Nucleotides and Nucleic acids

• Nucleotides: formed from a pentose sugar, nitrogen-containing organic base and a phosphate group. DNA nucleotides: contain a deoxyribose sugar, a phosphate group, and a nitrogenous base (Adenine/ Cytosine/ Guanine/ Thymine), RNA nucleotides: contain a ribose sugar, a phosphate group, and a nitrogenous base (Adenine/ Uracil/ Cytosine/ Thymine).
• Purines: Adenine and Guanine, have a double ring structure. Pyrimidine: Cytosine, thymine and uracil, have a single ring structure.
• Phosphodiester bonds: forms between the phosphate group of one nucleotide and the pentose sugar of the next nucleotide. This involves two ester bonds and the phosphate group.
• Hydrogen bonding: There always two hydrogen bonds are formed between A and T, three hydrogen bonds between G and C.
• DNA Purification: involves breaking the cells and disrupting the nuclear membranes to release the DNA, using enzymes to denature and remove the proteins associated with the DNA, precipitating the DNA using an organic solvent
• Semi-conservative replication: in each new DNA molecules produced one of the polynucleotide DNA strands is from the original DNA molecule being copied. The other strand is newly created by the cell, therefore the molecule is half conserved. Maintaining genetic continuity is importance because all genetic information is conserved, means new cells produced inherit all their genes from the parent cells.
• DNA replication: the double helix unwinds and the hydrogen bonds between the complementary bases break using DNA helicase - which separates the two strands, both strands are used as templates and complementary base pairing occurs between the template strand and free nucleotides. Adjacent nucleotides are joined by phosphodiester bonds formed in condensation reactions using DNA polymerase.
• Genetic code: the order of bases on DNA, consists of a triplets of bases each triplet of bases codes for a particular amino acid known as a codon. Amino acids are joined together by peptide bonds to form a polypeptide chain. A gene is a sequence of bases on a DNA molecule coding coding for a sequence of amino acids in a polypeptide chain. Not all of the genomes code for proteins- the non-coding sections are called introns and the coding regions are called exons
• features of the genetic code: non-overlapping (each triplet is only read one and doesn't share bases), degenerate (each triplet can code for more than one amino acid), universal (all living organisms use the same code).
• Transcription: the hydrogen bonds between complementary bases break and DNA uncoils- separating the strands, one of the DNA strands is used as a template by RNA polymerase to make the mRNA molecule. Free nucleotides line up by complementary base pairing, phosphodiester bonds form between adjacent nucleotides, which forms a single stranded molecules of mRNA. mRNA then moves out of the nucleus through a pore and attaches to a ribosome in the cytoplasm
• Translation: mRNA attaches to a ribosome and tRNA collects amino acids from the cytoplasm and carriers them to the ribosome. tRNA is a single stranded molecule with a binding site at one end thus it can only carry one type of amino acid a triplet at the other end. tRNA attaches itself to mRNA through complementary base pairing (two molecules attach to mRNA at one time), tRNA molecules join by a peptide bond the detach from the amino acid, this leads to a polypeptide chains until a stop codon is attached.