CHEM113-Lesson-1-Nucleic-Acids

1. Nucleic Acids

  • Definition: Discovered in 1869 by Swiss physiologist Friedrich Miescher; unbranched polymers made of monomers called nucleotides.

  • Types: Two main types - DNA (Deoxyribonucleic Acid) and RNA (Ribonucleic Acid).

  • Function: Key end products of nucleic acids are proteins or amino acids.

1.1 Nucleotide Structure

  • Components: Composed of three subunits:

    • Pentose Sugar: A monosaccharide with five carbon atoms; differs in RNA (ribose) and DNA (deoxyribose).

      • Attachment: Base attaches at Carbon 1 (C1); phosphate group at Carbon 5 (C5).

      • Structural Difference: RNA has -OH at Carbon 2 (C2) while DNA has -H (deoxyribose indicates absence of oxygen).

    • Phosphate Group: Links the nucleotides, forming the sugar-phosphate backbone of nucleic acids.

    • Nitrogen Base: Five types;

      • Pyrimidines: Thymine (T), Cytosine (C), Uracil (U).

      • Purines: Adenine (A), Guanine (G).

      • Characteristics: Pyrimidines are monocyclic (six-membered ring); purines are bicyclic (fused five-and six-membered rings).

      • Presence: Uracil is exclusive to RNA; Thymine is exclusive to DNA.

1.2 Nucleosides

  • Definition: A two-subunit molecule made of pentose sugar and nitrogen base.

  • Formation: Nucleoside names have suffixes:

    • Pyrimidine bases end with -idine.

    • Purine bases end with -osine.

    • The prefix -deoxy indicates the presence of deoxyribose sugar.

    • Examples:

      • RNA: adenosine (A), guanosine (G), cytidine (C), uridine (U).

      • DNA: deoxyadenosine, deoxyguanosine, deoxycytidine, deoxythymidine.

2. Nucleotide Formation

  • Nucleotide Synthesis: A nucleotide forms from the combination of a sugar, base, and phosphate, with the release of water.

2.1 Nucleotide Nomenclature

  • For DNA:

    • Nucleotide Names:

      • Adenine: deoxyadenosine 5'-monophosphate

      • Guanine: deoxyguanosine 5'-monophosphate

      • Cytosine: deoxycytidine 5'-monophosphate

      • Thymine: deoxythymidine 5'-monophosphate

  • For RNA:

    • Nucleotide Names:

      • Adenine: adenosine 5'-monophosphate

      • Guanine: guanosine 5'-monophosphate

      • Cytosine: cytidine 5'-monophosphate

      • Uracil: uridine 5'-monophosphate

3. Primary Structure of Nucleic Acids

  • Ribonucleic Acid (RNA):

    • Contains ribose; forms a backbone with alternating phosphate and ribose units.

  • Deoxyribonucleic Acid (DNA):

    • Contains deoxyribose; forms a backbone with alternating phosphate and deoxyribose.

  • Structure: The arrangement of nucleotides creates a specific sequence linked by phosphodiester bonds (3', 5') between the sugar molecules.

4. DNA Structure and Function

  • Directionality: Nucleotide chains have directionality; 5' end carries a free phosphate, while 3' end has a free hydroxyl group.

  • Characteristics:

    • Double helix structure, located in the nucleus.

    • Replication of genetic information; base pair composition is consistent: A% = T% and C% = G%.

    • Strand Orientation: Two strands run antiparallel (5' to 3' and vice versa).

  • Base Pairing:

    • Pyrimidine pairs with a purine: A ↔ T and G ↔ C.

    • Hydrogen Bonds: Stronger bonding observed between A-T and G-C pairs.

4.1 Chromosomal Structure

  • Composition: Chromosomes are complexes of DNA and histone proteins.

  • Numbers: Different species have varying chromosome counts (e.g., humans have 46).

5. Protein Synthesis

  • Occurs under the direction of DNA through transcription and translation.

  • Transcription:

    • Process of synthesizing mRNA from DNA.

    • Involves unwinding DNA and aligning ribonucleotides along the template.

  • Translation:

    • Synthesis of proteins from mRNA codons.

    • Includes activation of tRNA, initiation, elongation, and termination.

6. The Role of RNA

  • Types of RNA:

    1. Heterogeneous Nuclear RNA (hnRNA): Direct transcription product.

    2. Messenger RNA (mRNA): Carries instructions for protein synthesis.

    3. Ribosomal RNA (rRNA): Forms ribosomes with proteins.

    4. Transfer RNA (tRNA): Transfers amino acids during protein synthesis.

7. Transcription & Post-Transcription Processing

  • Transcription requires RNA polymerase and ends upon reaching a stop signal.

  • Post-transcriptional Modification: Involves splicing out introns to produce mRNA.

  • SnRNPs and Spliceosomes: Complexes that facilitate intron removal.

8. Genetic Code Characteristics

  • Degeneracy: Multiple codons can code for the same amino acid.

  • Universality: The genetic code is consistent across many organisms.

  • Start Codon: AUG starts protein synthesis.

9. Mutations and Genetic Engineering

  • Mutations: Errors in DNA replication, leading to point or frameshift mutations.

  • Genetic Engineering: Modifying organisms at a molecular level, including the creation of recombinant DNA.

  • PCR: Polymerase chain reaction for rapid DNA copy generation.

9.1 Procedures in Genetic Engineering

  1. Cell Membrane Dissolution: E. coli cells in a solution to release contents.

  2. Plasmid Isolation: Fractionating cellular contents for plasmids.

  3. Cleavage of DNA: Using restriction enzymes to cut DNA.

  4. Gene Removal: Isolating genes of interest from other DNA.

  5. Gene-Plasmid Splicing: Combining genes with plasmids using DNA ligase.

  6. Uptake of Recombinant DNA: Introduced to live cells for replication.