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 aroma. Understanding these molecules provides insight into the chemical diversity found in living organisms.

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

• Volatile organic compounds: Small molecules such as geraniol and citronellol that produce the characteristic scent of roses.

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

Holistic vs Reductionist Approaches

Scientific Perspectives in Biology

Biology can be studied using holistic or reductionist approaches. The holistic approach considers the entire system, while the reductionist approach breaks down complex phenomena into simpler components. Both perspectives are valuable for understanding biological processes.

• Holistic approach: Examines organisms or systems as integrated wholes.

• Reductionist approach: Focuses on individual parts, such as molecules or cells, to explain biological phenomena.

• Example: Studying the human body as a whole (holistic) versus analyzing the function of a single enzyme (reductionist).

Matter, Atoms, and Elements

Basic Chemical Concepts

All living and non-living things are composed of matter, which consists of atoms. Atoms combine to form elements, molecules, and compounds, each with distinct properties.

• Matter: Anything that has mass and occupies space.

• Element: A pure substance consisting of only one type of atom (e.g., Sodium (Na), Chlorine (Cl)).

• Atom: The smallest unit of an element, composed of protons, neutrons, and electrons.

• Molecule: Two or more atoms bonded together (e.g., O2).

• Compound: A substance formed from two or more different elements chemically bonded (e.g., Sodium chloride (NaCl)).

• Example: Sodium (Na) and chlorine (Cl) react to form sodium chloride (NaCl), a common table salt.

Elements in the Human Body

Major and Trace Elements

The human body is composed of several elements, with a few making up the majority of body mass. Trace elements are present 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 required in very small amounts.

• Example: Iron (Fe) is a trace element essential for oxygen transport in blood.

Parts of an Atom

Atomic Structure

Atoms consist of a nucleus containing protons and neutrons, surrounded by electrons in an electron cloud. The arrangement of these subatomic particles determines the atom's properties.

• Protons: Positively charged particles in the nucleus.

• Neutrons: Neutral particles in the nucleus.

• Electrons: Negatively charged particles in the electron cloud.

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

Atomic Properties

Key Atomic Characteristics

Atoms are characterized by their atomic number, mass number, and the presence of isotopes. These properties influence chemical behavior and stability.

• Atomic number: Number of protons in the nucleus; defines the element.

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

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

• 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 around the nucleus.

• Example: (carbon-12) is stable, while (carbon-14) is radioactive.

Electrons and Chemical Bonds

Formation of Chemical Bonds

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 formation: Atoms interact to fill their valence shells, resulting in chemical bonds.

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

Types of Chemical Bonds

Covalent, Ionic, Hydrogen, and Van der Waals Bonds

Atoms can form different types of chemical bonds, each with unique properties and biological significance.

• Covalent bonds: Atoms share electrons; can be polar (unequal sharing) or nonpolar (equal sharing).

• Electronegativity: The tendency of an atom to attract electrons in a covalent bond.

• Polar covalent bonds: Electrons are shared unequally, creating partial charges (e.g., water molecule).

• Ionic bonds: Electrons are transferred from one atom to another, forming ions (e.g., NaCl).

• Hydrogen bonds: Weak attractions between a hydrogen atom and an electronegative atom (e.g., between water molecules).

• Van der Waals interactions: Weak, transient attractions between molecules due to temporary charge fluctuations.

• Example: Water molecules are held together by hydrogen bonds, giving water its unique properties.

Chemical Reactions and Bonds

Reactants, Products, and Equilibrium

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

• Chemical reaction: Process in which substances (reactants) are transformed into new substances (products).

• Reversible reaction: Reactants and products can interconvert; equilibrium is reached when the rates of forward and reverse reactions are equal.

• Example:

Water and Hydrogen Bonding

Properties of Water

Water's unique properties arise from hydrogen bonding between molecules, which affects cohesion, adhesion, temperature moderation, density, and its role as a universal solvent.

• Cohesion: Water molecules stick to each other due to hydrogen bonds.

• Adhesion: Water molecules stick to other surfaces.

• Temperature moderation: Water absorbs and releases heat slowly, stabilizing temperatures.

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

• 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. Buffers help maintain stable pH in biological systems.

• pH:

• Acids: Substances that increase H+ concentration (lower pH).

• Bases: Substances that decrease H+ concentration or release OH- (raise pH).

• Buffer: Substance that resists changes in pH by absorbing or releasing H+ or OH-.

• Example: Blood contains buffers to maintain pH near 7.4.

Molecular Structure and Function

Relationship Between Structure and Biological Activity

The structure of molecules determines their function in biological systems. Strong and weak bonds influence molecular interactions, affecting processes such as enzyme activity and cell signaling.

• Structure-function relationship: The shape and bonding of a molecule dictate its biological role.

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