Essential Knowledge

Enzymes

• The structure and function of enzymes contribute to the regulation of biological processes. Enzymes are proteins that are biological catalysts that facilitate chemical reactions in cells by lowering the activation energy..

• For an enzyme-mediated chemical reaction to occur, the shape and charge of the substrate must be compatible with the active site of the enzyme. This is illustrated by the enzyme-substrate complex model.

• Change to the molecular structure of a component in an enzymatic system may result in a change of the function or efficiency of the system—

• Denaturation of an enzyme occurs when the protein structure is disrupted, eliminating the ability to catalyze reactions.

• Environmental temperatures and pH outside the optimal range for a given enzyme will cause changes to its structure, altering the efficiency with which it catalyzes reactions

• Environmental pH can alter the efficiency of enzyme activity, including through disruption of hydrogen bonds that provide enzyme structure. 

• The relative concentrations of substrates and products determine how efficiently an enzymatic reaction proceeds. 

• Higher environmental temperatures increase the speed of movement of molecules in a solution, increasing the frequency of collisions between enzymes and substrates and therefore increasing the rate of reaction.

• Competitive inhibitor molecules can bind reversibly or irreversibly to the active site of the enzyme. Noncompetitive inhibitors can bind allosteric sites, changing the activity of the enzyme. 

Energy in Living Organisms

• All living systems require constant input of energy.

• Life requires a highly ordered system and does not violate the second law of thermodynamics

• Energy input must exceed energy loss to maintain order and to power cellular processes.

• Cellular processes that release energy may be coupled with cellular processes that require energy.

• Energy-related pathways in biological systems are sequential to allow for a more controlled and efficient transfer of energy. A product of a reaction in a metabolic pathway is generally the reactant for the subsequent step in the pathway.

Photosynthesis

• Describe the photosynthetic processes and structural features of the chloroplast that allow organisms to capture and store energy. 

• Explain how cells capture energy from light and transfer it to biological molecules for storage and use.

• Photosynthesis is the series of reactions that use carbon dioxide (CO2 ), water (H2O), and light energy to make carbohydrates and oxygen (O2 ). 

• Photosynthetic organisms capture energy from the sun and produce sugars that can be used in biological processes or stored. 

• Photosynthesis first evolved in prokaryotic organisms.

• Scientific evidence supports the claim that prokaryotic (cyanobacterial) photosynthesis was responsible for the production of an oxygenated atmosphere.

• Prokaryotic photosynthetic pathways were the foundation of eukaryotic photosynthesis.

• Stroma and thylakoids are found within the chloroplast.

  • The stroma is the fluid within the inner chloroplast membrane and outside the thylakoid. The carbon fixation (Calvin cycle) reactions of photosynthesis occur in the stroma.

  • The thylakoid membranes contain chlorophyll pigments organized into two photosystems, as well as electron transport proteins.

  • Thylakoids are organized in stacks called grana. The light reactions of photosynthesis occur in the grana.

  • The light reactions of photosynthesis in eukaryotes involve a series of coordinated reaction pathways that capture energy present in light to yield ATP and NADPH, which power the production of organic molecules in the Calvin cycle. This provides energy for metabolic processes.

• Electron transport chain (ETC) reactions occur in chloroplasts, in mitochondria, and across prokaryotic plasma membranes. In photosynthesis, electrons that pass through the thylakoid membrane are picked up and ultimately transferred to NADP+ reducing it to NADPH in photosystem I. 

  • During photosynthesis, chlorophylls absorb energy from light, boosting electrons to a higher energy level in photosystems I and II. Water then splits, supplying electrons to replace those lost from photosystem II.

  • Photosystems I and II are embedded in the thylakoid membranes of chloroplasts and are connected by the transfer of electrons through an ETC.

  • When electrons are transferred between molecules in a series of oxidation/reduction reactions as they pass through the ETC, an electrochemical gradient of protons (hydrogen ions) is established across the thylakoid membrane. The membrane separates a region of low proton concentration outside the thylakoid membrane from a region of high proton concentration inside the thylakoid membrane.

  • The formation of the proton gradient is linked to the synthesis of ATP from ADP and inorganic phosphate via ATP synthase. The flow of protons back through membrane bound ATP synthase by chemiosmosis drives the formation of ATP from ADP and inorganic phosphate; this is known as photophosphorylation.

• The energy captured in the light reactions and transferred to ATP and NADPH powers the production of carbohydrates from carbon dioxide in the Calvin cycle. This in the stroma of the chloroplast.

Cellular Respiration

• Cellular respiration uses energy from biological macromolecules to synthesize ATP. Respiration and fermentation are characteristic of all forms of life.

• Aerobic cellular respiration in eukaryotes involves a series of coordinated enzyme catalyzed reactions that capture energy from biological macromolecules.

• The ETC transfers electrons in a series of oxidation-reduction reactions that establish an electrochemical gradient across membranes. 

• In cellular respiration, electrons delivered by  NADH and FADH2 are passed to a series of electron acceptors as they move toward the terminal electron acceptor, oxygen. Aerobic prokaryotes use oxygen as a terminal electron acceptor, while anaerobic prokaryotes use other molecules.

• The transfer of electrons, through the ETC, is accompanied by the formation of a proton gradient across the inner mitochondrial membrane, with the membrane(s) separating a region of high proton concentration outside the membrane from a region of low proton concentration inside the membrane. The folding of the inner membrane increases the surface area, which allows for more ATP to be synthesized. In prokaryotes, the passage of electrons is accompanied by the movement of protons across the plasma membrane.

• The flow of protons back through membrane-bound ATP synthase by chemiosmosis drives the formation of ATP from ADP and inorganic phosphate. This is known as oxidative phosphorylation in aerobic cellular respiration. 

• In aerobic cellular respiration, decoupling oxidative phosphorylation from electron transport generates heat. This heat can be used by endothermic org

• Fermentation and cellular respiration use energy from biological macromolecules to produce ATP. Respiration and fermentation are characteristic of all forms of life.

• Cellular respiration in eukaryotes involves a series of coordinated enzyme-catalyzed reactions that capture energy from biological macromolecules.

• The electron transport chain transfers energy from electrons in a series of coupled reactions that establish an electrochemical gradient across membranes.

• Electron transport chain reactions occur in chloroplasts, mitochondria, and prokaryotic plasma membranes.

• In cellular respiration, electrons delivered by NADH and FADH are passed to a series of electron acceptor2s as they move toward the terminal electron acceptor, oxygen. In photosynthesis, the terminal electron acceptor is NADP+. Aerobic prokaryotes use oxygen as a terminal electron acceptor, while anaerobic prokaryotes use other molecules.

• The transfer of electrons is accompanied by the formation of a proton gradient across the inner mitochondrial membrane or the internal membrane of chloroplasts, with the membrane(s) separating a region of high proton concentration from a region of low proton concentration. In prokaryotes, the passage of electrons is accompanied by the movement of protons across the plasma membrane.

• The flow of protons back through membrane-bound ATP synthase by chemiosmosis drives the formation of ATP from ADP and inorganic phosphate. This is known as oxidative phosphorylation in cellular respiration, and photophosphorylation in photosynthesis.

• In cellular respiration, decoupling oxidative phosphorylation from electron transport generates heat. This heat can be used by endothermic organisms to regulate body temperature.

• Glycolysis is a biochemical pathway that releases energy in glucose to form ATP from ADP and inorganic phosphate, NADH from NAD+, and pyruvate.

• Pyruvate is transported from the cytosol to the mitochondrion, where further oxidation occurs.

• The Krebs cycle takes place in the mitochondrial matrix. During the Krebs cycle, carbon dioxide is released from organic intermediates, ATP is synthesized from ADP and inorganic phosphate, and electrons are transferred by the coenzymes NAD+ and FAD.

• Electrons extracted in glycolysis and  citric acid cycle reactions are transferred by NADH and FADH2 to the electron transport chain in the inner mitochondrial membrane.

• When electrons are transferred between molecules in a sequence of reactions as they pass through the ETC, an electrochemical gradient of protons (hydrogen ions) across the inner mitochondrial membrane is established.

• Fermentation allows glycolysis to proceed in the absence of oxygen and produces organic molecules, including alcohol and lactic acid, as waste products.

• The conversion of ATP to ADP releases energy, which is used to power many metabolic processes.