Respiration

Cells - energy to do work - stored as organic molecules - broken down to get energy. 2 ways - 1 in absence of oxygen (fermentation). Other aerobic (presence of oxygen) - respiration.

Formula for respiration: C 6 H 12 O 6 + 6O 2 -> 6CO 2 + 6H 2 O + Energy (ATP + heat) Glucose traditionally used - any organic molecule can be starting material.

ATP (adenosine triphosphate) molecule used in energy. When has phosphate group - like loaded spring; when loses phosphate group, energy released. Energy comes from conversion of ATP to ADP and inorganic phosphate (P i ). Animal cells can regenerate ATP back from P i and ADP by breaking down organic molecules.

Movement of end phosphorus group from one molecule to another - phosphorylation. Temporarily changes shape of molecule; changes back to original shape when phosphate leaves.

Redox reaction - electrons transferred from 1 reactant to another. Loss of electrons - oxidation. Addition of electrons - reduction. Electron donor - reducing agent; electron recipient - oxidizing agent.

Respiration is a redox reaction. Glucose oxidized, oxygen reduced, electrons lose potential energy.

At key steps, hydrogen atoms stripped from glucose, passed 1 st to coenzyme (i.e. NAD + ) Turns NAD + into NADH.

NADH shuttles electrons from food to “top” of chain. At “bottom,” oxygen captures electrons and H + to form water.

3 stages in respiration: glycolysis, Krebs cycle, electron transport chain and oxidative phosphorylation. Glycolysis – cytoplasm; Krebs cycle - mitochondrial matrix.

Glycolysis and Krebs cycle - electrons passed from substrates to NAD +, forming NADH. NADH passes electrons to electron transport chain (ETC). In ETC electrons move from molecule to molecule until they combine with O 2 and H + ions to form water.

During ETC energy carried by electrons stored in mitochondrion in form used to synthesize ATP via oxidative phosphorylation. ATP also generated in glycolysis and Krebs cycle by substrate-level phosphorylation. Enzyme transfers phosphate group from organic molecule (substrate) to ADP, forming ATP.

* 38 ATP produced per mole of glucose - broken down to CO 2 and H 2 O by respiration. 34 ATP made through oxidative phosphorylation, 4 ATP from substrate-level phosphorylation giving 38 total ATP molecules.

During glycolysis, glucose, 6-C sugar split into (2) 3-C sugars. Net yield from glycolysis 2 ATP and 2 NADH per glucose. Glycolysis occurs whether O 2 present or not. O 2 present, pyruvate moves into Krebs cycle.

More than ¾ of original energy in glucose still present in 2 molecules of pyruvate. Pyruvate first modified into acetyl CoA (actually enters Krebs cycle) Each turn of Krebs cycle produces 1 ATP, 3 NADH, 1 FADH 2 (electron carrier) for every molecule of acetyl CoA.

Most ATP generated during respiration comes from energy in electrons carried by NADH (and FADH 2 ). Energy in these electrons used in ETC to make ATP.

As electrons move down ETC they pass energy. Transported by either NADH or FADH 2.. Purpose of ETC - break up energy into smaller amounts - released in smaller amounts.

ATP synthase makes ATP from ADP and P i. ATP synthesis generated through proton gradient produced by movement of electrons along ETC. Gradient made when there is higher concentration in one area.

Several chain molecules use flow of electrons to pump H + from matrix to intermembrane space. Concentration of H + - proton-motive force.

ATP synthase molecules only place that allow H + to diffuse back to matrix of mitochondria. Coupling ETC with ATP synthesis called chemiosmosis - helps generate ATP.

Glycolysis produces 2 ATP whether or not O 2 present. O 2 present, additional ATP generated when NADH delivers electrons to ETC. If no O 2 present - process fermentation.

If NAD + present, electrons accepted whether or not O 2 present. During fermentation, ATP generated by glycolysis; NAD + recycled by transferring electrons from NADH to pyruvate. Aerobic conditions, NADH transfers electrons to ETC, recycling NAD +.

Alcohol fermentation, pyruvate converted to ethanol in 2 steps. 1 st, pyruvate converted to 2-C compound (acetaldehyde) by removal of CO 2. 2 nd, acetaldehyde reduced by NADH to ethanol (used in brewery).

Lactic acid fermentation, pyruvate reduced directly by NADH to form lactate (form of lactic acid). Muscle cells switch from aerobic respiration to lactic acid fermentation to generate ATP when O 2 is scarce. Waste – lactate; buildup causes muscle soreness.

Aerobic respiration, 38 ATP generated (2 produced through anaerobic respiration for 1 molecule of glucose). Some organisms (facultative anaerobes), including yeast, bacteria, survive using either fermentation or respiration.

Glycolysis can occur with many organic molecules. If not carbohydrate - must be broken down 1 st. Fats give 2x as much ATP as carbohydrates.

Respiration monitored through supply and demand. Glycolysis - phosphofructokinase (enzyme) speeds up or slows down glycolysis. If enzyme active - because ATP levels low - respiration speeds up.

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