Where Are Energy Storage Molecules?

Energy storage molecules are organic compounds that living organisms use to store energy. These molecules allow energy to be packed into a small space so it can be available when needed. There are several key types of energy storage molecules that serve crucial roles in biology.

The ability to store energy is extremely important for life. Organisms need to be able to stockpile energy when there is an abundant supply, often from food sources, and then tap into these reserves when energy demands arise. Energy storage gives organisms flexibility in when they use energy. It also allows energy to be transported within and between cells. Some stationary organisms, like plants, use energy storage to save up energy for times when they cannot produce their own energy like at night. Many mobile organisms also rely heavily on internal energy storage so they can travel long distances without constant energy intake.


Carbohydrates are one of the main types of energy storage molecules found in living things. They consist of carbon, hydrogen and oxygen arranged in rings or chains. The main function of carbohydrates is to store and transport energy in organisms.

There are three main types of carbohydrates – monosaccharides, disaccharides, and polysaccharides. Monosaccharides like glucose are simple sugars made up of a single sugar unit. Disaccharides like sucrose are made up of two sugar units joined together. Polysaccharides like starch contain long chains of sugar units bonded together.

The way the carbon, hydrogen and oxygen atoms are arranged gives carbohydrates their structure and function. The oxygen and hydrogen are on the outside of the rings and chains, while the carbon atoms are on the inside. This makes carbohydrates polar molecules, meaning they can dissolve in water and be transported around organisms. They also contain a lot of potential energy in their bonds, which can be released to fuel cellular processes.


Fats serve as an important energy storage molecule in the body. They consist of fatty acids and glycerol, and are the main form of energy storage in adipose tissue. Fats provide more energy per gram than carbohydrates – each gram of fat contains 9 calories, compared to 4 calories in a gram of carbohydrate or protein.

When the body needs energy, hormones signal fat cells to break down triglycerides into glycerol and fatty acids. Glycerol can be used to produce glucose via gluconeogenesis, while fatty acids are broken down into acetyl CoA which enters the citric acid cycle to generate ATP, the body’s energy currency. The acetyl CoA produced from fat breakdown also feeds into ketogenesis, producing ketone bodies that can serve as an alternative energy source.

fat tissue stores triglycerides that can be broken down to release energy.

During times of excess energy intake, the body efficiently stores any excess glucose as glycogen, and converts any remaining excess into triglycerides for long-term energy storage in adipose tissue. This allows the body to store larger amounts of energy in a compact form.

In summary, fats serve a crucial role in the body as a high-density storage form of energy that can meet the body’s needs when glucose levels fall.


Proteins are another important source of energy storage in the body. They are made up of chains of amino acids and have a more complex structure compared to carbohydrates and fats. When carbohydrate and fat stores are depleted, the body breaks down proteins for energy.

Specific proteins can serve as energy storage molecules. For example, ferritin is a protein that stores and releases iron in cells. It can form hollow protein shells that store up to 4,500 iron atoms. The liver produces ferritin to store iron when iron levels in the body are high. When iron is needed, ferritin releases it for use in various cellular processes.

Egg white and milk proteins like casein and whey are also efficient at storing amino acids. The branched chain amino acids (leucine, isoleucine and valine) bind to these proteins in a stable way that allows the amino acids to be stored and used when needed for energy production.

Additionally, seed and grain proteins have evolved to store amino acids in stable quaternary structures. They serve as a reservoir of amino acids to nourish the plant embryo when it starts to germinate and grow.


Glycogen is a complex carbohydrate that serves as a form of energy storage in humans and animals. It is made up of glucose units and is primarily found in the liver and skeletal muscles.

In the muscles, glycogen acts as an immediate energy source for contraction. When the muscles require energy, glycogen is quickly broken down through a process called glycogenolysis, which releases glucose to be used for ATP production.

The amount of glycogen stored in the muscles depends on physical activity levels. Endurance training promotes greater glycogen storage while inactivity leads to glycogen depletion in muscles.

In the liver, glycogen forms a vital glucose reserve. When blood glucose levels drop, the liver breaks down its glycogen stores to release glucose. This helps maintain normal blood sugar levels between meals or during long periods without food. The minimum liver glycogen amount in humans appears to be around 100 grams.

Glycogen synthesis occurs during times of glucose abundance. The glucose molecules are added onto glycogen molecules in chains by glycogen synthase enzymes. Glycogen branches off, forming highly branched polysaccharides that allow for compact storage.

In summary, glycogen serves as a critical short-term energy storage form in the body that helps provide a steady supply of glucose when needed.

Locations in the body

The human body stores energy molecules like carbohydrates, fats, and proteins in various locations to fuel cellular activities. The main storage sites are:

Liver – The liver stores glucose in the form of glycogen. It can store around 100 grams of glycogen. When blood glucose levels drop, the liver breaks down glycogen into glucose and releases it into the bloodstream.

Muscles – Skeletal muscles also store glycogen. They can store approximately 500 grams of glycogen. Muscles use this glycogen to fuel contractions.

Adipose tissue – Fat cells or adipocytes make up adipose tissue. This tissue stores triglycerides or fat, the major form of energy storage in the body. Adipose tissue protects and insulates organs.

The amount of energy molecules stored in various tissues depends on factors like diet, activity levels, and hormones. When the body needs an immediate energy source, it mobilizes these molecules by breaking them down through metabolic pathways.


Plants store energy in the form of carbohydrates and lipids. Starch and sugars like glucose are carbohydrates that plants produce through photosynthesis. These molecules contain chemical energy that the plant can use for fuel. Starch is the main way plants store excess glucose. It is made up of long chains of glucose molecules and is insoluble and compacted, allowing plants to stockpile large amounts of it.

Plants also store energy in lipids like oils and waxes. Fatty acids are assembled into triglycerides, which cluster together into lipid droplets. These provide dense, stable forms of energy storage. Oil seeds like sunflower and rapeseed seeds accumulate oils, while plants like eucalyptus and sunflowers produce waxes on their leaves and stems.

When plants need energy, like for nighttime respiration, growth, or repair, they can break down starches and lipids to release glucose and fatty acids. The energy stored in the bonds of these carbon compounds can then fuel essential plant metabolic processes.

Bacterial energy storage

Bacteria store energy in several different molecules that serve purposes similar to carbohydrates and fats in animals and plants. Two important energy storage molecules in bacteria are:

  • Glycogen – This is similar to the glycogen found in animals, but with some structural differences. Bacteria store glycogen as an energy reserve that can be quickly broken down into glucose molecules when energy is needed.
  • Polyhydroxyalkanoates (PHAs) – These are unique energy storage polymers found in bacteria. They serve as a way for bacteria to store carbon and energy. PHAs form granule structures within bacterial cells that can be tapped for energy when needed.

Having energy storage capabilities allows bacteria to survive periods of nutrient starvation. The stored glycogen and PHAs can be metabolized to produce ATP when an external energy source is not available. Some bacteria also use these stored nutrients to power flagella and motility when searching for new food sources.


Energy storage molecules like carbohydrates, fats, and proteins have many important practical applications. Here are some examples:

For nutrition and food production. Storing energy in carbohydrates, fats, and proteins allows plants and animals to stockpile energy for later use. This is essential for nutrition and food production.

For metabolism and exercise. The energy stored in carbohydrates gets metabolized to fuel daily activities. Glycogen provides readily available energy for muscles during exercise.

For medical applications. Intravenous feeding provides carbohydrates, fats, and proteins to hospital patients who cannot eat normally. Stored energy supports bodily functions during illness or recovery.

For commercial uses. Vegetable oils and animal fats get used to produce soaps, cosmetics, lubricants, and biodiesel fuel.

As a renewable energy source. Energy crops like sugarcane and corn can be grown and processed into biofuels like ethanol to power engines and generate electricity.

For weight management. The amount of stored energy as fat relates closely to body weight. Understanding energy storage impacts nutrition guidance for weight loss or gain.

In summary, harnessing the energy in storage molecules offers many practical benefits for health, food production, industry, energy generation, and more.


Energy storage molecules like carbohydrates, fats, and proteins play a crucial role in sustaining life. These molecules are produced by plants, animals, and bacteria through processes like photosynthesis and digestion. The energy they contain can then be released and harnessed to fuel cellular activities. Key energy storage molecules are stored in places like muscles, fat tissue, and the liver for later use when the body needs it.

These molecules allow organisms to have reserves of energy that they can draw on when food sources are scarce. This prevents starvation and allows activities to continue even without constant food intake. The storage and release of energy from these molecules is essential to maintaining life. Understanding where these molecules are found and how they function provides key insights into biology at the molecular level.

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