Glossary
ATP (adenosine triphosphate)
The primary energy currency of the cell, used to power most cellular activities and processes.
Example:
Your brain cells constantly use ATP to send signals and process information.
ATP synthase
An enzyme complex that uses the energy from a proton gradient to synthesize ATP from ADP and inorganic phosphate.
Example:
The spinning action of ATP synthase is often compared to a tiny molecular motor, generating vast amounts of ATP.
Active site
The specific region on an enzyme where the substrate binds and catalysis occurs.
Example:
The shape of an enzyme's active site is crucial; if it's altered, the enzyme might not be able to bind its specific molecule.
Allosteric site
A site on an enzyme, distinct from the active site, where regulatory molecules (like noncompetitive inhibitors) can bind to either activate or inhibit enzyme activity.
Example:
The binding of a molecule to an allosteric site can act like an 'on/off' switch for enzyme activity, regulating metabolic pathways.
Cellular energetics
The study of how cells manage energy resources, including the processes of making, moving, and using energy.
Example:
Understanding cellular energetics helps explain how a muscle cell contracts or how a plant cell grows.
Cellular respiration
An aerobic metabolic process that breaks down glucose and other organic molecules to produce ATP, primarily occurring in the mitochondria of eukaryotes.
Example:
When you exercise, your muscle cells perform cellular respiration to generate the ATP needed for movement.
Chemiosmosis
The process by which ATP is synthesized using the energy released from the movement of protons across a membrane, down their electrochemical gradient, through ATP synthase.
Example:
The generation of ATP in both photosynthesis and cellular respiration relies on chemiosmosis to harness the energy of a proton gradient.
Competitive inhibitor
An inhibitor that binds directly to the active site of an enzyme, competing with the substrate and preventing it from binding.
Example:
A drug designed as a competitive inhibitor might mimic the natural substrate to block an enzyme's function in a disease pathway.
Coupled reactions
Pairs of reactions in which an energy-releasing (exergonic) reaction provides the energy needed to drive an energy-requiring (endergonic) reaction.
Example:
In cells, the energy released from ATP hydrolysis is often used in coupled reactions to power processes like muscle contraction or active transport.
Cytosol
The jelly-like substance that fills the cytoplasm of a cell, where many metabolic reactions, including glycolysis, occur.
Example:
The initial breakdown of glucose begins in the cytosol before the products move into the mitochondria.
Denaturation
The process by which a protein, such as an enzyme, loses its characteristic three-dimensional structure and biological activity due to extreme conditions like high temperature or pH.
Example:
Boiling an egg causes the proteins in the egg white to undergo denaturation, turning them solid and opaque.
Electron Transport Chain (ETC)
A series of protein complexes and electron carriers embedded in a membrane that transfer electrons, releasing energy to pump protons and create a gradient.
Example:
In both photosynthesis and cellular respiration, the Electron Transport Chain is crucial for generating a proton gradient that drives ATP synthesis.
Electron carriers (NADH, FADH2, NADPH)
Molecules that temporarily store and transport high-energy electrons and protons, playing crucial roles in energy transfer pathways like cellular respiration and photosynthesis.
Example:
NADH and FADH2 deliver electrons to the electron transport chain in cellular respiration, while NADPH carries electrons for sugar synthesis in photosynthesis.
Entropy
A measure of the disorder or randomness in a system; in biological systems, energy input is required to maintain order against the natural tendency towards increasing entropy.
Example:
A messy room has high entropy, while a neatly organized room has low entropy, requiring energy to maintain its order.
Enzyme-substrate complex
A temporary molecule formed when an enzyme binds to its specific substrate at the active site.
Example:
The formation of an enzyme-substrate complex is the first step in an enzyme-catalyzed reaction, like a key fitting into a lock.
Enzymes
Protein catalysts that speed up the rate of specific biochemical reactions without being consumed in the process.
Example:
The enzymes in your saliva, like amylase, begin breaking down starches as soon as you start chewing.
Fermentation
An anaerobic metabolic process that produces ATP without oxygen, typically by breaking down glucose into products like lactic acid or ethanol.
Example:
When oxygen is scarce during intense exercise, muscle cells resort to fermentation to produce a small amount of ATP, leading to lactic acid buildup.
Glycolysis
The first stage of cellular respiration, occurring in the cytosol, where glucose is broken down into two molecules of pyruvate, producing a small amount of ATP and NADH.
Example:
Even without oxygen, cells can perform glycolysis to generate a quick burst of energy.
Inhibitors
Molecules that decrease the activity of an enzyme by binding to it, preventing or slowing down the reaction.
Example:
Many medications act as inhibitors to specific enzymes in pathogens, preventing them from replicating or causing disease.
Krebs cycle (Citric acid cycle)
A central metabolic pathway in aerobic respiration, occurring in the mitochondrial matrix, that completes the oxidation of glucose derivatives, producing CO2, ATP, NADH, and FADH2.
Example:
The Krebs cycle is a metabolic hub, connecting the breakdown of carbohydrates, fats, and proteins to energy production.
Light-dependent reactions
The first stage of photosynthesis, where light energy is captured by photosystems and converted into chemical energy in the form of ATP and NADPH.
Example:
During the light-dependent reactions, water molecules are split, releasing oxygen and providing electrons for the electron transport chain.
Light-independent reactions (Calvin cycle)
The second stage of photosynthesis, where ATP and NADPH from the light-dependent reactions are used to fix carbon dioxide and synthesize sugars.
Example:
The light-independent reactions are where the actual sugar molecules are built, using the energy carriers produced earlier.
Mitochondria
Organelles in eukaryotic cells that are the primary sites of cellular respiration, responsible for generating most of the cell's supply of ATP.
Example:
Muscle cells have a high density of mitochondria to meet their substantial energy demands.
Noncompetitive inhibitor
An inhibitor that binds to an enzyme at an allosteric site, distinct from the active site, causing a conformational change that reduces the enzyme's activity.
Example:
Some heavy metals act as noncompetitive inhibitors by binding to enzymes and altering their shape, making them less effective.
Optimal range
The specific range of environmental conditions (like temperature or pH) at which an enzyme exhibits its maximum activity.
Example:
Human digestive enzymes have an optimal range of pH that matches the acidic environment of the stomach or the neutral environment of the small intestine.
Oxidative phosphorylation
The process in cellular respiration where ATP is formed as a result of the transfer of electrons from NADH and FADH2 to oxygen via an electron transport chain.
Example:
The majority of ATP produced during cellular respiration is generated through oxidative phosphorylation in the mitochondria.
Photophosphorylation
The process in photosynthesis where ATP is formed using the energy of sunlight to create a proton gradient that drives ATP synthase.
Example:
During the light-dependent reactions, photophosphorylation converts light energy into chemical energy stored in ATP.
Photosynthesis
The process used by plants, algae, and cyanobacteria to convert light energy into chemical energy in the form of sugars, using carbon dioxide and water.
Example:
Trees perform photosynthesis to create their own food, releasing oxygen as a byproduct that we breathe.
Photosystems (I and II)
Protein complexes embedded in the thylakoid membranes of chloroplasts that absorb light energy and initiate the electron transport chain in photosynthesis.
Example:
When light strikes Photosystem II, it excites electrons, which are then passed down an electron transport chain.
Prokaryotes
Single-celled organisms that lack a membrane-bound nucleus and other membrane-bound organelles, such as bacteria and archaea.
Example:
Cyanobacteria, a type of prokaryote, were among the first organisms to perform oxygenic photosynthesis, fundamentally changing Earth's atmosphere.
Proton gradient
A difference in the concentration of protons (H+ ions) across a biological membrane, storing potential energy that can be used to drive cellular processes.
Example:
The high concentration of protons in the intermembrane space of the mitochondria creates a strong proton gradient that powers ATP synthase.
Sequential pathways
A series of biochemical reactions where the product of one reaction serves as the reactant for the next, allowing for efficient energy transfer and complex molecule synthesis.
Example:
Glycolysis is a sequential pathway where glucose is broken down step-by-step, with each intermediate molecule feeding into the next reaction.
Stroma
The fluid-filled space within the chloroplast, surrounding the thylakoids, where the Calvin cycle of photosynthesis takes place.
Example:
Carbon dioxide is fixed into organic molecules in the stroma during the light-independent reactions of photosynthesis.
Terminal electron acceptor
The final molecule in an electron transport chain that accepts electrons, allowing the chain to continue functioning.
Example:
In aerobic cellular respiration, oxygen acts as the terminal electron acceptor, forming water.