Chapter 02 MH8 WS

Chapter 02: The Chemistry of Life

Introduction

Understanding chemistry is fundamental for making informed decisions about diet, medication, and health treatments. It underpins our understanding of biological processes and the molecular interactions that sustain life. Biochemistry examines the intricate chemical processes and substances in living organisms, including carbohydrates, fats, proteins, and nucleic acids. These biomolecules are crucial for comprehending cellular structures, physiology, nutrition, and health across various contexts.

2.1 Atoms, Ions, and Molecules

Expected Learning Outcomes

• Identify elements by their symbols.

• Differentiate between elements and compounds, understanding their unique properties.

• Understand the essential functions of minerals in maintaining body health.

• Explain the basics of radioactivity and the hazards associated with ionizing radiation.

• Differentiate between ions, electrolytes, and free radicals.

• Define and describe various types of chemical bonds and their significance in biological systems.

The Chemical Elements

Elements are the simplest forms of matter, possessing unique physical and chemical properties. Each element is defined by its atomic number, denoting the number of protons in its nucleus. The periodic table organizes these elements by atomic number and provides a one or two-letter symbol for each.In biological contexts, 24 elements are recognized as essential, with six key elements - oxygen, carbon, hydrogen, nitrogen, calcium, and phosphorus - accounting for approximately 98.5% of human body weight.

Major Elements of the Human Body

Lesser elements (totaling 0.8%) include sulfur (S), potassium (K), sodium (Na), among others, while trace elements (totaling 0.7%) such as chromium and molybdenum are required in minute amounts for various biochemical processes.

Minerals

Minerals are inorganic elements acquired primarily from soil by plants and represent approximately 4% of body weight. They play crucial roles in providing structural integrity to body tissues (e.g., calcium's role in bone structure) and are vital for the functioning of enzymes that catalyze biochemical reactions. Electrolytes, which include ions like sodium and potassium, are essential for nerve transmission and muscle contraction, manifesting significantly in physiological functions.

Atomic Structure

Niels Bohr's planetary model introduced in 1913 illustrated atomic structure effectively, positing concentric orbits around a nucleus. Each atom comprises protons (+1 charge), neutrons (neutral), and electrons (-1 charge), with a neutral atom balancing protons and electrons. Valence electrons, found in the outermost shell of an atom, dictate bonding properties and chemical interactions.

Isotopes and Radioactivity

Isotopes are variations of an element distinguished by differing neutron counts while retaining the same number of protons. Radioisotopes are unstable and emit radiation as they decay into stable forms. This process, known as radioactivity, can ionize surrounding molecules and may induce genetic mutations, with potential links to cancer development. The half-life, or the duration required for half of a radioactive isotope to decay, varies significantly across biological and physical contexts, influencing its applications in medicine and research.

Ions, Electrolytes, and Free Radicals

Ions are charged particles formed when atoms gain or lose electrons. They can be categorized as anions (gained electrons, thus negative) and cations (lost electrons, thus positive). Electrolytes are ions dissolved in solution that conduct electric currents and play critical roles in physiological processes. Free radicals are unstable molecules that possess unpaired electrons, causing oxidative damage to cells. Antioxidants help mitigate this damage by neutralizing free radicals.

Molecules and Chemical Bonds

Molecules are defined as combinations of two or more atoms bonded together, whereas compounds are a subset of molecules comprised of different elements. The types of chemical bonds include:

• Ionic Bonds: These occur due to the attraction between cations and anions, and they are weaker when in an aqueous environment.

• Covalent Bonds: Formed by the sharing of electrons, these bonds are stronger and can be polar (unequal sharing) or nonpolar (equal sharing).

• Hydrogen Bonds: Weaker attractions that are crucial for the properties of water and the structure of biological molecules.

• Van der Waals Forces: These weak, transient forces are vital for physiological interactions.

Water and Mixtures

Expected Learning Outcomes

• Differentiate between mixtures and compounds.

• Describe the essential properties of water and their importance for life.

• Identify and characterize various types of mixtures including solutions, colloids, and suspensions.

• Define acids and bases, and understand the pH scale and its significance in biological systems.

Properties of Water

Water, a universal solvent, is vital for metabolic reactions, enabling various chemical reactions to take place. Its unique properties stem from its polar nature, with hydrogen bonding imparting high cohesion, aiding in surface tension essential for various biological processes. Water molecules also exhibit adhesion, enabling interaction with other substances, which is crucial for organ function and nutrient transport. Furthermore, water's thermal stability, attributed to hydrogen bond interactions, allows it to regulate body temperature effectively.

Solutions, Colloids, and Suspensions

• Solution: A clear mixture with solute particles smaller than 1 nm (e.g., saltwater).

• Colloid: Contains particles sized between 1-100 nm and appears cloudy, remaining evenly distributed (e.g., milk).

• Suspension: Contains larger particles (greater than 100 nm) that separate upon standing (e.g., blood).

Acids, Bases, and pH

• Acid: A substance that donates protons (H+) to a solution.

• Base: A proton acceptor, often releasing hydroxide ions (OH-).

• pH Scale: A logarithmic scale ranging from 0 (highly acidic) to 14 (highly basic), with neutral pH at 7. Normal blood pH is tightly regulated within the range of 7.35-7.45. Buffers are solutions that resist pH changes, critical for maintaining homeostasis in biological systems.

Energy and Chemical Reactions

Expected Learning Outcomes

• Define the different types of energy and explain various chemical reactions.

• Classify chemical reactions into decomposition, synthesis, or exchange types.

• Understand key metabolic processes and their biological significance.

Energy Types

• Potential Energy: The stored energy within chemical bonds.

• Kinetic Energy: The energy of motion, with heat and electromagnetic energy as examples.

Classes of Chemical Reactions

• Decomposition Reaction: A single large molecule disassembles into smaller molecules or atoms.

• Synthesis Reaction: Smaller molecular components combine to form larger, more complex molecules.

• Exchange Reaction: Atoms or groups are swapped between molecules (e.g., the interaction of HCl and NaHCO3 in neutralization).

Organic Compounds

Expected Learning Outcomes

• Discuss the significance of various organic molecules within biological contexts and their classifications.

Carbon Compounds

Organic chemistry is primarily concerned with carbon-containing compounds that are central to biological structures and functions. The four major categories include carbohydrates, lipids, proteins, and nucleic acids, each serving vital roles in cellular processes. Functional groups, molecular attachments that dictate the properties of organic molecules (such as hydroxyl and carboxyl groups), also play significant roles in defining their reactivity and interactions.

Carbohydrates

Carbohydrates are hydrophilic organic molecules, serving as energy sources as well as structural components of cells. Their general formula can be represented as (C(H2O))n, where ‘n’ denotes the number of repeating units. Main types include:

• Monosaccharides: Simple sugars, the most basic carbohydrate units.

• Disaccharides: Composed of two monosaccharides linked together.

• Oligosaccharides: Short chains of monosaccharides (3-10 units).

• Polysaccharides: Long chains serving functions like energy storage and structural roles (e.g., starch and cellulose).

Lipids

Lipids are defined as hydrophobic compounds, holding high caloric values per gram compared to carbohydrates. Major types comprise:

• Fatty Acids: Building blocks for many lipids, can be saturated or unsaturated.

• Triglycerides: Formed from glycerol and three fatty acids, serving as energy reserves.

• Phospholipids: Key structural components of cell membranes, providing barriers between compartments.

• Steroids: Four-ring structures playing roles in signaling and cell membrane integrity.

• Eicosanoids: Signaling molecules derived from fatty acids involved in inflammation and cellular signaling.

Proteins

Proteins are fundamental polymers composed of amino acids, integral to a multitude of biological functions, including structural integrity, transport of molecules, and catalysis of chemical reactions (enzymes). They exist in various structures:

• Primary Structure: Sequence of amino acids.

• Secondary Structure: Local folding patterns (e.g., alpha-helices and beta-sheets).

• Tertiary Structure: Overall three-dimensional shape determined by interactions among side chains.

• Quaternary Structure: Assembly of multiple polypeptide subunits.

Nucleic Acids and ATP

Nucleic acids encompass DNA and RNA, which are polymers of nucleotides. These molecules carry the genetic blueprint necessary for organism function and heredity. ATP (adenosine triphosphate) serves as a crucial energy-transfer molecule in metabolism, facilitating various energy-requiring processes in cells.