The Chemical Basis of Life

The Colour and Aroma of Roses

The colour and aroma of roses are determined by specific chemical compounds. Pigments such as anthocyanins are responsible for the red coloration, while volatile organic compounds contribute to the characteristic scent of roses.

• Anthocyanins: Water-soluble pigments that give roses their red, purple, or blue hues.

• Volatile Compounds: Molecules such as geraniol, citronellol, and phenylethyl alcohol contribute to the aroma of roses.

• Example: The molecular structures of anthocyanins and aromatic compounds can be compared to understand their roles in plant biology.

Additional info: The study of plant pigments and aromas is important in botany and biochemistry, as these compounds affect pollination and ecological interactions.

Holistic vs Reductionist Approaches

Scientific Perspectives

Biology can be studied using holistic or reductionist approaches. Holistic approaches consider the entire system, while reductionist approaches break down complex phenomena into simpler components.

• Holistic Approach: Examines biological systems as integrated wholes.

• Reductionist Approach: Focuses on individual parts, such as molecules or cells, to understand the system.

• Example: The cartoon illustrates how different scientific fields relate to each other, with biology positioned between chemistry and psychology.

Matter, Atoms, and Elements

Basic Definitions

All living and non-living things are composed of matter, which consists of atoms and molecules. Elements are pure substances made of one type of atom.

• Matter: Anything that has mass and occupies space.

• Element: A substance that cannot be broken down into simpler substances by chemical means.

• Atom: The smallest unit of an element, retaining its chemical properties.

• Molecule: Two or more atoms bonded together.

• Compound: A substance formed from two or more different elements chemically bonded.

• Example: Sodium (Na) and chlorine (Cl) combine to form sodium chloride (NaCl), a compound.

Elements in the Human Body

Major and Trace Elements

The human body is composed of several elements, with oxygen, carbon, hydrogen, and nitrogen making up the majority of body weight. Trace elements are required in very small amounts but are essential for health.

• Trace Elements: Elements such as boron, chromium, copper, iodine, iron, manganese, molybdenum, selenium, silicon, tin, vanadium, and zinc are present in less than 0.01% of body weight.

Parts of an Atom

Atomic Structure

Atoms consist of a nucleus containing protons and neutrons, surrounded by electrons in an electron cloud.

• Proton: Positively charged particle in the nucleus.

• Neutron: Neutral particle in the nucleus.

• Electron: Negatively charged particle in the electron cloud.

• Example: A helium atom has 2 protons, 2 neutrons, and 2 electrons.

Atomic Properties

Key Characteristics

Atoms are defined by their atomic number, mass number, and the arrangement of their electrons. Isotopes are atoms of the same element with different numbers of neutrons.

• Atomic Number (Z): Number of protons in the nucleus.

• Atomic Mass (A): Total number of protons and neutrons.

• Isotope: Atoms of the same element with different neutron numbers.

• Radioisotope: An isotope that is unstable and emits radiation.

• Cation: Positively charged ion (loss of electrons).

• Anion: Negatively charged ion (gain of electrons).

• Electron Shells: Energy levels where electrons reside.

• Example: (stable) vs (radioactive).

Electrons and Chemical Bonds

Bond Formation

Chemical bonds form when atoms share, gain, or lose electrons to achieve a stable electron configuration, usually a filled valence shell.

• Valence Shell: The outermost electron shell of an atom.

• Stable Configuration: Atoms are most stable when their valence shell is full.

• Bond Types: Atoms may form covalent, ionic, or hydrogen bonds.

• Example: Sodium (Na) loses an electron to become Na+, while chlorine (Cl) gains an electron to become Cl-, forming NaCl.

Covalent Bonds

Electron Sharing

Covalent bonds are formed when two atoms share one or more pairs of electrons. These bonds are strong and common in biological molecules.

• Single Covalent Bond: Sharing one pair of electrons.

• Double Covalent Bond: Sharing two pairs of electrons.

• Polar Covalent Bond: Unequal sharing of electrons, leading to partial charges (e.g., in water).

• Nonpolar Covalent Bond: Equal sharing of electrons.

• Example: has polar covalent bonds between hydrogen and oxygen.

Ionic Bonds

Electron Transfer

Ionic bonds are formed when one atom transfers electrons to another, resulting in oppositely charged ions that attract each other.

• Cation: Atom that loses electrons and becomes positively charged.

• Anion: Atom that gains electrons and becomes negatively charged.

• Example: Sodium chloride () is formed by the transfer of an electron from sodium to chlorine.

Hydrogen Bonds

Weak Interactions

Hydrogen bonds are weak attractions between a hydrogen atom covalently bonded to an electronegative atom (like oxygen or nitrogen) and another electronegative atom.

• Importance: Hydrogen bonds are crucial for the structure of water, DNA, and proteins.

• Example: Hydrogen bonds hold water molecules together, contributing to its unique properties.

Van der Waals Interactions

Transient Forces

Van der Waals interactions are weak, transient attractions between molecules due to temporary shifts in electron density.

• Role: Important in stabilizing biological macromolecules.

• Example: These interactions help proteins fold and maintain their shape.

Chemical Reactions and Bonds

Formation and Breaking of Bonds

Chemical reactions involve the making and breaking of chemical bonds, converting reactants into products. Some reactions are reversible and can reach equilibrium.

• Reactants: Substances that start a chemical reaction.

• Products: Substances formed by the reaction.

• Chemical Equilibrium: The state where the rate of the forward reaction equals the rate of the reverse reaction.

• Example:

Water and Hydrogen Bonding

Unique Properties of Water

Water's structure and hydrogen bonding give it unique properties essential for life, including cohesion, adhesion, temperature moderation, density, and solvent abilities.

• Cohesion: Water molecules stick together due to hydrogen bonding.

• Adhesion: Water molecules stick to other surfaces.

• Temperature Moderation: Water absorbs and releases heat slowly.

• Density: Ice is less dense than liquid water due to hydrogen bonds.

• Universal Solvent: Water dissolves many substances due to its polarity.

• Example: Salt (NaCl) dissolves in water as Na+ and Cl- ions are stabilized by water molecules.

Water and pH

Acids, Bases, and Buffers

Water can dissociate into hydrogen ions (H+) and hydroxide ions (OH-). The pH scale measures the concentration of H+ ions, indicating acidity or basicity.

• Acid: Substance that increases H+ concentration (pH < 7).

• Base: Substance that decreases H+ concentration or increases OH- (pH > 7).

• Neutral: pH = 7, equal concentrations of H+ and OH-.

• Buffer: Substance that resists changes in pH.

• Example: The bicarbonate buffer system in blood maintains pH stability.

pH Equation:

Molecular Structure and Function

Relationship Between Structure and Activity

The structure of molecules determines their function in biological systems. Strong and weak bonds influence molecular interactions and biological activity.

• Structure-Function Relationship: The shape and bonding of molecules affect how they interact in living organisms.

• Example: Morphine and endorphins have similar structures, allowing both to bind to the same brain receptors.

Additional info: Understanding molecular structure is fundamental to biochemistry and molecular biology.