nucleic acids Q

• Describe the structure of a nucleotide. (2)

  Answer: A nucleotide consists of a phosphate group, pentose sugar, and a nitrogenous base (A, T, C, G).
• What bonds hold DNA strands together? (2)

  Answer: Hydrogen bonds between complementary base pairs (A-T and C-G)
• Compare DNA and RNA. (3)

  Answer:

  • DNA is double-stranded, RNA is single-stranded
  • DNA has deoxyribose, RNA has ribose
  • DNA uses thymine (T), RNA uses uracil (U
• Describe the structure of DNA. (3)

  Answer: DNA is a double-helix made of two antiparallel polynucleotide strands held together by hydrogen bonds between complementary base pairs (A-T, C-G).
• Compare the structures of DNA and ATP. (3)

  Answer:

  • DNA nucleotide has deoxyribose, ATP has ribose.
  • DNA has one phosphate group, ATP has three phosphate groups.
  • DNA contains a nitrogenous base (A, T, C, G), while ATP only has adenine.
• What is the role of DNA helicase in DNA replication? (2)

  Answer: DNA helicase breaks hydrogen bonds between bases, unwinding the double helix and separating the strands
• Explain the role of DNA polymerase in DNA replication. (2)

  Answer: DNA polymerase joins free nucleotides by forming phosphodiester bonds, synthesizing the new complementary strand.
• Describe the process of semi-conservative replication. (3)

  Answer:

  • DNA helicase unwinds the double helix and breaks hydrogen bonds.
  • Free nucleotides pair with complementary bases on the exposed strands.
  • DNA polymerase forms phosphodiester bonds, creating two identical DNA molecule’s
• What evidence supports the semi-conservative replication model? (3)

  Answer: The Meselson-Stahl experiment used heavy (N15) and light (N14) nitrogen to show that DNA strands mix, producing intermediate and light bands in density-gradient centrifugation
• What is the function of RNA in protein synthesis? (2)

  Answer:

  • mRNA carries genetic code from DNA to ribosomes.-
  • tRNA transports amino acids to ribosomes for translation.
• Describe the structure of mRNA. (2)

  Answer: mRNA is a single-stranded polynucleotide with codons (triplets of bases) complementary to DNA.
• How does tRNA differ from mRNA? (3)

  Answer:

  • tRNA has a cloverleaf shape, mRNA is linear.
  • tRNA has an anticodon and an amino acid attachment site.
  • tRNA is shorter than mRNA.
• Explain how ATP provides energy for cellular processes. (3)

  Answer:

  • ATP is hydrolyzed into ADP and Pi by ATP hydrolase, releasing energy.
  • The inorganic phosphate (Pi) is used for phosphorylation to make other molecules more reactive.
• How is ATP resynthesized? (2)

  Answer: ATP is resynthesized from ADP and Pi by ATP synthase during respiration or photosynthesis in a condensation reaction.
• Why is ATP described as an immediate energy source (2)

  Answer: ATP releases energy in a single-step reaction and cannot be stored, so it is continuously synthesized when needed