LESSON 3 - Nucleotides, Purines and Pyrimidines

Nucleoside

____ are derivatives of purines and pyrimidines that have a sugar linked to a ring nitrogen of a purine or pyrimidine

FALSE

In the regulation of the conversion of NDPs to NTPs, deoxythymidine triphosphate binding at the specificity sites causes a conformational change that allows reduction of CDP to dGDP at the catalytic site.

TRUE

With the exception of parasitic protozoa, all forms of life synthesize purine and pyrimidine nucleotides.

TRUE

Purine and pyrimidine biosynthesis parallel one another quantitatively, that is, mole for mole, suggesting coordinated control of their biosynthesis.

FALSE

In purine synthesis, following synthesis of IMP, a single branch lead to AMP and GMP.

FALSE

While both syn and anti-conformers of nucleotides occur in nature, the syn conformers predominate.

Xanthine

"In the conversion of guanosine to uric acid, guanine is deaminated to form _________"

TRUE

"In purine synthesis, GMP feedback inhibits PRPP glutamyl amidotransferase"

Xanthine oxidase

"In the catabolism of purines, xanthine is oxidized to uric acid by the enzyme ____"

260

"Regarding nucleotides, while their spectra are pH-dependent, at pH 7.0 all the common nucleotides absorb light at a wavelength close to ___ nm."

TRUE

"The oxo and amino groups of purines and pyrimidines exhibit keto-enol and amine-imine tautomerism although physiologic conditions strongly favor the amino and oxo forms."

TRUE

"Conversion of purines, their ribonucleosides, and their deoxyribonucleosides to mononucleotides involves "salvage reactions" that require far less energy than de novo synthesis."

All of the above

"Nucleotides that serve as second messengers: cAMP cGMP"

ATP

"Nucleotide that is the principal biologic transducer of free energy:"

FALSE

The sugar in ribonucleosides is 2-deoxy-D-ribose.

TRUE

"AMP and GMP inhibit hypoxanthine-guanine phosphoribosyltransferase, which converts hypoxanthine

FALSE

"Conversion of GDP to GTP is achieved primarily by oxidative phosphorylation"

thymidylate synthase

"The reaction catalyzed by which enzyme is the only reaction of pyrimidine nucleotide biosynthesis that requires a tetrahydrofolate derivative?"

PRPP synthetase

"The initial reaction of purine biosynthesis is catalyzed by which enzyme?"

FALSE

Like in purine biosynthesis, PRPP serves as a scaffold for assembly of the pyrimidine ring.

AOTA

"Select All That Apply - Which of the following pathways require the use of a nucleotide sugar? Glycogen synthesis, Ganglioside synthesis, Glycosaminoglycan synthesis, Glycoprotein synthesis"

TRUE

Steric hindrance by the heterocycle dictates that there is no freedom of rotation about the B-N-glycosidic bond of nucleosides or nucleotides. Both therefore exist as noninterconvertible syn or anti conformers

UDP-sugar derivatives

MCQ - Which of the following participate in sugar epimerizations and in biosynthesis of glycogen, glucosyl disaccharides, and the oligosaccharides of glycoproteins and proteoglycans.

TRUE

In purine synthesis, GMP feedback inhibits PRPP glutamyl amidotransferase

FALSE

In GTP synthesis AMP inhibits IMP dehydrogenase.

A - 5-Methycytosine
B - 5-Hydroxymethylcytosine
C - Dimethylaminoadenine
D - 7-Methylguanine

Match the structure with their names:

Synthesis from amphibolic intermediates

Select All That Apply - Which of the following contribute to purine nucleotide synthesis?

NAD+, FMN, S-adenosylmethionine, and coenzyme A all are derivatives of ribonucleotides.

Which of the following statements about nucleotide structures is NOT CORRECT?

nucleosides

_____ are derivatives of purines and pyrimidines that have a sugar linked to a ring nitrogen of a purine or pyrimidine.

TRUE

Nucleoside disphosphates and triphosphates are nucleotides.

TRUE

The conjugated double bonds of purine and pyrimidine derivatives absorb ultraviolet light.

AOTA

Select All That Apply - what nucleotides serve as second messengers?

TRUE

Steric hindrance by the heterocycle dictates that there is no freedom of rotation about the B-N-glycosidic bond of nucleosides or nucleotides. Both therefore exist as noninterconvertible syn or anti conformers

" AMP, GDP, GMP, ADP "

PRPP synthetase activity is feedback inhibited by which of the following?

TRUE

Nucleotides bear significant negative charge at physiologic pH.

"Carbamoyl phosphate synthetase II, Aspartate Transcarboylase, Dihidroorotase"

Enzyme activities in CAD, which participate in pyrimidine synthesis:

TRUE

Purines and pyrimidines are nitrogen-containing heterocycles, cyclic structures that contain, in addition to carbon, other (hetero) atoms such as nitrogen.

cGMP

Serves as a second messenger in response to nitric oxide during relaxation of smooth muscle:

FALSE

Nucleotide triphosphates have three acid anhydride bonds which have a high-group transfer potential.

TRUE

Conversion of purines, their ribonucleosides, and their deoxyribonucleosides to mononucleotides involves "salvage reactions" that require far less energy than de novo synthesis.

"deoxycitidine kinase, adenosine kinase "

Which of the following enzymes is/are involved in salvage reactions that involves phosphoryl transfer from ATP to a purine ribonucleoside?

TRUE

"Nucleotides bear significant negative charge at physiologic pH."

FALSE

Conversion of GDP to GTP is achieved primarily by oxidative phosphorylation

TRUE

"PRPP synthetase which forms a precursor essential for purine and pyrimidine synthesis is feedback inhibited by both purine and pyrimidine nucleotides."

TRUE

"Normal human tissues can synthesize purines and pyrimidines from amphibolic intermediates in quantities and at times appropriate to meet variable physiologic demand."

cGMP

"Serves as a second messenger in response to nitric oxide during relaxation of smooth muscle:"

adenosine 3′-phosphate-5′-phosphosulfate

"Nucleotides that serve as sulfate donor for sulfated proteoglycans: Cysteine, H2S, Methionine adenosine 3′-phosphate-5′-phosphosulfate "

TRUE

"At the level of enzyme activity, the carbamoyl phosphate synthetase II (CPS) activity of CAD is activated by PRPP and is feedback inhibited by UTP."

ATP

"Which of the following will generally activate ribonucleotide reductase by binding to its allosteric sites/activity sites?"

TRUE

"Steric hindrance by the heterocycle dictates that there is no freedom of rotation about the β-N-glycosidic bond of nucleosides or nucleotides. Both therefore exist as noninterconvertible syn or anti conformers"

UDP-sugar derivatives

"Which of the following participate in sugar epimerizations and in biosynthesis of glycogen, glucosyl disaccharides, and the oligosaccharides of glycoproteins and proteoglycans. ADP-sugar derivatives, UDP-sugar derivatives, CDP-sugar derivatives, GDP-sugar derivatives, TDP-sugar derivatives"

260

Regarding nucleotides, while their spectra are pH-dependent, at pH 7.0 all the common nucleotides absorb light at a wavelength close to ___ nm.

FALSE

Like the low solubility products of purine catabolism, catabolism of the pyrimidines forms poorly water-soluble products—CO2, NH3, β-alanine, and β-aminoisobutyrate.

PRPP

The overall determinant of the rate of de novo purine nucleotide biosynthesis is the concentration of which of the following?

adenosine 3′-phosphate-5′-phosphosulfate

Nucleotides that serve as sulfate donor for sulfated proteoglycans:

False

In ATP synthesis GMP feedback inhibits adenylosuccinate synthetase,

ATP

Which of the following will generally activate ribonucleotide reductase by binding to its allosteric sites/activity sites?

dATP

Which of the following will generally inhibit ribonucleotide reductase by binding to its allosteric sites/activity sites?

FALSE

The sugar in ribonucleosides is 2-deoxy-D-ribose.

TRUE

Purine and pyrimidine biosynthesis parallel one another quantitatively, that is, mole for mole, suggesting coordinated control of their biosynthesis.

FALSE

In the regulation of the conversion of NDPs to NTPs, deoxythymidine triphosphate binding at the specificity sites causes a conformational change that allows reduction of CDP to dGDP at the catalytic site.

260

Regarding nucleotides, while their spectra are pH-dependent, at pH 7.0 all the common nucleotides absorb light at a wavelength close to ___ nm.

Adenosine kinase

Which of the following enzymes is/are involved in salvage reactions that involves phosphoryl transfer from ATP to a purine ribonucleoside?

nucleotides

_____ are nucleosides with a phosphoryl group esterified to a hydroxyl group of the sugar.

dATP

Which of the following will generally inhibit ribonucleotide reductase by binding to its allosteric sites/activity sites?

dihydrofolate reductase

In synthesis of thymine for further pyrimidine synthesis to occur, dihydrofolate must be reduced back to tetrahydrofolate by the enzyme _____

FALSE

In nucleosides, sugars are linked to the heterocycle by an a phosphodiester bond, almost always to the N-1 of a purine or to N-9 of a pyrimidine.

FALSE

While both syn and anti-conformers of nucleotides occur in nature, the syn conformers predominate.

AOTA

Which of the following are consumed in the synthesis of IMP?

ATP

Nucleotide that is the principal biologic transducer of free energy:

TRUE

The enzyme responsible for the reduction of purine nucleoside diphosphates and pyrimidine nucleoside diphosphates (CDP and UDP) to their deoxy forms (dADP, dGDP, dCDP, and dUDP) is composed of two nonidentical dimeric subunits, R1 and R2.

cGMP

Serves as a second messenger in response to nitric oxide during relaxation of smooth muscle:

TRUE

In addition to serving as precursors of nucleic acids, purine and pyrimidine nucleotides participate in metabolic functions as diverse as energy metabolism, protein synthesis, regulation of enzyme activity, and signal transduction. True or False

TRUE

In GTP synthesis, conversion of xanthinylate (XMP) to GMP requires ATP

FALSE

Like the low solubility products of purine catabolism, catabolism of the pyrimidines forms poorly water-soluble products—CO2, NH3, β-alanine, and β-aminoisobutyrate.

TRUE

AMP and GMP inhibit hypoxanthine-guanine phosphoribosyltransferase, which converts hypoxanthine and guanine to IMP and GMP

FALSE

The catalyst for the initial reaction of pyrmidine synthesis is cytosolic carbamoy! phosphate synthetase I.

TRUE

PRPP synthetase which forms a precursor essential for purine and pyrimidine synthesis is feedback inhibited by both purine and pyrimidine nucleotides.

TRUE

Purines and pyrimidines are nitrogen-containing heterocycles, cyclic structures that contain, in addition to carbon, other (hetero) atoms such as nitrogen.

PRPP

The overall determinant of the rate of de novo purine nucleotide biosynthesis is the concentration of which of the following?

FALSE

The catalyst for the initial reaction of pyrmidine synthesis is cytosolic carbamoyl phosphate synthetase I.

CTP

"Which of the following participates in biosynthesis of phosphoglycerides, sphingomyelin, and other substituted sphingosines? GTP, CTP, ATP, TTP, UTP "

FAD, NADP, Coenzyme A, NAD "

Coenzyme derivative of adenosine monophosphate:

" Coenzyme A, SAM, FAD(2H), NADP+ "

"Adenine nucleotides have roles other than for nucleic acid synthesis. Which of the following compounds contain adenine as part of their structure Ubiquitin, Coenzyme A, SAM, FAD(2H), NADP+ "

FALSE

"In ATP synthesis GMP feedback inhibits adenylosuccinate synthetase,

FALSE

"In purine synthesis, following synthesis of IMP, a single branch lead to AMP and GMP

TRUE

"Steric hindrance by the heterocycle dictates that there is no freedom of rotation about the β-N-glycosidic bond of nucleosides or nucleotides. Both therefore exist as noninterconvertible syn or anti conformers

"HGPRT , Adenine phosphoribosyltransferase "

"Which of the following enzymes is/are involved in salvage reactions that involves phosphoribosylation by PRPP of a free purine? Adenosine kinase , HGPRT, deoxycytidine kinase, Adenine phosphoribosyltransferase "

TRUE

CAD represents the primary focus for regulation on pyrimidine biosynthesis. Expression of the CAD gene is regulated at the level both of transcription and of translation.