chapter reviews - Key Concepts ch. 9 In cells, the...

Info iconThis preview shows pages 1–2. Sign up to view the full content.

View Full Document Right Arrow Icon
Key Concepts ch. 9 In cells, the endergonic reactions required for life occur in conjunction with an exergonic reaction involving ATP. Cellular respiration produces ATP from molecules with high potential energy—often glucose. Glucose processing has four components: (1) glycolysis, (2) pyruvate processing, (3) the Krebs cycle, and (4) electron transport, coupled with oxidative phosphorylation. Fermentation pathways allow glycolysis to continue when the lack of an electron acceptor shuts down electron transport chains. Respiration and fermentation are carefully regulated. Section 9.1 Outline: The Nature of Chemical Energy and Redox Reactions How Does ATP Drive Endergonic Reactions? H What Is a Redox Reaction? W Some Other Approaches to Understanding RedoxWhat Happens When Glucose Is Oxidized? In cells, electrons are the most important source of chemical potential energy. The electrons in ATP have high potential energy (Figure 9.1).ATP has high potential energy due to the repulsive forces of the four negative charges in the three phosphate groups (Figure 9.1a).Hydrolysis of the bond between the two outermost phosphate groups results in formation of ADP and P i (H 2 PO 4 ) in a highly exergonic reaction, with 7.3 kilocalories (kcal) of energy released per mole of ATP hydrolyzed (Figure 9.1b).The phosphate group released from ATP is transferred to protein. Phosphorylation adds a negative charge to a protein and the molecule's conformation is usually altered (Figure 9.2). How Does ATP Drive Endergonic Reactions? When either a substrate or an enzyme is phosphorylated, the exergonic phosphorylation reaction is "coupled" to an endergonic reaction. In cells, endergonic reactions become exergonic when the substrates or enzymes involved are phosphorylated (Figure 9.3). What Is a Redox Reaction? Reduction–oxidation reactions ( redox reactions ) are a class of chemical reactions that involve loss or gain of an electron. Redox reactions drive the formation of ATP. Reduced compounds typically have many C–H bonds with high potential energy. Oxidized molecules have many C–O bonds with low potential energy. In a redox reaction, the atom that loses one or more electrons is oxidized , and the atom that gains one or more electrons is reduced . Oxidation events are always coupled with a reduction—an electron donor is always paired with a reactant that acts as an electron acceptor . During a redox reaction, electrons can be transferred completely from one atom to another, or they can simply shift their position in covalent bonds (Figure 9.4). Some Other Approaches to Understanding Redox Each electron transferred from one molecule to another during a redox reaction is usually accompanied by a proton (H + ). The molecule that contains the reduced atom gains a hydrogen (H) atom and has higher potential energy. Molecules that are oxidized in cells often lose a proton along with an electron, and have
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Image of page 2
This is the end of the preview. Sign up to access the rest of the document.

Page1 / 33

chapter reviews - Key Concepts ch. 9 In cells, the...

This preview shows document pages 1 - 2. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online