Functions and Structure of Nucleotides

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Questions and Answers

What are the functions of nucleotides? (Select all that apply)

Adenine nucleotides used for cofactors that facilitate pathways (correct)

Signaling and metabolic pathways (correct)

Polysaccharide synthesis (correct)

ATP is an energy source in all required pathways (correct)

DNA and RNA synthesis (correct)

What is the function of ATP?

Energy and cofactors

What is the function of GTP?

G protein signaling

What is the function of CTP?

Lipid precursors Signup and view all the answers

What is the function of UTP?

UDP sugars for polysaccharides Signup and view all the answers

What three components make up a nucleotide?

Sugar, nitrogenous base, and a phosphate group Signup and view all the answers

How are nucleotide components combined?

Sugar + nitrogenous base = glycosidic bond; sugar + phosphate group = phosphodiester bond Signup and view all the answers

What are the two classes of bases that make up nucleotides?

Purines and pyrimidines Signup and view all the answers

Which bases are found in DNA?

A-T, G-C Signup and view all the answers

Which bases are found in RNA?

A-U, G-C Signup and view all the answers

What is the difference between a ribonucleotide and a ribonucleoside?

Ribonucleotides have phosphate groups; ribonucleosides only have a sugar and nitrogenous base Signup and view all the answers

What deoxyribonucleotide is important in metabolism but not incorporated into DNA?

dUMP Signup and view all the answers

What happens in the first committed step of purine de novo synthesis?

PRPP formed from ribose 5 phosphate is converted to beta-5-phosphoribosylamine Signup and view all the answers

Why is pyrimidine de novo synthesis considered modular while purine synthesis is not?

In pyrimidine synthesis, the base is constructed first and then added to ribose; purine synthesis lacks an initial base and adds nitrogen to PRPP. Signup and view all the answers

What enzymes convert nucleoside monophosphates to nucleoside diphosphates?

A specific kinase for each NMP Signup and view all the answers

What converts nucleoside diphosphates to nucleoside triphosphates?

Nucleoside diphosphate kinase Signup and view all the answers

What are the three types of reactions for the salvage pathway?

<ol> <li>Nucleoside phosphorylases; 2. Nucleoside kinase; 3. Phosphoribosyl transferase</li> </ol> Signup and view all the answers

Where do molecules to be salvaged come from?

Dietary sources and degraded cellular nucleic acids Signup and view all the answers

What are the key control points in the de novo purine synthesis pathway?

<ol> <li>Increased levels of AMP and GMP inhibit IMP conversion; 2. High levels of GDP and ADP inhibit PRPP formation; 3. Abundance of purine nucleotides inhibits PRPP to beta-5-phosphoribosylamine.</li> </ol> Signup and view all the answers

What mechanisms contribute to providing an appropriate balance of ATP and GTP production?

Energy from GTP contributes to adenyl succinate synthesis, while energy from ATP contributes to GMP synthesis. Signup and view all the answers

How can an HGPRT deficiency cause Lesch-Nyhan Syndrome?

<ol> <li>HGPRT breakdown of PRPP is inactive; 2. Overaccumulation of PRPP occurs; 3. Excess PRPP stimulates de novo purine synthesis; 4. Unnecessary purines degrade to uric acid.</li> </ol> Signup and view all the answers

How is it that eukaryotes and prokaryotes have different first committed steps in the pyrimidine de novo synthesis pathway?

Eukaryotes utilize CPSII while prokaryotes utilize CPS then ATCase. Signup and view all the answers

What are eukaryotes inhibited by in de novo pyrimidine synthesis?

CPSII regulated by UDP to UTP conversion Signup and view all the answers

Why are certain enzymes of nucleotide synthesis regulated according to the cell cycle? Give 3 examples.

Production of deoxyribonucleotides depends on ribonucleotides, needing regulation during various stages of the cell cycle. Signup and view all the answers

Study Notes

Functions of Nucleotides

Key roles include DNA/RNA synthesis, signaling, and metabolism.
ATP serves as the primary energy source across multiple pathways.
Adenine nucleotides act as cofactors facilitating biochemical processes.
Nucleotide derivatives are essential for polysaccharide synthesis.

ATP and Other Nucleotides

ATP acts as an energy source and cofactor in various cellular reactions.
GTP is involved in G protein signaling pathways.
CTP contributes to the synthesis of lipid precursors such as phospholipids and sphingolipids.
UTP is integral for forming UDP sugars, which are precursors for polysaccharides.

Structure of Nucleotides

Nucleotides consist of three components: a sugar, a nitrogenous base, and a phosphate group.
Nucleotides are formed through glycosidic bonds between sugars and bases, and phosphodiester bonds between sugars and phosphates.

Classes and Bases of Nucleotides

Two classes of nitrogenous bases: purines (A, G) and pyrimidines (C, T/U).
DNA bases include adenine (A) and thymine (T); guanine (G) pairs with cytosine (C).
RNA bases substitute uracil (U) for thymine, pairing with adenine (A) and guanine (G) with cytosine (C).

Differences in Nucleotides

Ribonucleotides contain a phosphate group, while ribonucleosides lack it.
dUMP is a deoxyribonucleotide crucial for metabolism but is not integrated into DNA.

Synthesis Pathways

The first committed step of purine de novo synthesis involves converting PRPP to beta-5-phosphoribosylamine.
Pyrimidine synthesis is modular; the base is synthesized first and then attached to ribose.
Purine synthesis requires adding nitrogen to PRPP to build the base.

Enzymatic Conversion

Nucleoside monophosphates (NMPs) convert to diphosphates (NDPs) via specific kinases.
NDPs are phosphorylated to nucleoside triphosphates (NTPs) by nucleoside diphosphate kinase.

Salvage Pathway Mechanisms

Key reactions in the salvage pathway include nucleoside phosphorylases, nucleoside kinases, and phosphoribosyl transferases.
Salvaged nucleotides primarily originate from dietary sources and degraded nucleic acids.

Regulation in Purine Synthesis

Negative control: High levels of AMP and GMP inhibit steps leading to adenylosuccinate and XMP.
Positive control: Abundant PRPP activates amidophosphoribosyl transferase; GTP enhances IMP conversion to adenylosuccinate; ATP promotes XMP to GMP.
Balances ATP and GTP production through energy contributions.

Lesch-Nyhan Syndrome

Caused by HGPRT deficiency, leading to PRPP overaccumulation.
Excess PRPP stimulates unwanted de novo purine synthesis, resulting in elevated uric acid and neurological issues.

Eukaryotic vs Prokaryotic Pathways

Eukaryotes utilize CPSII, while prokaryotes use CPS followed by ATCase for pyrimidine synthesis.
These enzymes differ in location and regulation despite their catalytic similarities.

Regulation in Pyrimidine Synthesis

Eukaryotic CPSII is regulated by the nucleotide UTP derived from UDP.
Enzyme regulation may vary according to the cell cycle, ensuring proper nucleotide availability during DNA replication and repair processes.

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Description

Explore the key roles of nucleotides in biological systems, including their structure, functions in energy transfer, and significance in metabolic pathways. This quiz covers ATP, GTP, CTP, and UTP and their integral parts in cellular reactions and synthesis processes.