Nucleic Acids

Monomers and Types of Nucleic Acids

Nucleic acids are essential biomolecules that store and transmit genetic information in living organisms. They are polymers made up of repeating units called nucleotides.

• Monomer Units: Nucleotides are the monomers that join together to form nucleic acids.

• Types of Nucleic Acids: The two main types are DNA (Deoxyribonucleic Acid) and RNA (Ribonucleic Acid).

• Main Components of Nucleic Acids: Each nucleotide consists of a phosphate group, a pentose sugar (deoxyribose in DNA, ribose in RNA), and a nitrogenous base.

Comparison Between DNA and RNA

DNA and RNA differ in structure, function, and chemical composition.

• Sugar: DNA contains deoxyribose; RNA contains ribose.

• Bases: DNA uses thymine; RNA uses uracil instead of thymine.

• Strands: DNA is typically double-stranded; RNA is usually single-stranded.

• Function: DNA stores genetic information; RNA is involved in protein synthesis and gene regulation.

Structure of Nucleic Acids

The structure of nucleic acids is crucial for their function in genetic information storage and transfer.

• Nucleotide: Consists of a phosphate group, a pentose sugar, and a nitrogenous base.

• Phosphodiester Bond: Nucleotides are joined by phosphodiester bonds between the 5' phosphate and 3' hydroxyl groups.

• Double Helix: DNA forms a double helix with two antiparallel strands held together by hydrogen bonds between complementary bases.

• Base Pairing: Adenine pairs with thymine (A-T), and guanine pairs with cytosine (G-C) in DNA. In RNA, adenine pairs with uracil (A-U).

Nitrogenous Bases

Nitrogenous bases are classified as purines or pyrimidines.

• Purines: Adenine (A) and Guanine (G)

• Pyrimidines: Cytosine (C), Thymine (T, in DNA), and Uracil (U, in RNA)

• Base Pairing: A-T (2 hydrogen bonds), G-C (3 hydrogen bonds)

Watson and Crick's Discoveries

Watson and Crick elucidated the structure of DNA, leading to several key findings:

• DNA is a double helix.

• Strands are antiparallel.

• Base pairing is specific (A-T, G-C).

• Genetic information is encoded in the sequence of bases.

DNA Replication

DNA replication is the process by which DNA makes a copy of itself during cell division.

• Semiconservative Replication: Each new DNA molecule consists of one old strand and one new strand.

• Enzymes: DNA polymerase synthesizes new DNA strands.

• Steps: Unwinding of the double helix, base pairing, and joining of nucleotides.

Functions of DNA and RNA

DNA and RNA have distinct roles in the cell.

• DNA: Stores genetic information, directs cell activities, and is inherited by offspring.

• RNA: Transfers genetic information from DNA to ribosomes, where proteins are synthesized; some RNA molecules have catalytic activity (ribozymes).

Differences Between DNA and RNA

• DNA contains deoxyribose; RNA contains ribose.

• DNA uses thymine; RNA uses uracil.

• DNA is double-stranded; RNA is single-stranded.

• DNA is stable; RNA is more reactive and can have catalytic functions.

Structure Levels of DNA

• Primary Structure: Sequence of nucleotides.

• Secondary Structure: Double helix formed by base pairing.

• Tertiary Structure: Higher-order folding (e.g., supercoiling).

• Quaternary Structure: Association with proteins (e.g., histones in chromatin).

Types of Nucleic Acids and Nucleotides

Nucleic acids and nucleotides can be identified by their structure and function.

Important Chemical Structures

• Ribose: A five-carbon sugar found in RNA.

• Deoxyribose: A five-carbon sugar found in DNA, lacking one oxygen atom compared to ribose.

Base Pairing and Complementary Strands

DNA strands are complementary, meaning each base on one strand pairs with a specific base on the opposite strand.

• Example: The complementary strand to 3' ATTGCGGAAC 5' is 5' TAACGCCTTG 3'.

• Transcription: When DNA is copied into RNA, thymine (T) is replaced by uracil (U).

Catalytic Activity of RNA

RNA can have catalytic activity due to its ability to form complex three-dimensional structures, allowing some RNA molecules (ribozymes) to act as enzymes. DNA does not have this property because it is more stable and less flexible.

Summary Table: DNA vs. RNA

Key Equations and Chemical Reactions

• Phosphodiester Bond Formation:

• Base Pairing:

• Directionality: DNA and RNA strands have a 5' to 3' direction.

Additional info:

• DNA replication is semiconservative, meaning each daughter molecule contains one parental and one new strand.

• RNA's catalytic activity is due to its ability to fold into complex structures, forming active sites similar to protein enzymes.

• DNA is packaged with proteins (histones) in eukaryotic cells to form chromatin.