DNA Structure, Replication, and Cell Division

Human Cell Numbers

The approximate number of cells in an adult human body, which is 30{,}000{,}000{,}000{,}000 (30 trillion).

Zygote

The single fertilized egg from which every person begins, undergoing a sequence of doublings to form a complex organism.

Mitosis

A mode of eukaryotic cell division occurring in somatic cells, resulting in 2 identical diploid daughter cells. Its purposes include growth, tissue repair, and routine cell replacement.

Meiosis

A mode of eukaryotic cell division occurring in germ-line cells to generate gametes (sperm & eggs), resulting in 4 non-identical haploid gametes.

Interphase

The phase of the cell cycle where the cell grows, performs normal functions, and duplicates its DNA, occurring before mitosis proper.

Cytokinesis

The physical separation of a cell into two daughter cells, which follows the mitotic phases.

DNA Replication

The process by which a cell duplicates its DNA, ensuring each daughter cell inherits a complete genome before division.

Rosalind Franklin

British chemist whose X-ray crystallography images of DNA fibers were critical for understanding DNA's 3-D structure.

James Watson & Francis Crick

Scientists who, in 1953, synthesized existing data (including Franklin's) to propose the double-helix model of DNA.

Double-helix model

The molecular structure of DNA, characterized by two antiparallel strands twisting into a right-handed spiral.

Nucleic Acid

The biological polymer class to which DNA belongs; its monomers are nucleotides.

Nucleotide

The monomer unit of DNA, composed of a pentose sugar (deoxyribose), a phosphate group, and a nitrogenous base.

Complementary Base Pairing Rules

The pairs formed between complementary bases in DNA: Adenine (A) always pairs with Thymine (T), and Cytosine (C) always pairs with Guanine (G) via hydrogen bonding.

Central Dogma

The fundamental concept describing the flow of genetic information in biological systems: DNA \rightarrow RNA \rightarrow Protein.

Cancer

A disease often resulting from errors in DNA replication or cell-cycle regulation.