nucleic acid

• Enzyme


  A globular protein which functions as a biological catalyst, speeding up reaction rate by lowering activation energy without being affected by the reaction it catalyses
• Protein monomer


  Amino acids
• Standard amino acids


  • At least 4 standard amino acids
• Hydrolases


  One of the six categories of enzymes that serves a hydrolysis for the substrate
• Nucleic acids are biopolymers made up of monomeric units of nucleotides
• Nucleic acids


  • To hold genetic information
  • To perform a variety of other functions
• Types of nucleic acids

  • DNA: Deoxyribonucleic Acid
  • RNA: Ribonucleic Acid
• DNA


  Found within cell nucleus, storage and transfer of genetic information, passed from one cell to other during cell division
• RNA


  Occurs in all parts of cell, primary function is to synthesize the proteins
• Nucleotide


  A polymer in which the monomer units are nucleotides, has three components: pentose sugar, phosphate group, heterocyclic base
• Pentose sugar


  Ribose is present in RNA, 2-deoxyribose is present in DNA
• RNA and DNA differ in the identity of the sugar unit in their nucleotides
• Phosphate group


  Derived from phosphoric acid, fully dissociated to give a hydrogen phosphate ion under cellular pH conditions
• Nitrogen-containing heterocyclic bases


  • Thymine (T), cytosine (C), uracil (U), adenine (A), guanine (G)
• Nucleotide formation


  1. First, the pentose sugar and nitrogen-containing base react to form a nucleoside

  2. The nucleoside reacts with a phosphate group to form the nucleotide
• Nucleoside


  A two-subunit entity formed from the pentose sugar and nitrogen-containing base
• Nucleotide


  A three-subunit entity formed from the nucleoside and phosphate group, the building blocks for nucleic acids
• Phosphate is attached to C-5' and base is attached to C-1' position of pentose in nucleotides
• Nucleoside nomenclature


  Pyrimidine bases use the suffix -idine, purine bases use the suffix -osine, the prefix deoxy- indicates deoxyribose sugar
• RNA is a nucleotide polymer with ribose, phosphate, and one of the bases adenine, cytosine, guanine, or uracil
• DNA is a nucleotide polymer with deoxyribose, phosphate, and one of the bases adenine, cytosine, guanine, or thymine
• Primary nucleic acid structure

  • Sugar-phosphate groups form the backbone, sugars are different in DNA and RNA
• Primary nucleic acid structure

  Sequence of nucleotides, phosphodiester bonds at 3' and 5' positions, sequence read from 5' to 3' end
• Nucleic acids and proteins have different backbones
• DNA double helix


  • Two polynucleotide chains coiled around each other, run anti-parallel, bases hydrogen bonded (A=T, G≡C), base composition %A = %T and %C = %G
• Complementary DNA strands


  Strands with base pairing such that each base is located opposite its complementary base
• Stronger hydrogen bonding occurs with A-T and G-C base pairs
• DNA replication


  Old strands act as templates for synthesis of new strands, DNA polymerase checks base pairing and catalyzes phosphodiester bond formation, newly synthesized DNA has one new and one old strand
• DNA replication


  • DNA polymerase functions in 5'-to-3' direction, leading strand grows continuously, lagging strand grows in Okazaki fragments, multiple replication sites enable rapid synthesis, replication is bidirectional
• Chromosomes


  Histone-DNA complexes, contain 15% DNA and 85% protein, different organisms have different numbers of chromosomes, occur in homologous pairs
• Protein synthesis


  1. Transcription: DNA directs synthesis of mRNA

  2. Translation: mRNA is deciphered to synthesize protein
• Types of RNA molecules

  • Heterogeneous nuclear RNA (hnRNA)
  • Messenger RNA (mRNA)
  • Small nuclear RNA
  • Ribosomal RNA (rRNA)
  • Transfer RNA (tRNA)
• Transcription


  Unwinding of DNA double helix, alignment of free ribonucleotides along exposed DNA template, RNA polymerase catalyzes linkage to form mRNA, transcription ends when stop signal is encountered
• Post-transcription processing


  Splicing: Excision of introns and joining of exons, driven by snRNA, alternative splicing produces protein variants
• Transcription


  Two-step process - (1) synthesis of hnRNA and (2) editing to yield mRNA molecule
• Gene


  A segment of a DNA base sequence responsible for the production of a specific hnRNA/mRNA molecule
• Genome


  All of the genetic material (the total DNA) contained in the chromosomes of an organism
• Transcription Process


  1. Unwinding of DNA double helix to expose some bases (a gene)

  2. Alignment of free ribonucleotides along the exposed DNA strand (template) forming new base pairs

  3. RNA polymerase catalyzes the linkage of ribonucleotides one by one to form mRNA molecule

  4. Transcription ends when the RNA polymerase enzyme encounters a stop signal on the DNA template
• hnRNA


  Precursor to mRNA
• Exon


  A gene segment that codes for genetic information