Detailed Notes on Nucleic Acids, DNA, and RNA

Nucleic Acids and Hereditary Information

• Nucleic acids, particularly DNA, serve as the storage medium for hereditary information.
• The structure of DNA is optimized for accurate replication, ensuring the faithful transmission of genetic information.

DNA: The Genetic Material of Living Organisms

• DNA functions as the genetic material in all living organisms.
• Viruses may use RNA as their genetic material, but they are not considered living entities.

Shared Cellular Features

• All living cells share three common features:
  • Cell membrane
  • Cytoplasm
  • Genetic material in the form of DNA
• Prokaryotic cells: feature circular DNA located in the nucleoid region.
• Eukaryotic cells: contain linear DNA organized into chromosomes within a membrane-bound nucleus.

Viruses and Nucleic Acids

• Viruses, while non-living, may contain either DNA or RNA within their capsids to carry genetic information.

Major Biological Molecules

• Four major types of biological molecules are essential for life:
  • Lipids
  • Nucleic acids
  • Carbohydrates
  • Proteins
• Nucleic acids include nuclear and organelle DNA (in mitochondria and chloroplasts) and various types of RNA (ribosomal, messenger, transfer RNA).

Primary Functions of Nucleic Acids

• DNA serves as the genetic blueprint for producing building blocks through gene expression.
  • Gene expression involves:
    • Transcription: DNA is copied into RNA.
    • Translation: RNA is translated into proteins.
• DNA replication: information stored in DNA is passed from cell to cell through generations.

Components of a Nucleotide

• Both DNA and RNA consist of monomers called nucleotides, forming a polymer.
• Each nucleotide is composed of three parts:
  • A pentose sugar (5 carbon atoms):
    • Deoxyribose in DNA
    • Ribose in RNA
  • An acidic phosphate group (negatively charged)
  • One of four or five different nitrogenous bases

Key Differences

• RNA contains a ribose sugar, while DNA contains a deoxyribose sugar.
• RNA contains the nitrogenous base Uracil (U) instead of Thymine (T).
• Both nucleotides have the bases Cytosine (C), Adenine (A), and Guanine (G).

Sugar-Phosphate Backbone

• Individual nucleotides in a DNA or RNA strand are linked together to form long polymer chains through a condensation reaction (releasing water).
• This reaction forms covalent bonds between nucleotides, creating long, continuous strands with a sugar-phosphate backbone.

Condensation Reaction

• A condensation reaction combines two molecules into a single molecule, with the loss of a water molecule.
• The phosphate group attached to the 5’ carbon atom of one nucleotide forms a covalent bond with the 3’ carbon on the pentose of the next nucleotide.

Bases as Genetic Code

• The sequence of nitrogenous bases in a nucleic acid (DNA or RNA) forms the basis of the genetic code.
• The order of bases in the DNA of a gene codes for the order of amino acids in a protein.

DNA Double Helix

• DNA exists as a double helix, composed of two strands that twist around each other in an antiparallel manner.
• Each strand is made of nucleotides and has a sugar-phosphate backbone.
• Hydrogen bonds connect the bases of the two strands.

Antiparallel Strands

• The two DNA strands run antiparallel, meaning they run in opposite directions (5’ to 3’ and 3’ to 5’).
• The numbers (5’ and 3’) refer to the numbered carbon atoms in the deoxyribose sugar ring.

Key Features of the DNA Double Helix

• The phosphate and sugar form the hydrophilic ‘backbone’ of DNA.
• Nitrogenous bases are hydrophobic and reactive, sticking inward.
• Covalent bonds are formed between the phosphate and sugar.
• Antiparallel arrangement: the two strands run in opposite directions.
• Complementary base pairing:
  • Adenine (A) pairs with Thymine (T).
  • Cytosine (C) pairs with Guanine (G).

Complementary Base Pairing

• Complementary base pairing describes the alignment of nitrogenous bases in DNA molecules.
• Adenine (A) always pairs with Thymine (T), and Guanine (G) always pairs with Cytosine (C).
• Complementary base pairing ensures regular arrangement and geometry within the double helix, allowing for exact replication.

Hydrogen Bonding

• Complementary base pairing depends on hydrogen bonding between matching bases.
• A hydrogen bond is an electrostatic attraction between a hydrogen atom covalently bonded to an electronegative atom (N, O, F) and another electronegative atom with a lone pair of electrons.
• Guanine and Cytosine form three hydrogen bonds, while Adenine and Thymine form two hydrogen bonds.

DNA vs RNA

Similarities

• Both RNA & DNA are chains of nucleotides
• Both have a sugar-phosphate backbone with the bases projecting from it

Differences

• DNA: type of molecule is deoxyribonucleic acid
• RNA: type of molecule is ribonucleic acid
  • Has various functions including gene expression and regulation, protein synthesis
  • Components include:
    • mRNA (messenger RNA)
    • tRNA (transfer RNA)
    • rRNA (ribosomal RNA)
  • Bonds include:
    • Phosphodiester bonds
    • Hydrogen bonds (in some RNA structures)

Diversity and Information Storage

• Genetic information is stored in the base sequence of one of the two strands of a DNA molecule.
• Any base sequence is possible, offering vast storage capacity.
• There are four different bases (A, C, G, T) that can be arranged in any order, allowing for numerous possibilities.
• DNA has an enormous capacity for storing data with great economy; capable of storing 215 petabytes (215 million gigabytes) in a single gram.

DNA Storage Capacity

*The amount of DNA in your body could store every movie released this century… 3 billion times over

• Every movie released in the 21st century = 48 terabytes data
• DNA storage capacity of a human body = 150,000,000,000 terabytes of data

Conservation of Genetic Code

• The sequence of bases in DNA or RNA contains information in a coded form.
• This information is decoded during protein synthesis.
• Groups of three bases (codons) code for one specific amino acid.
• Nearly all organisms (bacteria, plants, animals, fungi, etc.) share the same genetic code, indicating a universal common ancestry.
• Scientists have genetically engineered plants to glow by transferring genes from a firefly, which are subsequently expressed by the plant.