Biochem Test #2

What is the ΔG for transport of glutamate from the outside of the cell, where the concentration of 0.1 mM to the inside of the cell where the concentration is 10 mM? Assume the cell potential is -70 mV and the temperature is 37°C

+18.6 kJ/mol

What is the free energy cost at 25°C of pumping Ca2+ out of a cell when the cytoplasmic concentration is 4 μM, the extracellular concentration is 1.5 mM and the membrane potential is -60 mV?

+32 kJ/mol

The drug known as botox is a preparation of botulinum toxin. How does this account for its use by plastic surgeons to alleviate facial wrinkles?

- Botulinum toxin targets SNAREs for degradation by proteolysis - SNAREs are necessary for transmission of signals from facial nerves to muscle via synaptic - SNAREs function by forming alpha-helical bundles to fuse synaptic vesicles with the plasma membrane

What is the membrane potential created by a sodium gradient where [Na+]out = 145 mM and [Na+]in = 12 mM at 37°C?

-67 mV

ADH question

0.017 μmol/min

How many acyl chains are added to a sphingosine backbone in order to form a sphingomyelin molecule?

1

If an enzyme-catalyzed reaction has a velocity of 2mM/min and a Vmax of 10 mM/min when the substrate concentration is 0.5 mM, what is the Km

2 mM

Which of the following is NOT a general feature of the lipid bilayer in biological membrane 1. The polar head groups of the membrane lipids face outwards to interact with the aqueous environment 2. The bilayer is stabilized by covalent interactions between the lipid molecules and integral membrane proteins 3. Individual lipid molecules are free to diffuse laterally within one leaflet of the bilayer 4. The thickness of the bilayer depends on the length of the fatty acids in the lipids

2. The bilayer is stabilized by covalent interactions between the lipid molecules and integral membrane proteins

A 30 mM solution of hippurylphenylalanine was monitored for amide bond hydrolysis by monitoring the formation of product, phenylalanine. At the end of 50 days, 25 μM phenylalanine is hydrolyzed 4.7 x 10^11 times faster in the presence of an enzyme. What is the rate of formation of phenylalanine in the presence of the enzyme (M/s)?

2.7 M/s

An insect aminopeptidase was purified and its catalytic activity was investigated using an artificial peptide substrate. The Vmax was 4.0 x 10 ^-7 M/s and the Km was 1.4 x 10^-4 M. The enzyme concentration used in the assay was 1.0 x 10^-7 M. What is the catalytic efficiency of the enzyme?

2.8 x 10^4

Hydrolysis of ATP by the Na,K-ATPase moves _________ while dephosphorylation moves __________.

3 Na+; 2 K+

The total concentration of receptors is a sample of 25 mM. The concentration of free ligand (L) is 10 mMand Kd is 10 mM. Calculate the percentage of receptors that are occupied by ligand.

50%

ADP binds to platelets in order to initiate the activation process. Two binding sites were identified on platelets, one with a Kd of 350 nM and one with a Kd of 7.9 μM. Which of these is the low affinity binding site?

7.9 μM

What is not a consequence of the cis double bonds of fatty acids

A higher melting temperature

A pH/rate curve with an inflection point at pH ~ 4 suggests the involvement of a(n) ___________ in the catalytic step

Acidic amino acid

Which of the following components of the insulin response pathway do not possess catalytic activity?

Adapter protiens

There are few examples of inhibitors that decrease Vmax but do now affect Km. These inhibitors

Affect Kcat Affect the catalytic function but not the binding of the substrate Are called noncompetitive

Which of the following will cause the opening or closing of a gated ion channel 1. pH change 2. Phosphorylation 3. Voltage change 4. Ligand binding

All of them

The Na,K-ATPase is a(n) _____________ that moves Na+ from ________ and K+ from _________

Antiporter Inside to out Outside to in

Which amino acid in the aquaporin channel hydrogen bonds with water to prevent the movement of protons?

Asn

What is responsible for the extremely rapid propagation of action potential?

Axons are insulated with a myelin sheath which prevents ion movement except at the nodes between myelinated segments

Which of the following is true regarding the glucose transporter?

Binding of glucose causes a conformational change so that the transporter is never open on both sides of the membrane

Which of the following statements about allosteric control of enzymatic activity is FALSE? 1. Allosteric inhibitors give sigmoidal plots 2. Allosteric enzymes are usually multi-subunit complexes 3. An effector may either inhibit or activate an enzyme 4. Binding of the effector changes the conformation of the enzyme molecule 5. Allosteric regulators are often a downstream product of the pathway

Binding of the effector changes the conformation of the enzyme molecule

Glucose is added to cells and the rate of glucose transport is plotted against glucose concentration. In the presence of a galactose derivative, the curve is shifted to the right (with no other change). What kind of agent is the galactose derivative?

Competitive

G proteins

Consist of three subunits: Ga, Gb, and Gγ

Chymotrypsin, a serine protease, preferentially cleaves a peptide bind adjoining a bulky non-polar side-chain. This is because chymotrypsin's "specificity pocket":

Contains small hydrophobic side chains

Which of the following second messengers would NOT be found free floating in the cytosol? DAG Ca 2+ ions cAMP IP3

DAG

A mutation in the active site of an enzyme results in a large increase in stabilization of the ES complex, while there is no change in the stabilization of the transition state complex. What effect will this have on the rate of product formation?

Decrease rate

In the reaction mechanism of the glycolytic enzyme aldolase, an active site tyrosine residue accepts a proton from the substrate. In this form the side chain of Tyr must be _________ and it is acting as a(n) __________ catalyst.

Deprotonated; base

Prodrugs are inactive compounds that need to be cleaved in order to yield an active drug. A novel tumor therapy has recently involved the delivery of an enzyme, capable of catalyzing this cleavage reaction, to the tumor site. This is followed by administration of the prodrug, which in this instance is acting as the substrate. Suppose there are two enzymes capable of catalyzing this reaction. Enzyme A has a Km for the prodrug of 1 μM and Enzyme B has a Km of 1 nM. Which enzyme would you use in patients?

Enzyme B

The GLUT transporter moves glucose through a transport protein in the same direction as its concentration gradient. The action of the glucose transporter is an example of ____________. The SGLT transporter uses the sodium concentration gradient created by the sodium-potassium ATPase to move glucose against its concentration grandient. The action of the SGLT transporter is an example of _______________.

Facilitated transport Secondary active transport

The glucose transporter is an example of

Facilitated transport and a uniporter

Activity of the Ras protein is analogous to the _________ in terms of its ability to bind GTP

G protein alpha subunit

Activation of a G protein in response to hormone binding requires binding of _________ to the __________ subunit

GTP alpha

Small mammalian hibernators can withstand body temperatures of 0°C to 5°C without injury. However, the body fats of most mammals have melting temperatures of approximately 25°C. Predict how the composition of the body fat of hibernators differ from that of their non-hibernating cousins

Hibernators will contain a higher percentage of polyunsaturated fatty acids

The complex formed between a lipid hormone and its receptor binds to ________ which are specific DNA sequences

Hormone response elements

What is the major factor in determining the types of secondary structures that form in the transmembrane portions of integral membrane proteins?

Hydrogen bonding interactions of protein backbone groups

Sarin gas is a fatal nerve agent that acts as an irreversible inhibitor of the enzyme acetylcholine esterase. Acetylcholine esterase hydrolyzes acetylcholine to render it inactive in the synapse. Atropine is an antagonist of acetylcholine. Which of the following physiological features would you expect to find in an individual exposed to sarin gas? Would you treat this individual with atropine or latrotoxins to reverse the symptoms?

Increased muscle contraction; atropine

Which of the following is a tyrosine kinase?

Insulin receptor

Which of the following is the primary building block for the synthesis of molecules like cholesterol or ubiquinone?

Isoprene

Which of the following statements regarding Kcat is FALSE? 1. It is also called the the turnover number 2. It is the rate constant of the reaction when enzyme is saturated with substrate 3. It is the total number of catalytic cycles completed by all of the enzyme molecules per unit of time 4. It is a measure of how fast the ES complex proceeds to E + P

It is the total number of catalytic cycles completed by all of the enzyme molecules per unit of time

Laminaria groenlandica is a type of kelp that grows along the rocky shores of Alaska. Due to its geographic distribution, the species is subjected to cold temps and potential freezes. Macrocystis pyrifera is a type of kelp that grows off the coast of South America and encounters much warmer temps. Which of these two species would you expect to have a higher concentration of unsaturated fatty acid tails incorporated into its bilayer?

Laminaria groenlandica

Which of the following open in response to an extracellular stimulus such as a neurotransmitter?

Ligand-gated channels

Rank the following melting points of the following fatty acids Laurate (12:0) Linoleate (18:3) Oleate (18:1) Stearate (18:0)

Linoleate < Oleate < Laurate < Stearate

Which of the following amino acids could bind to the specificity pocket of Trypsin?

Lys

What would occur when the action potential for muscle contraction reaches its terminus if SNARE complexes were not functioning?

Membrane fusion would not occur and there would be no release of acetylcholine into the synaptic cleft

Which of the following may undergo transverse diffusion within the lipid bilayer?

Membrane lipids

Which type of secondary structure present in integral membrane proteins is readily detectable in the primary structure?

Membrane-spanning alpha helix

An enzyme can be inhibited by a number of cellular agents whose Ki values are listed below. Which is the most effective inhibitor? Which inhibitor is likely to to completely ineffective under normal cellular conditions? Inorganic phosphate: 1.0 x 10^-1 Glucosamine: 7.2 x 10^-4 NADPH: 2.7 x 10 ^-5

Most effective: NADPH Ineffective: Inorganic Phosphate

Given the information below, does this enzyme obey Michaelis-Menten Kinetics? aminobutyric acid + glutamate + ATP --> --> trypanthione Substrate Km Glutamate 5.9 Aminobutyric 6.1 ATP 1.4

No

Hexokinase undergoes a large conformational change in order to exclude water from the active site. Would chymotrypsin undergo such a change upon binding its substrate?

No

Which of the following is NOT a way in which biological catalysts differ from nonbiological catalysts?

Only biological catalysts are not permanently altered or consumed as a result of the reaction

What is the effect of phosphofructokinase in the presence of phosphoenolpyruvate and what type of interaction do they have?

Phosphoenolpyruvate allosterically inhibits phosphofructokinase; engage in feedback inhibition

Ligand binding to a receptor tyrosine kinase causes _________ of the receptor which then __________ the next protein in the signaling pathway.

Phosphorylation phosphorylates

cAMP binds to the ________ subunits of protein kinase A allowing the tetramer to dissociate into _________

Regulatory subunits Two active monomers and an inactive dimer

Renin or chymosin is a protease similar to chymotrypsin, except that it belongs to a class of enzymes called aspartyl proteases -- in which aspartate residues....

Renin uses acid-base catalysis Asp 32 has the lower pK value

The rate constant associated with the reaction below would be 2A ----> B

Second Order

The rate associated with the action below would be A + B --> C

Second order

What amino acid performs the nucleophilic attack during the chymotrypsin mechanism?

Serine

The chymotrypsin/trypsin family of proteases has which combination of amino acids in the active site

Serine, Histidine, and Aspartic Acid

Nerve cells contain high levels of _________ which is a derivative of ____________

Sphingomyelin; sphingosine

A pore that simultaneously transports two different molecules two different molecules in the same direction is called a(n)

Symporter

Concerning the effects of mixed inhibitors on a reaction

The Vmax decreases and the apparent Km may decrease or increase

Which of the following statements about the insulin receptor is FALSE? 1. It is a dimer of dimers 2. The individual polypeptide chains are connected by disulfide bonds 3. Insulin binds to the dimer of alpha subunits 4. The tyrosine kinase activity resides in the beta subunits 5. The receptor does not undergo a conformational change upon binding insulin because it is already in a dimer form

The receptor does not undergo a conformational change upon binding insulin because it is already in a dimer form

A mutated form of the alpha subunit of the heterotrimeric G protein has been identified; this form of readily exchanges nucleotides even in the absence of an activated receptor. What would be the effect on a signaling pathway containing the mutated alpha subunit?

The signaling pathway will remain activated

Kinetic studies are carried out for a Michaelis-Menten enzyme at a specific concentration of enzyme. What wpuld be the effect on Km and Vmax if half as much enzyme is used?

The value of Vmax will be half but the value of Km will remain the same

Phorbol esters, which are compounds isolated from plants, are structurally similar to diacylglycerol. How does the addition of phorbol esters affect the signaling pathways of cells in culture?

They would activate protein kinase C

Some G protein-linked receptors are associated with a protein called RGS (regulator of G protein signaling). RGS stimulated the GTPase activity of the G protein associated with the receptor. What effect does RGS have on the signaling process?

This will shorten the duration of the signaling

What type of chemical species can participate in catalysis by binding substrates to orient them properly, by undergoing reversible changes in oxidation state, and stabilizing negative charges?

Transition metal cations

Which of the following is FALSE regarding transition state stabilization?

Transition state stabilization refers to the shift in the equilibrium of the reaction

All known porins are _____________ proteins composed of ________________

Trimeric beta barrels

A patient suffers from premature zymogen activation, so that the pancreatic enzymes are activated in the pancreas rather than in the small intestine, causing damage to the pancreas. What would be the most effective in preventing these effects?

Trypsin inhibitor

In which type of reversible inhibition does binding substrate facilitate binding of the inhibitor?

Uncompetitive

Under certain conditions, peptide bond formation is more thermodynamically favorable than peptide bond hydrolysis. Would you expect chymotrypsin to catalyze peptide bond formation?

Yes

What is the relationship between Km and [S] when an enzyme-catalyzed reaction proceeds at 90% of Vmax?

[S] = 9 Km

A molecule moves across a membrane from a lower to a higher concentration with the aid of a membrane protein. This process is known as

active transport

Acetylcholine and nicotine competitively bind to nicotinic acetylcholine receptors to cause the same second messenger activation. Nicotine is considered an _________ of the receptors

agonist

How does the addition of an enzyme to a chemical reaction affect the activation energy of the reaction?

decreases it

It is necessary to know the value of [E]t in order to determine the values of

kcat

Which of the following is a ligand of the b2-adrenergic receptor? 1. Tyrosine 2. Serotonin 3. Norepinephrine 4. Caffeine 5. Adenosine

norepinephrine

Cerebrosides and gangliosides are glycolipids that are built on a ____________ backbone

sphingosine

A membrane consisting only of phospholipids undergoes a sharp transition from the crystalline form to the fluid form as it is heated. What would be the effect on this transition in a membrane containing 80% phospholipid and 20% cholesterol?

the shift from the crystalline transition would be more gradual

Voltage-gated channels are more likely to be composed of

transmembrane α helices

Rank the melting points of the following fatty acids cis-oleate (18:1) trans-oleate (18:1) linoleate (18:2)

transoleate > cis-oleate > linoleate

Which of the following lipid types are not found in animal membranes?

triacylglycerols

What is the primary storage form of fatty acids?

triglycerides

Which of the following would be a proper representation of enzyme velocity?

v = (+) d[P]/ dt v = (-) d[S]/ dt