Logo
memo(formerly PDF2Anki)
What enzyme catalyzes the decarboxylation of orotidylate to form uridylate (UMP)? A) Dihydroorotase B) Orotidylate decarboxylase C) Thymidylate synthase D) Aspartate transcarbamoylase E) Aminoacyl tRNA synthetase
B) Orotidylate decarboxylase Explanation: Orotidylate decarboxylase is the enzyme responsible for catalyzing the decarboxylation of orotidylate to uridylate (UMP), which is a key pyrimidine nucleotide precursor for RNA.
The deficiency in which vitamin can cause neural tube defects during development? A) Thiamine (B1) B) Riboflavin (B2) C) Niacin (B3) D) Pantothenate (B5) E) Folic acid (B9)
E) Folic acid (B9) Explanation: A deficiency in folic acid (B9) during pregnancy is well-documented to cause neural tube defects, making it crucial for fetal development.
1/59
p.10
Biosynthesis Pathways of Nucleotides

What enzyme catalyzes the decarboxylation of orotidylate to form uridylate (UMP)?
A) Dihydroorotase
B) Orotidylate decarboxylase
C) Thymidylate synthase
D) Aspartate transcarbamoylase
E) Aminoacyl tRNA synthetase

B) Orotidylate decarboxylase
Explanation: Orotidylate decarboxylase is the enzyme responsible for catalyzing the decarboxylation of orotidylate to uridylate (UMP), which is a key pyrimidine nucleotide precursor for RNA.

p.5
Vitamin Functions and Deficiencies

The deficiency in which vitamin can cause neural tube defects during development?
A) Thiamine (B1)
B) Riboflavin (B2)
C) Niacin (B3)
D) Pantothenate (B5)
E) Folic acid (B9)

E) Folic acid (B9)
Explanation: A deficiency in folic acid (B9) during pregnancy is well-documented to cause neural tube defects, making it crucial for fetal development.

p.10
Gene Expression and Transcription Processes

What is the sequence of the mRNA produced from the given DNA sequence 3’…CGCCGCTGCGCG…5’?
A) CGCGCUCGCCGC
B) GCGGCGACGCGC
C) GCGCGUCGCCGC
D) GCGCGTGCGGCG
E) GCGGCGUCGCGC

B) GCGGCGACGCGC
Explanation: The mRNA sequence is complementary to the DNA template strand and is synthesized in the 5' to 3' direction, resulting in the sequence GCGGCGACGCGC.

p.7
Biosynthesis Pathways of Nucleotides

What process is affected by the defective enzyme in severe combined immunodeficiency?
A) Formation of ATP
B) Conversion of adenosine to inosine
C) Conversion of xanthine to xanthylate
D) Synthesis of IMP
E) Conversion of ribonucleotides to deoxyribonucleotides

B) Conversion of adenosine to inosine
Explanation: The defective enzyme in severe combined immunodeficiency is crucial for the conversion of adenosine to inosine, which is vital for lymphocyte development and function.

p.3
Enzyme Mechanisms and Kinetics

Which statement about the active site of an enzyme is NOT TRUE?
A) Binds substrate by means of the 'lock-and-key' model
B) Is three-dimensional and is formed by groups from different parts of the protein structure
C) Typically occupies a small portion of the overall enzyme structure
D) Is usually found in the cleft or crevice within the protein
E) Binds substrate via weak, non-covalent forces of attraction

A) Binds substrate by means of the 'lock-and-key' model
Explanation: While the 'lock-and-key' model is a common analogy, it is not entirely accurate as it oversimplifies the dynamic nature of enzyme-substrate interactions, which can also involve induced fit.

p.3
Enzyme Mechanisms and Kinetics

To which class would the enzyme that catalyzes the reaction shown in the box below belong?
A) The transferases
B) The isomerases
C) The dehydrogenases
D) The hydrolases
E) The oxidoreductases

A) The transferases
Explanation: Transferases are enzymes that catalyze the transfer of functional groups from one molecule to another, which is likely the case for the reaction in question.

p.5
Enzyme Mechanisms and Kinetics

Phosphofructokinase belongs to which enzyme class?
A) The Oxidoreductases
B) The Transferases
C) The Hydrolases
D) The Lyases
E) The Isomerases

B) The Transferases
Explanation: Phosphofructokinase is classified as a transferase because it catalyzes the transfer of a phosphate group from ATP to fructose-6-phosphate, which is characteristic of this enzyme class.

p.5
Enzyme Mechanisms and Kinetics

Which of the following statements is TRUE regarding the Michaelis constant Km for an enzyme that obeys Michaelis-Menten kinetics?
A) Km is the substrate concentration that gives an initial velocity equal to Vmax
B) Km is equal to the rate constant for the formation of the E-S complex divided by the sum of the rate constants for the breakdown of the E-S complex
C) Km is an equilibrium constant for the dissociation of the substrate S from the enzyme E only when k1 << k2
D) Km is equal to the negative reciprocal of the x-intercept in the Lineweaver-Burk plot
E) Km is a measure of how efficiently an enzyme-catalyzed reaction can occur

D) Km is equal to the negative reciprocal of the x-intercept in the Lineweaver-Burk plot
Explanation: In the Lineweaver-Burk plot, the x-intercept is related to Km, making this statement true in the context of enzyme kinetics.

p.3
Vitamin Functions and Deficiencies

What is the vitamin whose structure is shown below?
A) Ascorbic acid
B) Pantothenate
C) Niacin
D) Riboflavin
E) Pyridoxine

D) Riboflavin
Explanation: The structure in question corresponds to Riboflavin, which is a vitamin important for energy production and metabolism.

p.2
DNA and RNA Structure and Function

What is the primary reason for the strong affinity between DNA strands in the double helix?
A) There is a cooperative effect of the many hydrogen bonds that hold adjacent base pairs together
B) There is cooperative binding of transcription factors that ensure the stability of the DNA molecule
C) The antiparallel nature of the DNA molecule conforms to the structure of the B-DNA structure
D) There is covalent binding of each base to its cognate partner, according to Watson-Crick modeling
E) The sugar-phosphate backbone utilizes ATP in the formation of the 3’-5’ phosphodiester bond

A) There is a cooperative effect of the many hydrogen bonds that hold adjacent base pairs together
Explanation: The tremendous affinity of DNA strands for each other is primarily due to the cooperative effect of multiple hydrogen bonds formed between adjacent base pairs, which stabilizes the double helix structure.

p.12
Gene Expression and Transcription Processes

Which of the following is TRUE for gene expression in both prokaryotes and eukaryotes?
A) After transcription, a 3’ poly A tail and a 5’ cap are added to mRNA
B) Mature mRNA is always colinear to the gene from which it was copied
C) RNA polymerase may bind at a promoter region upstream from the gene
D) Translation of mRNA can initiate before transcription is complete
E) Messenger RNA (mRNA) is synthesized in the 3’ to 5’ direction

C) RNA polymerase may bind at a promoter region upstream from the gene
Explanation: In both prokaryotes and eukaryotes, RNA polymerase binds to a promoter region upstream of the gene to initiate transcription, making this statement true.

p.12
DNA and RNA Structure and Function

In the illustration of base excision repair, at what step does DNA ligase function?
A) a
B) b
C) c
D) d
E) e

E) e
Explanation: DNA ligase functions at the final step of base excision repair, where it seals the nicks in the DNA backbone after the repair process is complete.

p.6
Enzyme Mechanisms and Kinetics

Which of the following algebraic equations describes a rectangular hyperbolic plot of Vₒ versus [S] for an enzyme-catalyzed reaction?
A) Vₒ = (Vmax + [S])/(Km x [S])
B) Vₒ = (Vmax x [S])/(Km + [S])
C) Vmax = Kcat x [E]T
D) None of the above
E) Vₒ = Km + [S]

B) Vₒ = (Vmax x [S])/(Km + [S])
Explanation: This equation represents the Michaelis-Menten kinetics, which describes the relationship between the reaction velocity (Vₒ) and substrate concentration ([S]) in enzyme-catalyzed reactions.

p.7
Suicide Inhibitors and Enzyme Regulation

Which agent acts as a suicide inhibitor of its target enzyme?
A) Ribonucleotide reductase
B) Allopurinol
C) FAD
D) Xanthine oxidase
E) PRPP

B) Allopurinol
Explanation: Allopurinol is known to act as a suicide inhibitor for xanthine oxidase, which is involved in purine metabolism, thereby reducing uric acid production.

p.3
Biosynthesis Pathways of Nucleotides

What is the structure shown in the attached figure?
A) Oxidized Nicotinamide Adenine Dinucleotide (NAD+)
B) Reduced Nicotinamide Adenine Dinucleotide (NADH)
C) Oxidized Flavin Adenine Dinucleotide (FAD)
D) Reduced Flavin Adenine Dinucleotide (FADH2)
E) Adenosine Triphosphate (ATP)

A) Oxidized Nicotinamide Adenine Dinucleotide (NAD+)
Explanation: The structure corresponds to NAD+, which plays a crucial role in redox reactions and energy metabolism.

p.2
Enzyme Mechanisms and Kinetics

What occurs in the step of the catalytic cycle of chymotrypsin described in the attached figure?
A) A peptide substrate is binding in the active site
B) A tetrahedral intermediate is collapsing to form P1, the amine-containing peptide fragment, and an acyl-enzyme intermediate
C) Water is binding in the active site
D) With the help of histidine acting as a general base catalyst, water is attacking the carbonyl of the acyl-enzyme intermediate and the tetrahedral intermediate is forming
E) A tetrahedral intermediate is collapsing to form P2, the carboxylic acid product, and the catalytic triad is being regenerated

B) A tetrahedral intermediate is collapsing to form P1, the amine-containing peptide fragment, and an acyl-enzyme intermediate
Explanation: In this step of the catalytic cycle of chymotrypsin, the tetrahedral intermediate collapses, resulting in the formation of P1, which is the amine-containing peptide fragment, along with the acyl-enzyme intermediate.

p.7
Biosynthesis Pathways of Nucleotides

Which of the following can inhibit purine nucleotide biosynthesis?
A) GTP
B) UMP
C) ATP
D) IDP
E) AMP

E) AMP
Explanation: AMP acts as a feedback inhibitor in purine nucleotide biosynthesis, regulating the pathway to maintain balance in nucleotide levels.

p.7
Biosynthesis Pathways of Nucleotides

Which three amino acids donate amine groups for purine biosynthesis?
A) Glycine, glutamine, aspartate
B) Glycine, alanine, aspartate
C) Lysine, glutamine, aspartate
D) Lysine, glutamate, asparagine
E) Lysine, glycine, asparagine

A) Glycine, glutamine, aspartate
Explanation: Glycine, glutamine, and aspartate are the three amino acids that provide amine groups necessary for the biosynthesis of purines.

p.12
Mutations and Their Effects on Protein Synthesis

Lesch-Nyhan syndrome is due to defective which of the following?
A) Hypoxanthine guanine phosphoribosyl transferase
B) De novo synthesis of purines
C) Xanthine oxidase
D) PRPP synthetase
E) Carbamoylphosphate synthetase

A) Hypoxanthine guanine phosphoribosyl transferase
Explanation: Lesch-Nyhan syndrome is caused by a deficiency in hypoxanthine guanine phosphoribosyl transferase, leading to elevated uric acid levels and associated symptoms.

p.13
Mutations and Their Effects on Protein Synthesis

What is the most direct explanation for the decrease in crackhead protein due to a point mutation?
A) There is deficiency in the guanosine cap on the 5’ end of the crackhead mRNA containing the intron.
B) The mutation affects an adenosine residue within the crackhead mRNA intron
C) The mutation is found in the TATA box region of the crkh gene
D) The mutation is located at the 5’ or 3’ end of the splice junction of the crackhead mRNA intron
E) The mutation affects a guanine residue within the crackhead mRNA intron

B) The mutation affects an adenosine residue within the crackhead mRNA intron
Explanation: The mutation disrupting the Group II splicing event indicates that it affects an adenosine residue, which is crucial for lariat formation during splicing, leading to decreased levels of the crackhead protein.

p.8
Purine and Pyrimidine Nucleotide Structures

What enzyme is deficient in Lesch-Nyhan Syndrome?
A) PRPP synthetase
B) Adenosine deaminase
C) HGPRT
D) APRT
E) Xanthine oxidase

C) HGPRT
Explanation: Lesch-Nyhan Syndrome is specifically associated with a deficiency of the enzyme Hypoxanthine-guanine phosphoribosyltransferase (HGPRT), which plays a crucial role in purine metabolism.

p.11
Gene Expression and Transcription Processes

Which option correctly identifies the functional roles of the anatomy of a eukaryotic gene promoter?
A) A=TFIID binding site; B=sigma 70 binding site; C=translation start site
B) A=GC/CAAT box; B=TFIID binding site; C=transcription start site
C) A=transcription start site; B=TFIID binding site; C=translation start site
D) A=sigma 70 binding site; B=Hogness box; C=transcription start site
E) A=GC/CAAT box; B=Pribnow box; C=transcription start site

B) A=GC/CAAT box; B=TFIID binding site; C=transcription start site
Explanation: This option accurately describes the roles of the elements in a eukaryotic gene promoter, where the GC/CAAT box is involved in transcription regulation.

p.10
cDNA Libraries and Molecular Cloning

Which is the correct sequence for constructing a genomic DNA library?
A) 1) isolate genomic DNA; 2) introduction of plasmids into bacteria; 3) cleave with restriction endonuclease; 4) insert DNA fragments into plasmids
B) 1) introduction of plasmids into bacteria; 2) insert DNA fragments into plasmids; 3) isolate genomic DNA; 4) cleave with restriction endonuclease; select resistant clones in bacteria
C) 1) isolate genomic DNA; 2) insert DNA fragments into plasmids; 3) cleave with restriction endonuclease; 4) introduction of plasmids into bacteria
D) 1) isolate genomic DNA; 2) cleave with restriction endonuclease; 3) insert DNA fragments into plasmids; 4) introduction of plasmids into bacteria
E) 1) cleave with restriction endonuclease; 2) insert DNA fragments into plasmids; 3) isolate genomic DNA; 4) introduction of plasmids into bacteria

D) 1) isolate genomic DNA; 2) cleave with restriction endonuclease; 3) insert DNA fragments into plasmids; 4) introduction of plasmids into bacteria
Explanation: The correct order for constructing a genomic DNA library involves isolating genomic DNA, cleaving it with restriction endonucleases, inserting the fragments into plasmids, and then introducing those plasmids into bacteria.

p.3
Enzyme Mechanisms and Kinetics

Which statement about enzymes is NOT TRUE?
A) Cannot shift the position of the equilibrium of a reaction
B) Speed up reactions in their forward and reverse directions to equal extents
C) Are highly specific for their substrates
D) Can make a reaction occur more spontaneously
E) Lower the free energy of activation for the reactions they catalyze

D) Can make a reaction occur more spontaneously
Explanation: Enzymes do not change the spontaneity of a reaction; they only lower the activation energy required for the reaction to proceed.

p.12
cDNA Libraries and Molecular Cloning

Which of the following statements about cDNAs and cDNA libraries is INCORRECT?
A) They can provide researchers and clinicians with a tissue-specific profile of gene expression
B) They can be treated with restriction enzymes and cloned into plasmid vectors
C) They can provide researchers and clinicians with a profile of normal vs. disease status of a given tissue or organ
D) They can provide tools to express a given gene (i.e., protein expression) for in vitro/in vivo therapeutics and characterization.
E) They are a snapshot of the genomic DNA, because cDNAs contain both introns and exons.

E) They are a snapshot of the genomic DNA, because cDNAs contain both introns and exons.
Explanation: cDNAs are synthesized from mature mRNA and do not contain introns, making this statement incorrect.

p.9
Biosynthesis Pathways of Nucleotides

Regulating the levels of PRPP is necessary to prevent:
A) Pellagra
B) Gout
C) Cancer
D) Tryptophan deficiency
E) Lesch Nyhan syndrome

E) Lesch Nyhan syndrome
Explanation: Lesch Nyhan syndrome is caused by a deficiency in the enzyme HGPRT, which is involved in the purine salvage pathway, making regulation of PRPP crucial.

p.9
Gene Expression and Transcription Processes

Which of the following sequences correctly represents a growing polypeptide sequence?
A) +H3N-lys-arg-arg-his-trp-asn-met-coo(-)
B) 5-AATAACGCGAGCTGACGTACGTCT-3’
C) 5’-Lys-arg-his-trp-asn-met-asn-coo-3’
D) 5’-AUGTTCTGACGTGCACTCAAAAAA-3’
E) OOC-Lys-arg-arg-his-trp-asn-met-arg-NH3+

A) +H3N-lys-arg-arg-his-trp-asn-met-coo(-)
Explanation: This sequence correctly represents a growing polypeptide chain, starting with the amino group and ending with the carboxyl group.

p.4
Enzyme Mechanisms and Kinetics

The enzyme aspartate transcarbamoylase is heterotropically activated by which compound listed below?
A) Aspartate
B) Adenosine triphosphate, ATP
C) Guanosine triphosphate, GTP
D) Cytidine triphosphate, CTP
E) Carbamoyl phosphate

B) Adenosine triphosphate, ATP
Explanation: Aspartate transcarbamoylase is activated by ATP, which serves as a heterotropic effector, enhancing the enzyme's activity.

p.7
Biosynthesis Pathways of Nucleotides

What is required for the conversion of inosine monophosphate (IMP) to GMP?
A) To AMP is inhibited by GMP
B) To AMP requires UMP
C) To GMP requires GMP Kinase
D) To GMP requires Glutamine
E) To GDP requires ribonucleotide reductase

D) To GMP requires Glutamine
Explanation: The conversion of IMP to GMP requires glutamine as a nitrogen donor, which is essential for the synthesis of guanine nucleotides.

p.13
Gene Expression and Transcription Processes

Which process below possesses the least degree of correctivity or fidelity?
A) Restriction endonuclease activity
B) RNA synthesis
C) DNA replication
D) mRNA translation
E) Aminoacyl activation

B) RNA synthesis
Explanation: RNA synthesis has the least degree of fidelity compared to other processes listed, as RNA polymerases do not have proofreading capabilities, leading to a higher rate of errors.

p.13
Vitamin Functions and Deficiencies

NAD, FAD, and FMN are all examples of:
A) Nucleotide salvage
B) Tryptophan biosynthesis
C) Nucleotide coenzymes
D) De novo pathways of biosynthesis
E) Nicotinate nucleotides

C) Nucleotide coenzymes
Explanation: NAD, FAD, and FMN are classified as nucleotide coenzymes, which play essential roles in various biochemical reactions as electron carriers.

p.12
cDNA Libraries and Molecular Cloning

True or False: A cDNA library will reflect identical quantitative expression of mammalian genomic DNA between tissues and organs, because the blueprint remains unchanged.
A) true
B) false

B) false
Explanation: A cDNA library does not reflect identical quantitative expression across different tissues and organs, as gene expression can vary significantly depending on the tissue type and environmental factors.

p.11
Biosynthesis Pathways of Nucleotides

What is most likely missing from the in vitro DNA replication reaction?
A) dATP, dCTP, dTTP, dGTP
B) ATP, CTP, TTP, GTP
C) ATP, CTP, UTP, GTP
D) Orotate and inosinate
E) Reverse transcriptase and primase

A) dATP, dCTP, dTTP, dGTP
Explanation: The missing components for DNA replication are the deoxynucleotide triphosphates (dNTPs), which are essential for synthesizing new DNA strands.

p.8
Gene Expression and Transcription Processes

What is the correct order of events in the transcription process?
A) A=unwinding, B=template strand, C=nascent RNA, D=RNA polymerase, E=elongation site, F=rewinding, G=coding strand
B) A=unwinding, B=coding strand, C=nascent RNA, D=RNA Polymerase, E=template strand, F=rewinding, G=elongation site
C) A=rewinding, B=nascent RNA, C=template strand, D=RNA polymerase, E=coding strand, F=elongation site, G=unwinding
D) A=rewinding, B=template strand, C=elongation site, D=RNA Polymerase, E=coding strand, F=nascent RNA, G=unwinding
E) A=unwinding, B=nascent RNA, C=coding strand, D=RNA polymerase, E=template strand, F=elongation site, G=rewinding

C) A=rewinding, B=nascent RNA, C=template strand, D=RNA polymerase, E=coding strand, F=elongation site, G=unwinding
Explanation: The correct order of events in transcription involves unwinding the DNA, synthesizing nascent RNA, and involves the roles of RNA polymerase, template strand, and elongation site.

p.2
Enzyme Mechanisms and Kinetics

In the ordered sequential displacement kinetic mechanism of lactate dehydrogenase, what is the correct order of substrate and product species?
A) Pyruvate, NAD+, lactate, NADH
B) NAD+, pyruvate, lactate, NADH
C) Pyruvate, NADH, NAD+, lactate
D) NADH, pyruvate, lactate, NAD+
E) NADH, lactate, pyruvate, NAD+

B) NAD+, pyruvate, lactate, NADH
Explanation: The correct order of substrate and product species in the mechanism of lactate dehydrogenase is NAD+ followed by pyruvate, then lactate, and finally NADH, reflecting the sequential nature of the enzymatic reaction.

p.1
Purine and Pyrimidine Nucleotide Structures

Which list of nucleotides contains only Purines?
A) Xanthine, inosine, guanine
B) Cytidine, guanine, uracil
C) Uracil, thymidine, cytidine
D) Adenosine, guanine, cytidine
E) Thymidine, adenosine, cytidine

A) Xanthine, inosine, guanine
Explanation: Purines are a class of nucleotides that include adenine and guanine. Xanthine and inosine are also purines, making option A the correct choice.

p.6
Enzyme Mechanisms and Kinetics

The post-translational phosphorylation of an essential serine residue is important for the activation of which enzyme listed below?
A) Chymotrypsin
B) A heterotrimeric G-protein
C) Glycogen phosphorylase
D) Lactate dehydrogenase
E) Thrombin

C) Glycogen phosphorylase
Explanation: The phosphorylation of serine residues is crucial for the activation of glycogen phosphorylase, which plays a key role in glycogen metabolism.

p.6
Enzyme Mechanisms and Kinetics

Which of the following has units of reciprocal time and is known as the turnover number for an enzyme?
A) Km
B) Vmax
C) Kcat
D) Kcat/Km
E) Km/Kcat

C) Kcat
Explanation: Kcat, or the turnover number, is defined as the number of substrate molecules converted to product per enzyme molecule per unit time, and it has units of reciprocal time.

p.6
Biosynthesis Pathways of Nucleotides

Imidazole ring formation is consistently observed in what series of reactions?
A) Purine biosynthesis
B) Pyrimidine biosynthesis
C) Xanthine oxidase/uric acid conversion pathway
D) HGPRT salvage
E) IMP conversion to AMP or GMP

A) Purine biosynthesis
Explanation: The formation of the imidazole ring is a key step in purine biosynthesis, which is essential for the synthesis of nucleotides and nucleic acids.

p.5
Suicide Inhibitors and Enzyme Regulation

All but one of the statements below about the compound PALA are true. Which statement is NOT TRUE?
A) PALA stands for N-(phophonacetyl)-L-aspartate
B) PALA is a bisubstrate analog for the aspartate transcarbamoylase (ATCase)-catalyzed reaction
C) PALA cannot participate in the formation of product
D) PALA binds into the regulatory site on the “r” type subunit of ATCase
E) PALA is a competitive inhibitor with respect to the substrates of ATCase

D) PALA binds into the regulatory site on the “r” type subunit of ATCase
Explanation: PALA actually binds to the active site of ATCase, not the regulatory site, making this statement incorrect.

p.9
Purine and Pyrimidine Nucleotide Structures

Which statement best describes Xanthine?
A) It is a direct precursor to guanine
B) It is oxidized to form uric acid
C) It is oxidized to form hypoxanthine
D) It covalently binds to allopurinol
E) It is a substrate rather than a product of xanthine oxidase

B) It is oxidized to form uric acid
Explanation: Xanthine is a purine derivative that is oxidized to form uric acid, which is a key step in purine metabolism.

p.1
Purine and Pyrimidine Nucleotide Structures

Which of the following is a ribonucleoside?
A) Deoxyguanosine
B) Guanosine
C) Guanine
D) Guanylate
E) Thymidine

B) Guanosine
Explanation: Guanosine is a ribonucleoside composed of the sugar ribose and the base guanine, distinguishing it from the other options.

p.4
Vitamin Functions and Deficiencies

A modified form of which vitamin becomes part of the structure of the seven-transmembrane-segment protein rhodopsin, which is involved in the visual signaling cascade?
A) A
B) B2
C) C
D) D2
E) E

A) A
Explanation: Vitamin A, in its modified form as retinal, is integral to the structure of rhodopsin, a protein crucial for visual signaling in the retina.

p.4
Enzyme Mechanisms and Kinetics

Which of the following enzyme(s) obey(s) a Ping-Pong kinetic mechanism?
A) Aspartate aminotransferase
B) Chymotrypsin
C) Lactate dehydrogenase
D) Creatine kinase
E) Both A and B

E) Both A and B
Explanation: Both aspartate aminotransferase and chymotrypsin exhibit a Ping-Pong kinetic mechanism, where one substrate is released before the next substrate binds.

p.13
Biosynthesis Pathways of Nucleotides

Which of the following molecules serves as a substrate for ribonucleotide reductase?
A) AMP
B) dAMP
C) ADP
D) dADP
E) dATP

C) ADP
Explanation: ADP is a substrate for ribonucleotide reductase, which is involved in the conversion of ribonucleotides to deoxyribonucleotides, essential for DNA synthesis.

p.1
Suicide Inhibitors and Enzyme Regulation

One agent that acts as a suicide inhibitor of its target enzyme is
A) Ribonucleotide reductase
B) Allopurinol
C) FAD
D) Xanthine oxidase
E) PRPP

B) Allopurinol
Explanation: Allopurinol is known to act as a suicide inhibitor for xanthine oxidase, effectively inhibiting its activity by mimicking its substrate.

p.1
DNA and RNA Structure and Function

Identify the correct order of the molecules shown in the figure below:
A) A=DNA; B=RNA
B) A=RNA; B=DNA
C) A=Protein; B=DNA
D) A=RNA; B=Protein
E) A=DNA; B=Protein

A) A=DNA; B=RNA
Explanation: Without the figure, the context suggests that the correct identification of nucleic acids is essential, and typically DNA is represented before RNA in molecular biology.

p.8
Biosynthesis Pathways of Nucleotides

What molecule serves as the starting point for the de novo synthesis of purines?
A) Ribose-5-phosphate
B) Adenosine
C) AMP and GMP precursors
D) HGPRT
E) Xanthylate

A) Ribose-5-phosphate
Explanation: The de novo synthesis of purines begins with the addition of atoms to Ribose-5-phosphate, which is a key precursor in the purine biosynthesis pathway.

p.13
Vitamin Functions and Deficiencies

Spina bifida is one class of birth defects caused by:
A) Folic acid deficiency
B) Tryptophan deficiency
C) HGPRT deficiency
D) Xanthine oxidase increases
E) Increase in uric acid

A) Folic acid deficiency
Explanation: Spina bifida is primarily associated with a deficiency in folic acid during pregnancy, which is crucial for proper neural tube development.

p.9
Electrophoresis Techniques in Molecular Biology

Which statement is INCORRECT regarding electrophoresis of polynucleotides and proteins with respect to Southern blotting and Western blotting techniques?
A) Polynucleotides and proteins are separated on the basis of their size
B) Larger molecules will migrate faster to the bottom of the gel; smaller sizes will migrate at a slower rate
C) There is a net negative charge that is associated with each molecule
D) Migration is toward the positive pole
E) None of the above

B) Larger molecules will migrate faster to the bottom of the gel; smaller sizes will migrate at a slower rate
Explanation: This statement is incorrect because, in electrophoresis, smaller molecules migrate faster through the gel than larger ones.

p.9
Purine and Pyrimidine Nucleotide Structures

A pentose with a 5’ phosphate group, a 2’-OH group, and a 1’ pyrimidine group describes which of the following structures?
A) Guanosine
B) Cytidylate
C) Thymidylate
D) Cytosine
E) Thymidine

B) Cytidylate
Explanation: Cytidylate is a nucleotide that contains a pentose sugar with a 5’ phosphate group, a 2’-OH group, and a pyrimidine base (cytosine).

p.8
Purine and Pyrimidine Nucleotide Structures

Which of the following lists contains only purine nucleotides?
A) Xanthine, inosine, guanine
B) Cytidine, guanine, uracil
C) Uracil, thymidine, cytidine
D) Adenosine, guanine, cytidine
E) Hypoxanthine, cytidine, adenosine

A) Xanthine, inosine, guanine
Explanation: The correct list of purine nucleotides includes Xanthine, Inosine, and Guanine, as they are all classified as purines, while the other options contain pyrimidines.

p.11
Purine and Pyrimidine Nucleotide Structures

Which original atoms in the pyridine ring are mostly contributed by?
A) fumarate
B) N^10 – tetrahydrofolate
C) phosphoribosylamine
D) carbamoyl phosphate
E) aspartate

D) carbamoyl phosphate
Explanation: Carbamoyl phosphate is a key precursor that contributes to the formation of the pyridine ring, making it the correct choice.

p.1
Enzyme Mechanisms and Kinetics

The following reaction represents the action of what kind of enzyme? XDP + YTP → XTP + YDP
A) Nucleoside diphosphate kinase
B) Xanthine oxidase
C) Nucleoside monophosphate kinase
D) Nucleoside triphosphate kinase
E) Ribonucleotide reductase

A) Nucleoside diphosphate kinase
Explanation: The reaction involves the transfer of phosphate groups between nucleotides, which is characteristic of nucleoside diphosphate kinases.

p.1
Biosynthesis Pathways of Nucleotides

Imidazole ring formation is consistently observed in what series of reactions?
A) Purine biosynthesis
B) Pyrimidine biosynthesis
C) Xanthine oxidase/uric acid conversion pathway
D) HGPRT salvage
E) IMP conversion to AMP or GMP

A) Purine biosynthesis
Explanation: The formation of the imidazole ring is a key step in the biosynthesis of purines, making option A the correct answer.

p.6
Suicide Inhibitors and Enzyme Regulation

Which of the following compounds is a reactive substrate analog that becomes covalently attached to a glutamate residue in the active site of the enzyme it inhibits?
A) Methotrexate
B) PALA
C) 3-bromoacetal phosphate
D) Diisopropylphosphofluoridate, DIPF
E) Penicillin

C) 3-bromoacetal phosphate
Explanation: 3-bromoacetal phosphate is known to act as a reactive substrate analog that covalently modifies a glutamate residue in the active site of the enzyme, thereby inhibiting its activity.

p.11
cDNA Libraries and Molecular Cloning

Which steps correctly supply the necessary factors for the synthesis of double-stranded cDNA from an mRNA transcript?
A) Step 1: oligo T primer, dNTPs, reverse transcriptase; Step 2: NaOH; Step 3: Oligo primer, dNTPs, DNA polymerase
B) Step 1: poly A polymerase, dNTPs; Step 2: exonuclease, exinuclease; Step 3: primase, dNTPs, RNA polymerase
C) Step 1: oligo dA primer, NTPs, reverse transcriptase; Step 2: NaOH, exonuclease; Step 3: okazaki fragments, DNA polymerase
D) Step 1: oligo T primer, dNTPs, reverse transcriptase; Step 2: NaOH; Step 3: poly A polymerase
E) Step 1: oligo T primer, reverse transcriptase; Step 2: NaOH, exonuclease; Step 3: oligo A primer, DNA polymerase

A) Step 1: oligo T primer, dNTPs, reverse transcriptase; Step 2: NaOH; Step 3: Oligo primer, dNTPs, DNA polymerase
Explanation: This sequence correctly outlines the steps and reagents needed to synthesize double-stranded cDNA from mRNA, including the use of reverse transcriptase and DNA polymerase.

p.4
Enzyme Mechanisms and Kinetics

What does the attached figure describing the proteolytic activation of chymotrypsin indicate?
A) IIe-16 forms a salt-bridge with Asp-194 in the uncleaved zymogen structure
B) A conformational change occurs when chymotrypsinogen is proteolytically cleaved
C) The singly-cleaved π-chymotrypsin is inactive as a protease
D) Fully-processed α-chymotrypsin consists of two polypeptide chains
E) Proteolytic processing of chymotrypsin does not change the structure of the protein

B) A conformational change occurs when chymotrypsinogen is proteolytically cleaved
Explanation: The proteolytic cleavage of chymotrypsinogen leads to a significant conformational change that activates the enzyme, allowing it to function as a protease.

p.4
Enzyme Mechanisms and Kinetics

Which catalytic strategy does the enzyme chymotrypsin NOT employ in the reaction it catalyzes?
A) Covalent catalysis
B) Catalysis by approximation
C) General acid-base catalysis
D) Metal ion catalysis
E) Both B and D

E) Both B and D
Explanation: Chymotrypsin does not utilize metal ion catalysis and primarily relies on covalent catalysis and general acid-base catalysis in its mechanism.

Study Smarter, Not Harder
Study Smarter, Not Harder