Elemental building blocks of biological molecules | Chemistry of life | AP Biology | Khan Academy

The video introduces various biological molecules, starting with an amino acid. It identifies the common elements present: carbon (dark gray), hydrogen (white), oxygen (red), and nitrogen (blue). It notes that these elements, along with phosphorus, frequently appear in biological systems.

ATP (adenosine triphosphate) is presented as the molecular currency of energy. The elemental composition of ATP is analyzed, showing carbon, hydrogen, oxygen, nitrogen, and phosphorus (yellow). This reinforces the recurring presence of these key elements.

A triglyceride (fat molecule) is shown as an example for energy storage, primarily composed of carbons, hydrogens, and some oxygens. A segment of DNA is then examined, highlighting its complexity but reiterating the same elemental building blocks: carbon, hydrogen, oxygen, nitrogen, and phosphorus.

Beyond elemental composition, the video discusses molecular building blocks. ATP is broken down into a nitrogenous base, a five-carbon sugar, and three phosphate groups. DNA is shown to share similar components, with its backbone made of five-carbon sugars and phosphates.

The video explains why these specific elements are so common in biological molecules. Nitrogen is abundant in the atmosphere, and hydrogen and oxygen are plentiful in water. Carbon, though less common in the atmosphere, is fixed by photosynthetic organisms and incorporated into biological systems.

A chart illustrates the elemental composition of the human body, showing oxygen as the most abundant element (due to water content), followed by carbon, hydrogen, nitrogen, phosphorus, and calcium (important for bones and muscle contraction). This emphasizes that biological systems are fundamentally constructed from a common set of elemental and molecular building blocks, which originate from their environment.