Catalyze Chemical BreakdownLife depends upon the building up and breaking down of biological molecules. Catalysts, in the form of proteins or RNA, play an important role by dramatically increasing the rate of a chemical transformation––without being consumed in the reaction. The regulatory role that catalysts play in complex biochemical cascades is one reason so many simultaneous chemical transformations can occur inside living cells in water at ambient conditions. For example, the 10‑enzyme catalytic breakdown and transformation of glucose to pyruvate in the glycolysis metabolicpathway.
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Chemically Assemble OrganicCompounds
Part of the reason that synthesis reactions (chemical assembly) can occur under such mild conditions as ambient temperature and pressure in water is because most often, they occur in a stepwise, enzyme‑mediated fashion, sipping or releasing small amounts of energy at each step. For example, the synthesis of glucose from carbon dioxide in the Calvin cycle is a 15‑step process, each step regulated by a differentenzyme.
Transform Chemical Energy
Life’s chemistry runs on the transformation of energy stored in chemical bonds. For example, glucose is a major energy storage molecule in living systems because the oxidative breakdown of glucose into carbon dioxide and water releases energy. Animals, fungi, and bacteria store up to 30,000 units of glucose in a single unit of glycogen, a 3‑D structured molecule with branching chains of glucose molecules emanating from a protein core. When energy is needed for metabolic processes, glucose molecules are detached and oxidized.
Transform Radiant Energy(Light)
The sun is the ultimate source of energy for many living systems. The sun emits radiant energy, which is carried by light and other electromagnetic radiation as streams of photons. When radiant energy reaches a living system, two events can happen. The radiant energy can convert to heat, or living systems can convert it to chemical energy. The latter conversion is not simple, but is a multi‑step process starting when living systems such as algae, some bacteria, and plants capture photons. For example, a potato plant captures photons then converts the light energy into chemical energy through photosynthesis, storing the chemical energy underground as carbohydrates. The carbohydrates in turn feed other livingsystems.
Phylum Plantae (“plants”): Angiosperms, gymnosperms, green algae, and more
Plants have evolved by using special structures within their cells to harness energy directly from sunlight. There are currently over 350,000 known species of plants which include angiosperms (flowering trees and plants), gymnosperms (conifers, Gingkos, and others), ferns, hornworts, liverworts, mosses, and green algae. While most get energy through the process of photosynthesis, some are partially carnivores, feeding on the bodies of insects, and others are plant parasites, feeding entirely off of other plants. Plants reproduce through fruits, seeds, spores, and even asexually. They evolved around 500 million years ago and can now be found on every continent worldwide.
Photosynthesis converts solar energy into chemical energy that plants use to make glucose so they cangrow.
For the first half of Earth’s life to date, oxygen was all but absent from an atmosphere made mostly of nitrogen, carbon dioxide, and methane. The evolution of animals and life as we now know it owe everything to photosynthesis.
About 2.5 billion years ago, cyanobacteria—the first organisms that used sunlight and carbon dioxide to produce oxygen and sugars via photosynthesis—transformed our atmosphere. Later, algae evolved with this ability, and about 0.5 billion years ago, the first land plants sprouted.
Algae, plankton, and land plants now work together to keep our atmosphere full of oxygen.
Photosynthesis occurs in special plant cells called chloroplasts, which are the type of cells found in leaves. A single chloroplast is like a bag filled with the main ingredients needed for photosynthesis. It has water soaked up from the plant’s roots, atmospheric carbon dioxide absorbed by the leaves, and chlorophyll contained in folded, maze-like organelles called thylakoids.
Chlorophyll is the true catalyst of photosynthesis. Cyanobacteria, plankton, and land plants all rely on this light-sensitive molecule to spark the process.
Chlorophyll molecules are so bad at absorbing green light that they reflect it like tiny mirrors, causing our eyes to see most leaves as green. It’s usually only in autumn, after chlorophyll degrades, that we peep those infinite shades of yellow and orange produced by carotenoid pigments.
Image: Anna Guerrero,
The process of photosynthesis in plants involves a series of steps and reactions that usesunlight, water, and carbon dioxide to produce sugars that the plant uses to grow. Oxygen is released from the leaves as a byproduct.
But chlorophyll’s superpower isn’t the ability to reflect green light—it’s the ability to absorb blue and red light like a sponge. The sun’s blue and red light energizes chlorophyll, causing it to lose electrons, which become mobile forms of chemical energy that powers plant growth. The chlorophyll replenishes its lost electrons not by drinking water but by splitting it apart and taking electrons from the hydrogen, leaving oxygen as a byproduct to be “exhaled”.
The electrons freed from chlorophyll need something to carry them to where they can be put to use, and two molecules ( ATP and NADPH ) work much like energy transport buckets. They bring the electrons to the space outside of the thylakoid folds but still inside the chloroplast “bag.” In this area, called the stroma, the energy brought by the molecular buckets forces carbon dioxide to combine with other molecules, forming glucose. After these reactions occur, the buckets—now empty of electrons—return to the thylakoid folds to receive another batch from sunlight-stimulated chlorophyll.
When plants have enough sunlight, water, and fertile soil, the photosynthesis cycle continues to churn out more and more glucose. Glucose is like food that plants use to build their bodies. They combine thousands of glucose molecules to make cellulose, the main component of their cell walls. The more cellulose they make, the more they grow.
Nature, through photosynthesis, enables plants to convert the sun’s energy into a form that they and other living things can make use of. Plants transfer that energy directly to most other living things as food or as food for animals that other animals eat.
Humans also extract this energy indirectly from wood, or from plants that decayed millions of years ago into oil, coal, and natural gas. Burning these materials to provide electricity and heat has, through overexploitation, led to dire consequences that have upset the balance of life on Earth.
What if humans could harness this power in a different way? Imagine green chemistry that’s catalyzed by sunlight instead of having to mine for heavy metals like copper, tin, or platinum. Think of the potential that chemical processes requiring little heat have to reduce energy consumption. With a better understanding of photosynthesis, we may transform agriculture to consume less water and preserve more land for native plants and forests. As we continue to grapple with climate change, listening to what plants can teach us can shine a light down a greener path.
Efficient Fuel Creation Inspired byPlants
Technion‑Israel Institute of Technology
Stable solar‑to‑energy conversion from Technion‑Israel Institute of Technology uses full cycle redox transformation to break water into hydrogenfuel.
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Electrocatalyst from Oregon State University is made of a unique molecule that promotes stability and selectivity.