UIUC MCB 450 EXAM 2
LON-CAPA PROBLEMS
Questions With All Correct
Answers
At what speeds do phospholipids laterally diffuse? - ANSWER-1-2 micrometers/second
Does a better inhibitor have a higher or lower Ki? - ANSWER-lower
,How are lipid-linked proteins released from the membrane? - ANSWER-By treatment
with phospholipase C
What is the shape of the graph of [S] versus V0? - ANSWER-rectangular hyperbola
What is the simplest phosphoglyceride? - ANSWER-Phosphatidate
What is the structure of sphingomyelin? - ANSWER-Fatty acid linked to sphingosine
amino group via amide bond; primary sphingosine hydroxyl ester-linked to
phosphorylcholine
What is the structure of sphingosine? - ANSWER-Amino alcohol with long, unsaturated
hydrocarbon chain
What is the symmetry rule in cooperative binding? - ANSWER-concerted model - all
subunits must be in the same state, so all T or all R
What is the third step of Na+-K+ ATPase activity? - ANSWER-2 extracellular K+ bind to
the pump
What is the turnover number for an enzyme? - ANSWER-the number of substrate
molecules an enzyme can turn into product per unit time when enzyme is fully saturated
What is the unit for k in first order reactions? - ANSWER-reciprocal time
What is the unit for k in second order reactions? - ANSWER-reciprocal concentration *
reciprocal time
What is the usual allosteric activator? - ANSWER-the substrate
What is the usual allosteric inhibitor? - ANSWER-the end product
What is the velocity equation for first order reactions? - ANSWER-v = k[S]
What is the velocity equation for second order reactions? - ANSWER-v = k[S1][S2]
What is V0 when [S] << Km? - ANSWER-V0 has linear dependence on [S]
What is V0 when S >> Km? - ANSWER-V0 = Vmax
What is ΔG' at equilibrium? - ANSWER-ΔG' = 0
What kind of enzymes does iodoacetamide inhibit? - ANSWER-those with cysteines in
the active site
, What kind of structures are bundles of amphipathic alpha-helices most common in? -
ANSWER-Transport proteins and pores
What limits Kcat/Km? - ANSWER-K1 limits it, so K1 cannot be faster than diffusion-
controlled encounters between E and S
What occurs in the separation step of lipid analysis? - ANSWER-Phase partitioning
against water removes the polar molecules, leaving the lipids for analysis
What tissue homogenized with at first when doing lipid analysis? - ANSWER-Mixture of
chloroform, methanol, and water
What two types of H bonds can the phosphoryl group form with the enzyme? -
ANSWER-with NH of peptide backbone and with the positively charged guanidinium
group on arginine
What was the initial burst of activity in the chymotrypsin experiment? - ANSWER-
Acylation phase, where chymotrypsin and p-nitrophenyl acetate formed acyl enzyme
and p-nitrophenylate
What were the products of acylation in the chymotrypsin experiment? - ANSWER-PNP
and acyl enzyme
What were the products of deacylation in the chymotrypsin experiment? - ANSWER-N-
acetyl phenylalanine and active chymotrypsin
What, mathematically, is an enzyme's specificity constant? - ANSWER-Kcat/Km
When are the weak interactions between S and E optimized? - ANSWER-when S is in
its transition state
When does a K+ channel desolvate K+ ions? - ANSWER-The pore narrows ~2/3
through the bilayer, where the interact with the protein instead
When does His57 act as a base in chymotrypsin catalysis? - ANSWER-1) deprotonates
Ser195 OH
2) deprotonates water to create OH- nucleophile
When does His57 act as an acid in chymotrypsin catalysis? - ANSWER-1) donates
proton to NH of attacked peptide bond to allow amino group to be released
2) donates proton to Ser195 to restore its OH group
When is Km a good measure of the enzyme's affinity for substrate? - ANSWER-when
K2 << K-1, so that the two steps that are really being taken into account are K1 and K-1
LON-CAPA PROBLEMS
Questions With All Correct
Answers
At what speeds do phospholipids laterally diffuse? - ANSWER-1-2 micrometers/second
Does a better inhibitor have a higher or lower Ki? - ANSWER-lower
,How are lipid-linked proteins released from the membrane? - ANSWER-By treatment
with phospholipase C
What is the shape of the graph of [S] versus V0? - ANSWER-rectangular hyperbola
What is the simplest phosphoglyceride? - ANSWER-Phosphatidate
What is the structure of sphingomyelin? - ANSWER-Fatty acid linked to sphingosine
amino group via amide bond; primary sphingosine hydroxyl ester-linked to
phosphorylcholine
What is the structure of sphingosine? - ANSWER-Amino alcohol with long, unsaturated
hydrocarbon chain
What is the symmetry rule in cooperative binding? - ANSWER-concerted model - all
subunits must be in the same state, so all T or all R
What is the third step of Na+-K+ ATPase activity? - ANSWER-2 extracellular K+ bind to
the pump
What is the turnover number for an enzyme? - ANSWER-the number of substrate
molecules an enzyme can turn into product per unit time when enzyme is fully saturated
What is the unit for k in first order reactions? - ANSWER-reciprocal time
What is the unit for k in second order reactions? - ANSWER-reciprocal concentration *
reciprocal time
What is the usual allosteric activator? - ANSWER-the substrate
What is the usual allosteric inhibitor? - ANSWER-the end product
What is the velocity equation for first order reactions? - ANSWER-v = k[S]
What is the velocity equation for second order reactions? - ANSWER-v = k[S1][S2]
What is V0 when [S] << Km? - ANSWER-V0 has linear dependence on [S]
What is V0 when S >> Km? - ANSWER-V0 = Vmax
What is ΔG' at equilibrium? - ANSWER-ΔG' = 0
What kind of enzymes does iodoacetamide inhibit? - ANSWER-those with cysteines in
the active site
, What kind of structures are bundles of amphipathic alpha-helices most common in? -
ANSWER-Transport proteins and pores
What limits Kcat/Km? - ANSWER-K1 limits it, so K1 cannot be faster than diffusion-
controlled encounters between E and S
What occurs in the separation step of lipid analysis? - ANSWER-Phase partitioning
against water removes the polar molecules, leaving the lipids for analysis
What tissue homogenized with at first when doing lipid analysis? - ANSWER-Mixture of
chloroform, methanol, and water
What two types of H bonds can the phosphoryl group form with the enzyme? -
ANSWER-with NH of peptide backbone and with the positively charged guanidinium
group on arginine
What was the initial burst of activity in the chymotrypsin experiment? - ANSWER-
Acylation phase, where chymotrypsin and p-nitrophenyl acetate formed acyl enzyme
and p-nitrophenylate
What were the products of acylation in the chymotrypsin experiment? - ANSWER-PNP
and acyl enzyme
What were the products of deacylation in the chymotrypsin experiment? - ANSWER-N-
acetyl phenylalanine and active chymotrypsin
What, mathematically, is an enzyme's specificity constant? - ANSWER-Kcat/Km
When are the weak interactions between S and E optimized? - ANSWER-when S is in
its transition state
When does a K+ channel desolvate K+ ions? - ANSWER-The pore narrows ~2/3
through the bilayer, where the interact with the protein instead
When does His57 act as a base in chymotrypsin catalysis? - ANSWER-1) deprotonates
Ser195 OH
2) deprotonates water to create OH- nucleophile
When does His57 act as an acid in chymotrypsin catalysis? - ANSWER-1) donates
proton to NH of attacked peptide bond to allow amino group to be released
2) donates proton to Ser195 to restore its OH group
When is Km a good measure of the enzyme's affinity for substrate? - ANSWER-when
K2 << K-1, so that the two steps that are really being taken into account are K1 and K-1
