16 Respiration

• In both processes, chemiosmosis drives the synthesis of ATP.
• In aerobic respiration, most of the ATP (34 out of 38) are produced via oxidative phosphorylation.
• The formation of ethanol in yeast and lactate in mammals is significant in the regeneration of NAD.
• Factors that affect the rate of respiration include substrate concentration, type of substrate, and temperature.
• Chemiosmosis is outlined in photosynthesis and respiration.
• The products of glycolysis per glucose molecule are 2 ATP and 1 NADH, yielding a net gain of 2 ATP and 2 NADH per glucose.
• The Krebs cycle involves three main stages: Acetyl CoA (2C) joins the cycle by combining with oxaloacetate (4C) to form citrate (6C), citrate is decarboxylated and oxidised by dehydrogenation to form α-ketoglutarate (5C) and NADH, and oxaloacetate (4C) is regenerated.
• The Krebs cycle produces 1 ATP, 1 CO2, 2 NADH, and 1 FADH2 per molecule of α-ketoglutarate.
• Acetyl CoA moves on to the Krebs cycle, which also takes place in the mitochondrion matrix.
• Pyruvate is converted into ethanol or lactate during anaerobic respiration when oxygen is unavailable.
• Each pyruvate molecule is converted to acetyl CoA, resulting in the formation of acetyl CoA and the net production of 1 molecule of CO2 and NADH.
• Pyruvate enters the mitochondrion to proceed to the following stages of aerobic respiration: link reaction, Krebs cycle, and oxidative phosphorylation when oxygen is available.
• The link reaction involves the transport of pyruvate from the cytosol into the mitochondrion matrix via a transport protein, its decarboxylation, oxidation by dehydrogenation, and the attachment of coenzyme A.
• Glycolysis can be divided into four stages: Phosphorylation of sugar, Lysis (6C → 2), Oxidation by dehydrogenation, and Substrate-level phosphorylation.
• Biochemical reactions in the cell require small molecules to act as mobile electron carriers that can move between large protein complexes embedded in membranes.
• Nicotinamide adenine dinucleotide (NAD) + H+ + 2 e- → NADH.
• Glycolysis is the first stage of respiration and involves the oxidation of glucose (6C) to 2 pyruvate (3C) (in effect, a 6-carbon sugar is split into two 3-carbon compounds).
• During the fourth stage of glycolysis, ATP is produced by direct enzyme action on the substrate ADP + phosphate group from substrate → ATP.
• PFK is an allosteric enzyme that is activated by ADP & AMP, inhibited by citrate (from Krebs cycle) and ATP.
• The activity of PFK helps to control the rate of glycolysis.
• During the third stage of glycolysis, NAD+ is reduced to NADH and an inorganic phosphate group is added to G3P in the process.
• Glycolysis does not require oxygen and does not release CO2.
• Energy from a redox reaction is used to add an inorganic phosphate ion (P i ) to G3P.
• Flavin adenine dinucleotide (FAD) + 2 H+ + 2 e- → FADH2.
• During the first stage of glycolysis, ATP is invested, glucose is activated, and the commitment to the glycolysis pathway is allosterically regulated by PFK.
• During the second stage of glycolysis, 6C is split into 2 (3C).
• ATP is a ribonucleotide, is universally used, soluble in water, highly mobile, and can be transported easily.
• Cellular respiration is the process by which chemical energy in organic molecules is released by oxidation, allowing organisms to obtain energy from organic molecules.
• Examples of where ATP is required include muscle contraction, beating of cilia or flagella, active transport of substances into or out of cells, synthesis of substances for growth and repair, electrical transmission of nerve impulses, and maintenance of constant body temperature in homoeothermic animals.
• ATP can be interconverted into Adenosine diphosphate (ADP) and vice versa, leading to energy release for cellular work.
• In chemistry, redox reactions occur due to the transfer of electrons between atoms.
• Reduction involves the gain of electrons and/or hydrogen, while oxidation involves the loss of electrons and/or hydrogen.
• The main function of cellular respiration is to produce ATP for all cellular activities.
• There are two main pathways in cellular respiration: aerobic respiration which occurs in the presence of oxygen, and anaerobic respiration which occurs in the absence of oxygen.
• When ATP loses its terminal phosphate group, it results in an ADP molecule.
• FADH2 → FAD+2e- (donated to ETC) + 2 H+ (remain in matrix).
• The process of oxidative phosphorylation involves the role of oxygen and the electron transport chain in aerobic respiration.
• The only passage where H+ can traverse the membrane is through ATP synthase.
• The hydrogen atoms split to form hydrogen ions (H+) and electrons.
• The electrons are donated to the first electron carrier of electron transport chain (first electron carrier becomes reduced) , which then passes its electrons to the next carrier, and so on.