Lecture Eleven - Heterocyclic chemistry and nucleic acids Flashcards
What is a heterocycle?
A heteroatom is an atom other than C or H.
Hetero is a prefic meaning different.
heterocyclic compounds are compounds in which on eor more of the atoms in the ring is a heteroatom.
E.g. when there is an aromatic ring with a nitrogen, oxygen or sulphur atom where a carbon atom would ususally sit.
A large proportion of naturally occuring organic compounds are heterocyclic and are of biological importance.
E.g. Sugars, vitamins, alkaloids and nucleic acids.
Drug manufacturers rely heavily on heterocyclic compounds.
Drug synthesis -> heterocyclic compounds synthesis.
What are nucleic acids?
Storage of molecules for genetic information.
DNA is found in the cells nucleus.
RNA is found in the cells cytoplasm.
The building blocks of DNA and RNA are nucleotides.
Nucleic acid:
A biopolymer containing -
1) Heterocyclic aromatic amine bases (purines (two rings) and pyrimidines (one ring)).
2) Monosaccharides (D-ribose or 2-deoxy-D-ribose).
3) Phosphoric acid (H3PO4).
What are nucleosides and nucleotides?
NucleoSide = A building block of nucleic acids consisting of:
D-ribose or 2-deoxy-D-ribose, bonded to a heterocyclic amine base, by a beta-glucosidic bond.
NucleoTide = A phosphate ester of a nucleoside (OH at 3’ or 5’ position esterified with phosphoric acid).
D-ribose or 2-deoxy-D-ribose.
Heterocyclic amine base.
Phosphate ester.
What is an example of a nucleoside (moleculuar diagram)?
What is an example of a nucleotide (molecular diagram)?
What are nucleoside phosphates?
nucleoside monophosphates can be further phosphorylated to form nucleoside di and triphosphates.
E.g. Adenosine 5’-triphosphate (ATP).
Nomenclature: [parent nucleoside] [position at which nucleoside phosphorylated either 5’ or 3’] - [mono/di/tri etc phosphate].
What are nucleoside phosphates as acids?
These are polyacids:
Monophosphates = diprotic acids, pKa ≈ 1 and 6. Diphosphates = triprotic acids etc.
◆ e.g. ATP has 4 acidic protons (H+)
• pKa1 –pKa3<7.0andpKa4≈7.0
• @ pH = 7.0; ATP4- : ATP3- = approx. 1:1
What is the strucuture of DNA?
Deoxyribonucleic acids (DNA): A biopolymer consisting of a backbone of alternating units of 2-deoxy-D-ribose and phosphate in which the 3’-OH of one 2-deoxy-D-ribose is joined by a phosphodiester bond to the 5’-OH of another 2-deoxy-D-ribose unit.
Primary structure:
the sequence of bases along the pentose-phosphodiester backbone of a DNA molecule (or an RNA molecule) read from the 5’ end to the 3’ end.
Primary structure of DNA is the order of heterocyclic bases along the pentose-phosphodiester backbone (read from the 5’ to the 3’ end).
Secondary structure:
The ordered arrangement of nucleic acid strands.
Double helix:
A type of 2° structure of DNA molecules in which two antiparallel polynucleotide strands are coiled in a right-handed manner about the same axis.
Base pairs occur in the double strand of DNA.
Thymine (T) is always paired with Adenine (A).
Cytosine (C) is always paired with Guanine (G).
- Hydrogen bonds hold the base pairs together.
How does base pairing work between purines and pyrimidines?
How is RNA similar and different to DNA?
RNA are similar to DNA:
They consist of long, unbranched chains of nucleotides joined by phosphodiester bonds between the 3’-OH of one pentose and the 5’-OH of the next; however…
- The pentose unit is β-D-ribose not β-2-deoxy-D-ribose (the name tells you this).
- The pyrimidine base thymine (T) is replaced by uracil (U).
- RNA is single stranded not double stranded.
What are the different kinds of RNA?
RNA are classified by structure and function. Ribosomal RNA (rRNA): found in ribosomes, the site of protein synthesis.
Transfer RNA (tRNA): Carries a specific amino acid to the site of protein synthesis.
Messenger RNA (mRNA): carries coded genetic information (from DNA) to the ribosomes for the synthesis of proteins.
A complementary strand of mRNA is synthesised along one strand of an unwound DNA, starting from the 3’ end.
This is called transcription.
What are properties of the genetic code?
Only 61 triplets code for amino acids (aas) UAA, UAG, and UGA signal chain termination.
The code is degenerate.
I.e. several aas are coded for >1 triplet.
E.g. Leu, Ser, and Arg are coded for by six triplets.
15 amino acids are coded for by >1 codon only the third letter of the codon varies.
E.g. Gly is coded for by GGA, GGG, GGC, and GGU.
Each triplet codes for one and only one aa.
The code is universal.
