Nucleic Acid Structure and DNA Replication

Nucleic Acid Structure

• Nucleotides are the basic building blocks of DNA.
• A DNA strand is a linear polymer, also called a polynucleotide.
• The double helix structure is formed by two complementary DNA strands.
• Chromosomes are DNA associated with proteins, forming a complex structure.
• The genome is the complete set of genetic material in an organism.

DNA Structure

• Nucleotides have three components: a phosphate group, a pentose sugar (deoxyribose), and a nitrogenous base.
• Nitrogenous bases are classified as either purines (adenine, guanine) or pyrimidines (cytosine, thymine).
• DNA is a linear polymer of nucleotides, a polynucleotide.
• The sugar-phosphate backbone forms the structural framework of the DNA molecule.

DNA Replication

• Replication begins at origins of replication, creating replication forks.
• DNA replication proceeds in both directions from the origin.
• Eukaryotic chromosomes have multiple origins of replication.
• Replication bubbles fuse, resulting in two identical DNA molecules.

Proteins Involved in DNA Replication and Repair

• Helicase unwinds the DNA double helix at the replication fork.
• Primase generates RNA primers, starting points for DNA synthesis.
• DNA polymerase synthesizes DNA polymers.
• Topoisomerase relieves additional twisting ahead of the replication fork.
• DNA ligase joins Okazaki fragments.
• Single-strand binding proteins prevent the DNA strands from re-forming a double helix.
• DNA polymerase links nucleotides covalently using deoxynucleoside triphosphates

Steps of DNA Replication

• Step 1: Unwinding
• Step 2: Initiation
• Step 3: Elongation of leading and lagging strands
• Step 4: Completion of lagging strand
• Step 5: Proofreading

DNA Replication: Leading and Lagging Strands

• Leading strand DNA is synthesized continuously, following the replication fork in the 5' to 3' direction with a single primer.
• Lagging strand DNA is synthesized discontinuously in short segments called Okazaki fragments. These fragments are produced in the 5' to 3' direction, away from the replication fork. Multiple primers are necessary.
• RNA primers are removed, and the Okazaki fragments are joined by DNA ligase.

Problems with Linear DNA

• Linear DNA has ends that cannot be completely replicated due to the need for primers.
• Repeated rounds of replication lead to shorter DNA molecules in both the lagging and leading strand.

Telomeres

• Eukaryotic chromosomes have specialized nucleotide sequences called telomeres at their ends.
• Telomeres protect genes from erosion during DNA replication.
• Telomere shortening is associated with aging.

This quiz covers the fundamental concepts of nucleic acids, focusing on the structure of DNA, the role of nucleotides, and the process of DNA replication. Test your knowledge on nucleotide components, the double helix structure, and the mechanisms involved in DNA replication.