Biologych7 - 7.1 Overview of Energy-Releasing Pathways...

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1. Overview of Energy-Releasing Pathways Anaerobic Reactions → do not use free oxygen - m a ny prokaryotes and protists live in places where oxygen is a bs ent; m ake ATP by ferm ent a a nd other a n a erobic pathways - m a ny eukaryotic cells still use ferm ent ation, including skelet al m uscle cells - b egins a nd e nds in cytoplas m - n et yield of (2) ATP Aerobic Respiration → oxygen-dep end ent p athway; m ost sp ecies extract e n ergy from glucos - Begins in cytoplas m and ends in mitochondrion where oxygen accepts and removes electro drove rxns - Most ATP for e ach glucose, typically ≥ 3 6 C 6 H 12 O 6 + 6O 2 → 6CO 2 + 6H 2 O In all cells, all of main energy-releasing pathways start with same rxns in cytoplasm - Glycolysis → initial rxns during which enzym es cleave/rearrange glucose into (2) pyruvat e m olecules →organic com pound with 3-C b ackbone - After glycolysis, en ergy-releasing pathways differ Enzym es cat alyze st eps a nd inter m ediates in one st ep are substrat es for next e nzym e in pa Coenzym es NAD + (nicotinamide adenine dinucleotide) and FAD (flavin adenine dinucleotide) accept electrons and hydrogen derived from intermediates of glucose breakdown - When carrying e-or H +, they are reduced to NADH and FADH 2 2. The First Stage: Glycolysis Process by which bond energy of glucose converted to bond energy of ATP (transportable form) Occurs in cytoplasm of all prokaryotic and eukaryotic cells 1. (1) 6-C sugar partly broken down to (2) 3-C pyruvate molecules 2. Initial steps are energy-requiring (investment of 2 ATP) - d elivered by ATP which activat es glucose by transferring P-group to it - s econd ATP transfers P-group to interm ediat e that forms 3. Second inter m ediate split into one PGAL (phosphorglyceraldehyde)
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