Biology module 2.3

• DNA


  Carries genetic information
• RNA


  Transfers genetic information from DNA to ribosomes
• Nucleotides


  Consist of pentose (5 carbon sugar), a nitrogen containing organic base, and a phosphate group
• Components of a DNA nucleotide

  • Deoxyribose
  • Phosphate group
  • Adenine, cytosine, guanine or thymine

  
• Components of an RNA nucleotide


  • Ribose
  • Phosphate group
  • Adenine, cytosine, guanine or uracil
• Nucleotides joining together


  Phosphodiester bonds formed in condensation reactions
• DNA molecule

  • Double helix composed of two polynucleotides joined by hydrogen bonds between complementary bases
• RNA


  • Relatively short single polynucleotide chain
• ATP


  Nucleotide derivative consisting of ribose, adenine and three phosphate groups
• ATP hydrolysis


  Releases energy to form ADP and a phosphate molecule, catalysed by ATP hydrolase
• Phosphorylation of other compounds

  Using the inorganic phosphate released from ATP hydrolysis, making them more reactive
• ATP synthesis


  Condensation of ADP and inorganic phosphate catalysed by ATP synthase, occurs during photosynthesis and respiration
• DNA replication


  Semi-conservative replication ensures genetic continuity between generations of cells
• Steps of semi-conservative DNA replication

  1. DNA helicase unwinds double helix and separates strands

  2. Complementary base pairing occurs between template strands and free nucleotides

  3. DNA polymerase joins adjacent nucleotides by phosphodiester bonds
• Genetic code


  Order of bases on DNA, triplets of bases code for particular amino acids (codons)
• Genetic code


  • Non-overlapping, degenerate (more than one triplet codes for same amino acid), contains start and stop codons
• Protein synthesis


  Transcription (in nucleus) and translation (at ribosomes)
• Transcription


  DNA strand used as template by RNA polymerase to make mRNA molecule, mRNA moves to cytoplasm
• Translation


  mRNA attaches to ribosome, tRNA collects amino acids and carries them to ribosome, amino acids join by peptide bonds until stop codon reached
• Not all genome codes for proteins, non-coding sections are introns and coding regions are exons
• Mutations in DNA can alter amino acid sequence and protein structure, some mutations are harmful
• Nucleotides


  Monomers that make up DNA and RNA

  
• DNA and RNA


  • Nucleic acids: polymers made up of many repeating nucleotide units

  
• Components of a nucleotide


  • Pentose sugar
  • Nitrogen-containing organic base
  • Phosphate group

  
• DNA nucleotide


  Contains deoxyribose sugar, phosphate group, and one of four nitrogenous bases (A, C, G, T)

  
• RNA nucleotide


  Contains ribose sugar, phosphate group, and one of four nitrogenous bases (A, C, G, U)

  
• The 2' hydroxyl group in RNA makes it more susceptible to hydrolysis compared to DNA

  
• DNA is the storage molecule and RNA is the transport molecule with a shorter molecular lifespan
• Purines


  Nitrogenous bases with a double ring structure (adenine, guanine)

  
• Pyrimidines


  Nitrogenous bases with a single ring structure (cytosine, thymine, uracil)

  
• DNA and RNA nucleotides differ in the pentose sugar (deoxyribose vs ribose) and the nitrogenous base (thymine vs uracil)

  
• Phosphodiester bond


  Bond formed between the phosphate group of one nucleotide and the pentose sugar of the next nucleotide

  
• Condensation reactions form phosphodiester bonds, hydrolysis reactions break them
• Sugar-phosphate backbone


  Chain of alternating phosphate groups and pentose sugars formed by phosphodiester bonds

  
• ATP


  Adenosine triphosphate, the energy-carrying molecule that provides energy for cellular processes
• AMP, ADP, ATP


  Nucleotides with 1, 2, or 3 phosphate groups respectively

  
• DNA structure


  • Two antiparallel polynucleotide strands
  • Alternating deoxyribose sugars and phosphate groups forming the sugar-phosphate backbone
  • Nitrogenous bases projecting inwards
  • Complementary base pairing (A-T, C-G)

  
• Complementary base pairing


  A pairs with T, C pairs with G, held together by hydrogen bonds
• DNA double helix


  Three-dimensional structure formed by the twisting of the two antiparallel DNA polynucleotide strands

  
• DNA purification


  1. Cell lysis to release DNA

  2. Enzyme treatment to denature and remove proteins

  3. Precipitation to isolate DNA