NUCLEIC ACID NG PAPA MO

• Nucleic Acids: Polymers in which repeating unit is nucleotide

  
• Nucleotide


  Has three components: Pentose Sugar, Phosphate Group, Heterocyclic Base
• Pentose Sugar


  • Ribose is present in RNA, 2-deoxyribose is present in DNA
  • Structural difference: a —OH group present on carbon 2' in ribose, a —H atom in 2-deoxyribose
• Nitrogen-Containing Heterocyclic Bases


  • Thymine (T), Cytosine (C), Uracil (U) (Pyrimidine derivatives)
  • Adenine (A), Guanine (G) (Purine derivatives)
• Adenine (A), Guanine (G), and Cytosine (C) are found in both DNA and RNA. Uracil (U) found only in RNA, Thymine (T) found only in DNA.
• Phosphate


  Derived from phosphoric acid (H3PO4), under cellular pH conditions, the phosphoric acid is fully dissociated to give a hydrogen phosphate ion (HPO4^2-)
• Nucleotide Formation


  Phosphate attached to C-5' and base is attached to C-1' position of pentose
• Primary Nucleic Acid Structure

  Sugar-phosphate groups are referred to as nucleic acid backbone, Sugars are different in DNA and RNA

  
• Ribonucleic Acid (RNA)


  Nucleotide polymer in which each monomer contains ribose, a phosphate group, and one of the heterocyclic bases adenine, cytosine, guanine, or uracil
• Deoxyribonucleic Acid (DNA)


  Nucleotide polymer in which each monomer contains deoxyribose, a phosphate group, and one of the heterocyclic bases adenine, cytosine, guanine, or thymine
• Primary Structure


  Sequence of nucleotides in DNA or RNA, due to changes in the bases, Phosphodiester bond at 3' and 5' position, Sequence of bases read from 5' to 3'

  
• DNA Double Helix


  • Two polynucleotide chains coiled around each other in a helical fashion, Polynucleotides run anti-parallel, Bases located at the center and hydrogen bonded (A=T and G≡C), Base composition: %A = %T and %C = %G
• Complementary DNA Strands


  Strands of DNA in a double helix with base pairing such that each base is located opposite its complementary base
• DNA Sequence: the sequence of bases on one polynucleotide is complementary to the other polynucleotide

  
• DNA Replication


  Old strands act as templates for the synthesis of new strands, DNA polymerase checks the correct base pairing and catalyzes the formation of phosphodiester linkages, Newly synthesized DNA has one new DNA strand and old DNA strand
• DNA Replication


  • DNA polymerase enzyme can only function in the 5'-to-3' direction, Leading strand grows continuously, Lagging strand grows in segments (Okazaki fragments), DNA ligase connects the segments, DNA replication occurs at multiple sites (origin of replication), Bidirectional replication from these sites (replication forks)
• Chromosomes


  Histone–DNA complexes, Cells of different organisms have different numbers of chromosomes, Occur in matched (homologous) pairs
• Protein Synthesis


  Transcription - DNA directs the synthesis of mRNA molecules, Translation - mRNA is deciphered to synthesize a protein molecule
• RNA Molecules

  • RNA is single-stranded, RNA molecules are much smaller than DNA molecules, ranging from 75 nucleotides to a few thousand nucleotides

  
• 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 the exposed DNA strand, RNA polymerase catalyzes the linkage of ribonucleotides, Transcription ends when the RNA polymerase enzyme encounters a stop signal
• Post-Transcription Processing


  Splicing - Excision of introns and joining of exons, Alternative splicing - Excision of one or more exons
• Transcriptome


  All of the mRNA molecules that can be generated from the genetic material in a genome, Different from a genome, Responsible for the biochemical complexity created by splice variants obtained by hnRNA

  
• Codon


  A three-nucleotide sequence in an mRNA molecule that codes for a specific amino acid

  
• Genetic Code


  The assignment of the 64 mRNA codons to specific amino acids (or stop signals)
• Characteristics of Genetic Code

  • The genetic code is highly degenerate - Many amino acids are designated by more than one codon, The genetic code is universal - The same code applies to all organisms, The genetic code is unambiguous - Each codon specifies only one amino acid
• Transcriptome


  Different from a genome, responsible for the biochemical complexity created by splice variants obtained by hnRNA
• There are 64 possible codon combinations based on all possible combinations of bases A, G, C, U
• 3 of the 64 codons are termination codons ("stop" signals)
• Genetic code


  • It is highly degenerate - many amino acids are designated by more than one codon
  • It has a pattern where synonyms for an amino acid fall within a single box in the genetic code table unless there are more than four synonyms
• The genetic code is almost universal - with minor exceptions the code is the same in all organisms
• Initiation codon


  The codon coding for the amino acid methionine (AUG) functions as the initiation codon
• Anticodon


  A three-nucleotide sequence on a tRNA molecule that is complementary to a codon on an mRNA molecule

  
• Translation: Protein synthesis


  1. Activation of tRNA

  2. Initiation of protein synthesis

  3. Elongation

  4. Termination

  5. Post-translational processing
• Polysome (polyribosome)


  Complex of mRNA and several ribosomes
• The multiple use of mRNA molecules in polysomes reduces the amount of resources and energy that the cell expends to synthesize needed protein
• Mutation


  An error in base sequence reproduced during DNA replication
• Mutagen

  A substance or agent that causes a change in the structure of a gene
• Radiation and chemical agents are two important types of mutagens
• Under normal conditions mutations are repaired by repair enzymes