Processing Energy With Mitochondria (Animals) — Overview

The Powerhouse of the Cell

Mitochondria (singular: mitochondrion) convert chemical energy into energy that our cells can actually use. This process is called cellular respiration. The mitochondria use it to turn glucose and oxygen into a high-energy molecule called ATP. Adenosine triphosphate (ATP) is the money of the cell world. Well, if money was energy.

Say this out loud: "The mitochondrion is the powerhouse of the cell."

Now keep saying it. You'll never forget it.

The mitochondria break down glucose to harvest chemical energy (ATP). This process is known as catabolism. The prefix cata- means breakdown, downward. We can also recognize the -bolism in metabolism, which refers to change. So, catabolism refers to the breaking down of metabolic compounds.

Mitochondrion Structure

Mitochondria have the perfect shape for their functions. They resemble a grain of rice. They also have two mitochondrial membranes, known as the inner and the outer membranes, separated by an intermembrane space.

The outer membrane encompasses the organelle like skin. It has small tunnels made of protein in it called porins, which only allow specific molecules to pass through.

The inner membrane is folded into layered structures called cristae that increase the surface area of the inside of the cell. The cristae also only allow specific molecules to pass through, but they are much more selective than the outer membrane.

Working together, the two membranes ensure that only necessary molecules can enter the inside of the mitochondrion, which is called the matrix. Within the cellular matrix, mitochondria have DNA, ribosomes, granules, and ATP synthase particles.

Mitochondria possess their own circular DNA that is very similar to the DNA of prokaryotes. You got your mitochondrial DNA from your mother, and she got it from her mother. Mitochondria can reproduce and grow without any assistance because they contain their own DNA; they are self-replicating.

ATP synthase is an enzyme that converts ADP to ATP by metabolizing sugars and other molecules. The ATP synthase particles are embedded in the inner membrane of the mitochondrion. This is where the large surface area of the cristae come into play: the greater the surface area, the more enzymes can be embedded in the membrane. The more enzymes embedded, the more energy can be produced by the mitochondrion.

$$\color{#8925AE}{\text{Vocabulary Review:}}$$

$\color{#8925AE}{\text{Plastids}}$ : Organelles which create and store food for plant cells

$\color{#8925AE}{\text{Mitochondria}}$ : Make ATP during cellular respiration for energy

ATP and Aerobic Respiration

Mitochondria are often referred to as the powerhouse of the cell. This is because each mitochondrion is a rod-shaped organelle that is great at converting nutrients and oxygen into adenosine triphosphate, or ATP. This molecule powers metabolic processes and many forms of active transport.

The metabolic pathways require oxygen. This is the reason that animals breathe. Mitochondria are very efficient at producing ATP through aerobic respiration. The ATP yield of mitochondria through cellular respiration is a net production of 34 molecules per glucose molecule. On the other hand, anaerobic respiration yields only two ATP molecules.

In biology, structure dictates function, and the mitochondrion is no exception. The two membranes of the organelle allow for the formation of cristae within the organelle. The outer membrane surrounds the mitochondrion like a skin, while the inner membrane folds in on itself, creating the cristae. Mitochondria are also filled with a fluid called matrix.

Mitochondria (Energy Metabolism)

Mitochondria are the sites of cellular respiration, which is the process that makes the energetic molecule ATP. Mitochondria are found in all eukaryotic organisms. Different types of cells have different numbers of mitochondria. It all depends on their energy needs. For example, muscle cells need a lot of energy to help your body move around.

Mitochondria have an outer membrane which is very similar in composition to the cell membrane of eukaryotic cells. It has many integral proteins called porins which allow molecules to freely diffuse across the membrane. The porins allow pyruvate, a molecule produced during glycolysis, in the cytosol to enter this organelle.

Mitochondria also have an inner membrane, which has many folds called cristae. These cristae are extremely important because they increase the surface area of the inner membrane.

Having more surface area is important for the inner membrane because cellular respiration occurs across this membrane. Ions are transported back and forth into the intermembrane space using a bunch of different proteins. These proteins make up the electron transport chain (ETC). When the ions move back and forth across the membrane, they generate ATP in the process. So, having a more folded membrane allows for more ATP to be made.

Inside of the mitochondrial inner membrane is the mitochondrial matrix. This matrix contains enzymes, ribosomes, and mitochondrial DNA, which is different from the nuclear DNA normally found in cells. It is also where the citric acid cycle takes place. The citric acid cycle uses pyruvate, a molecule made from glucose in the cytosol, to produce ATP.

$$\color{#8925AE}{\text{Vocabulary Review:}}$$

$\color{#8925AE}{\text{Inner membrane}}$ : A semi-permeable membrane that regulates the flow of oxygen, water, carbon dioxide, and pyruvate

$\color{#8925AE}{\text{Outer membrane}}$ : A porous membrane that allows many molecules to flow freely into the mitochondrion. It stops large proteins and lipids.

$\color{#8925AE}{\text{Cristae}}$ : The folds in the inner membrane that increase the internal surface area of the mitochondrion

$\color{#8925AE}{\text{Matrix}}$ : The space inside of the inner membrane, which contains enzymes, DNA, and is where the citric acid cycle occurs

$\color{#8925AE}{\text{Citric acid cycle}}$ : A process that turns pyruvate into NADH, FADH and ATP

$\color{#8925AE}{\text{Electron transport chain}}$ : A bunch of proteins in the inner membrane that pump ions, generating a bunch of ATP

$\color{#8925AE}{\text{Glycolysis}}$ : A process that occurs in the cytosol and turns glucose into pyruvate

$\color{#8925AE}{\text{Intermembrane space}}$ : The space between the inner and outer membrane space that has a high ion concentration

(Video) Cellular Respiration and the Mighty Mitochondria

by Amoeba Sisters

Mitochondria produce a molecule called ATP through cellular respiration. The Amoeba Sisters give a great explanation of cellular respiration in this video. Don't worry too much about memorizing all of the details now. Just remember that mitochondria produce ATP, which is used as energy by the cell.