Nucleotides and nucleic acids

• Describe the structure of nucleotide


  - pentose sugar (5carbon sugar)

  - nitrogenous base

  - phosphate group
• What charge does phopshate have


  PO43-
• Name the pentose sugar in DNA and RNA

  DNA: deoxyribose

  RNA: ribose
• Describe how polynucleotide strands are formed and broken down


  Condensation reactions between adjacent nucleotides form phosphodiester bonds between pentose sugar and phosphate (sugar-phosphate backbone). Also, hydrogen bonding is formed between complementary nitrogenous bases

  Hydrolysis reaction is used to break these bonds

  
  

  Enzymes catalyse these reactions
• Describe the structure of DNA

  - Molecule twists to form double helix of 2 deoxyribose polynucleotide strands (so there are 2 sugar-phosphate backbones).

  
  

  - Hydrogen bonds form between complementary base pairs (AT & GC) on strands that run antiparallel.
• Name the purine bases


  Adenine, Guanine
• What is a purine molecule


  Two-ring molecule
• Name the pyrimidine molecule


  Thymine, cytosine and uracil
• What is a pyrimidine


  One ring molecule
• Name the complementary bases and number of hydrogen bonds formed between them


  A and T/U - 2 hydrogen bonds

  C and G - 3 hydrogen bonds
• Why is DNA replication described as semi-conservative


  Strands from original DNA molecule act as template

  
  

  New DNA molecule contains one newly synthesised strand and one old/original strand
• What is the role of DNA helicase in semi conservative replication


  Breaks hydrogen bonds between base pairs to form 2 single strands, each of which act as a template
• How is a new strand formed during semi-conservative replication


  1. Free DNA nucleotide aligns next to original DNA template and attach to complementary bases

  
  

  2. DNA polymerase joins adjacent nucleotides on new strand in 5' —> 3' direction via condensation. To form phosphodiester bonds

  
  

  3. H-bonds reform
• What type of nucleotide is ATP


  Purine
• What type of nucleotide is ADP


  Purine
• What's ADP composed of

  - adenine

  - ribose

  - 2 inorganic phosphate groups
• What's ATP composed of

  - adenine

  - ribose sugar

  - 3 inorganic phosphate groups
• Identify the 3 features of the genetic code

  - non overlapping = each triplet is read only once

  - degenerate = more than 1 triplet codes for the same amino acid (64 possible triplets for 20 amino acids)

  - universal same bases and sequence used by all species
• How many bases does one codon contain


  3
• Describe non-overlapping and an example of where it occurs

  E.g protein synthesis

  
  

  When adjacent codons(3 bases) don't overlap. Each base is only read once in the codon its part of
• Describe universal genetic code


  The same triplet codes code for the same amino acid in all living organisms (makes genetic engineering possible)
• Describe dengenrate coding


  Multiple codons can code for the same amino acid
• What occurs to the bond when active site and substrate bind


  Bonds in substrate can weaken
• How does gene determine the sequence of amino acids in protein?


  Consist of base triplets that code for a specific amino acid
• What does transcription produce and where does it occur


  Produces mRNA

  
  

  Occurs in nucleus
• What is mutation


  An alteration to the DNA base sequence. Often arise spontaneously during DNA replication.
• Outline the process of translation


  1. The DNA helix unwinds to expose the bases to act as a template

  2. Only one chain of the DNA acts as a template

  3. Like with DNA replication, this unwinding and unzipping is catalysed by DNA helicase

  4. DNA helicase breaks the hydrogen bond between bases

  5. Free mRNA nucleotides in the nucleus align opposite exposed complementary DNA bases

  6. The enzyme RNA polymerase bonds together the RNA nucleotides between the ribose sugar and phosphate to create a new polymer chain. One entire gene is copied

  
  

  Once copied the mRNA is modified and then leaves the nucleus through the nuclear envelope pores
• What are the two stages of protein synthesis/ polypeptide synthesis


  Transcription

  Translation
• What occurs in transcription

  Where one gene of the DNA is copied into mRNA
• What occur is in translation


  Where the mRNA joins with a ribosome, and corresponding tRNA molecules bring the specific amino acids the codon codes for
• Where does translation take place and what does it produce


  Produce protein and takes place in cytoplasm on ribosome
• When does pre mRNA and mRNA occur

  After translation
• What occurs in pre mRNA and mRNA

  Following transcription, pre-mRNA has to be modified to become mRNA that is ready to leave the nucleus and take part in translation.

  
  

  The introns are spliced out by a protein called a splicesome. This leaves behind just the exons, the coding regions.
• Outline the process of translation


  1. Once the modified mRNA has left the nucleus is attaches to a ribosome in the cytoplasm.

  2. The ribosome attaches at the start codon.

  
  

  3. The tRNA molecule with the complementary anticodon to the start codon aligns opposite the mRNA, held in place by the ribosome.

  The ribosome will move along the mRNA molecule to enable another complementary tRNA to attach to the next codon on the mRNA.

  5. The two amino acids that have been delivered by the tRNA molecule are joined by a peptide bond. This is catalysed by an enzyme and requires ATP.

  This continues until the ribosome reaches the stop codon at the end of the mRNA molecule. The stop codon does not code for an amino acid and therefore the ribosome detaches and translation ends.

  
  

  The polypeptide chain is now created and will enter the Golgi body for folding and modification.
• Name the 3 types of RNA

  TRNA - transfers specific amino acids to the ribosome during translation

  
  

  MRNA - carries specific genetic information from DNA to the ribosome for protein synthesis

  
  

  RRNA - forms the core component of ribosomes, the site of protein synthesis
• How many DNA bases code for one amino acid

  3
• What's the function of a gene

  Code for a specific protein or RNA. Codes for production of polypeptide
• Explain why complementary base pairing is important

  - DNA can be replicated without error

  - reduces occurrence of mutation

  - allows re-formation of H-bonds
• State ways in which glucose molecule is well suited to its function in living organisms

  Soluble - easily transported

  Small molecule - easily transported
• How many maximum base combinations are in DNA


  64