BIOL&253Ch25NotesFall11

BIOL&253Ch25NotesFall11 - Ch. 25 Metabolism and...

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1 Ch. 25 – Metabolism and Energetics • Slides marked “MP” in the upper left corner indicate information that is important for understanding and completing the Metabolic Pathways Exam and ARE NOT fair game for Lecture Exam 2. • Slides marked “KNOW” in the upper left corner indicate information that IS fair game for Lecture Exam 2. • We will not be covering Ch. 25 in its entirety, but we will be pulling bits and pieces of info from it – Read the parts of this chapter that help you understand the material on the lecture slides, but be assured that material that we don’t cover in lecture will not be fair game for the exams (Metabolic Pathways or Lecture Exam 2) Metabolism • = the sum of all chemical reactions occurring in the body – Chemical reactions convert energy from one form to another • Chemical bonds are broken, atoms are rearranged, and new bonds are formed – Electrons are transferred, rearranged, and/or shared • Anabolic reactions : – Require an input of energy (i.e., they are endergonic) – Synthesize complex organic molecules from simpler ones • Catabolic reactions : – Release energy (i.e., they are exergonic) – Break down complex organic molecules into simpler ones – E.g. glycolysis, the TCA cycle, and the electron transport system (ETS) • Both types of reactions require enzymes • Energy derived from catabolism is used to drive anabolism • The efficiency of ATP (energy) generation = ~ 40% – I.e., ~ 60% is lost as heat • But this efficiency is actually much higher than the efficiency of many human-made machines! KNOW
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2 Fig. 25-1, p. 931 KNOW An overview of cellular metabolism Electrons and chemical energy • 1. Electrons (e - ) are the “glue” that hold atoms together in covalent bonds, and they store chemical energy – E.g., the bonds between carbons in organic compounds such as carbohydrates, lipids, and proteins – E.g., the “high-energy bonds” that involve phosphate groups in molecules such as ATP or GTP – Breaking these bonds releases chemical energy • 2. So-called “high-energy electrons” can be passed between molecules in oxidation-reduction (redox) reactions, releasing chemical energy Oxidation is the loss of electrons from a molecule (which is called the donor molecule) Reduction is the gain of electrons by a molecule (which is called the acceptor molecule) • Note that the acceptor molecule’s oxidation state ( charge) is “reduced” (i.e., it becomes more negative) by the addition of negatively charged electrons MP
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3 Electron/hydrogen carriers • Biological redox reactions often involve the transfer of 2 hydrogen (H) atoms (and their electrons) in the form of a proton (H + ) and a hydride ion (H - = H + + 2 e - ) • 2 important coenzymes that carry the electrons and hydrogens from one redox reaction to another are: –1 . NAD + (nicotine adenine dinucleotide) •NAD + (oxidized) + 2 H•• NADH•• (reduced) + H + –2
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BIOL&253Ch25NotesFall11 - Ch. 25 Metabolism and...

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