boundless. The Evolution of Mitochondria. Bio.libretexts.org. Published August 14, 2020. 

Cleveland Clinic. Mitochondrial Diseases. My.clevelandclinic.org. Accessed September 2021. 

Cooper GM. Mitochondria. Ncbi.nlm.nih.gov. Published 2000. 

Davidson MW. Mitochondria. Micro.magnet.fsu.edu. Published November 13, 2015. 

Elliot K, Wand H. Symptoms of MERRF Syndrome. Rarediseases.org. Accessed September 2021. 

Gahl W. Mitochondria. Genome.gov. Accessed September 2021. 

Genetic Engineering & Biotechnology News. Mitochondrial Diseases May Potentially Be Improved by New Approach. Genengnews.com. Published August 30, 2021.  

MRC Mitochondrial Biology Unit. Mitochondrial Disease. Mrc-mbu.cam.ac.uk. Accessed 2021.

MRC Mitochondrial Biology Unit. What Are Mitochondria? Mrc-mbu.cam.ac.uk. Accessed 2021.

Nature Education. Microtubules and Filaments. Nature.com. Published 2014. 

Nature Education. Mitochondria. Nature.com. Published 2014. 

National Institute of Neurological Disorders and Stroke. Kearns-Sayre Syndrome Information Page. Ninds.nih.gov. Accessed September 2021. 

Scaglia F. MELAS Syndrome. Rarediseases.org. Accessed September 2021. 

United Mitochondrial Disease Foundation. Understanding & Navigating Mitochondrial Disease. Umdf.org. Published 2020. 

Western. All About Mitochondria. Lhsc.on.ca. Accessed 2021.

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