Mitochondria — Structure & Function

What Are Mitochondria?

Mitochondria (singular: mitochondrion) are the powerhouses of the cell. They produce energy for plant and animal cells. Cells that require a lot of energy, like muscle cells, can have thousands of them per cell.

These organelles take glucose (sugar) in the cell and break it down to release energy in little usable chunks. This process is called cellular respiration and the usable form of energy is called ATP.

Mitochondria honestly look like little potatoes in the cell. They're pretty plain on the outside, but inside, they have a second membrane that is highly folded. This inner membrane is very selective to even small molecules and ions.

The inner membrane folds back and forth inside the mitochondrion. These folds are called cristae.

The folds are also filled with a water-based goop (kind of like cytosol) called the mitochondrial matrix.

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$\color{#8925AE}{\text{Vacuole}}$ : Organelle that contains water and nutrients. Refrigerator of the cell

$\color{#8925AE}{\text{Golgi Apparatus}}$ : Stores, sorts, and modifies proteins and lipids. Post office of the cell

$\color{#8925AE}{\text{Cytoskeleton}}$ : Helps the cell maintain its shape and assists with movement. Skeleton of the cell

$\color{#8925AE}{\text{Mitochondrion}}$ : Makes ATP (a source of energy). Powerhouse of the cell

$\color{#8925AE}{\text{Ribosome}}$ : Creates polypeptide chains and proteins. Factory of the cell

$\color{#8925AE}{\text{Endoplasmic Reticulum}}$ : The smooth ER makes lipids for the cellular membrane. The rough ER assembles proteins and transports them into and out of the cell

$\color{#8925AE}{\text{Nucleus}}$ : Contains the genetic material, DNA, of the cell. Brain of the cell

Powerhouse of the Cell

Almost all eukaryotic cells possess some mitochondria, with a few rare exceptions like red blood cells. These organelles are the location of cellular respiration, particularly the citric acid cycle and the ETC. Cellular respiration occurs across the inner membrane. The folds in the inner membrane are called cristae. These folds increase surface area and allow for greater ATP production. Mitochondria also possess fragments of their own unique DNA.

(Video) Mitochondria Aren't Just the Powerhouse of the Cell

by Seeker

A mitochondrion makes ATP (a source of energy). You may know it as the powerhouse of the cell, but there is so much more to it than that.

In this video, you will see the structure of mitochondria, learn about the endosymbiosis theory, and find out why we all share similar mitochondrial DNA.

A Cell's Source of Energy

Sometimes, you might see something like a jelly bean or potato in a cell. These are known as mitochondria. Usually there are a lot of them (around 300 to 400) in a cell. In cells that use a lot of energy, the number is even larger.

Internal Structure

Each mitochondrion has two membranes made of a lipoprotein bilayer. The outer membrane is smooth, but the inner one has finger-like structures called cristae. The inner chamber is filled with a jelly-like substance called matrix. Matrix contains crucial enzymes and coenzymes for cellular respiration.

Cristae have some round things called ATP-synthases. They create ATP from ADP via oxidative phosphorylation. There are also numerous electron transport chains along the cristae which generate energy. The highest energy-yielding part of cellular respiration, the Krebs cycle, takes place in mitochondria. That’s why these organelles are called the powerhouses of a cell.

Where Did Mitochondria Come From?

The most interesting thing about these organelles is that they more or less behave like prokaryotes. They have their own DNA and ribosomes. It is very different from the nuclear DNA found in eukaryotes. The mitochondrial genome is circular and its ribosomes are type 70S, which are key characteristics of a prokaryote. Even during cell division, when other organelles are merely redistributed, mitochondria divide by fission and increase in number like most bacteria.

The most accepted hypothesis about this organelle is that it was once an independent bacterium. Somehow, it got engulfed by a eukaryotic cell via phagocytosis. Later on, the host cell found the bacterium to be useful, and it became a necessary organelle of eukaryotic cells.