1) nitrogenous base

2) 5-carbon sugar

3) phosphate group

▪ Nucleoside = base w/o phosphates

▪ Nucleotide = base w/ phosphates 

Name the nitrogenous bases and

distinguish purines vs. pyrimidines.

▪ Purines - Adenine, Guanine, Hypoxanthine

▪ Pyrimidines - Cytosine, Thymine, Uracil

PRPP 

=

5-phosphoribosyl-alpha-pyrophosphate

▪ making nucleotides from scratch

▪ Requires - amino acids, ATP, tetrahydrofolate derivatives, PRPP

▪ lymphocytes especially dependent

▪ recycling free bases and nucleosides

▪ Requires - PRPP

▪ used by resting cells

Ribose-5-phosphate from the

pentose phosphate pathway

Ribose-5-Phosphate → PRPP

Enzyme?

Ribose-5-Phosphate → PRPP

Regulation?

▪ Amino Acids (ASP,GLY,GLN)

▪ carbon dioxide

▪ tetrahydrofolate derivatives (formate)

▪ PRPP

PRPP→PRA→IMP→branch point

Branch 1 = IMP→Adenylosuccinate→AMP→ADP→ATP

Branch 2 =

IMP→XMP→GMP→GDP→GTP

PRPP→PRA

Enzyme?

Regulation?

▪ Enzyme =

glutamine phosphoribosyl amidotransferase

▪ Regulation - ↑ by PRPP, ↓ by AMP/GMP

**rate-limiting step**

IMP→Adenylosuccinate

Enzyme?

Key Co-factor?

Regulation?

▪ Enzyme = adenylosuccinate synthetase

▪ Key Co-factor = GTP

▪ ↓ by AMP, ↑ by GTP from other branch 

Adenylosuccinate→AMP

Enzyme?

IMP→XMP

Enzyme?

Regulation?

▪ Enzyme = IMP dehydrogenase

**a drug target**

▪ Regulation - ↓ by GMP

XMP→GMP

Enzyme?

Key Co-Factor?

Regulation?

▪ Enzyme =

XMP-glutamine amidotransferase

▪ Key Co-Factor = ATP

▪ Regulation = ↑ by ATP from other branch

Monophosphates→Diphosphates

Enzymes?

Specific Kinases

(AMP/GMP kinase, etc.)

Diphosphates→Triphosphates

Enzyme?

Nucleoside Diphosphate Kinase

**non-specific for all diphosphates**

Purine Salvage

General 1st Steps?

Nucleic acids→monophosphates→ nucleosides

Nucleic Acids→monophosphates

Enzymes?

Monophosphates→Nucleosides

Enzymes?

Purine Salvage - Guanosine

Pathway?

Guanosine→Guanine + ribose-1-phosphate

Enzyme = 

purine nucleoside phosphorylase (PNP)

Purine Salvage - Adenosine

Pathways (2)?

Path 1 - Adenosine→Inosine→

Hypoxanthine + ribose-1-phosphate

Path 2 - AMP→IMP→Inosine→

Hypoxanthine + ribose-1-phosphate

Adenosine→Inosine

Enzyme?

Inosine→Hypoxanthine

Enzyme?

AMP→IMP

Enzyme?

Remaking GMP

Pathway?

Enzyme?

Guanine + R-5-P (from PRPP)→GMP

Enzyme = HGPRT

Remaking IMP

Pathway?

Enzyme?

Hypoxanthine + R-5-P (from PRPP)→IMP

Enzyme = HGPRT

Remaking AMP

Pathways (2)?

Enzymes?

Path 1 - Adenosine→AMP

Enzyme = Adenosine Kinase

Path 2 - IMP→AMP through De Novo path

Degradation of Guanine

Pathway?

Enzymes?

Guanine→Xanthine→Uric Acid

Enzymes = 

none for Guanine→Xanthine

Xanthine Oxidase for Xanthine→Uric Acid

Degradation of Hypoxanthine (Adenosine)

Pathway?

Enzymes?

Hypoxanthine→Xanthine→Uric Acid

**Adenosine→Hypoxanthine via salvage path**

Enzyme = Xanthine Oxidase for all steps

Gout

Cause?

Gout

Why high uric acid levels?

▪ Excessive purine metabolism

▪ kidney function

▪ disease

▪ medications

▪ diet - EX. ↑ alcohol

Gout

Treatments?

▪ Diet modification

▪ Colchicine

▪ Allopurinol - inhibits Xanthine Oxidase

▪ Febuxostat (Uloric) - inhibits XO

Lesch-Nyhan syndrome

Cause?

HGPRT deficiency→ ↑ PRPP→ ↑ purines→

↑ uric acid

Lesch-Nyhan Syndrome

Symptoms?

Treatment?

▪ Symptoms = Gout-like + nuerological (spasticity, learning disability, self-mutilation)

▪ Treatment = none (Allopurinol lowers uric acid)

▪ Purine - longer, ring built on sugar

▪ Pyrimidine - shorter, ring built separately then attached to sugar

▪ amino acids (ASP, GLN)

▪ Carbon dioxide

▪ PRPP

Formation of Carbamoyl Phosphate

Enzyme?

Regulation?

▪ Enzyme = Carbamoyl Synthetase II (CSII)

▪ Regulation - ↑ by PRPP, ↑ by S phase, 

↓ by UTP

**rate-limiting**

Carbamoyl Phosphate→Carbamoyl Aspartate→Dihyroorotate→Orotate→OMP

→UMP→UDP→UTP→CTP (optional)

Orotate→OMP

Enzyme?

Key Co-Factor?

▪ Enzyme = OPRT

▪ Key Co-Factor = PRPP (provides R-5-P for transfer)

OMP→UMP

Enzyme?

Formation of CTP

Pathway?

Enzyme?

Key Co-Factor?

▪ Pathway - use De Novo to get UTP, then...

UTP→CTP

▪ Enzyme = CTP synthetase

▪ Key Co-Factor = glutamine (provides amino group)

Formation of dUMP from CTP

Pathway?

CDP→dCDP

Enzyme?

dCMP→dUMP

Enzyme?

Formation of dUMP from UTP

Pathway?

UDP→dUDP

Enzyme?

dUTP→dUMP

Enzyme?

Why do we do this?

▪ Enzyme = dUTPase

▪ Done to prevent uridine from getting into DNA

dUMP→TTP

Pathway?

dUMP→TMP

Enzyme?

Key Co-Factor?

▪ Enzyme = thymidylate synthase (TS)

▪ Key Co-Factor = methylene THF

(donates CH3)

Making methylene THF

Pathway?

DHF→THF

Enzyme?

5-fluorouracil

Target?

Use?

▪ Targets enzyme TS

▪ Used in cancer chemotherapy

Methotrexate

Target?

Use?

▪ Targets enzyme DHFR

▪ Use in cancer chemotherapy

Trimethoprim

Target?

Use?

▪ Targets enzyme DHFR

▪ Use for antimicrobial therapy

REMEMBER - 

Monophosphates→Nucleosides

Enzyme?

Degradation of UMP

Pathway?

Uridine→Uracil + R-1-P

Enzyme?

Degradation of CMP

Pathway?

Cytidine→Uridine

Enzyme?

UMP Salvage

Pathways (2)?

Path 1 - Uracil→Uridine→UMP

Path 2 - Uracil→UMP

Uracil→Uridine

Enzyme?

Key Co-Factor?

▪ Enzyme = Uridine phophorylase

▪ Key Co-Factor = R-1-P 

Uracil→UMP

Enzyme?

Key Co-Factor?

▪ Enzyme = UPRT

▪ Key Co-Factor = PRPP (gives R-5-P group)

CMP Salvage

Pathway?

Pyrimidine Nucleosides→Monophosphates

Enzyme?

Key Co-Factor?

▪ Enzyme = Uridine-Cytidine Kinase

▪ Key Co-Factor = ATP or GTP (donates phosphate)

Degradation of Uracil

Pathway?

Uracil→5,6-Dihydrouracil→N-Carbamyl-B-Alanine→B-alanine

Uracil→5,6-dihydrouracil

Enzyme?

Enzyme Facts?

▪ Enzyme = DPD

▪ Fact - Enzyme is polymorphic (some people have some don't), only a problem in 5-fluorouracil treatment

Orotic Aciduria

Types (2)?

buildup of orotate and too little UMP

▪ Type 1 - OPRT and OMP decarboxylase deficiency

▪ Type 2 - only OMP decarboxylase deficiency

Orotic Aciduria

Symptoms?

Treatment?

▪ Symptoms - ↑ orotate in urine, anemia, mental/physical retardation

▪ Treatment - give uridine (or cytidine to go to uridine), goes to UTP, regulates 1st step pyrimidine synthesis

Conversion of ribonucleotides

to deoxyribonucleotides

Enzyme?

Which nucleotides?

▪ Enzyme = Ribonucleotide Reductase

▪ Nucleotides =

ADP→dADP

GDP→dGDP

UDP→dUDP

Which dNTP is not used in DNA?

What does it make instead?

1) ATP - ↑ dCDP & dUDP

2) TTP - ↑ dGDP, ↓ dCDP & dUDP

3) dGTP - ↑ dADP, ↓ dUDP & dGDP

4) dATP - turns off everything

**"master switch"** 

Salvage of Deoxyribonucleotides

General Mechanism?

Salvage of Thymine

Pathway?

Enzyme?

thymine + deoxyribose-1-phosphate→

thymidine

Enzyme = Thymidine Phosphorylase

Degradation of Thymine

Product?

Degradation of Thymine

Key Reaction + Enzyme?

Thymine → 5,6-dihydrothymine

Enzyme = DPD

Monophosphates from deoxyribonucleotides

dAMP

Enzymes?

1) DCK - takes dA→dAMP

2) DGK - takes dA→dAMP

1) DCK - takes dG→dGMP

2) DGK - takes dG→DGMP

1) DCK - takes dC→dCMP

2) TK2 - takes dC→dCMP

1) TK1 - takes dU→dUMP

2) TK2 - takes dU→dUMP

Monophosphates from deoxyribonucleotides

TMP

Enzymes?

1) TK1 - takes T→TMP

2) TK2 - takes T→TMP

Severe Combined Immunodeficiency Disease (DCID)

Also known as?

What is it? What does it affect?

Prognosis?

▪ "bubble boy disease"

▪ group of genetic disorders affecting T and B cells of immune system

▪ if not diagnosed early, fatal within 1st year of life

Severe Combined Immunodeficiency Disease (DCID)

How related to purines/pyrimidines?

Mechanism of Disease?

▪ adenosine deaminase deficiency is

2nd most common cause

▪ adenosine and deoxyadenosine not converted to inosine forms, build up, become dATP, shut off RR

Severe Combined Immunodeficiency Disease (DCID)

Treatment?

bone marrow transplant or

gene therapy with adenosine deaminase