Metabolic reactions (Respiration and Photosynthesis)

Cellular respiration

The process by which cells break down glucose and other organic molecules to produce ATP.

Chloroplast

A specialized organelle found in plant cells that is responsible for photosynthesis.

Photosynthesis

The process by which plants and some other organisms convert light energy into chemical energy to produce glucose and oxygen.

Metabolism

All the biochemical reactions that occur in a cell or organism.

Catabolism

The breakdown of complex organic molecules into smaller molecules, releasing energy.

Anabolism

The process of building simple molecules into more complex ones, using energy.

ATP

Adenosine triphosphate, a molecule that stores and releases energy for cellular processes.

Glycolysis

The first stage of cellular respiration, where glucose is broken down into two molecules of pyruvate.

Citric acid cycle

Also known as the Krebs cycle, it is the second stage of cellular respiration where Acetyl CoA is further broken down to produce NADH, FADH2, and ATP.

Oxidative phosphorylation

The third stage of cellular respiration, where most of the ATP synthesis occurs through the electron transport chain and chemiosmosis.

Substrate-level phosphorylation

The process of transferring a phosphate group from an organic molecule to ADP to produce ATP.

NADH

Nicotinamide adenine dinucleotide, a coenzyme that carries electrons from one reaction to another in cellular respiration.

FADH2

Flavin adenine dinucleotide, another coenzyme that carries electrons in cellular respiration.

Pyruvate

A three-carbon molecule produced during glycolysis.

Acetyl CoA

A molecule formed from pyruvate that enters the citric acid cycle.

Matrix

The innermost compartment of the mitochondrion where the citric acid cycle occurs.

Citric Acid Cycle

Also known as the Krebs Cycle or tricarboxylic acid (TCA) cycle, it completes the oxidation of organic molecules, generating NADH and FADH2. Acetyl CoA is broken down to 2CO2 molecules, and the cycle generates 1 ATP per turn.

Oxidative Phosphorylation

The process in cellular respiration where NADH and FADH2 from glycolysis and the citric acid cycle transfer their energy to the electron transport chain and chemiosmosis, resulting in the production of ATP.

Electron Transport Chain

A series of proteins that exist in multiprotein complexes and alternate between reduced and oxidized states as they accept and donate electrons. Electrons drop in free energy as they go down the chain and are finally passed to O2, forming H2O.

Chemiosmosis

The process in oxidative phosphorylation where the H+ gradient drives H+ back through ATP synthase complex in the inner membrane, synthesizing ATP.

Photosynthesis

An anabolic reaction in green plants that converts solar energy into chemical energy. It occurs in plants, algae, certain other protists, and some prokaryotes.

Chloroplasts

The sites of photosynthesis in plants. They are surrounded by a double membrane and contain stacks of thylakoids and a thick fluid called stroma. The thylakoid membrane houses much of the machinery that converts light energy to chemical energy.

Calvin Cycle

The second stage of photosynthesis that occurs in the stroma. It forms sugar from CO2, using ATP and NADPH. The cycle begins with carbon fixation, incorporating CO2 into organic molecules.

Photosystem

A reaction-center complex associated with light-harvesting complexes. It consists of a protein complex surrounded by pigment molecules bound to proteins. The light-harvesting complexes funnel the energy of light to the reaction center.

Pigments

Substances that absorb visible light. When light is absorbed, its energy is transferred from one pigment to another, causing excitation of an electron from one of the two chlorophyll-a molecules. This excited electron is accepted by the primary electron acceptor.

Thylakoid

A membrane-bound compartment inside chloroplasts where the light reactions of photosynthesis occur. It contains pigment molecules and is the site of ATP and NADPH production.

ATP Synthesis

The process of generating ATP from ADP and inorganic phosphate (Pi) using the energy released during oxidative phosphorylation or photophosphorylation.

Light

Electromagnetic radiation that is visible to the human eye and is essential for photosynthesis.

Cytochrome complex

A protein complex involved in the electron transport chain of photosynthesis.

ADP

Adenosine diphosphate, a molecule that serves as a precursor to ATP.

ATP

Adenosine triphosphate, a molecule that stores and releases energy for cellular processes.

ATP synthase

An enzyme complex that synthesizes ATP during the process of chemiosmosis.

Calvin Cycle

The series of chemical reactions that occur in the stroma of chloroplasts, leading to the synthesis of glucose.

STROMA

The fluid-filled space within the chloroplast, where the Calvin Cycle takes place.

Thylakoid membrane

The membrane system within the chloroplast that contains chlorophyll and other pigments for capturing light energy.

THYLAKOID SPACE

The space within the thylakoid membrane where protons (H+) accumulate during the light reactions.

Photosystem II

A protein complex that captures light energy and initiates the electron transport chain in photosynthesis.

Photosystem I

A protein complex that receives electrons from Photosystem II and generates NADPH.

Pq

Plastoquinone, a molecule involved in the transfer of electrons during the light reactions.

Pc

Plastocyanin, a protein that transfers electrons from Photosystem II to Photosystem I.

NADP+ reductase

An enzyme that catalyzes the conversion of NADP+ to NADPH during photosynthesis.