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M1 > Purine and Pyrimidine Synthesis > Flashcards

Purine and Pyrimidine Synthesis Flashcards

1
Q

Amino acids are precursors of:

A
  • proteins
  • hormones
  • coenzymes
  • nucleotides
  • alkaloids
  • cell wall polymers
  • porphyrins
  • antibiotics
  • pigments
  • neurotransmitters
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2
Q

Nucleotides roles in cellular metabolism:

A
  • energy currency in metabolic transactions
  • essential chemical links in the response of cells to hormones and other extracellular stimuli
  • structural components of an array of enzyme cofactors and metabolic intermediates
  • constituents of nucleic acids: deoxyribonucleic acid (DNA) and ribonucleic acid (RNA)
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3
Q

Nucleotides have three components:

A
  1. a nitrogenous base (pyrimdine or purine)
  2. A pentose
  3. 1+ phosphates
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4
Q

Nucleoside

A

nucleotide without a phosphate group

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5
Q

Nucleotide Bonds

A
  • N-β-glycosyl bond = covalently joins the 1′ carbon of the pentose to the base (at N-1 of pyrimidines and N-9 of purines)
    • formed by removal of the elements of water
  • the phosphate is esterified to the 5′ carbon
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6
Q

Nucleotide Nitrogenous Bases:

A
  • major purine bases:
    • adenine (A) = in DNA and RNA
    • guanine (G) = in DNA and RNA
  • major pyrimidine bases:
    • cytosine (C) = in DNA and RNA
    • thymine (T) = only in DNA
    • uracil (U) = only in RNA
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7
Q

Label

A
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8
Q

Nucleotide Pentoses

two kinds of pentoses:

form:

A
  • 2′-deoxy-d-ribose = in DNA
  • D-ribose = in RNA

Both are int their β-furanose (closed five-membered ring) form

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9
Q

structural units of RNA

A

ribonucleotides

also called ribonucleoside 5’-monophosphates

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10
Q

structural units of DNA

A

deoxyribonucleotides

also called deoxyribonucleoside 5′-monophosphates, deoxynucleotides, and deoxynucleoside triphosphates

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11
Q
A
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12
Q

label

*methylated foms - most common in DNA

A
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13
Q

Nucleotides with Phosphate Groups in Different Positions

A
  • ribonucleoside 2′,3′-cyclic monophosphates = isolatable intermediates
  • ribonucleoside 3′-monophosphates = end products of RNA hydrolysis
  • adenosine 3′,5′-cyclic monophosphate (cAMP)
  • guanosine 3′,5′-cyclic monophosphate (cGMP)
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14
Q
A
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15
Q

Solubility of Nucleotides

A
  • hydrophobic and relatively insoluble in pH 7.0 water
    • leads to stacking interactions (van der Waals and dipole-dipole)
  • charged and more soluble at acidic or alkaline pH values
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16
Q

Two Pathways Lead to Nucleotides

A
  • de novo pathways = begin with metabolic precursors: amino acids, ribose 5-phosphate, CO2, and NH3
    • bases are synthesized while attached to ribose
    • pyrimidine ring is synthesized as orotate
    • Glu provides most amino groups
    • Gly is the precursor for purines
    • Asp is the precursor for pyrimidines
  • salvage pathways = recycle the free bases and nucleosides released from nucleic acid breakdown
17
Q

Origin of Ring Atoms in Purines

A

adenine and guanine are synthesized as AMP and GMP.

18
Q

De Novo purine nucleotide synthesis begins with

A

PRPP

in the first committed step, an amino group donated by glutamine is attached at C-1 of PRPP to form 5-phosphoribosylamine

in the second step, three atoms are added from glycine

requires ATP

19
Q

in the eleventh step, a second ring closure occurs to form:

A

inosinate (IMP)

IMP is the first intermediate with a complete purine ring

20
Q

Addition of the Amino Groups of AMP and GMP

A
  • conversion of inosinate to adenylate requires an amino group from aspartate
    • requires GTP
  • conversion of inosinate to guanylate requires an amino group from glutamine
    • requires ATP
21
Q

Biosynthesis of AMP and GMP from IMP

A
22
Q

Nucleotide synthesis regulation overview

A

Tight regulation is needed to maintain balanced supplies of amino acids resources and nucleotide products.

The metabolic flux through most of these pathways is far less than for carbohydrate or lipid biosynthetic pathways;

most amino acids and nucleotides are not stored, but are synthesized as they are needed.

23
Q

Purine Nucleotide Biosynthesis is Regulated by

A

Feedback Inhibition

24
Q

four major feedback mechanisms cooperate in regulating:

A

the overall rate of de novo purine nucleotide synthesis

the relative rates of formation of AMP and GMP

25
Q
A
26
Q

Pyrimidine Nucleotides are Made from

A

Aspartate, PRPP, and Carbamoyl Phosphate

pyrimidine synthesis proceeds by first making the pyrimidine ring (in the form of orotate)

ribose 5-phosphate is attached after pyrimidine ring formation

aspartate and carbamoyl phosphate provide the atoms for the ring structure

27
Q

catalyzes the first committed step in pyrimidine nucleotides

highly regulated in bacteria

A

aspartate transcarbamoylase

28
Q

catalyzes the removal of water from N-carbamoylaspartate to close the pyrimidine ring

A

dihydroorotase

29
Q

in eukaryotes, the first three enzymes are part of

A

a single trifunctional protein (CAD)

30
Q
A
31
Q

is decarboxylated to uridylate, which is phosphorylated to UTP

A

orotidylate

32
Q

catalyzes the formation of CTP from UTP by way of an acyl phosphate intermediate

requires ATP

A

cytidylate synthetase

33
Q
A
34
Q

Pyrimidine Nucleotide Biosynthesis Is Regulated by

A

Feedback Inhibition

35
Q

aspartate transcarbamoylase (ATCase)

A
  • catalyzes the first reaction in the sequence
    • inhibited by end-product CTP
    • accelerated by ATP
36
Q

phosphorylates AMP to ADP

A

adenylate kinase

37
Q

ADP is phosphorylated to ATP by

A

glycolytic enzymes or through oxidative phosphorylation

38
Q

use ATP to form other nucleoside diphosphates

A

nucleoside monophosphate kinases

39
Q

convert nucleoside diphosphates to triphosphate

A

nucleoside diphosphate kinases

NTPD + NDPA ⇌ NDPD + NTPA

where A is the phosphate acceptor and D is the donor

M1 (48 decks)

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