Chapter 6 reading quiz

2. Chapter 6 reading quiz • What are ALL of the chemical reactions in your body known as? • What does it mean to be “phosphorylated”? • What does ATP stand for? • What do enzymes do? • Catabolic pathways _______ energy.

3. Catabolic Metabolic pathways that RELEASE energy by breaking down complex molecules to simpler compounds Ex: cellular respiration glucose  H2O + CO2 Anabolic Metabolic pathways that CONSUME energy to build complicated molecules from simpler ones Ex: photosynthesis H2O + CO2 glucose  1. Explain the role of catabolic and anabolic pathways in the energy exchanges of cellular metabolism.

4. Kinetic energy Energy in the process of doing work (energy of motion) Ex: heat (thermal energy) from the random movement of molecules Light energy which powers photosynthesis Potential energy Energy that matter possesses because of it’s location or arrangement Ex: Gravitational field (on a hill, water behind a dam) Chemical energy – arrangement of electrons in an atom  2. Distinguish between kinetic and potential energy.

5. Open system System in which energy can be transferred between the system and it’s surroundings The biosphere Closed system Collection of matter under study which is isolated from it’s surroundings A lab experiment  3. Distinguish between open and closed systems.

7. 1st Law Energy can be transferred and transformed, but it cannot be created or destroyed Energy of the universe is constant 2nd Law Every energy transfer or transformation makes the universe more disordered Every process increases the ENTROPY of the universe  4. Explain, in your own words, the 1st and 2nd Laws of thermodynamics.

9. 5. Explain why highly ordered living organisms do not violate the 2nd Law of thermodynamics. • Living things are OPEN systems • They maintain highly ordered structure at the expense of increased entropy of their surroundings • They take in complex high energy molecules as food and extract chemical energy to create and maintain order • They return to the surroundings simpler low-energy molecules (H2O & CO2) and heat The entropy of a system may decrease, but the entropy of a system plus it’s surroundings must increase 

10. 6. Distinguish between entropy and enthalpy. Entropy – the quantitative measure of disorder that is proportional to randomness – “S” Enthalpy – total energy – “H”

11. 7. Write the Gibbs equation for free energy change. ΔG = ΔH – TΔS Where: ΔG = the change in free energy ΔH = the change in total energy (enthalpy) ΔS = change in entropy T = absolute temperature in °K (°C + 273) 

12. 8. Explain how changes in enthalpy, entropy and temperature influence the maximum amount of useable energy that can be harvested from a reaction. • An increase in temperature enhances the effect of an entropy change. This tends to disrupt order as collisions increase. • When enthalpy and entropy changes in a system have an opposite effect on free energy, temperature will determine whether the reaction will occur (heat could denature proteins) 

13. Exergonic reactions A reaction that proceeds with a net loss of free energy Heat given off usually Endergonic reactions An energy-producing reaction that proceeds with a net gain of free energy A reaction that absorbs energy from it’s surroundings  9. Distinguish between exergonic and endergonic reactions.

15. 10. Describe the function of ATP in a cell. • ATP is the immediate source of energy that drives most cellular work Functions: • Mechanical work  cilia, contraction • Transport work  across membranes • Chemical work  polymerization 

17. 11. List the three components of ATP and identify the major class of macromolecules to which it belongs. ATP = adenosine triphosphate  a nucleotide with unstable phosphate bonds that the cell hydrolyzes for energy to drive endergonic reactions • Adenine (a nitrogenous base) • Ribose ( a 5 carbon sugar) • A chain of three phosphate groups 

18. 12. Explain how ATP performs cellular work. • Exergonic hydrolysis of ATP is coupled with endergonic processes by transferring a phosphate group to another molecule • The products of the hydrolysis reaction are more stable • Release of energy when a phosphate group is released ATP + H2O  ADP + Pi  (-55 kJ/mol)

20. 13. Describe the energy profile of a chemical reaction including activation energy, free energy change, and transition state. Activation energy – amount of energy that reactant molecules must absorb to start a reaction Free energy change – the difference in free energy between products and reactants Transition state – unstable condition of reactant molecules that have absorbed sufficient free energy to react 

21. 14. Describe the function of enzymes in biological systems. Enzymes are – biological catalysts made of protein Function - To speed up metabolic reactions by lowering energy barriers • Lower activation energy so that the transition state can be reached at cellular temperatures • They are selective to reactions 

22. 15. Explain the relationship between enzyme structure and enzyme specificity. • Enzymes are specific for a particular substrate, and that specificity depends upon the enzyme’s 3D shape Substrate – the substance an enzyme acts on and makes more reactive Active site – restricted region of an enzyme molecule which binds to the substrate • Determines enzyme specificity which is based on a compatible fit between the shape of the site and the substrate 

24. 16. Explain the induced fit model of enzyme function and describe the catalytic cycle of an enzyme. Induced fit  the change in the shape of an enzyme’s active site, which is induced by the substrate 

26. 16. Continued…catalytic cycle Catalytic cycle • Substrate binds to the active site forming an enzyme-substrate complex; the substrate is held in the active site by weak interactions (hydrogen and ionic bonds) • Induced fit of the active site around the substrate – side chains of a few amino acids in the active site catalyze the conversion of substrate to product • Product departs active site and the enzyme emerges in it’s original form. Since enzymes are used over and over, they can be effective in very small amounts 

28. 17. Describe 4 mechanisms by which enzymes lower activation energy. • The active site can hold 2 or more reactants in the proper position so they may react • Induced fit of the active site may distort the substrate’s chemical bonds so less thermal energy is needed to break them during the reaction • The active site may provide a micro-environment conducive to a particular type of reaction • Side chains of amino acids in the active site may participate directly in the reaction 

29. 18. Explain how substrate concentration affects the rate of an enzyme-controlled reaction. • The higher the [substrate], the faster the reaction will go  to a limit • If [substrate] is high enough, the enzyme becomes saturated with substrate (the active sites of all enzyme molecules are engaged) • When an enzyme is saturated, the reaction rate depends upon how fast the active sites can convert substrate to product • When enzymes are saturated, the reaction rate may be increased by adding more enzyme 

30. 19. Explain how enzyme activity can be regulated or controlled by environmental conditions (temperature and pH), cofactors, and enzyme inhibitors. Environmental conditions temperature and pH • Optimal conditions 35-40 °C, pH 6-8 • Reaction rate increases as temperature increases • Enzyme will denature if temperature is too high • Some enzymes operate at extreme pHs – pepsin in the stomach works at pH 2 Cofactors • Small nonprotein molecules that are required for proper enzyme catalysis • Bind tightly to the active site • If they are organic, called ‘coenzymes’ (vitamins) 

32. 19. Continued…enzyme inhibitors Enzyme inhibitors  • Certain chemicals can selectively inhibit enzyme activity • Competitive  chemicals that resemble an enzyme’s normal substrate and compete for the active site • Noncompetitive  do not enter the enzyme’s active site but bind to another part of the enzyme, perhaps altering the enzyme’s shape 

34. 20. Distinguish between allosteric activation and cooperativity. Allosteric regulators  • Specific receptor site on some part of the enzyme molecule other than the active site • Often is located where subunits join • 2 conformations – one catalytically active and the other inactive • Binding of an ACTIVATOR stabilizes the active conformation • Binding of an INHIBITOR (noncompetitive) will stabilize the inactive conformation • Subunits may interact so that a single activator/inhibitor will affect the active sites of other subunits 

36. 20. Continued…cooperativity Cooperativity  • The phenomenon where substrate binding to the active site of one subunit induces a conformational change that enhances substrate binding at the active sites of other subunits 

38. 21. Explain how metabolic pathways are regulated. • The localization of enzymes within the cell helps order metabolism • Cellular structure orders and compartmentalizes metabolic pathways - some enzymes and complexes have a fixed location and they are incorporated into a membrane - other enzymes and their substrates may be localized within membrane-enclosed eukaryotic organelles 