M2:S3 Nucleotides and Nucleic acids

• Nucleotides


  Biological molecules made from a pentose sugar, a nitrogenous base, and a phosphate group
• Nucleotides are the monomers that make up DNA and RNA
• DNA


  Nucleic acid used to store genetic information - the instructions an organism needs to grow and develop
• RNA


  Nucleic acid used to make proteins from the instructions in DNA
• ADP


  Nucleotide containing adenine, ribose, and two phosphate groups
• ATP


  Nucleotide containing adenine, ribose, and three phosphate groups. Provides energy for chemical reactions in the cell.
• ATP synthesis


  1. ADP and inorganic phosphate (P) combine using energy from an energy-releasing reaction (e.g. glucose breakdown)

  2. Phosphate bond forms, storing energy
• ATP breakdown


  1. ATP is broken down into ADP and inorganic phosphate (P)

  2. Energy is released from the phosphate bond and used by the cell
• The three main components of nucleotides are a pentose sugar, a nitrogenous base, and a phosphate group
• Deoxyribose


  The pentose sugar found in DNA nucleotides
• Ribose


  The pentose sugar found in RNA nucleotides
• Adenine


  The base found in ATP
• Adenine and guanine are purines, cytosine and thymine/uracil are pyrimidines
• Nucleotides joining to form polynucleotides

  1. Phosphate group of one nucleotide bonds to sugar of another via condensation reaction, forming phosphodiester bond

  2. Chain of sugars and phosphates is the sugar-phosphate backbone
• Polynucleotide strands joining to form double helix

  1. Two strands join by hydrogen bonding between complementary bases (A-T, C-G)

  2. Strands run in opposite directions (antiparallel)

  3. Hydrogen bonds and twisting form double helix structure
• DNA purification by precipitation

  1. Break up cells

  2. Add detergent, salt, incubate at 60°C

  3. Cool, filter, add enzymes to break down proteins and RNA

  4. Add cold ethanol, DNA precipitates out
• Semi-conservative DNA replication


  1. DNA helicase unzips DNA helix

  2. Each original strand acts as template for new complementary strand

  3. DNA polymerase joins new nucleotides to form new strands

  4. Each new DNA molecule has one original and one new strand
• DNA replication is very accurate but random mutations can still occur
• Gene


  Sequence of DNA nucleotides that codes for a polypeptide (sequence of amino acids in a protein)
• Gene


  A sequence of DNA nucleotides that codes for a polypeptide - the sequence of amino acids in a polypeptide forms the primary structure of a protein
• mRNA


  Carries the genetic code from the DNA in the nucleus to the cytoplasm, where it's used to make a protein during translation
• Genetic code


  • Non-overlapping - base triplets are read in sequence, separate from the triplet before and after
  • Degenerate - more possible combinations of triplets than there are amino acids, so some amino acids are coded for by more than one base triplet
  • Universal - the same specific base triplets code for the same amino acids in all living things
• Start and stop signals (codons) are found at the beginning and end of the gene
• Transcription


  1. RNA polymerase attaches to DNA

  2. DNA strands separate

  3. One strand used as template to make mRNA

  4. RNA nucleotides line up and join to form mRNA

  5. RNA polymerase moves along DNA, assembling mRNA

  6. DNA strands re-form

  7. RNA polymerase stops at stop codon, mRNA leaves nucleus
• Translation


  1. mRNA attaches to ribosome

  2. tRNA carries amino acids to ribosome

  3. tRNA anticodon binds to mRNA codon

  4. Ribosomal RNA catalyses peptide bond formation

  5. Amino acids join to form polypeptide chain

  6. Polypeptide chain moves away from ribosome
• There are three main types of RNA: mRNA, tRNA, rRNA
• mRNA has a codon sequence that codes for a specific sequence of amino acids
• tRNA has an anticodon that binds to the mRNA codon and carries the corresponding amino acid
• Nucleotides


  Biological molecules made from a pentose sugar, a nitrogenous base, and a phosphate group
• Nucleotides are the monomers that make up DNA and RNA
• DNA


  Nucleic acid that stores genetic information - the instructions an organism needs to grow and develop
• RNA


  Nucleic acid used to make proteins from the instructions in DNA
• ADP


  Nucleotide containing adenine, ribose, and two phosphate groups
• ATP


  Nucleotide containing adenine, ribose, and three phosphate groups. Provides energy for chemical reactions in the cell.
• ATP synthesis


  ADP and inorganic phosphate (P) combine, using energy from an energy-releasing reaction, to form ATP and release a phosphate bond
• ATP breakdown


  ATP is broken down into ADP and inorganic phosphate (P), releasing energy stored in the phosphate bond
• Deoxyribose


  The pentose sugar found in DNA nucleotides
• Ribose


  The pentose sugar found in RNA nucleotides
• Bases in DNA


  • Adenine
  • Thymine
  • Cytosine
  • Guanine
• Purines


  Adenine and guanine - bases with two carbon-nitrogen rings