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Chapter 9 MicrobioEC
Exam 2
| Question | Answer |
|---|---|
| define metabolism | total of all chemical reactions occuring in the cell |
| what type of reactions are part of catabolism | fueling reactions |
| define catabolism | the breakdown of larger, more complex molecules into smaller, simpler molecules with the release of energy |
| define anabolism | the synthesis of complex molecules from simpler molecules with the input of energy |
| what kind of things does catabolism do | conserve/capture energy from organisms energy source, generate a ready supply of electrons (reducing power), and generate precursors for biosynthesis |
| What three major types of work do cells carry otu | chemical work, transport work, and mechanical work |
| define chemical work | invovles synthesis of complex biological molecules from much simpler precursors; energy is needed to increase the molecular complexity of the cell |
| define transport work | requires energy to take up nutrients, eliminates wastes, and maintains ion balances; energy input needed because things often must be transported agaisnt gradients |
| define mechanical work | energy required for cell motility and the movement of sturctures within the cells, like partitioning chromosomes during cell division |
| What is the change in heat content | the change in enthalpy |
| what is the free energy change | the amount of energy in a system/cell available to do useful work at constant temp and pressure |
| what is change in entropy | measure of the proportion of the total energy change that the system cannot use in performing work |
| what is delta s | cange in entropy |
| what is delta G | change in free energy |
| what is delta H | change in enthalpy |
| when will a reaction occur spontaneously | if the free energy of the system decreases during the reaction; if delta G is negative; large change in entropy |
| when will a reaction be less favorable | a decrease in entropy, a more positive delta G |
| measure of the randomness or disorder of a system; a measure of that part of the total energy in a system that is unfavorable for useful work | entropy |
| what is the equilibirum constant of a reaction directly related to | its change in free energy |
| negative delta G; equilibrium concstant is greater than one; reaction goes to completion. what kind of reaction exergonic or endergonic | exergonic reaction |
| positive delta G; equilibrium constant less than 1; reaction not favorable. what kind of reaction exergonic or endergonic | endergonic reaction |
| Name three biochemical priniciples common to all types of metabolism | 1. use of ATP to store/conserve energy released during exergonic reactions to drive endergonic reactions 2. organization of metabolic reactions into pathways /cycles 3. catalysis of metabolic reactions by enzymes or riboenzymes |
| Name one more biochemical principle common to all types of metabolism | 4. importance of oxidation-reduction reactions in energy conservation |
| what is the most commonly used practical form of energy | adenosine 5'-triphosphate (ATP) |
| what serves as the link between exergonic and endergonic reactions | ATP |
| Why is ATP such a good energy currency | its a high energy molecule; hydrolyzes almost completely to the products adenosine diphosphate (ADP) and orthophosphate (Pi); strongly exergonic |
| what does ATP hydrolyze to | adenosine diphosphate (ADP)and orthophosphate (Pi) |
| why does ATP have a high phosphate transfer potential | it readily transfers its phophate to water; a higher transfer potential donates phosphate to lower potential so ATP readily donates a phosphate to glucose and glucose 6-phosphate |
| what is an example of a molecule with a higher phosphate transfer potential than ATP | phosphoenolpyruvate |
| what does the cell use phosphoenolpyruvate for | to regenerate ATP from ADP through substrate-level phosphorylation |
| what is guanosine 5'-triphosphate used for | supplies some of the energy used during protein synthesis |
| what is cytidine 5'-triphosphate used for | used during lipid synthesis |
| what is uridine 5-phosphate used for | synthesis of peptidoglycan and other polysaccharides |
| What are oxidation-reduction reactions | where electrons move from an electron donor to an electron acceptor; donor becomes less energy rich and acceptor becomes more energy rich |
| how many electrons can glucose donate in a redox reaction | 24 |
| how many half reactions do redox reactions consist of | two half reactions |
| describe each half reaction | one half reaction is the electron-donating half reaction (oxidation) and the other is the electon-accepting half reaction (reduction) |
| what are the acceptor and donor of a half reaction referred to as | conjugate redox pair |
| how are half reactions written as, reductions or oxidations | reductions |
| which side of the equation is the acceptor on | the left side because it is losing electrons and can now accept them |
| which side of the equation is the donator on | the right side because it now has electrons it can give up |
| what is the equilibrium constant for a redox reaction called | the standard reduction potential |
| what is the standard reduction potential a measure of | the tendency of the donor of a half reaction to lose electrons |
| which electron carrier in the ETC has the most negative electron potential | the first electron carrier and each successive carrier is slightly less negative |
| protein catalysts that have great specificity for hte reaction catalyzed, the molecules acted on, and the products they yield | enzymes |
| substance that increases the rate of a chemical reaction without being permanently altered itself | catalyst |
| what are substrates | the reacting molecules |
| some enzymes are composed of two parts. name them | apoenzyme: protein component co-factor: nonprotein component |
| what is the complete enzyme consisting of the apoenzyme and its cofactor called | the holoenzyme |
| what is it called if the cofactor is firmly attached to the apoenzyme | prosthetic group |
| what is it called if the cofactor is loosely attached and can dissociate from the apoenzyme after products have been formed | coenzyme |
| what do coenzymes do | carry one of the products to another enzyme or transfer chemical groups from one substrate to another |
| true or false: enzymes do not alter the equilibrium constant | true |
| how do enzymes accelerate reactrions | by lowering activation energy so more substrate molecules will have sufficient energy to come together and form products |
| what are the two ways that an enzyme can interact with its substrate | the lock and key model and the induced fit model |
| describe the lock and key model | active site is rigid and precisely shaped to it the substrate so specific substrate binds and is positioned properly for the reaction |
| describe the induced fit moedl | an enzyme may change shape when it binds the substrate so that the active site surrounds and precisely fits the substrate; used by hexokinase |
| how does the formation of an enzyme-substrate complex lower the activation energy | bringing substrates together at active site is concentrating them and speeding up the reaction; also bind them so they are correctly oriented with respect to eachother lowering amount of energy needed to reach transition state |
| what is the most important environmental factor that affects enzyme activity | substrate concentration; more substrate present=more often enzyme binds substrate and velocity of reaction is greater |
| what is the substrate concentration requried for the enzyme to achieve half-maximal velocity and is used as a measure of the apparent affinity of an enzyme for its substrate | Michaelis constant (Km) |
| are enzymes with a lower or higher Km value able to function better | a lower Km value function better because they have a high affinity for their substrates since the concentrations of substrates in cells are often low |
| NAme another environmental factor that affects enzyme activity | alterations in pH and temperature |
| this inhibitor directly competes with the substrate at an enzymes catalytic site and prevents the enzyme from forming product; resemble normal substrates | competitive inhibitor |
| affect enzyme activity by binding to the enzyme at some location other than the active site altering the enzymes shape and rendering it inactive or less active | noncompetitive inhibitors |
| what are ribozymes | catalytic RNA molecules |
| name three ways that metabolic pathways are regulated | 1. metabolic channeling 2. regulation of the synthesis of a particular enzyme 3. direct stimulation or inhibition of the activity of critical enzymes |
| this influences pathway activity by localizing metabolites and enzymes into different parts of a cell | metabolic channeling |
| what is the most commong metabolic channeling mechanism | compartmentation: differential distribution of enzymes and metabolites among separate cell structure or organelles |
| what is an example of compartmentalism | periplasm in gram negative bacteria |
| what are most regulatory enzymes | allosteric enzymes |
| what is the activity of an allosteric enzyme altered by | a small molecule called an allosteric effector |
| describe what an allosteric effector does | it binds reversibly by noncovalent forces to a regulatory site separate from the catalytic siet and causes a change in the conformation of the enzyme therefore altering the activity of the catalytic site |
| does a positive effector increase or decrease enzyme activity | increase |
| what are regulatory enzymes switched on and off by | reversible covalent modification |
| what is the most studied regualtory enzyme | e. coli glutamine synthetase involved in nitrogen assimilation |
| describe feedback inhibition | ensures balanced production of a pathway end product; if the end product becomes too concentrated, it inhibits the regulatory enzyme and slows its own synthesis; when concentration decreases, pathway activity again increases and more product is formed |
| what is a pacemaker enzyme | catalyzes the slowest or rate-limiting reaction in the pathway; changes in activity of this enzyme directly alters the speed with which a pathway operates; usually the first step in a pathway is a reaction catalyzed by this |
| what are isoenzymes | different forms of an enzyme that catalyze the same reaction |
| how are branched biosynthetic pathways regulated | usually achieve a balance among end products by using regulatory enzymes at branch points |
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kristinp1713
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