The Chemistry of Life, How Energy Stored in Chemical Bonds Sustains All Life on Earth

All living things require energy to function, and their cells require a constant and ongoing input of energy to power the various cellular processes and functions they perform. What’s truly miraculous is how nature’s energies external to living organisms are transmuted into internal cellular energies that drive the very processes of life itself.

To any inquiring mind, this obviously raises the question, where does the energy that sustains life come from, and how is it transported and used?

Introducing ATP, the Chemical Battery of Life

The energy that drives life on Earth is stored in chemical bonds within molecules, particularly in molecules such as ATP and glucose. These energy-rich molecules serve as currency for various cellular processes and provide the fuel necessary for the functioning, growth, and reproduction of all living organisms.

How Energy is Stored in Chemical Bonds

Chemical bonds are formed when atoms share or transfer electrons to achieve a more stable and lower energy state. Breaking these bonds requires an input of energy, while forming new bonds releases energy. This energy is stored within the chemical structure of molecules.

The most common energy transport and storage molecule in cells is adenosine triphosphate (ATP). It consists of ribose, a five-carbon sugar, attached to adenine the nitrogenous base, and a chain of three phosphate groups.

ATP is commonly referred to as the main “energy currency” of cells, much like money is the main economic currency in human societies. The bonds between the phosphate groups in ATP are high-energy bonds. When the bond between the second and third phosphate groups is broken, energy is released, which cells can then use to perform various tasks.

ATP is the main energy storage molecule in cells, it reacts with water and loses a phosphate and release energy like a battery, turning into ADP. The ADP can then be recycled by absorbing energy released by burning glucose from food to rebind the phosphate to reform ATP

The ATP molecule is highly unstable, and is hydrolysed (reacts with water) to lose an inorganic phosphate group (Pi) and break down into ADP, releasing energy, as in the following reaction:

ATP + H2O → ADP + Pi + free energy

Like most chemical reactions, the hydrolysis of ATP to ADP is reversible, requiring an input of free energy this time, to regenerate ATP from ADP + Pi, and releasing water in the process. The formation of ATP can be expressed in the following equation:

ADP + Pi + free energy → ATP + H2O

We mentioned a moment ago that the energy released by splitting off one inorganic phosphate group from ATP to produce ADP is used for various cellular processes.

What tasks do cells perform?

Cells exhibit distinct functionalities, depending on the type of cell. Some of these include:

  • Cell division to produce new cells.
  • Synthesis of various macromolecules such as proteins, nucleic acids, and lipids.
  • Active transport of molecules across cell membranes such as the transport of nutrients into cells and the removal of waste products.
  • Active transport to pump ions (electrically charged atoms or molecules) across cell membranes against their concentration gradients to maintain proper ion balance and cell volume.
  • Contraction and movement in muscle cells.
  • Nerve impulse transmission, neurotransmitter release, synthesis and degradation of signaling molecules in nerve cells.
  • In some organisms, such as fireflies, bioluminescence, which is light produced by a chemical reaction within a living organism.

What is Respiration?

Respiration is the process by which cells convert biochemical energy from nutrients into adenosine triphosphate (ATP), and then release waste products.

This complex series of chemical reactions allows cells to harness the energy stored in food molecules and use it for various cellular activities. There are two main types of respiration: aerobic respiration, which requires oxygen, and anaerobic respiration, which does not.

In aerobic respiration, glucose and oxygen react to produce carbon dioxide, water, and ATP. This process occurs in the mitochondria of cells and can be summarized by the following equation:

C6H12O6 + 6O2 → 6CO2 + 6H2O + ATP

In anaerobic respiration, cells generate energy without oxygen, typically resulting in less ATP. This can lead to the production of lactic acid in muscles or ethanol and carbon dioxide in yeast.

Respiration is crucial for maintaining the energy balance within cells and ensuring they have the necessary power to perform essential functions like growth, repair, and maintenance.

Energy is Finite in the Biosphere

We’ve discussed how energy is stored and transported, but energy doesn’t come from nowhere. In physics, the first law of thermodynamics, the Law of Conservation of Energy states that energy can neither be created nor destroyed, only converted from one form of energy to another. This means that a system always has the same amount of energy, unless it’s added from the outside.

In the case of a living organism, the energy comes from outside itself in the form of food, but in case of the biosphere, the global ecosystem of the planet Earth, where does the energy come from?

We know it continuously cycles matter, but if living organisms are constantly consuming food, and energy is lost from the system in the form of heat, through metabolic processes such as respiration, maintaining body temperature to offset heat loss to the environment, and heat lost through the process of decomposition, why hasn’t all life on the planet used up the limited and finite energy available and become extinct over hundreds of millions of years?

There must be something preventing such a global cataclysm!

The Ecological Role of Autotrophs or Producers

In ecology, autotrophs or producers are organisms that can make their own organic (carbon-containing) molecules from inorganic (non-carbon containing) ones, serving as primary producers of food in a food chain, hence their name.

Heterotrophs or consumers, on the other hand, can’t produce their own food, and obtain organic molecules by eating other organisms, either producers or other consumers, in effect creating a “food chain” where one organism eats another, which eats another, and so on.

Autotrophs (from Greek autos, meaning “self” and trophe, meaning “nutrition”) obtain energy and nutrients to create organic substances from inorganic ones by the following methods:

Photoautotrophs are able to capture the energy of sunlight through the process of photosynthesis, and convert it into chemical energy stored in molecules such as glucose. This group of organisms includes plants, algae, and cyanobacteria (blue-green algae). Lichens are also able to photosynthesise, but they’re actually composite organisms, composed of a fungus (the mycobiont) and either green algae or cyanobacteria (the photobiont) that form a mutually beneficial symbiotic relationship.

Less common are, chemoautotrophs which obtain chemical energy from the oxidation of inorganic substances, such as hydrogen sulfide (H₂S), elemental sulfur (S), ferrous iron (Fe²⁺), and ammonia (NH₃) and use it to fix carbon dioxide (CO₂) into organic molecules such as sugars, proteins, and lipids. These organisms are commonly found in hostile environments where plants cannot survive, such as deep sea vents in the bottom of the ocean where light cannot easily reach, and thrive in such environments due to their lack of dependence on outside sources of carbon other than carbon dioxide. Chemoautotrophs include nitrogen fixing bacteria in the soil, iron oxidizing bacteria in the lava beds, and sulfur oxidizing bacteria located in deep sea thermal vents.

How Energy Captured by Autotrophs is Stored and Transferred to Other Organisms

Autotrophs (producers) play a pivotal role in driving the process of capturing and storing energy in chemical bonds. Photosynthetic autotrophs, such as plants and certain types of bacteria, capture sunlight energy and convert it into stored chemical energy in the chemical bonds of the glucose molecules.

In the process of photosynthesis, the energy of sunlight is captured to combine carbon dioxide from the air and water from the soil to produce the sugar glucose, releasing oxygen as a byproduct

The glucose produced by photosynthesis serves as a primary energy storage molecule in plants, and can be used immediately to provide energy through the process of respiration, or converted into starch for storage in all parts of the plant, and converted back into glucose when needed.

The process of capture and transfer of energy from the external source (the sun) and transfer to other organisms, occurs through the following steps:

  1. Photosynthesis – Photosynthetic autotrophs use chlorophyll and other pigments to capture sunlight. They absorb light energy and use it to convert carbon dioxide and water into glucose and oxygen. This process occurs in specialized cellular structures called chloroplasts. The energy from sunlight is used to combine the atoms within carbon dioxide (CO2) and water (H2O) to form glucose (C6H12O6) while releasing oxygen (O2) as a byproduct.
  2. Storing Energy in Glucose – Glucose, a sugar molecule, contains a significant amount of energy stored in its chemical bonds. This energy is a result of the light-dependent and light-independent reactions that take place during photosynthesis. The glucose produced serves as an energy reservoir that can be used by the plant itself for growth, repair, and reproduction, or by other organisms in the ecosystem that consume plants.
  3. Energy Transfer – When herbivores or other organisms consume plants, they acquire the stored energy in the form of glucose. The energy is then transferred up the food chain as carnivores and other consumers feed on the herbivores. This transfer of energy continues through each trophic level of the ecosystem.

The Interdependent Web of Life

In summary, the energy that drives life is initially captured from external sources, primarily sunlight, and stored in the chemical bonds of molecules such as glucose. Autotrophs, or producers, play a crucial role in this process by converting light energy into chemical energy through photosynthesis. This stored energy flows through ecosystems as organisms consume each other, sustaining the balance and functioning of life on Earth.

The process of photosynthesis is a crucially in sustaining life on the planet. It is the means by which solar energy from our sun which is located 147.5 – 152 million km (91.3 – 94.5 million miles) away is captured to replenish the energy that is lost from our biosphere. If it ceased, there would soon be little food or other organic matter left on Earth, and most organisms would disappear, other than chemosynthetic bacteria.

Additionally, the process of photosynthesis keeps the levels of oxygen and carbon dioxide in the atmosphere in balance, without it the Earth’s atmosphere would very quickly become almost devoid of gaseous oxygen.

References

Related Posts

2 thoughts on “The Chemistry of Life, How Energy Stored in Chemical Bonds Sustains All Life on Earth”

  1. Hi Angelo
    Just a quick note to let you know how valuable your newsletters are to me. I always learn something new, and sometimes, actually retain it! Lol.
    I send you season’s greetings, and wishes for a bright and healthy 2024.
    Cheers,
    Meron

    Reply

    1. Hi Meron, thanks for the wonderful feedback, much appreciated!
      Seasons greetings to you too and best wished for 2024! 🙂

      Reply

Leave a Reply