Chemical and Physical Properties of Nucleic Acids PDF

# Chemical and Physical Properties of Nucleic Acids; Structure and Function of DNA, RNA ## Introduction Today, we will explore nucleic acids – DNA and RNA – focusing on their chemical and physical properties, structural features, functions, and their roles in prokaryotic and eukaryotic genomes. We'...

# Chemical and Physical Properties of Nucleic Acids; Structure and Function of DNA, RNA ## Introduction Today, we will explore nucleic acids – DNA and RNA – focusing on their chemical and physical properties, structural features, functions, and their roles in prokaryotic and eukaryotic genomes. We'll also examine the structure of chromosomes. ## I. Nucleic Acids: Overview ### A. Definition Nucleic acids are essential biopolymers that store and transmit genetic information. The two main types are: * DNA (Deoxyribonucleic Acid) * RNA (Ribonucleic Acid) ### B. Components of Nucleic Acids * **Nucleotides:** The monomers consist of: * A phosphate group * A five-carbon sugar (deoxyribose in DNA, ribose in RNA) * A nitrogenous base (A, T, C, G for DNA; A, U, C, G for RNA) * **Image Suggestions:** * **Chemical Structure of a Nucleotide:** Show the structure of a nucleotide, highlighting the phosphate group, sugar, and nitrogenous base. * **Comparison of DNA and RNA Nucleotides:** Diagram contrasting the differences between deoxyribose and ribose. ## II. Chemical and Physical Properties of Nucleic Acids ### A. Chemical Properties 1. **Polarity:** Nucleic acids have directionality due to the sugar-phosphate backbone. 2. **Hydrogen Bonding:** Base pairs (A-T, G-C in DNA; A-U, G-C in RNA) are stabilized by hydrogen bonds. 3. **Acidity:** The phosphate groups confer a negative charge, making nucleic acids acidic. 4. **Nucleotides and Nucleosides:** * A nucleoside is a nitrogenous base linked to a sugar molecule (deoxyribose or ribose). * A nucleotide is a nucleoside with one or more phosphate groups attached to the sugar. ## III. Structure and Function of DNA and RNA ### A. Structure of DNA 1. **Double Helix:** Two anti-parallel strands with a sugar-phosphate backbone and nitrogenous bases facing inward. 2. **Major and Minor Grooves:** Crucial for protein binding and function. Two grooves that run the length of the DNA double helix. The major groove is 12 Angstroms wide, while the minor groove is 6 Angstroms wide. The major groove is slightly deeper than the minor groove (8.5 versus. 7.5 Angstroms). The grooves have different widths because of the asymmetric attachment of the base pairs to the sugar-phosphate backbone. ### B. Function of DNA 1. **Genetic Information Storage:** DNA encodes the instructions for protein synthesis. 2. **Replication:** DNA can replicate itself to pass genetic information during cell division. ### C. Structure of RNA 1. **Single-Stranded:** RNA usually exists as a single strand but can form complex structures. 2. **Types of RNA:** * mRNA: Carries genetic information. * tRNA: Transfers amino acids. * rRNA: Component of ribosomes. ### D. Function of RNA 1. **Protein Synthesis:** RNA is key in translating genetic information into proteins. 2. **Regulatory Roles:** Includes siRNAs and miRNAs involved in gene regulation. ## Replication Replication is the biological process by which a cell duplicates its DNA, ensuring that each daughter cell receives an exact copy of the genetic material. This is essential for cell division and the propagation of genetic information. ### Process of Replication 1. **Initiation:** * Replication begins at specific locations on the DNA called origins of replication. * Enzymes like helicase unwind the double helix, separating the two strands and creating a replication fork. 2. **Elongation:** * DNA polymerase synthesizes new strands by adding nucleotides complementary to the template strands. This occurs in a 5' to 3' direction. The leading strand is synthesized continuously, while the lagging strand is synthesized in short segments (Okazaki fragments) due to its antiparallel orientation. 3. **Termination:** * Replication ends when the entire DNA molecule has been copied. In eukaryotes, telomeres, the protective ends of chromosomes, play a role in signaling the completion of replication. 4. **Proofreading and Repair:** * DNA polymerases also have proofreading abilities, correcting errors in nucleotide pairing to ensure high fidelity in DNA replication. Additional repair mechanisms are in place to fix any remaining mistakes. ### Key Enzymes * **Helicase:** Unwinds the double-stranded DNA by breaking the hydrogen bonds between the base pairs, creating two single strands. * **Single-strand binding proteins (SSBs):** Bind to the separated strands to prevent them from re-annealing and to protect them from degradation. * **Topoisomerase:** Relieves the tension generated ahead of the replication fork by cutting the DNA, allowing it to unwind, and then rejoining the strands. * **DNA Polymerase:** The main enzyme responsible for synthesizing new DNA strands by adding nucleotides. There are several types (e.g., DNA polymerase III in prokaryotes, DNA polymerase α, δ, and ε in eukaryotes). * **Primase:** Synthesizes short RNA primers that provide a starting point for DNA polymerase. * **Ligase:** Joins Okazaki fragments on the lagging strand by forming phosphodiester bonds. * **Telomerase (in eukaryotes):** Adds repetitive nucleotide sequences to the ends of chromosomes (telomeres) to prevent loss of important DNA during replication. ## Image Suggestions * **DNA Double Helix Model:** A 3D model illustrating the helical structure of DNA. * **Denaturation Process:** Diagram showing the separation of DNA strands upon heating. * **Diagram of Replication Process:** A diagram showing the detailed process of DNA replication for both the leading and lagging strands.