BISC 101 Cellular Respiration Notes PDF

Cellular Respiration Cellular respiration yields energy (ATP) by oxidizing organic fuels Cellular respiration is the set of metabolic reactions and processes that take place in the cells of organisms to convert biochemical energy from nutrients into ATP, and then release waste products A...

Cellular Respiration Cellular respiration yields energy (ATP) by oxidizing organic fuels Cellular respiration is the set of metabolic reactions and processes that take place in the cells of organisms to convert biochemical energy from nutrients into ATP, and then release waste products Although carbohydrates, fats, and proteins are all consumed as fuel, it is helpful to trace cellular respiration with the sugar glucose: C6H12O6 + 6 O2 → 6 CO2 + 6 H2O + Energy (ATP + heat) glucose Oxidation of organic fuel molecules during cellular respiration During cellular respiration, the glucose is oxidized, and O2 is reduced: becomes oxidized becomes reduced In cellular respiration, glucose and other organic molecules are broken down in a series of steps  The stages of cellular respiration: a preview Cellular respiration has three stages: – Glycolysis (breaks down glucose into two molecules of pyruvate) – The citric acid cycle (completes the breakdown of glucose) – Oxidative phosphorylation (accounts for most Citric acid cycle also refers of the ATP to as the Krebs cycle synthesis)  Glycolysis harvests chemical energy by oxidizing glucose to pyruvate Glycolysis (“splitting of sugar”) breaks down 1 molecule of glucose into 2 molecules of pyruvate (also known as pyruvic acid) – Glucose is a six-carbon molecule – Each pyruvate is a three-carbon molecule Involves a series of 10 enzyme-catalyzed reactions that ultimately yield net products like 2 ATP and 2 pyruvate Also yields 2 NADH molecules Glycolysis occurs in cytoplasm of eukaryotes NAD+ is a co-enzyme the accepts electrons to become NADH Citric acid cycle completes the energy-yielding oxidation of organic molecules Pyruvate enters the mitochondrion in eukaryotes Before the citric acid cycle can begin, pyruvate must be converted to acetyl co-enzyme A (acetyl CoA), which links the cycle to glycolysis This conversion from pyruvate to acetyl CoA is also enzyme- catalyzed  The citric acid cycle, also called the Krebs cycle, takes place within the mitochondrial matrix The citric acid cycle consists of eight enzyme-catalyzed steps In cycle, pyruvate leads to generation of ATP, CO2, NADH, and FADH2 – So, 2 molecules of pyruvate leads to 2 ATP, 4 CO2, 6 NADH, and 2 FADH2 FAD is also a co-enzyme the accepts electrons to become FADH2 During oxidative phosphorylation, chemiosmosis couples electron transport to ATP synthesis Following glycolysis and the citric acid cycle, NADH and FADH2 account for most of the energy extracted from glucose These two electron carriers donate electrons to the electron transport chain, which powers ATP synthesis via oxidative phosphorylation Two parts to oxidative phosphorylation: ̶ Electron Transport Chain ̶ Chemiosmosis  The pathway of electron transport Electron transport chain occurs at cristae within mitochondrion of eukaryotes Electrons are transferred from NADH or FADH2 to the electron transport chain!! Electrons are passed to O2 to form H2O through a series of four protein complexes containing electron carriers (high H+ concentration) called cytochromes cristae Electron transport chain generates no ATP directly!! Oxygen is final electron acceptor!!  Chemiosmosis: the energy-coupling mechanism Electron transfer in electron transport chain causes proteins to pump H+ ions (protons) from mitochondrial matrix to intermembrane space Afterwards, H+ ions then moves back across membrane into the matrix (eukaryotes) or cytoplasm (prokaryotes), passing through ATP synthase ATP synthase uses flow of H+ ions to drive phosphorylation of ADP into ATP An example of chemiosmosis (movement of H+ ions across a selectively-permeable membrane along its concentration gradient and ATP is generated) An accounting of ATP production by cellular respiration About 40% of the energy in a single glucose molecule is transferred to ATP during cellular respiration, making a maximum of 38 ATP  The process that generates most of the ATP is called oxidative phosphorylation…it accounts for almost 90% of ATP generated by cellular respiration – ATP is synthesized INDIRECTLY from creation of a proton (H+) gradient in the intermembrane space and movement of these protons back across the cristae through a protein channel, ATP synthase A smaller amount of ATP is formed in glycolysis and the citric acid cycle by substrate-level phosphorylation – DIRECT addition of a free phosphate (from substrate) to ADP to form ATP