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Nucleotides and Nucelic Acids

  • 3eNucleotides and Nucleic Acids

  • Nucleic acids are a macromolecule that are adapted to storing genetic information and have the ability to be used to transfer it

  • It is called semi-conservative as 1 of the strands of DNA in each of the new copies is preserved from the old DNA strand 

  • Purine vs Pyrimidine: 

  • Purines are two ringed (adenine or guanine) while Pyrimidines are composed of only one ring (THINK: when its time to DINE you eat at 1 table) 

  • The bases will hydrogen bond to each other such that Adenine and Thymine will hydrogen bond with 2 bond between them and  Guanine and Cytosine will hydrogen bond with 3 hydrogen bonds between them 

  • ATP and ADP (&AMP) 

  • These are all phosphorylated nucleotides, as a result they have a phosphate group. They are composed such that the phosphate group is bonded to a ribose sugar (pentose) and this is bonded to the nitrogenous base of Adenine 

  • This is similar to the structure of DNA as DNA would consist of a phosphate group bonded to a five carbon sugar of deoxyribose and then this too is bonded to a nitrogenous base but this base is variable 

  • DNA replication: 

  • Known as semi-conservative and DNA is a self-replicating molecule

  • Unwound and unzipped by DNA helicase

  • Unwound - gyrase enzyme 

  • Unzipped - DNA helicase

  • Free phosphorylated nucleotides will hydrogen bond the the exposed bases following the complementary base pair rule 

  • DNA polymerase will catalyse the formation of phosphodiester bonds between the nucleotides in the 5’ 3’ direction 

  • As it only functions in the 5’ 3’ direction a leading strand and a lagging strand will form with the leading strand being the strand that runs entirely in the 5’ 3’ direction. The lagging strand runs in the opposite direction and so it is catalysed in fragments such that they are then joined by ligase enzymes 

  • An RNA primer is a short segment of single-stranded RNA used as a binding site for DNA polymerase to initiate DNA replication. DNA polymerase is only able to add nucleotides to an existing nucleotide chain; it cannot "start from scratch," and therefore needs the RNA primer to start the process

  • Lagging runs in the 3 5 and so fragments occr because polymerase 

  • The extra phosphate groups if present will then be hydrolysed to provide extra energy for the formation of phosphodiester bonds 

  • RNA: has a ribose sugar molecule, the nitrogenous base of uracil replaces thymine, it is single stranded, shorter and comes in three forms mRNA, tRNA (serves as an adaptor [1] between the genetic instructions written in nucleic acid sequences and the protein products encoded in genes.) and rRNA (ribosomal combine with proteins and enzymes in the cytoplasm to form ribosomes, which act as the site of protein synthesis. These complex structures travel along the mRNA molecule during translation and facilitate the assembly of amino acids to form a polypeptide chain.) 

  • Nature of Genetic Code: 

  • Universal - In (almost) all living organisms the same triplet of DNA bases codes for the same amino acids 

  • Degenerate - all amino acids (other than methionine and tryptophan) have more than 1 triplet which codes for them. As a result the effect of a point mutation is somewhat decreased 

  • Non-overlapping - has to be read from a fixed point and if a base is added or deleted a frameshift is caused across all subsequent bases and the code for all amino acids after than is changed 

  • (the coding strand is the strand which the RNA is the same as (with the exception of uracil instead of thymine)) 

  • Transcription:

  • DNA is unwound and unzipped (same as with replication) 

  • Free floating RNA nucleotides bind the the complementary nucleotides through hydrogen bonding (URACIL and Adenine) 

  • RNA polymerase catalyses the formation of these bonds and the formation of phosphodiester bonds between the mRNA, the hydrogen bonds are temporary 

  • This occurs on one strand which is the template strand the other strand would be the coding strand 

  • mRNA passes out of the nucleus 

  •  

  • Translation: This polypeptide chain will then fold (via the rules of primary, secondary, tertiary and quaternary protein structure) into a protein 

  • There will be two tRNA molecules that bind at once and the two amino acids will bond via a peptide bond 

  • tRNA binds to an mRNA strand as the anticodon of the tRNA binds to the codon (one of) on the mRNA strand 

  • brought to a ribosome 

  • Ribosome moves along the length of the mRNA and synthesises the amino acids which form peptide binds between each other using ATP energy 

  • After protein assembled the tRNA breaks down 

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