UWorld Biochemistry Flashcards
What structural feature in phospholipid membrane would result in the greatest increase in cell membrane fluidity?
A.cis bond
B.trans bond
C.Carboxyl group o
D.Phosphate groups of phospholipids
A.cis bond
Fatty acids with no carbon-carbon double bonds are described as saturated because each carbon atom has the maximum number of hydrogen atoms possible. In contrast, an unsaturated fatty acid contains one (monounsaturated) or multiple (polyunsaturated) double bonds that may be in either the cis (Z) or the trans (E) configuration.
Phospholipids in the cell membrane could be separated experimentally according to their differences in:
charge.
mass.
solubility.
A.I only
B.III only
C.I and II only
D.I, II, and III
D.I, II, and III
The charge on phospholipids is determined by the structure of the polar heads. The phosphate component of the head group may be linked to various chemical groups. Positively charged groups such as choline or ethanolamine neutralize the negative charge of the phosphate, whereas neutral groups such as serine, inositol, or glycerol allow the head to maintain a net negative charge. Neutral and negative phospholipids may be separated by high-performance liquid chromatography
The glycogen branching enzyme forms a glycosidic bond between carbon 1 on the incoming glucose monomer and which of the following?
A.Carbon 3 on a glucose unit of the growing chain
B.Carbon 4 on a glucose unit of the growing chain
C.Carbon 5 on a glucose unit of the growing chain
D.Carbon 6 on a glucose unit of the growing chain
D.Carbon 6 on a glucose unit of the growing chain
When the cell is in need of glucose, glycogenolysis is upregulated, beginning with the activation of glycogen phosphorylase. Glycogen phosphorylase catalyzes the production of which of the following molecules?
A.UDP-glucose
B.UDP-galactose
C.Glucose 1-phosphate
D.Glucose 6-phosphate
C.Glucose 1-phosphate
POMT can use activated D-mannose, but not D-glucose, as a substrate. D-glucose and D-mannose are:
A.constitutional isomers.
B.enantiomers.
C.epimers.
D.anomers.
C.epimers.
O-linked D-mannose can form a glycosidic bond with any sugar that has a free anomeric carbon. Therefore it could theoretically form a glycosidic bond with all of the following sugars EXCEPT:
A.galactose.
B.ribose.
C.lactose.
D.sucrose.
D.sucrose. fructose + glucose
Klenow fragment (KF) polymerase, which has 3′-5′ but not 5′-3′ exonuclease activity
The Klenow fragment used in the experiment would be able to perform which of the following repair processes?
A.Excision of thymine dimers at the 5′ end of the growing strand
B.Replacement of nucleotides at the 3′ end of the growing strand
C.Correction of mismatched nucleotides in the middle of a completed strand
D.Removal of damaged bases from the middle of the template strand
B.Replacement of nucleotides at the 3′ end of the growing strand
DNA Poly reads in 5-3
If lower phospholipid levels in ME patients are due to inhibition of fatty acid synthesis, researchers would most likely observe which of the following?
A.Increased cytosolic NADPH.
B.Decreased mitochondrial acetyl-CoA.
C.Decreased mitochondrial fumarate.
D.Increased cytosolic lysine.
A.Increased cytosolic NADPH.
Which series depicts the order in which the precursors of steroid hormones are synthesized?
A.Isoprene → monoterpene → squalene → cholesterol
B.Cholesterol → isoprene → monoterpene → squalene
C.Monoterpene → isoprene → squalene → cholesterol
D.Isoprene → cholesterol → monoterpene → squalene
A.Isoprene → monoterpene → squalene → cholesterol
3 6 membered rings and 1 5 membered ring
During anaerobic exercise, the Cori cycle connects which two metabolic pathways?
A.Glycogenolysis and the citric acid cycle
B.The urea cycle and gluconeogenesis
C.The pentose phosphate pathway and glycogenesis
D.Gluconeogenesis and glycolysis
D.Gluconeogenesis and glycolysis
cori cycle is lactic acid cycle
Escherichia coli bacteria containing only 15N-labeled DNA were grown in media containing only 14N nucleotides. What percentage of double helices would be composed of one 15N strand and one 14N strand after three generations?
A.12.5%
B.25%
C.50%
D.100%
B.25%
Gen 1: 100% 15N
Gen 2: 50% 15N and 50% 14N
Gen 3: 25%15N and 75% 14N
Prior to inserting the STR sequences into K-ras DNA, the researchers perform MCA analysis using only the double-stranded STR sequences. Which sequence from Table 1 would have the fastest reannealing time in this experiment?
A.Sequence 1
B.Sequence 2
C.Sequence 3
D.Sequence 4
C.Sequence 3
An increase in which of the following would lead to decreased ethanol production in yeast?
A.Partial pressure of oxygen
B.Pyruvate kinase activity
C.Concentration of glucose
D.Krebs cycle inhibitors
A.Partial pressure of oxygen
ANAEROBIC
The electron transport chain results in the generation of:
A.protons, which produce an electrochemical gradient that drives phosphorylation of ADP.
B.protons, which reduce NAD+ in a coupling reaction that drives phosphorylation of ADP.
C.electrons, which produce an electrical gradient that drives phosphorylation of ADP.
D.electrons, which oxidize NADH in a coupling reaction that drives phosphorylation of ADP.
A.protons, which produce an electrochemical gradient that drives phosphorylation of ADP.
After galactose is released from GC and linearized, it contains all of the following functional groups EXCEPT:
A.an aldehyde.
B.a primary alcohol.
C.a ketone.
D.a secondary alcohol.
C.a ketone.
GC can be classified as:
A.a glycerophospholipid.
B.a phosphosphingolipid.
C.a glycosphingolipid.
D.a phosphoglycolipid.
C.a glycosphingolipid.
The amino acid methionine can be converted to succinyl-CoA to enter the citric acid cycle. How many NADH molecules can be produced by each methionine molecule that enters the citric acid cycle by this pathway?
A.1
B.2
C.3
D.4
A.1
Fatty acid synthesis proceeds according to the following reaction:
where n is a positive integer. Based on this, how many ADP and NADP+molecules will be produced during synthesis of a 16-carbon fatty acid?
A.7 ADP molecules and 14 NADP+ molecules
B.14 ADP molecules and 28 NADP+ molecules
C.8 ADP molecules and 15 NADP+ molecules
D.16 ADP molecules and 32 NADP+ molecules
A.7 ADP molecules and 14 NADP+ molecules
Von Gierke disease is a rare autosomal recessive disorder that arises from inactivating mutations in the liver enzyme glucose 6-phosphatase (G6Pase).
Which of the following processes would be directly impaired in von Gierke disease?
Glycogenolysis
Gluconeogenesis
Pentose phosphate pathway
A.I and II only
B.I and III only
C.II and III only
D.I, II, and III
A.I and II only
Pentose uses G6P
Inactivation of which enzyme is most likely to result in physiological effects similar to hypoglycemia?
A.Glucose 6-phosphate dehydrogenase
B.Pyruvate decarboxylase
C.Phosphoenolpyruvate carboxykinase
D.Acyl-CoA dehydrogenase
C.Phosphoenolpyruvate carboxykinase
Group A mice (giving G6Pase inhibitor), but not group B mice, could use which of the following dietary supplements to help maintain blood glucose levels after day 10?
A.Cholesterol
B.Alanine
C.Acetyl-CoA
D.Palmitic acid
B.Alanine
Which of the following steps in the citric acid cycle does NOT produce reduced electron carriers?
A.Conversion of isocitrate to α-ketoglutarate
B.Conversion of α-ketoglutarate to succinyl-CoA
C.Conversion of succinyl-CoA to succinate
D.Conversion of succinate to fumarate
C.Conversion of succinyl-CoA to succinate
In the electron transport chain, four electrons are required to fully reduce one O2molecule to two H2O molecules. Given this information, how many NADH molecules are required?
A.1
B.2
C.3
D.4
B.2
NADH is a 2 electron carrier (FMN in ETC)
FADH2 is a 1 electron carrier
D
Anabolism is the synthesis of complex biological molecules from simpler constituents, and it requires energy input. The energy needed for anabolic processes is generally provided by cleaving high-energy phosphodiester bondsin nucleotide triphosphates (NTPs) such as ATP, GTP, or UTP.
Under physiological conditions, peptide bond formation and degradation both require enzymes, but only formation requires coupling to GTP hydrolysis. Based on this information, peptide bonds under physiological conditions are:
A.both thermodynamically and kinetically stable.
B.thermodynamically unstable but kinetically stable.
C.thermodynamically stable but kinetically unstable.
D.both thermodynamically and kinetically unstable.
B.thermodynamically unstable but kinetically stable.
Kinetic stability due to enzyme
Energy input is required (GTP hydrolysis) (dehydration/condensation rxn)
Thermodynamics describes the energy difference between products and reactants (ΔG), and dictates whether a reaction requires energy input
Kinetics describes the energy required to initiate a reaction (activation energy), and determines how quickly a reaction proceeds.
If a reaction has a positive ΔG (as in anabolic processes such as protein synthesis), the product is thermodynamically unstable and the reaction requires energy input. In biological settings, this energy input is usually derived from the hydrolysis of ATP or GTP. The reverse reaction is thermodynamically favorable (negative ΔG) and requires no energy input; however, this does not mean the reverse reaction will proceed quickly
The pKa for the side chain of cysteine is 8.4. What is the ratio of protonated side chain (–SH) to deprotonated side chain (–S−) in a solution of cysteine at physiological pH of 7.4?
A.1:100
B.1:10
C.10:1
D.100:1
C.10:1
Which amino acid substitution would result in the greatest change in the net charge of a polypeptide at pH 7?
A.Glu to Lys
B.Asp to Ala
C.Lys to Arg
D.Arg to Ser
A.Glu to Lys
difference in charge is final - initial
- to + Net: 1- (-1) = 2
During protein folding, which of the following interactions help stabilize secondary, tertiary, or quaternary structure?
Hydrogen bonds
Ionic bonds
van der Waals forces
Amide bonds
A.I and II only
B.III and IV only
C.I, II, and III only
D.I, III, and IV only
C.I, II, and III only
amide bonds are primary structure
reflectins aggregate in response to acetylcholine (ACh),
In the absence of ACh, which of the following bond types best characterizes the structure of reflectins?
A.Hydrogen bonds between backbone carbonyls and amides
B.Covalent bonds between sulfur atoms
C.Hydrogen bonds between R group alcohols
D.Covalent bonds between carbon and nitrogen atoms
D.Covalent bonds between carbon and nitrogen atoms
Secondary structure is the set of local folds within a polypeptide and usually consists of α-helicesand β-sheets. These structures are primarily stabilized by hydrogen bonds between the carbonyls and amides of the polypeptide backbone
Based on information in the passage, NMR data indicated electrostatic interactions involving all of the following amino acids EXCEPT:
A.lysine.
B.aspartate.
C.arginine.
D.glutamate.
D.glutamate.
Which step is NOT required to generate the western blot shown in Figure 3?
A.Gel electrophoresis of BAZ2B proteins recovered from affinity columns
B.Transfer of proteins to a protein-binding membrane
C.Blocking of nonspecific antibody binding
D.Incubation with antibodies against histone subunit H3
D.Incubation with antibodies against histone subunit H3
In this case, the protein of interest is BAZ2B. Therefore, the primary antibodies must be specific to BAZ2B, not H3, to detect the amount of BAZ2B that was bound by the affinity column.
A western blot is a technique used to detect the presence specific proteins. It is performed by gel electrophoresis of the protein of interest, followed by transfer to a protein-binding membrane (eg, nitrocellulose) and incubation with antibodies specific to the protein of interest. The primary antibody or a labeled secondary antibody is then detected by fluorescence or chemiluminescence.
Thermolysin is a protease that can cleave peptides at the N-terminal side of branched alkyl residues. Which of the following peptides has the most thermolysin cleavage sites?
A.HQICSVGPKLNT
B.DNKGSTVYQRWC
C.GHPTLDQIWCER
D.RTHCQGYNESDK
A.HQICSVGPKLNT
Proline differs from the other standard amino acids in that only the former:
A.has a negative charge in its side chain.
B.forms peptide bonds that are planar.
C.contains a secondary amine in its backbone.
D.is commonly found in flexible loop regions of folded proteins
C.contains a secondary amine in its backbone.
Enzymes
Enzyme 1 only
Sigmoidal curves = cooperative binding of multiple active sites
For enzymes with a SINGLE active site, the reaction increases steadily –> hyperbolic curve (enzyme 2)
Explain how enzymes are mostly zero or first order reactions.
zero order = the enzyme isnt affected by the amount of substrate concentration (Noncompetitive inhibitors don’t need the substrate to bind unlike uncompetitive inhibitors). the rate is only dependent on the enzyme concentration and activity.
first order = depends on the substrate concentration and occur when the Km is greater than the substrate concentration
Size exclusion
Peptide 3
Q7
A
Q8
Q9
D
Q10
C
Q11
B
Q14
B
Q17
D
Its a mixed inhibitor
D
Q20
B
Q22
C
HILL Coefficient indicates cooperativity –> sigmoidal curve.
Q23
A
What does Comp 1 do to the enzyme?
Increased turnover rate
The vmax increased (vmax=kcat)
Q35
B
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For two carbohydrates to be considered anomers, what must be true?
A.They need to have different stereochemistry solely at the anomeric carbon, which is the atom that serves as the carbonyl carbon in the molecule’s straight-chain form.
B.They need to have different stereochemistry solely at the anomeric carbon, which is the atom that serves as the alpha carbon in the molecule’s straight-chain form.
C.They need to have different stereochemistry at only one stereocenter, but it can be any carbon on the molecule.
D.They need to have different connectivity or bonding between atoms.
A.They need to have different stereochemistry solely at the anomeric carbon, which is the atom that serves as the carbonyl carbon in the molecule’s straight-chain form.
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