The Chemical Basis of Life

The Colour and Aroma of Roses

The colour and aroma of roses are determined by specific chemical compounds. These compounds are products of complex biochemical pathways and illustrate the importance of molecular structure in biological function.

• Colour: Pigments such as anthocyanins are responsible for the red coloration in rose petals. Their molecular structure allows them to absorb certain wavelengths of light, resulting in visible colour.

• Aroma: The scent of roses is produced by volatile organic compounds, including geraniol, citronellol, and phenylethyl alcohol. These molecules interact with olfactory receptors in the nose.

• Example: The difference in aroma between rose varieties is due to the relative concentrations of these compounds.

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.

• Holistic: Focuses on the interactions and relationships within biological systems.

• Reductionist: Analyzes individual parts, such as molecules or cells, to understand the whole.

• Example: Studying the effect of a hormone on the whole organism (holistic) versus examining its molecular structure and receptor binding (reductionist).

Matter, Atoms, and Elements

Basic Chemical Concepts

All living things are composed of matter, which consists of atoms organized into elements, molecules, and compounds.

• 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, retaining its chemical properties.

• 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

The human body is composed of several key elements, each with specific roles in biological processes.

Trace elements (less than 0.01%): Boron (B), Chromium (Cr), Cobalt (Co), Copper (Cu), Fluorine (F), Iodine (I), Iron (Fe), Manganese (Mn), Molybdenum (Mo), Selenium (Se), Silicon (Si), Tin (Sn), Vanadium (V), Zinc (Zn).

Parts of an Atom

Atomic Structure

Atoms are composed of subatomic particles: protons, neutrons, and electrons. The arrangement of these particles determines the atom's properties.

• Protons: Positively charged particles located in the nucleus.

• Neutrons: Neutral particles also found in the nucleus.

• Electrons: Negatively charged particles that orbit the nucleus in electron clouds.

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

Atomic Properties

Key Atomic Characteristics

Atoms are defined by several important properties that influence their behavior in chemical reactions.

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

• Atomic Mass (Mass Number): The sum of protons and neutrons in the nucleus.

• Isotopes: Atoms of the same element with different numbers of neutrons. Some isotopes are radioactive (radioisotopes).

• Cation vs Anion: A cation is a positively charged ion (loss of electrons); an anion is a negatively charged ion (gain of electrons).

• Electron Shells: Electrons occupy energy levels or shells around the nucleus.

• Example: Carbon-12 () is stable, while Carbon-14 () is radioactive and used in radiometric dating.

Electrons and Chemical Bonds

Formation of Chemical Bonds

Chemical bonds are formed 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.

• Stability: 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+ (cation), while chlorine (Cl) gains an electron to become Cl- (anion), forming NaCl.

Types of Chemical Bonds

Covalent Bonds

Covalent bonds involve the sharing of electron pairs between atoms. These bonds are strong and common in biological molecules.

• Single, Double, Triple Bonds: Atoms can share one, two, or three pairs of electrons.

• Polar Covalent Bonds: Electrons are shared unequally, resulting in partial charges (e.g., water molecule).

• Nonpolar Covalent Bonds: Electrons are shared equally.

• Example: In H2O, oxygen is more electronegative than hydrogen, creating a polar covalent bond.

Ionic Bonds

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

• Cation: Positively charged ion (e.g., Na+).

• Anion: Negatively charged ion (e.g., Cl-).

• Example: Sodium chloride (NaCl) is formed by the ionic bond between Na+ and Cl-.

Hydrogen Bonds

Hydrogen bonds are weak attractions between a hydrogen atom in one molecule and an electronegative atom (such as oxygen or nitrogen) in another molecule.

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

• Example: Hydrogen bonds hold the two strands of DNA together.

Van der Waals Interactions

Van der Waals interactions are weak attractions between molecules due to temporary fluctuations in electron distribution.

• Role: Important in stabilizing the three-dimensional structure of large molecules.

• Example: These interactions help proteins fold into their functional shapes.

Chemical Reactions and Bonds

Nature of Chemical Reactions

Chemical reactions involve the making and breaking of chemical bonds, converting reactants into products.

• Reactants: Substances that start a chemical reaction.

• Products: Substances formed as a result of the reaction.

• Reversible Reactions: Some reactions can proceed in both directions and reach chemical equilibrium.

• Chemical Equation Example:

Water and Hydrogen Bonding

Cohesion and Adhesion

Water molecules exhibit cohesion (attraction to each other) and adhesion (attraction to other substances) due to hydrogen bonding.

• Cohesion: Responsible for surface tension in water.

• Adhesion: Allows water to climb up plant vessels (capillary action).

Temperature Moderation

Water moderates temperature due to its high specific heat, which is a result of hydrogen bonding.

• High Specific Heat: Water absorbs and releases heat slowly, helping organisms maintain stable internal temperatures.

Density of Water

Water is less dense as a solid than as a liquid, which is why ice floats. This property is due to the hydrogen bonds forming a crystalline structure in ice.

• Biological Importance: Ice floating insulates aquatic environments in winter.

The Universal Solvent

Water is called the universal solvent because it can dissolve many substances, facilitating chemical reactions in living organisms.

• Polarity: Water's polar nature allows it to dissolve ionic and polar compounds.

• Example: Table salt (NaCl) dissolves in water as Na+ and Cl- ions.

Water and pH

Acids, Bases, and the pH Scale

pH measures the concentration of hydrogen ions (H+) in a solution. Water can dissociate into H+ and OH- ions.

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

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

• Neutral: pH = 7, where [H+] = [OH-].

• Example: Hydrochloric acid (HCl) is an acid; sodium hydroxide (NaOH) is a base.

pH Equation:

pH Buffers

Buffers are substances that minimize changes in pH by absorbing or releasing H+ or OH- ions.

• Importance: Buffers help maintain stable pH environments necessary for biological function.

• Example: Blood contains bicarbonate buffer to maintain pH around 7.4.

Molecular Structure and Function

Relationship Between Structure and Function

The structure of molecules, determined by the types of chemical bonds they contain, is crucial for their biological function.

• Strong Bonds: Covalent and ionic bonds provide stability to molecules.

• Weak Bonds: Hydrogen bonds and van der Waals interactions allow flexibility and dynamic interactions.

• Example: The similarity in structure between natural endorphins and morphine allows both to bind to the same brain cell receptors, producing similar effects.

Additional info: The study notes have expanded on brief points and provided academic context for clarity and completeness.