Metabolism, Cell Respiration, and Photosynthesis (IB)

Metabolism

Metabolism

The sum of all biochemical reactions within cells, managing the conversion of nutrients into energy and the synthesis of essential molecules.

Anabolism

The process of building complex molecules from simpler ones, requiring energy input. Examples include protein synthesis and the formation of cell structures.

Catabolism

The process of breaking down complex molecules into simpler ones, releasing energy. Examples include cellular respiration and the digestion of food.

Metabolic Pathways

Series of interconnected chemical reactions that occur within a cell to convert substrates into products, often involving multiple enzymes. Metabolic pathways are interconnected, allowing the flow of molecules between them.

Activation Energy

The energy required to initiate a chemical reaction and start the conversion of reactants into products. It represents the energy hurdle that molecules must overcome for a reaction to occur.

Enzymes

Biological catalysts that enhance the rate of biological chemical reactions by lowering activation energy.

Exergonic reaction

A type of enzymatic reaction that releases energy to the surroundings. The final state has lower energy than the initial state. Common in catabolic processes like cellular respiration.

Endergonic reaction

A type of enzymatic reaction that absorbs energy from the surroundings. The final state has higher energy than the initial state. Typical in anabolic processes like protein synthesis.

Competitive inhibitors

Inhibitors that have a similar structure to the substrate and compete for the active site of the enzyme. They favor the lock and key hypothesis and are reversible in nature. They increase the Km but do not affect Vmax.

Non-competitive inhibitors

Inhibitors that do not compete for the active site of the enzyme but destroy the structure of the enzyme, altering its physical structure and preventing the formation of an enzyme-substrate complex. They favor the induced-fit theory and are irreversible in nature. They do not affect Km but change Vmax.

Glycolysis

The major process of oxidizing sugars, occurring in both aerobic and anaerobic reactions. It takes place in the cytoplasm of the cell and converts glucose into two molecules of pyruvate. Total ATP produced:8 ATP.

Kreb’s Cycle

Also known as the tricarboxylic acid cycle or citric acid cycle, it occurs in the mitochondrial matrix. It completely oxidizes acetyl CoA into CO2 and produces NADH, FADH2, and GTP. Total ATP produced:12 ATP.

Electron Transport System (ETS) / Oxidative Phosphorylation

The chain of hydrogen and electron carriers present in the inner mitochondrial membrane. It is responsible for the reoxidation of NADH and FADH2, producing ATP. The ETS consists of several complexes, including NADH dehydrogenase, cytochrome bc1 complex, cytochrome c oxidase complex, and ATP synthase. The number of ATP molecules synthesized depends on the nature of the electron donor.

Oxygen

Vital for the process of respiration, it acts as the final hydrogen acceptor by removing hydrogen from the system.

Photophosphorylation

Process in photosynthesis where light energy is used to produce the proton gradient required for phosphorylation.

Respiration

Process in which the energy of oxidation-reduction is utilized to produce the proton gradient required for phosphorylation.

Photosynthesis

The process by which green plants, algae, and some bacteria convert light energy into chemical energy in the form of glucose.

Chloroplast

Specialized intracellular organelle where photosynthesis primarily occurs in plant cells.

Light-Dependent Reactions

Occur in the thylakoid membrane and capture light energy to convert it into chemical energy (ATP and NADPH) while generating oxygen as a byproduct.

Light-Independent Reactions (Calvin Cycle)

Take place in the stroma of the chloroplast and utilize ATP and NADPH to convert carbon dioxide into glucose through a series of chemical reactions.

Chemiosmotic Process

Stage 1 involves the transfer of high-energy electrons along an electron-transport chain embedded in a membrane, generating a large electrochemical gradient across the membrane. Stage 2 involves the flow of protons back down their electrochemical gradient through ATP synthase, catalyzing the production of ATP.

Photosystems

Groups of photosynthetic pigments in the thylakoid membrane that capture light energy. Photosystem I (PS I) has a reaction center chlorophyll-a with an absorption peak at 700 nm (P700), while Photosystem II (PS II) has a reaction center chlorophyll-a with an absorption peak at 680 nm (P680).

Cyclic Photophosphorylation

Process in photosynthesis where light energy is absorbed, electrons are excited and passed through an electron transport chain, generating ATP through chemiosmosis.

Non-cyclic Photophosphorylation

Process in photosynthesis where light energy is absorbed, electrons are transferred to electron carriers, creating an electron transport chain that generates ATP through chemiosmosis and reduces NADP+ to NADPH.

Calvin Cycle

Also known as the light-independent reactions or dark reactions, it is a series of biochemical reactions that occur in the stroma of chloroplasts to convert carbon dioxide into carbohydrates, particularly glucose, through enzymatic reactions.

C4 Pathway

An alternative photosynthetic pathway found in certain plants that enhances carbon dioxide fixation, particularly in hot and dry environments. It involves the separation of CO2 fixation and the Calvin cycle into different cells to increase efficiency.

CAM Pathway

A specialized form of photosynthesis observed in certain plants, particularly succulents, that grow in arid or semi-arid environments. It allows plants to conserve water by opening stomata and conducting gas exchange during the night, storing CO2 as malate and releasing it during the day for photosynthesis.