BioChem exam 3
What is ΔG for transport of a solute into the cell when the extracellular concentration is 10 mM, the intracellular concentration is 0.1 mM, and T = 20°C?
-11.2 kj mol-1
for a cell with [Na+]out = 150 mM and [Na+]in= 15mM at 37 0C, what is the free energy for movement of sodium ions from outside the cell to inside if the potential across the membrane is -60mV?
-11.7 kj/mol
delta G* for a reaction is 800 what is delta G at 37 C when the ration of product to reactant concentration is 0.6
-520 J mol -1
What is the membrane potential created by a sodium gradient where [Na+]out =145 mM and [Na+]in=12 mM at 37 0C?
-67mV
when a reaction is at equilibrium, the G is equal to ____
0
A sample of cells has a total receptor concentration of 24 mM, and 40% of the receptors are occupied with ligand. The concentration of free ligand is 10 mM. Calculate Kd.
15 μM
hydrolysis of ATP by the Na,K-ATPase moves_____ while hydrolysis of the phosphate moves_____
3 Na+; 2 K+
Calculate the intracellular concentration of Na+ when the extracellular concentration is 160 mM and the membrane potential (due entirely to Na+) is -100 mV at 20°C
3.3 mM
calculate delta G* for a reaction at 25C when Keq=0.25
3400 J mol-1
What is the ratio [Na+]in/[Na+]out created by depolarization in a nerve cell if the final potential is +50 mV at 37 0C
6.5
An uncatalyzed reaction has a rate of 4.2 × 10-7 sec-1. When an enzyme is added the rate is 3.2 × 104 sec-1. Calculate the rate enhancement caused by the enzyme.
7.6 x 1010
which molecule is most reduced
A
receptor tyrosine kinases all use ____ as a substrate
ATP
the delta G* for the hydrolysis of acetyl CoA is most similiar to the delta G* for the hydrolysis of ____
ATP
which sentence best describes ATP's role as a source of energy
ATP is less stable than its hydrolysis reaction products
primary active transport is usually driven by _____, and secondary active transport by _____
ATP; an ion gradient
Which of the following is not an accurate description of an event in a G protein signaling system?
Adenylate cyclase is activated by phosphorylation-Adenylate cyclase is activated by its interation with the α subunit of certain G proteins.
Which of the following does NOT occur in biological signaling systems?
All of the above processes may occur.
N-linked oligosaccharides can be covalently linked to proteins at the amino acid ____
Asn
which structure represents an acetyl group
B
which of the monosaccharides seen below are L sugars?
C and D
which elements are most abundant in carbohydrates?
C, H, O
the ___-terminus of ubiquitin is linked to a ____ residue of proteins to be degraded
C; lys
at a nerve-muscle synapse,
Ca2+ flow in the neuron triggers the release of acetylcholine
the molecular formula for a monosaccharide is ____ where _____
CnH2nOn; n>3
which monosaccharide seen below is the enantiomers of A?
D
which of the following Haworth projections correctly shows the alpha-anomer of galactose
D
in the following structure, which carbon is the anomeric carbon
E
the two main types of receptor systems involve
G proteins and receptor tyrosine kinases
activation of a G protein in response to hormone binding requires binding of _____ to the ____ subunit
GTP, alpha
The imidazole side chain of histidine can function as either a general acid catalyst or a general base catalyst because
I, II
Which of the following amino acid residues would not provide a side chain for acid-base catalysis at physiological pH? (Assume pK values of each amino acid are equal to the pK value for the free amino acid in solution.)I. leucineII. lysineIII. aspartic acidIV. histidine
I, II, III
If you add enzyme to a solution containing only the product(s) of a reaction, would you expect any substrate to form?
It depends on the energy difference between E + P and the transition state.You got it right
which substance is not a second messenger
K+
the oxidized form of NADH is
NAD+
which of the following does not serve as a cellular energy currency?
NAD+
Which of the following statements concerning receptors is FALSE?
Receptors bind signal molecules specifically and irreversibly.-Receptors interact with their ligands in a reversible manner.
A new serine protease was discovered that preferentially cleaves a peptide bond adjoining a negatively charged side chain. Which of the following is true?
The specificity pocket is likely lined with amino acids such as Arg and Lys.
Which of the following statements concerning receptors is CORRECT?
They have a ligand binding site on the extracellular side of the membrane.
what two amino acid residues are the targets of protein kinase A?
Thr and Ser
which of the following statements regarding G proteins is true?
When activated, the α-subunit can cause adenylate cyclase to synthesize cAMP.
arrestin helps terminate G protein signaling by binding to
a G protein-coupled receptor
a nucleotide consists of
a base linked to a phosphorylated ribose
In affinity labeling, a technique used to study enzyme mechanisms,
a compound designed to bind at the active site reacts with and therefore permits the identification of a nearby group
a fatty acid can be linked to glycerol by ____ reaction
a condensation
an ion transport protein constructed entirely from beta strands is most likely to be
a porin
in endocytosis
a vesicle buds inward from the plasma membrane
which of the following is more highly oxidized than acetaldehyde?
acetic acid
The following diagram shows a portion of a reaction sequence of an enzyme. What type(s) of catalysis is (are) occurring in this first step?
acid-base catalysis
what enzyme is activated by association with an active G protein
adenylate cyclase
the bulk of triaclyglycerols in the human body are stored in _____
adipocytes
the molecule shown here is a
aldopentose
which of the following is true regarding SNARE complex formation?
all of the above
which of the following can be regulared by eicosanoids
all of the above -blood pressure -blood coagulation -inflammation -fever
Which of the following can be a hormone?
all of the above -amino acid derivatives -steroids -polypeptides -eicosanoids
the cellular effects of signaling via receptor tyrosine kinases may include
all of the above -phosphorylation of proteins -changes in gene expression -activation of G proteins
amino acids can be converted to ____
all of the above -carbohydrates -fatty acids -nucleotides -peptides
why can histidine NOT act as a base in the lysosome (an organelle where the pH is close to 4.5)?
all of the above are correct
which of the following will cause the opening or closing of a gated ion channel?
all of the above: pH change phosphorylation voltage change ligand binding
which of the following are characteristics of cellulose
all of the above: -highly extended fibers -beta (1->4) glycosidic bonds -extensive hydrogen bonding -between individual molecules unbranched polymer
a transporters activity can be described in terms of
all of the above: -velocity of solute transport -K M for the solute -the maximum rate of transport
amylopectin contains primarily ____ glycosidic bonds with _____ glycosidic bonds as branch points
alpha (1 ->4); alpha (1->6)
an allosteric regulator
alters an enzymes activity
the transformation of a monosaccharide into its _____ occurs easily and does not require the assistance of a catalyst
anomer
the Na,K-ATPase is an ______ that moves Na+ ions from _____ and K+ ions from _____
antiporter; inside to out; outside to in
what type of transported is responsible for moving water across membranes?
aquaporin
the eicosanoids are derived from the membrane fatty acid
arachidonic acid
eicosanoids
are derived from membrane lipids
N-linked oligosaccharides
are modified by glycosidases
which of the following is an inhibitor of cyclooxygenase
aspririn
the conformation changes responsible for ion transport in the Na,K-ATPase are triggered by
attachment and release of a phosphoryl group
lactase, the enzyme responsible for breaking lactose into its monomers, is a ____ enzyme
beta-galactosidase
the following is a ____ disaccharide with a _____ glycosidic bond
beta; alpha (1 ->4
an enzyme does all of the following except
bind a wide variety of substrates
lipid hormones
bind to intracellular receptors
which of the following would be the first to occur following opening of Ca2+ channels during acetylcholine-mediated neurotransmission to a muscle cell?
binding of SNARE complex to synaptic vesicles and pre-synaptic membrane
which of the following is glucose-6-phosphate?
c
protein kinase A is activated by
cAMP and phosphorylation
a protein with two stable conformations
can alternate between conformations
energy is generated during ____, the breakdown of larger molecules into smaller while energy is consumed during ____, the building of larger molecules from smaller ones
catabolic reactions; anabolic reactions
generally speaking, ATP is produced by ____ reactions and used by ____ reactions
catabolic; anabolic
the oligosaccharides of glycoproteins do all of the following except
catalyze chemical reactions
in a metabolic pathway, the reactions that control flux through the pathway
catalyze irreversible reactions
the fusion of a vesicle membrane with the plasma membrane depends on
changes in membrane curvature
ion channels select their solutes by
charge and size
Acid-base catalysis may be accomplished by:
charge delocalization
Since proteins are limited in their abilities to catalyze oxidation-reduction reactions, enzymes often employ ________ to assist with catalysis
coenzymes
which of the following is TRUE regarding cofactors?
cofactor is a broad term used for all enzyme "helpers"
Simultaneous stimulation of a reaction by general acid and general base catalysis is defined as
concerted acid-base catalysis
the ability for some receptor tyrosine kinases to ultimately activate phospholipase C is an example of _____
cross talk
olfactory receptors generate _____ as a second messenger
cyclic AMP
which of the following factors contributes to the highly exergonic nature of ATP hydrolysis?
decrease in negative-ion repulsion in ATP
a cells response to a hormone signal diminishes as a result of
desensitization
The action of phospholipase C on phosphatidylinositol-4,5-bisphosphate generates two important signalling molecules. What are they?
diacyl glycerol and inositol-1, 4, 5- trisphosphate
what is the only monosaccharide that is achiral?
dihydroxyacetone
Curved arrows are conventionally used to illustrate the movement of
electron pairs
changing the configuration of C3 of glucose generates an
epimer
glucose and galactose are ____ of each other
epimers
the conversion of a carbohydrate into CO2 is a ____ process; the conversion of CO2 into a carbohydrate is a ____ process
exergonic; endergonic
Alcohol dehydrogenase catalyzes the conversion of methanol to _________ and is, therefore, classified as a(an)________.
formaldehyde; oxiodoreductase
an autophagosome
forms following membrane fusion
which of the following describes glycosaminoglycans?
found in extracellular space
starch and glycogen function as
fuel storage molecules
this molecule is derived from
galactose
Proton transfer from an acid, lowering the free energy of a reaction's transition state, is characteristic of
general acid catalysis
proton transfer from an acid, lowering the free energy of a reactions transition state, is characteristic of
general acid catalysis
which of the following would be positively charged at physiological pH
glucosamine
the three-carbon monosaccharide ____ is a _____
glyceraldehyde; aldose
which of the following is mobilized for energy use by a phosphorolysis reaction, not a hydrolysis
glycogen
which type of stored metabolic fuel is not mobilized by hydrolysis
glycogen
which of the following is the major difference between glycogen and amylopectin
glycogen contains about twice the number of branch points as amylopectin
the reaction between an alcohol and an anomeric carbon of a carbohydrate forms a ____ bond
glycosidic
monosaccharide residues in polysaccharides are linked by
glycosidic bonds
a transmembrane protein
has regular secondary structure in its transmembrane segments
choose the true statement about autotrophs and heterotrophs
heterotrophs obtain nutrients from autotrophs
The catalytic mechanism of bovine pancreatic RNase A relies upon acid-base catalysis involving the amino acid __________.
histidine
The complex formed between a lipid hormone and its receptor binds to _____ which are specific DNA sequences.
hormone response elements
compounds containing hydroxyl groups interact with water molecules via
hydrogen bonds
digestion of food utilizes enzymes that catalyze ____ reactions
hydrolysis
which is not a function of lipids
information storage
the second messenger ____ opens Ca2+ channels in the endoplasmic reticulum
inositol trisphosphate
the ____ receptor is a receptor tyrosine kinase
insulin
cellulose is a rigid molecule as a result of
interchain hydrogen bonds
the interior of a lipid bilayer
is completely nonpolar
the transition state of an enzyme and substrate reaction
is stabilized due to the specificity of the active site for the substrate
Which of the following amino acid residues would provide a side chain capable of increasing the hydrophobicity of a binding site?
isoleucine
which amino acid side chain is most likely to be found on a membrane-spanning helix?
isoleucine
before a G protein can activate adenylate cyclase
it dissociates into two parts
in a G protein signal-transduction system, what role does the G protein play?
it transmits the signal from the receptor to other components of the signaling system
Research scientists are trying to clone a gene. In order to accomplish this task they join two pieces of DNA. Which class of the enzymes below might accomplish this task?
ligase
which of the following is used to move lipids around the blood stream?
lipoproteins
the ____ stores glucose as glycogen and converts excess glucose to _____
liver; fatty acids
On a transition state diagram for a one-step very spontaneous reaction a large peak (high deltaG) would imply a ______ rate for the reaction
low
inside a nerve cell at rest, [Na+] is _____ and [K+] _____ relative to the concentrations seen outside the cell
low; high
degradation of proteins within a cell can occur within the ____ or by use of ____
lysosome; a proteasome
which of the following molecules is in the most reduced state?
methane
Which of these amino acid groups would not make a good nucleophilic catalyst?
methyl
is this molecule more oxidized or more reduced than glyceraldehyde-3-phosphate
more oxidized
which of the following is correct regarding metabolic pathways?
none of the above are correct
which of the following is a ligand of the 2-adrenergic receptor?
norepinephrine
which class of biological molecule is not a major metabolic fuel?
nucleic acids
unlike proteins and oligonucleotides, polysaccharides _____
often have branched structures
the signal molecule shown below would need a receptor that is located
on the cell surface, because the signal is a hydrophilic molecule
which of the following best describes the relationship between the following molecules?
one is a D sugar, one is an L sugar
the correct order of events during nerve cell signaling is
opening Na+ channels, depolarization, opening K+ channels, repolarization
Metal ion cofactors offer various _______ states that allow enzymes to accomplished oxidation reduction reactions.
oxidation
Metal ion cofactors offer various ________ states that allow enzyme,es to accomplished oxidation reduction reactions
oxidation
a reaction that results in the loss of electrons from a molcule is a ___
oxidation
Enzyme X catalyzes the addition of a hydroxyl group to substrate Y. In the process a metal cofactor is reduced and then reoxidized. What class of enzyme is X?
oxiodoreductase
the movement of glucose into a cell when blood sugar is high is accomplished by____. The movement of K+ ions against its concentration gradient is accomplished by______
passive transport; active transport
which of the following is a heteropolysaccharide?
pectin
in a protein, amino acids are linked by
peptide bonds
bacterial cells are surrounded by a cell wall made from
peptidoglycan
which of the following has the most spontaneous hydrolysis?
phosphoenolpyruvate
plants are considered ____
photoautotrophs
In a G protein signaling pathway, what would happen if phosphodiesterase were inactivated?
protein kinase A would remain active
in a ____, the carbohydrate is responsible for most of the mass; in a ____ the protein is responsible for most of the mass
proteoglycan; glycoprotein
A pH versus rate curve with an inflection point at pH~4 suggests the involvement of a(n) ________ in the catalytic step.
proton transfer with a pK close to 4
choose the true statement
receptor tyrosine kinases undergo autophosphorylation
any sugar that has a free aldehyde group is call a
reducing sugar
cAMP binds to the ____ subunits of protein kinase A allowing the tetramer to dissociate into _____
regulatory subunits; two active monomers and an inactive dimer
A small molecule produced inside a cell in response to a hormone binding to its receptor is called a(n) _____.
second messenger
in G protein signal transduction systems, what role does cAMP play?
second messenger
choose the most accurate statement about vitamins
some vitamins are the precursors of enzyme cofactors
which of the following disaccharides has both anomeric carbons involved in the glycosidic bond?
sucrose
what is a transporter that moves two different molecules or ions in the same direction?
symporter
Transport of glucose from the intestine into the intestinal cells is accomplished by a _____. This is an example of ______
symporter; secondary active transport
the oligosaccharide groups of glycoproteins
tend to be located outside the cell
a primary active transport protein moves a solute in only on direction because
the ATP -> ADP reaction is not reversible
ion transport in the Na, K-ATPase is driven by
the ATP hydrolysis reaction
at equilibrium in solution, D-glucose consists of a mixture of its anomers. Which statement most accurately describes the solution?
the beta-anomer predominates over the alpha-anomer by a ratio of approximately 2:1
choose the true statement about metabolic pathways
the products of one pathway are substrates for another pathway
in a spontaneous reaction
the reactants have higher free energy than the products
the main difference between starch and cellulose is that
the residues are connected differently in starch and cellulose
the main difference between active and passive transport systems is
the source of free energy that drives the transport
which property of proteoglycans allows them to function as shock absorbers?
their hydrophilicity
O-linked oligosaccharides are commonly attached to the oxygen of ____
threonine
an ion will spontaneously move
to an area where it is less concentrated
_____ metals are the most common metallic enzyme cofactors
transition
the monomeric products of digestive polymers are mostly
transported to the liver
digestion of food by mammals converts ____ into ____ which can be absorbed from the intestines
triacylglycerols; fatty acids
an allosteric regulator
triggers shape changes in the protein
all known porins are _____ proteins composed of _______
trimeric; beta barrels
which of the following is a lipid-soluble electron carrier in its reduced state?
ubiquinol
the GLUT transporter changes conformation
when glucose binds and when glucose dissociates
lactose can be described as
β-galactose (1->4) glucose
