BIOCHEM 1.5

• What is the structure of a nucleotide?

  A nucleotide consists of one or more phosphate groups, a pentose sugar, and an organic base containing nitrogen.
• What is an example of a nucleotide?

  Adenosine triphosphate (ATP).
• What is the major function of ATP in cells?

  It provides energy for most reactions in most cells.
• What happens when the bond between the middle and terminal phosphate group of ATP is broken?

  Energy is released, forming ADP and a phosphate group (Pi).
• What is phosphorylation?

  The process of adding a phosphate group to ADP to form ATP.
• How much energy is released when the bond between the middle and terminal phosphate group of ATP is broken?

  30 kJ mol$^{-1}$ of energy is released.
• What type of reaction occurs when ATP is formed from ADP and Pi?

  It is a reversible reaction that requires energy input.
• What is the role of the enzyme ATPase?

  ATPase catalyses the hydrolysis of ATP, breaking the bond between phosphate groups to release energy.
• What is the reaction that occurs when ATP is hydrolyzed?

  ATP + Water → ADP + Pi + Energy
• What enzyme is responsible for breaking the bond in ATP to release energy?

  The enzyme ATPase breaks the bond between the middle and terminal phosphate group.
• What is formed when ATP is hydrolyzed?

  Adenosine diphosphate (ADP) and a phosphate group (Pi) are formed.
• What is the nature of the reaction when ADP and Pi re-form ATP?

  This is a reversible reaction that requires energy input.
• What is the process of adding a phosphate group to ADP called?

  This process is called phosphorylation.
• How much energy is released when the bond between the middle and terminal phosphate group of ATP is broken?

  30 kJ mol^-1 of energy is released.
• What type of reaction occurs when a phosphate group is added to ADP?

  This is an endergonic reaction that requires energy.
• Where is ATP produced in the cell?

  • Cytoplasm
  • Mitochondria (matrix and inner membranes)
  • Chloroplasts (thylakoid membranes)
• What are the uses of ATP in biological processes?

  • Metabolic processes
  • Movement (muscle contraction)
  • Nerve transmission
  • Active transport (e.g., sodium-potassium pumps)
  • Secretion (packaging and transport of products)
• What are the advantages of using ATP as an energy source?

  • Immediate energy release through a single reaction
  • Requires only one enzyme (ATPase) for energy release
  • Releases energy in small amounts as needed
  • Soluble and easily transported
  • Universal intermediary for energy reactions
• What are the two types of nucleic acids mentioned?

  Deoxyribonucleic acid (DNA) and ribonucleic acid (RNA).
• What are the three components of a nucleotide?

  A phosphate group, a pentose sugar, and an organic base containing nitrogen.
• What sugar is found in DNA nucleotides?

  The pentose sugar in DNA is deoxyribose.

  
• What bases are found in DNA nucleotides?

  The bases are adenine, thymine, cytosine, and guanine.

  
• What type of bases are adenine and guanine?

  Adenine and guanine are purine bases with a double ring structure.
• What type of bases are thymine, uracil, and cytosine?

  Thymine, uracil, and cytosine are pyrimidine bases with a single ring structure.
• How do complementary bases bond in DNA?

  Adenine bonds with thymine (or uracil) and cytosine bonds with guanine.

  
• What is the structure of DNA?

  DNA is a double-stranded polymer of nucleotides forming a double helix.

  
• What maintains the shape of the DNA double helix?

  The shape is maintained by hydrogen bonding between complementary bases.

  
• Where is DNA found in eukaryotic cells?

  DNA is found in the nucleus of eukaryotic cells.
• What are the two functions of DNA?

  The two functions of DNA are replication and protein synthesis.
• If a sample of DNA has 10% adenine, what percentage of thymine does it have?

  It must also have 10% thymine due to complementary base pairing.
• What is the remaining percentage of bases if 10% are adenine and 10% are thymine?

  The remaining 80% of bases belong to cytosine and guanine (40% each).

  
• What is the structure of messenger RNA (mRNA)?

  mRNA is a long single-stranded molecule.
• What is the function of mRNA?

  mRNA carries the genetic code from DNA to the ribosomes in the cytoplasm.
• What is the role of ribosomal RNA (rRNA)?

  rRNA is a component part of ribosomes and is involved in protein synthesis.
• What is the structure of transfer RNA (tRNA)?

  tRNA is a small single-stranded molecule folded into a cloverleaf shape.

  
• What is the function of tRNA?

  tRNA transports amino acids to the ribosomes for protein synthesis.

  
• What is the role of the anticodon in tRNA?

  The anticodon forms a complex with complementary bases on the mRNA molecule.

  
• What is the process of DNA replication?

  DNA replication involves unwinding, separating strands, and adding free nucleotides to form two identical DNA molecules.

  
• What hypothesis did Meselson and Stahl propose regarding DNA replication?

  They proposed the semi-conservative hypothesis, where each new DNA strand is composed of one original and one newly synthesized strand.

  
• What was the method used by Meselson and Stahl in their experiment?

  They cultured Escherichia coli in a medium containing the heavy isotope 15N and then transferred it to a lighter isotope 14N.