Structure and function of nucleosides and nucleotides

Which nucleotides are pyrimidine

(Cytosine-C, Thymine-T, Uracil-C) depending on the shape of their heterocyclic nitrogen base

What are the 4 key enzymes in purine nucleotides biosynthesis

1. 5-phsphoribosyl 1-pyrophosphate (PRPP) synthasase- important (activating enzyme) 2.5' phosphoribosyl-glycinamide synthetase (PRPP glutamyl amido transferase). This enzyme uses PRPP and glutamine and represent the committed step in the pathway 3. Glycinamide ribosyl 5-phosphate (GAR) synthetase 4. Ribonucleotide reductase convert a ribonucleotide (NDP) to the corresponding deoxyribonucleotide (dNDP).

All of the following enzymes are unique to purine nucleotide synthesis except (A) PRPP synthetase (B) PRPP glutamyl amido transferase (C) Adenylosuccinate synthetase (D) IMP dehydrogenase

A

An enzyme which acts as allosteric regulator and sensitive to both phosphate concentration and to the purine nucleotides is (A) PRPP synthetase (B) PRPP glutamyl midotransferase (C) HGPR Tase (D) Formyl transferase

A

Group of adjacent nucleotides are joined by a) Phosphodiester bond b) Peptide bond c) Ionic bond d) Covalent bond

A

Which nucleotides are purines

Adenine-A, Guanine-G

Which of the following is true about phosphodiester linkage? a) 5'-phosphate group of one nucleotide unit is joined to the 3'-hydroxyl group of the next nucleotide b) 3'-phosphate group of one nucleotide unit is joined to the 5'-hydroxyl group of the next nucleotide c) 5'-phosphate group of one nucleotide unit is joined to the 5'-hydroxyl group of the next nucleotide d) 3'-phosphate group of one nucleotide unit is joined to the 3'-hydroxyl group of the next nucleotide

Answer: A:::::: Explanation: 5'-phosphate group of one nucleotide unit is joined to the 3'-hydroxyl group of the next nucleotide.

What are nucleotides used for?

As the universal energy currency of the cell (ATP) As second messengers in regulatory pathways (cAMP) As components in phosphoglycerides biosynthesis (CTP, CDP) As allosteric regulators of enzymes activity As components of coenzymes (FAD, NAD, CoA) As the building blocks of DNA and RNA

What are the purine atom sources

Aspartate CO2 Glycine Formate Amide N of gutamine

The first reaction unique to purine nucleotide synthesis is catalysed by (A) PRPP synthetase (B) PRPP glutamyl amido transferase (C) Phosphoribosyl glycinamide synthetase (D) Formyl transferase

B

What is the composition of nucleoside? a) a sugar + a phosphate b) a base + a sugar c) a base + a phosphate d) a base + a sugar + phosphate

B

How are nitrogenous bases connected to sugars?

Betta-N-gluycosidic bond

5-Phosphoribosyl-1-pyrophosphate is required for the synthesis of (A) Purine nucleotides (B) Pyrimidine nucleotides (C) Both (A) and (B) (D) None of these

C

AMP is an allosteric inhibitor of (A) PRPP synthetase (B) Adenylosucciante synthetase (C) Both (A) and (B) (D) None of these

C

An allosteric inhibitor of PRPP glutamyl amido transferase is (A) AMP (B) ADP (C) GMP (D) All of these

C

Salvage of purine bases is regulated by (A) Adenosine phosphoribosyl transferase (B) Hypoxanthine guanine phosphoribosyl transferase (C) Availability of PRPP (D) None of these

C

The enzyme required for salvage of free purine bases is (A) Adenine phosphoribosyl transferase (B) Hypoxanthine guanine phosphoribosyl transferase (C) Both (A) and (B) (D) None of these

C

The nitrogen atoms for de novo synthesis of purine nucleotides are provided by (A) Aspartate and glutamate (B) Aspartate and glycine (C) Aspartate, glutamine and glycine (D) Aspartate, glutamate and glycine

C GLUTAMINE

For de novo synthesis of purine nucleotides, glycine provides (A) One nitrogen atom (B) One nitrogen and one carbon atom (C) Two carbon atoms (D) One nitrogen and two carbon atoms

D

Free purine bases which can be salvaged are (A) Adenine and guanine (B) Adenine and hypoxanthine (C) Guanine and hypoxanthine (D) Adenine, guanine and hypoxanthine

D

GMP is an allosteric inhibitor of all the following except (A) PRPP synthetase (B) PRPP glutamyl amido synthetase (C) IMP dehydrogenase (D) Adenylosuccinate synthetase

D

Identify the purine base of nucleic acids in the following a) Cytosine b) Thymine c) Uracil d) Adenine

D

In the pathway of de novo synthesis of purine nucleotides, all the following are allosteric enzymes except (A) PRPP glutamyl amido transferase (B) Adenylosuccinate synthetase (C) IMP dehydrogenase (D) Adenylosuccinase

D

PRPP synthetase is allosterically inhibited by (A) AMP (B) ADP (C) GMP (D) All of these

D

The end product of purine catabolism in man is (A) Inosine (B) Hypoxanthine (C) Xanthine (D) Uric acid

D

What is the composition of nucleotide? a) a sugar + a phosphate b) a base + a sugar c) a base + a phosphate d) a base + a sugar + phosphate

D

the major site of purine nucleotide biosynthesis

IN THE LIVER- in the cytosol of heaptocytes

The tautomeric forms of nitrogenous bases do what?

Note how the tautomeric forms lose the ability to make correct pairings and, worse still, create viable pairings with incorrect partners!

DNA and RNA are degraded by

Nucleases degrade DNA and RNA, and

The biosynthesis of purine nucleotides is tightly regulated, primarily by what two things

PRPP availability, and via pathway intermediates AMP and GMP.

Explain how purine nucleotides may be synthesized does it require energy input

Purine nucleotides may be synthesized by either a de novo pathway from activated ribose unit, 5-phophoribosylpyrophosphate (PRPP) to inosine monophosphate (IMP) in a 10 step reaction that requires energy input

Give the general pathway of the de novo synthesis of purines

Purine---> IMP-->AMP or GMP--> which make ATP or GTP

How are pyrimidines arranged?

Pyrimidines are arranged in a single ring and possess 6 atoms (4C, 2N) and their atoms are numbered in opposite way to the arrangement in Purines.

In the salvage pathway, reactions are specifically catalyzed by what? And what is it inhibited by?

Reactions are specifically catalyzed by hypoxanthine-guanine phsophoribosyltransferase (HGPRT) which is inhibited by IMP and GMP

What does tautomerization do nitrogenous bases

Tautomerization alters the base-pairing properties of a nucleotide as a result of interaction with water-that's where the

What is the rate limiting step in the pathway of purine nucleotide biosynthesis and how is it regulated?

The activity of glutamine-PRPP amidotransferase is the rate limiting step in the pathway of purine nucleotide biosynthesis and is controlled by feedback inhibition by the pathway products.

What do the nitrogenous bases form?

The bases are capable of forming specific pairs that are stabilized by 2 or 3 hydrogen bonds, allowing for DNA to replicate. G-C makes 3 hydrogen bonds, and A-T makes two hydrogen bonds which is why A-T are easier to break

Describe the shape of the nitrogenous base, its saturation, and solubility in H20

The bases are planar, unsaturated, and insoluble in water

The rate of PRPP synthesis is regulated by the availability of what?

The rate of PRPP synthesis is regulated by the availability of ribose 5-phosphate from the pentose phosphate pathway, and by the activity of the PRPP synthetase (ribose phosphate pyrophosphokinase-an enzyme that is sensitive to both [phosphate], and to allosteric regulation by the purine ribonucleotides (inhibited by both ADP and GDP)

Purine nucleotide metabolism rate limiting step

When PRPP ----> 5 Phosphoribosylamine via GutymlAminotransdferase

Describe the structure of a nucleotide

are monomeric subunits of nucleic acids containing 3 distinct parts: heterocyclic nitrogenous bases (purine, pyrimidine), five carbon sugar (ribose, deoxyribose), one or more phosphate groups

How does pyrimidine biosynthesis occur

begins with the formation of the base that is then added to the sugar phosphate moiety

What does purine biosynthesis begin with

begins with the sugar phosphate moiety onto which the rings of the base are assembled

What are the functions of nucleotides

building blocks of DNA and RNA, second messengers, allosteric regulators of enzyme activity, components of coenzymes

How are polynucleotides connected

by a stable 3' to 5' phosphodiester bond- (the connection) that forms the spine of the polynucleotide

Which of the following statements is true? a) Sugar component of a nucleotide is ribose b) Sugar component of a nucleotide is deoxyribose c) The bases in nucleotides are attached to a pentose sugar moiety by a glycosidic linkage d) The sugar molecule of the nucleotide is in L-configuration

c

What is the structure of a nucleoside

heterocyclic nitrogenous bases (purine, pyrimidine), five carbon sugar (ribose, deoxyribose), DO NOT HAVE THE PHOSPHATE

What degrade individual nucleotides

nucelotidases

Which requires less energy the salvage pathway or the de novo

the salvage pathway

The degradation of purine nucleotides, nucleosides, and bases follows a common pathway leading to the formation of what?

uric acid

What does the salvage pathway begin with

which utilizes phosphoribosylation of an existing (recycled) base, or phosphorylation of existing purine nucleoside.