nucleotides and nucleic acids

• Both DNA and RNA carry information
• DNA holds genetic information
• RNA transfers genetic information from DNA to ribosomes made of RNA and proteins
• DNA and RNA are polymers of nucleotides
• Nucleotides consist of pentose (5 carbon sugar), a nitrogen-containing organic base, and a phosphate group
• Components of a DNA nucleotide: deoxyribose, a phosphate group, and one of the organic bases adenine, cytosine, guanine, or thymine
• Components of an RNA nucleotide: ribose, a phosphate group, and one of the organic bases adenine, cytosine, guanine, or uracil
• Nucleotides join together by phosphodiester bonds formed in condensation reactions
• ATP (Adenosine triphosphate) is a nucleotide derivative
• Consists of ribose, adenine, and three phosphate groups
• Energy is released when ATP is hydrolysed to form ADP and a phosphate molecule, catalysed by ATP hydrolase
• Inorganic phosphate from ATP hydrolysis can phosphorylate other compounds, making them more reactive
• Condensation of ADP and inorganic phosphate catalysed by ATP synthase produces ATP during photosynthesis and respiration
• DNA replication is semi-conservative
• Ensures genetic continuity between generations of cells
• Steps of semi-conservative replication of DNA:

  • Double helix unwinds and hydrogen bonds between complementary bases break using DNA helicase
  • Complementary base pairing occurs between template strands and free nucleotides
  • Adjacent nucleotides are joined by phosphodiester bonds formed in condensation reactions using DNA polymerase
• Genetic code is the order of bases on DNA
• Consists of triplets of bases, each coding for a particular amino acid (codon)
• Non-coding sections of DNA are introns, coding regions are exons
• Features of the genetic code:

  • Non-overlapping, each triplet is only read once
  • Degenerate, more than one triplet codes for the same amino acid
  • Contains start and stop codons
• Protein synthesis involves transcription and translation
• Transcription occurs in the nucleus and involves DNA and mRNA
• Translation involves mRNA, tRNA, and ribosomes
• During transcription, DNA is transcribed into mRNA using RNA polymerase
• During translation, amino acids are assembled to form a polypeptide chain
• tRNA carries amino acids to the ribosome and attaches to mRNA by complementary base pairing
• Amino acids join by peptide bonds to form a polypeptide chain until a stop codon is reached on mRNA