2.3 Nucleic acids

• The structure of a nucleotide is represented by a pentose sugar and a nitrogenous base.
• The pentose sugars in DNA & RNA are deoxyribose and ribose respectively.
• ATP, the nucleotide derivative of adenine, has 3 inorganic phosphate groups.
• ADP, the nucleotide derivative of adenine, has 2 inorganic phosphate groups.
• Polynucleotide strands are formed and broken down through condensation reactions that form strong phosphodiester bonds (sugar-phosphate backbone) and hydrolysis reactions that use a molecule of water to break these bonds.
• The structure of DNA involves a molecule twisting to form a double helix of 2 deoxyribose polynucleotide strands, with H-bonds forming between complementary base pairs (AT & GC) on strands that run antiparallel.
• The purine bases in DNA are adenine and guanine, which are two-ring molecules.
• The pyrimidine bases in DNA are thymine, cytosine, and uracil, which are one-ring molecules.
• The complementary base pairs in DNA and RNA are adenine and thymine, guanine and cytosine, and uracil and cytosine.
• DNA can be purified by precipitation by adding ethanol and a salt to an aqueous solution, causing nucleic acids to precipitate out of solution, then centrifuging to obtain a pellet of nucleic acid, and washing the pellet with ethanol and centrifuging again.
• The process of transcription involves RNA polymerase binding to a promoter region on a gene, uncoiling a section of DNA into two strands with exposed bases, attracting free nucleotides to their complementary bases, and joining adjacent nucleotides to form phosphodiester bonds.
• DNA: 2 H-bonds between adenine ( A ) + thymine ( T )
• The genetic code is non-overlapping, degenerate, and universal.
• Both have 3 H-bonds between guanine ( G ) + cytosine ( C )
• A gene determines the sequence of amino acids in a protein by consisting of base triplets that code for a specific amino acids.
• DNA helicase breaks H-bonds between base pairs to form two single strands, each of which can act as a template.
• In semiconservative replication, a new strand is formed by attaching free nucleotides from nuclear sap to exposed bases by complementary base pairing.
• DNA polymerase joins adjacent nucleotides on the new strand in a 5’ → 3’ direction via condensation reactions to form phosphodiester bonds.
• H-bonds reform after DNA replication.
• RNA: 2 H-bonds between adenine ( A ) + uracil ( U )
• DNA replication is described as semiconservative because the strands from the original DNA molecule act as templates and the new DNA molecule contains one old strand and one new strand.
• Transcription produces mRNA which occurs in the nucleus.
• The process of translation involves a ribosome moving along mRNA until the ‘start’ codon, with tRNA anticodon attaching to complementary bases on mRNA, condensation reactions between amino acids on tRNA forming peptide bonds, and the process continuing to form a polypeptide chain until the ‘stop’ codon is reached.
• mRNA moves out of the nucleus via a nuclear pore and attaches to a ribosome.
• After a strand of mRNA is transcribed, RNA polymerase detaches at the terminator region, allowing H-bonds to reform and DNA to rewind.
• Translation produces proteins which occurs in the cytoplasm on ribosomes, which are made of protein and rRNA.
• In eukaryotic cells, splicing removes introns from pre-mRNA during translation.