DNA Structure and Function

• Deoxyribonucleic acid (DNA) carries genetic information in cells.
• DNA is located in the nucleus, condensed into chromatin, which further condenses into chromosomes during cell division.
• DNA is grouped into genes that are the basic units of inheritance.
• Genes are expressed into proteins responsible for cellular function and observable traits.

DNA Structure

• DNA is a double helix, composed of two strands twisted around each other.
• Each strand consists of covalently bonded monomers called nucleotides.
• Nucleotides are comprised of a sugar (deoxyribose), a phosphate group, and a nitrogenous base.
• Nitrogenous bases: purines (adenine (A) and guanine (G)) and pyrimidines (thymine (T) and cytosine (C)).
• Base pairing occurs between nucleotides: adenine (A) and thymine (T) form two hydrogen bonds, while cytosine (C) and guanine (G) form three hydrogen bonds.
• During expression, DNA is transcribed into messenger RNA (mRNA) in the nucleus.
• mRNA is then translated into proteins in the ribosome.

DNA Replication

• The cell cycle includes G1, S, G2, and M stages.
• The stages prior to M prepare the cell for division.
• During the S stage, DNA is replicated to produce two identical copies.
• DNA strands run in opposite directions, termed antiparallel.
• Replication is semi-conservative, resulting in two new DNA molecules each containing one original and one new strand.
• Helicase unzips DNA by breaking hydrogen bonds between bases, forming a replication fork.
• Unzipped strands act as templates.
• The leading strand runs in the 3'-5' direction.
• RNA primer attaches to the leading strand, facilitating DNA polymerase, which adds complementary bases to form a new DNA strand.
• The lagging strand runs in the 5'-3' direction.
• Multiple RNA primers attach to the lagging strand for DNA polymerase to create Okazaki fragments.
• DNA ligase glues the bases together, forming two new DNA molecules.

DNA vs RNA

• Ribonucleic acid (RNA) is similar to DNA but single-stranded.
• RNA has ribose sugar instead of deoxyribose, with an extra hydroxyl (OH) group.
• RNA contains uracil instead of thymine, and uracil pairs with adenine.
• RNA can act as a primer during DNA replication or as messenger RNA in gene expression.
• RNA molecules can also function as enzymes.

DNA Molecule

• The DNA in a single cell is approximately 2 meters long.
• DNA compaction into chromatin using histone proteins is necessary to fit within the nucleus.
• DNA was discovered by Frederich Miescher in the late 1800s, with its structure and function defined in the 1950s.
• Rosalind Franklin, James Watson, and Francis Crick used X-ray diffraction to uncover the double helix structure.
• Genes, which can be up to 1 million bases long, make up 1% of the DNA sequence and code for proteins.
• Non-coding segments, or introns, are thought to control gene expression.
• Coding segments of DNA are called exons.

DNA Sequencing

• DNA sequencing uncovers the genetic makeup of a cell by revealing base pairing (A/T/C/G) content.
• Sanger sequencing, developed by Frederick Sanger, uses base pairing complementarity with fluorescently tagged nucleotides.
• Next-generation sequencing has largely replaced Sanger sequencing due to increased efficiency and reduced cost.
• Sanger sequencing is still valued for its high accuracy.
• DNA sequencing is used in diagnostics and research for genetically inherited diseases.
• The Human Genome Project, completed in 2003, revealed the entire human genome sequence.

This lesson explores the structure and function of DNA. It covers DNA's role in carrying genetic information within cells and its organization into genes. Key topics include the double helix structure, nucleotide composition, and base pairing rules.