Cell Respiration and Energy Transformations

NAD+ accepts two electrons and one proton from hydrogen atoms, becoming reduced NAD (NADH).

Glycolysis is the first stage of aerobic respiration where glucose is converted to pyruvate. It occurs in the cytoplasm of cells.

Phosphorylation is the addition of a phosphate group to a molecule. This requires energy and makes the molecule more reactive.

In the first stage of glycolysis, glucose is phosphorylated by the transfer of a phosphate group from ATP.

Lysis is the splitting of a molecule into two smaller molecules. In glycolysis, fructose bisphosphate is split into two molecules of triose phosphate.

Oxidation in glycolysis involves the removal of hydrogen atoms from triose phosphate. These hydrogen atoms are accepted by NAD, reducing it to NADH.

ATP is produced in the final stages of glycolysis by transferring phosphate groups from high-energy molecules to ADP.

Glycolysis is divided into four stages: phosphorylation, lysis, oxidation, and ATP formation. Each stage involves specific reactions catalyzed by enzymes.

In the inner mitochondrial membrane, a series of protein molecules act as electron carriers, receiving and passing along pairs of electrons. This sequence of carriers forms the electron transport chain. The first carrier in the chain accepts a pair of electrons from NADH, becoming reduced and converting NADH back to NAD. The energy from the electron transport chain is used to pump protons across the membrane, creating an electrochemical gradient.

Reduced NAD (NADH) is a crucial molecule in cellular respiration. It carries high-energy electrons from the Krebs cycle to the electron transport chain. These electrons release energy as they travel through the chain, which is used to power proton pumps. This process ultimately drives the synthesis of ATP, the cell's energy currency.

The flow of electrons along the electron transport chain generates a proton gradient. As electrons move from one carrier to the next, they lose energy. This energy is used by certain carriers to actively pump protons (H+) across the inner mitochondrial membrane from the matrix to the intermembrane space. This pumping action creates a higher concentration of protons outside the matrix, establishing an electrochemical gradient.

Chemiosmosis refers to the movement of ions across a selectively permeable membrane, down their electrochemical gradient. In cellular respiration, the proton gradient established by the electron transport chain is used by ATP synthase to generate ATP. As protons flow back into the matrix through ATP synthase, their potential energy is harnessed to drive phosphorylation of ADP into ATP.

The process where pyruvate is converted to lactate, allowing glycolysis to continue even when oxygen is limited.

The process of converting pyruvate to ethanol and carbon dioxide, commonly used by yeast for energy production.

A type of organism that can survive and thrive both in the presence and absence of oxygen. Yeast is an example.

The metabolic process of breaking down glucose into pyruvate, yielding a net gain of 2 ATP molecules.

A molecule used as an energy carrier in cells, often referred to as the energy currency of the cell.

A form of reduced NAD, carrying electrons and hydrogen ions, important for electron transport in cellular respiration.

The final product of glycolysis, further processed in the mitochondria for more energy.

A chemical compound involved in glycolysis, produced from glucose and converted to pyruvate.

ATP is made of a nitrogenous base (adenine), a five-carbon sugar (ribose), and three phosphate groups. The phosphate groups carry negative charges, making ATP a nucleotide.

ATP is often called the cell's energy currency because it's used for temporary energy storage and transfer. It's like a rechargeable battery for cell processes.

ATP is hydrolyzed to ADP and inorganic phosphate (Pi) releasing a small amount of energy. This energy is enough for many cellular processes. The reaction can be reversed to regenerate ATP from ADP and Pi.

ATP is needed to build macromolecules like DNA, RNA, and proteins. These are anabolic processes where monomers are linked to form polymers.

ATP is required for active transport where molecules are moved across cell membranes against their concentration gradients. This requires energy to pump molecules uphill.

ATP provides the energy for muscle contraction. Actin and myosin filaments slide past each other, powered by ATP hydrolysis, causing muscle fibers to shorten.

When ATP is hydrolyzed to ADP, energy is released because ATP has more chemical potential energy than ADP. The reverse reaction (ADP to ATP) requires energy input.

Cellular processes like macromolecule synthesis, active transport, and muscle contraction use ATP's energy. The energy released from ATP hydrolysis is used to drive these processes.

In Photosystem II, light energy excites electrons in a special chlorophyll molecule called P680, causing it to lose electrons and become oxidized. P680 then obtains electrons by splitting water molecules, a process called photolysis.

The Oxygen Evolving Complex (OEC) is a group of manganese, calcium, and oxygen atoms within Photosystem II that facilitates the splitting of water molecules.

The splitting of water molecules in Photosystem II releases electrons, protons, and oxygen. The electrons replace those lost by P680, while the protons are released into the thylakoid space, contributing to a proton gradient. Oxygen is a byproduct and diffuses out.

The excited electrons from Photosystem II are passed through a series of electron carriers in the thylakoid membrane, releasing energy. This energy is used to pump protons from the stroma into the thylakoid space, creating a proton gradient across the membrane.

The proton gradient created across the thylakoid membrane is a form of potential energy. ATP synthase harnesses this potential energy to produce ATP.

The process by which ATP is synthesized using the proton gradient across the thylakoid membrane is called photophosphorylation.

Plastoquinone, an electron carrier in the thylakoid membrane, accepts electrons and protons from Photosystem II. It carries these electrons and protons through the electron transport chain.

The thylakoid membrane, containing Photosystem II, the electron transport chain, and ATP synthase, is crucial for the light-dependent reactions of photosynthesis. It provides the structural framework for these processes and facilitates the movement of electrons and protons.

The process of converting inorganic carbon dioxide into an organic compound, typically a three-carbon molecule called glycerate-3-phosphate.

Ribulose bisphosphate (RuBP) is a five-carbon sugar that combines with carbon dioxide to form two molecules of glycerate-3-phosphate.

It is the enzyme responsible for catalyzing the carbon fixation reaction, adding carbon dioxide to RuBP.

The reaction catalyzed by Rubisco to convert RuBP into glycerate-3-phosphate requires the addition of carbon and oxygen, but not hydrogen. This results in a lower ratio of hydrogen to oxygen than in carbohydrates, necessitating reduction to produce carbohydrates.

The Calvin cycle converts glycerate-3-phosphate (GP) into triose phosphate (TP) using ATP and reduced NADP produced in the light-dependent reactions.

The Calvin cycle regenerates RuBP from triose phosphate, ensuring the continuation of carbon fixation and photosynthesis.

The first carbohydrate product of photosynthesis is triose phosphate, which can be further converted to hexose phosphate and then to starch as the primary form of carbon storage.

The accumulation of hexose phosphate and starch within chloroplasts can deplete RuBP reserves, interrupting carbon fixation. Therefore, some triose phosphate must be used to regenerate RuBP to keep the cycle going.