Carbon and the Molecular Diversity of Life: Study Notes

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Carbon and the Molecular Diversity of Life

Introduction to Carbon in Biology

Carbon is the foundational element for all biological molecules due to its unique chemical properties. Its ability to form four covalent bonds allows for a vast diversity of organic compounds, which are essential for life. The versatility of carbon is a key factor in the molecular complexity observed in living organisms.

Organic chemistry is the study of carbon-containing compounds, regardless of their origin.
Major elements in biological molecules include carbon (C), hydrogen (H), oxygen (O), nitrogen (N), sulfur (S), and phosphorus (P).
Carbon's four-bond capacity enables the formation of large, complex molecules.
The diversity of life is largely due to the versatility of carbon in forming various molecular structures.

Carbon as the basis for biological molecules

Formation of Bonds with Carbon

Carbon atoms can form diverse molecules by bonding to four other atoms. The electron configuration of carbon determines the types and numbers of bonds it can form, which is central to its chemical characteristics.

Carbon has four valence electrons, allowing it to form four covalent bonds.
In molecules with multiple carbons, each carbon bonded to four other atoms adopts a tetrahedral shape.
When two carbon atoms are joined by a double bond, the atoms attached to the carbons are in the same plane.

Methane structural formula Methane tetrahedral geometry Methane space-filling model Ethene structural formula Ethene planar geometry Ethene space-filling model

Valence and Bonding Partners

The number of unpaired electrons in the valence shell of an atom determines its valence, or the number of covalent bonds it can form. Carbon's electron configuration allows it to bond with many elements, most frequently hydrogen, oxygen, and nitrogen.

Valence is the number of covalent bonds an atom can form.
Carbon's frequent bonding partners are hydrogen, oxygen, and nitrogen.

Hydrogen electron configuration Oxygen electron configuration Nitrogen electron configuration Carbon electron configuration

Molecular Diversity from Carbon Skeletons

Carbon atoms can partner with atoms other than hydrogen, such as oxygen and nitrogen, forming a variety of molecules. Carbon chains form the skeletons of most organic molecules, and these chains can vary in length and shape, contributing to molecular diversity.

Carbon dioxide (CO2) and urea are examples of carbon partnering with other elements.
Carbon chains can be straight, branched, or arranged in rings.

Carbon dioxide structure Urea structure Carbon chain variations Four ways carbon skeletons can vary

Hydrocarbons

Hydrocarbons are organic molecules consisting only of carbon and hydrogen. They are found in many biological molecules, such as fats, and can undergo reactions that release significant amounts of energy.

Hydrocarbons are nonpolar and hydrophobic.
They serve as energy storage molecules in biological systems.

Fat molecule and adipose cell

Isomers

Isomers are compounds with the same molecular formula but different structures and properties. There are three main types: structural isomers, cis-trans (geometric) isomers, and enantiomers.

Structural isomers differ in the covalent arrangement of their atoms.
Cis-trans isomers have the same covalent bonds but differ in spatial arrangement.
Enantiomers are mirror images of each other and can have different biological activities.

Three types of isomers

Biological Importance of Enantiomers

Enantiomers are especially important in pharmaceuticals, as often only one enantiomer is biologically active. Organisms are sensitive to even subtle variations in molecular structure.

Functional Groups and Molecular Function

Distinctive properties of organic molecules depend on their carbon skeleton and the chemical groups attached. Functional groups are the components most commonly involved in chemical reactions, and their number and arrangement give each molecule its unique properties.

Estradiol and testosterone are steroids with a common carbon skeleton but differ in functional groups, resulting in different biological functions.
The seven most important functional groups in biological chemistry are: hydroxyl, carbonyl, carboxyl, amino, sulfhydryl, phosphate, and methyl.

Estradiol and testosterone structures Table of functional groups

ATP: An Important Source of Energy

Adenosine triphosphate (ATP) is a crucial organic phosphate in cellular processes. ATP consists of adenosine attached to three phosphate groups and stores potential energy to react with water, releasing energy for cellular use.

ATP hydrolysis releases energy used by cells for various functions.
The reaction:

ATP phosphate chain ATP to ADP reaction

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