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Chapter 7 Cellular Respiration Glycolysis and Fermentation • Cellular respiration: cells make ATP by breaking down organic compounds • Both autotrophs and heterotrophs undergo cellular respiration – Break down organic compounds into simple molecules and energy – Some energy used to make more ATP, some is used by the cells to do work Overview of Cellular Respiration Cellular Respiration Overview Overview of Cellular Respiration 1. Glycolysis – Organic compounds are converted into carbon molecules of pyruvic acid, which makes a small amount of ATP and NADH (electron carrier) – Anaerobic process = does not require oxygen – Occurs outside of the mitochondria Overview of Cellular Respiration 2. Aerobic Respiration (oxygen present) – Pyruvic acid is broken down and NADH is used to make a large amount of ATP Note: pyruvic acid can enter other pathways when no oxygen is present. Glycolysis and other anaerobic pathways = fermentation Overview of Cellular Respiration Glycolysis • Series of chemical rxns catalyzed by specific enzymes to create pyruvic acid from 6carbon molecules 1. Phosphate groups are attached to glucose to form a 6-carbon molecule 2. 6-carbon molecule splits into two G3P molecules 3. G3P molecules are oxidized and receive a phosphate group – NAD+ to NADH 4. Phosphate groups (4) added in step 1 and 3 are removed, forming pyruvic acid, produce 4 ATP Glycolysis Glycolysis • Two ATP molecules used, but four are produced • Glycolysis has a net yield of 2 ATP molecules Fermentation • In anaerobic environments some cells can still produce carbon compounds • Using glycolysis and additional pathways to generate NAD+ is called fermentation – Lactic acid fermentation – Alcoholic fermentation Fermentation • Lactic acid fermentation: pyruvic acid is converted into lactic acid • Involves transfer of one hydrogen atom from NADH and the addition of one proton (H+) to pyruvic acid (NADH NAD+) • NAD+ is used in glycolysis, and helps keep this process going • Why is this process important? Lactic Acid Fermentation Fermentation • Alcoholic fermentation: converts pyruvic acid into ethyl alcohol • Two steps: – 1.) CO2 molecule removed from pyruvic acid • Leaves a two carbon compound – 2.) Two hydrogen atoms are added to the twocarbon compound to form ethyl alcohol – The hydrogen atoms come from NADH and H+, and regenerates NAD+ for glycolysis Aerobic Respiraton • Aerobic = Uses oxygen • Two major stages: – Krebs Cycle – Electron Transport Chain • Krebs cycle involves completing the oxidation of glucose in glycolysis. NAD+ NADH • Electron transport chain uses NADH to make large quantities of ATP Aerobic Respiraton • In prokaryotes, occurs in the cytosol of the cell • In eukaryotes, occurs inside the mitochondria – Pyruvic acid produced in glycolysis diffuses across mitochondria’s double membrane and into the matrix Aerobic Respiration • Pyruvic acid enters the mitochondrial matrix and reacts with a molecule called coenzyme A to form acetyl coenzyme A, acetyl CoA The Krebs Cycle • Biochemical pathway that breaks down acetyle CoA, producing CO2, hydrogen, and ATP The Krebs Cycle 1. Acetyl CoA combines with oxaloacetic acid to produce citric acid – Regenerates coenzyme A 2. Citric acid releases CO2 and hydrogen forming a five carbon compound – NAD+ NADH 3. Five carbon molecule releases CO2 and Hydrogen forming a four carbon molecule The Krebs Cycle 4. Four carbon compound from step three creates another four carbon compound by releasing a hydrogen – FADFADH2 5. Step four molecule releases a hydrogen to regenerate oxaloacetic acid to keep krebs cycle going – NAD+ NADH Electron Transport Chain • Second stage of aerobic respiration • Couples with chemiosmosis • ETC and ATP synthase are embedded into the membrane of the mitochondria – In prokaryotes this occurs on the cell membrane • ATP is produced when NADH and FADH2 release hydrogen, regenerating NAD+ and FAD Electron transport chain 1. NADH and FADH2 give up electrons 2. electrons passed down chain, losing energy moving from molecule to molecule 3. energy from electrons pumps protons from the matrix building a concentration gradient between inner and outer membranes Electron transport chain • 4. concentration gradients of protons drive the synthesis of ATP by chemiosmosis (same as photosynthesis) • 5. Oxygen is the final acceptor of electrons that pass down the ETC – Protons, electrons and oxygen all combine to form water