01.03.12+-+Introduction+to+Metabolism


 * Introduction to Metabolism**


 * 1. Be able to define dG° and describe its relationship to Keq**

 - ΔG° measures the extent to which a reaction will proceed forward starting with 1M reactants and 1M products. If this number is positive, the reaction is endergonic (NOT spontaneous- require energy or higher concentration of reactants). If this number is negative, the reaction is exergonic (spontaneous- release energy). Regulated enzymes in a pathway are normally irreversible and have a very negative ΔG°. ΔG° = -RT ln Keq So, if ΔG° is negative, then the reaction will proceed forward and Keq >1 and products are favored. If, ΔG° is positive, then the reaction is unfavorable and Keq <1 and reactants are favored.


 * 2. Explain why metabolic pathways are able to generate products even though some of the reactions in the pathway have a positive standard free energy of hydrolysis**

 - Pathways can still generate products because the sum of ΔG° for all reactions is negative.


 * 3. Compare the dG° for ATP hydrolysis with that for creatine phosphate and glucose phosphate. Explain the significance of ATP in intermediary metabolism**

 - ΔG° for ATP hydrolysis = -7 to -8 Kcal/mole  - ΔG° for creatine phosphate = -10 Kcal/mole  - ΔG° for glucose phosphate = -3.3 Kcal/mole ATP stores free energy in the form of phosphoanhydride bonds. Chemically stable, it slowly hydrolyzes in an aqueous solution, but thermodynamically unstable due to a high density of negative charges, it has a negative ΔG°.


 * 4. Know three chemical factors that contribute to the high negative dG° exhibited by ATP**

 - Products are stabilized by water because it has greater total charges.  - Pi is resonance stabilized.  - High density of negative charges in ATP makes it unstable.


 * 5. Explain the significance of creatine phosphate in muscle and its relationship to ATP**

 - Creatine phosphate provides a source of phosphate bond energy that can be used in muscle contraction. Phosphocreatine can anaerobically donate a phosphate group to [|ADP] to form [|ATP] during the first 2 to 7 seconds following an intense muscular or neuronal effort. Conversely, excess [|ATP] can be used during a period of low effort to convert [|creatine] to phosphocreatine.


 * 6. Structurally differentiate between flavin, nicotinamide adenine nucleotides, and acetyl CoA, know which of these are prosthetic groups, and explain the role of each in intermediary metabolism**

 - Nicotinic acid (B vitamin) à  NAD+. Cofactor. 2-electron carrier. Catabolic pathways.  Particpates in oxidative phosphorylation. <span style="font-family: 'Times New Roman',serif;"> -NADPH. Reducing agent. Cytosol. Anabolic pathways.. <span style="font-family: 'Times New Roman',serif;"> - Riboflavin à <span style="font-family: 'Times New Roman',serif;"> FAD. Prosthetic group. 2-electron carrier. Transfer electrons from intermediates <span style="font-family: 'Times New Roman',serif;"> like NADH and feed to ETC. <span style="font-family: 'Times New Roman',serif;"> - Pantothenic acid à <span style="font-family: 'Times New Roman',serif;"> CoA. Carrier of –COOH (acyl groups) due to free sulfhydryl group. Acetyl <span style="font-family: 'Times New Roman',serif;"> CoA at center of fuel metabolism.


 * 7. List three mechanisms by which metabolic pathways are regulated**

<span style="font-family: 'Times New Roman',serif;"> - Amount of enzyme protein: via control transcription and degradation <span style="font-family: 'Times New Roman',serif;"> - Control of enzyme activity: via covalent modification, proteolysis, and allosteric control. <span style="font-family: 'Times New Roman',serif;"> - Control of access to substrate: via compartmentalization.


 * 8. List three general mechanisms by which metabolic enzymes are regulated**

<span style="font-family: 'Times New Roman',serif;"> - Covalent modification, Proteolysis, and allosteric control


 * 9. Define the following terms: catabolism, anabolism, endergonic, exergonic, phosphoanhydride bond, and kinase**

<span style="font-family: 'Times New Roman',serif;"> - Catabolism: Breakdown/oxidation of reduced compounds to generate energy <span style="font-family: 'Times New Roman',serif;"> -Anabolism: Synthesis of metabolites from small molecules. Requires energy. <span style="font-family: 'Times New Roman',serif;"> - Endergonic/Exergonic: See question 1. Phosphoanhydride bond: see question 3. <span style="font-family: 'Times New Roman',serif;"> - Kinase: enzymes that phosphorylate. Can be activated by various compounds.