Exam 6: Enzymes

Why is the Lineweaver-Burk (double reciprocal)plot (see Box 6,p.206)more useful than the standard V vs.[S] plot in determining kinetic constants for an enzyme? (Your answer should probably show typical plots. )

Fifteen $\mu$ g of an enzyme of M_r 30,000 working at V_max catalyzes the conversion of 60 $\mu$ mol of substrate into product in 3 min.What is the enzyme's turnover number?

Sometimes the difference in (standard)free-energy content, $\Delta$ G'°,between a substrate S and a product P is very large,yet the rate of chemical conversion,S $\rightarrow$ P,is quite slow.Why?

On the enzyme hexokinase,ATP reacts with glucose to produce glucose 6-phosphate and ADP five orders of magnitude faster than ATP reacts with H₂O to form phosphate and ADP.The intrinsic chemical reactivity of the -OH group in water is about the same as that of the glucose molecule,and water can certainly fit into the active site.Explain this rate differential in two sentences or less.

Two different enzymes are able to catalyze the same reaction,A $\rightarrow$ B.They both have the same V_max,but differ their K_m the substrate A.For enzyme 1,the K_m is 1.0 mM;for enzyme 2,the K_m is 10 mM.When enzyme 1 was incubated with 0.1 mM A,it was observed that B was produced at a rate of 0.0020 mmoles/minute. a)What is the value of the V_max of the enzymes? b)What will be the rate of production of B when enzyme 2 is incubated with 0.1 mM A? c)What will be the rate of production of B when enzyme 1 is incubated with 1 M (i.e. ,1000 mM)A?

Cells can develop a resistance to drugs by increasing the cellular concentration of the enzyme that that drug inhibits.If a cell increases its concentration of a given enzyme to 10 times the normal amount,which parameters listed below will be increased ten-fold? K_m K_I [S] V_max v₀ when [S] = K_m k_cat Catalytic efficiency

The double-reciprocal transformation of the Michaelis-Menten equation,also called the Lineweaver-Burk plot,is given by 1/V₀ = K_m /(V_max[S])+ 1/V_max To determine K_m from a double-reciprocal plot,you would:

In competitive inhibition,an inhibitor:

Define the term "suicide inhibitor."

Blood coagulation involves:

An enzyme-catalyzed reaction was carried out with the substrate concentration initially a thousand times greater than the K_m for that substrate.After 9 minutes,1% of the substrate had been converted to product,and the amount of product formed in the reaction mixture was 12 $\mu$ mol.If,in a separate experiment,one-third as much enzyme and twice as much substrate had been combined,how long would it take for the same amount (12 $\mu$ mol)of product to be formed?

Which one of the following statements is true of enzyme catalysts?

The concept of "induced fit" refers to the fact that:

Compare the two reaction coordinate diagrams below and select the answer that correctly describes their relationship.In each case,the single intermediate is the ES complex.

To calculate the turnover number of an enzyme,you need to know:

Phenyl-methane-sulfonyl-fluoride (PMSF)inactivates serine proteases by binding covalently to the catalytic serine residue at the active site;this enzyme-inhibitor bond is not cleaved by the enzyme.This is an example of what kind of inhibition?

V_max for an enzyme-catalyzed reaction:

In the following diagram of the first step in the reaction catalyzed by the protease chymotrypsin,the process of general base catalysis is illustrated by the number ________,and the process of covalent catalysis is illustrated by the number _________.

Enzymes are potent catalysts because they:

Which of the following has not been shown to play a role in determining the specificity of protein kinases?