Nucleotides and Metabolism Quiz

Nucleotides

• Structure:
  • Composed of a nitrogenous base, a sugar, and one to three phosphate groups.
  • Nitrogenous bases:
    • Purines: Adenine (A), Guanine (G)
    • Pyrimidines: Thymine (T) - DNA only, Cytosine (C), Uracil (U) - RNA only
  • Sugar:
    • Ribose (RNA)
    • Deoxyribose (DNA)
• Functions:
  • Building blocks:
    • RNA & DNA
  • Energy: ATP & GTP
  • Hormones: cAMP & cGMP are second messengers
  • Coenzymes: NAD, FAD, Co-enzyme A

Nucleotide Metabolism

• Synthesis (Anabolism):
  • Purine ring atoms:
    • Derived from Glycine, Aspartate, Glutamine, CO2, and Tetrahydrofolate.
  • Pyrimidine ring atoms:
    • Derived from Aspartate, Carbamoyl phosphate and Tetrahydrofolate.
• Degradation (Catabolism):
  • Purine rings:
    • Degraded to Uric acid
    • Excreted by the kidneys.
    • Hyperuricemia: High blood uric acid levels
    • Gout: A disease caused by uric acid deposition into joints and kidneys.
  • Pyrimidine rings:
    • Degraded to β-alanine, β-aminoisobutyrate, CO2, and NH3

DNA

• Importance:
  • Genetic material: Stores and carries genetic information
  • Replication:
    • Template for DNA synthesis, ensuring genetic information is passed onto new cells.
  • Transcription:
    • Template for mRNA synthesis, allowing protein synthesis to occur.
• Location:
  • Eukaryotes: Nucleus and mitochondria
• Structure:
  • Single strand:
    • A polynucleotide chain of deoxyribose, phosphate groups, and nitrogenous bases (A, T, C, G).
    • Linked via phosphodiester bonds.
    • Two ends: 5' phosphate end and 3' hydroxyl end.
  • Double stranded:
    • Two anti-parallel strands held together by hydrogen bonds between the bases.
    • A-T: Two hydrogen bonds
    • C-G: Three hydrogen bonds
  • Tertiary structure:
    • In eukaryotes, DNA is packaged into chromosomes.
• Types:
  • Linear: Chromosomal DNA in eukaryotes.
  • Circular:
    • Mitochondria (eukaryotes)
    • Prokaryotic chromosomes (nucleoid)
    • Plasmids (bacteria)
    • Plant chloroplasts

Mitochondrial DNA

• Circular, double-stranded DNA molecule.
• Maternally inherited:
  • Only egg mitochondria are passed to a zygote.
• High mutation rate:
  • ~5-10 times higher than nuclear DNA.

RNA

• General Structure:
  • Polyribonucleotide chain:
    • Sugar, phosphate groups, and nitrogenous bases (A, U, C, G).
    • Linked via Phosphodiester bonds
  • Single-stranded:
    • May fold into complex 3D structures.
  • Linear:
    • Two ends: 5' phosphate and 3' hydroxyl end.
  • Sugar: Ribose

RNA vs DNA

• Key Differences:
  • Sugar:
    • Ribose (RNA)
    • Deoxyribose (DNA)
  • Bases:
    • Uracil (RNA)
    • Thymine (DNA)
  • Structure:
    • Single-stranded (RNA)
    • Double-stranded (DNA)

Types of RNA

• Ribosomal RNA (rRNA):
  • Most abundant type of RNA.
  • Function:
    • Found in ribosomes, responsible for protein synthesis.
  • Location: Cytoplasm
• Transfer RNA (tRNA):
  • Structure:
    • Cloverleaf-shaped.
    • Contains modified bases (pseudouridine, dihydrouridine, ribothymidine).
    • Anticodon loop: Recognizes codons in mRNA.
    • CCA sequence: Carries amino acids.
  • Function:
    • Deliver amino acids to the ribosomes during protein synthesis.
• Messenger RNA (mRNA):
  • Structure:
    • A linear molecule with a 5' cap and a 3' poly(A) tail.
  • Synthesis: Transcription in the nucleus.
  • Function:
    • Carries genetic information from DNA to ribosomes.
    • Guides protein synthesis.

Genetic Code

• Sequence of bases in mRNA:
  • Translated into the amino acid sequence of a protein.
• Codon:
  • Three consecutive bases on mRNA that code for one amino acid.
  • Read in the 5' to 3' direction.
• Total number of codons: 64
  • 61: Code for the 20 common amino acids.
  • 3: Stop codons (UAG, UGA, UAA) - Terminate protein synthesis.

Protein Synthesis (Translation)

• Ribosomes:

  • Eukaryotes: 80S (60S + 40S)
  • Prokaryotes: 70S (50S + 30S)

• Steps:

  • Initiation:
    • Small ribosomal subunit binds to mRNA.
    • Initiator tRNA carrying methionine binds to the start codon (AUG).
    • Large ribosomal subunit joins the complex.
  • Elongation:
    • tRNA carrying the next amino acid binds to the A site.
    • Peptide bond forms between the amino acids.
    • Ribosome moves along mRNA (translocation).
  • Termination:
    • Stop codon in the mRNA is reached.
    • Release factors bind to the ribosome, releasing the polypeptide chain.
    • Ribosome subunits dissociate.

• Elongation Factors:

  • EF-Tu:
    • Helps tRNA bind to the ribosome A site.
  • EF-Ts:
    • Recycles EF-Tu.
  • EF-G:
    • Helps translocation of the ribosome along the mRNA.

Test your knowledge on the structure and functions of nucleotides as well as their metabolism. This quiz covers important concepts including the roles of nitrogenous bases, synthesis pathways, and degradation processes. Perfect for students studying biochemistry and molecular biology.