Chemistry Fundamentals for Biology Students

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Chemistry for Biology

Introduction

Chemistry is fundamental to understanding biological processes. This section introduces the basic chemical principles that underlie the structure and function of biological molecules and systems.

Elements and Compounds: Understanding the building blocks of matter and how they combine to form the molecules essential for life.
Atomic Structure: Exploring the structure of atoms, the smallest units of elements.
Chemical Bonding: Examining how atoms bond to form molecules and how these bonds influence molecular function.
Chemical Reactions: Investigating how molecules interact and change during chemical reactions.

Elements and Compounds

Definitions and Properties

Element: A pure substance that cannot be broken down into other substances by chemical reactions. Each element is defined by its number of protons.
Compound: A substance formed when two or more elements combine in a fixed ratio. Compounds have properties different from their constituent elements.
Example: Water (H2O) is a compound made from hydrogen and oxygen, both of which are gases in their elemental forms, but together form a liquid essential for life.

Atomic Structure

Subatomic Particles and Atomic Models

Protons: Positively charged particles in the nucleus; determine the atomic number.
Neutrons: Neutral particles in the nucleus; contribute to atomic mass.
Electrons: Negatively charged particles orbiting the nucleus; involved in chemical bonding.
Atomic Number: Number of protons in an atom.
Atomic Mass: Sum of protons and neutrons.
Electron Shells: Electrons occupy shells around the nucleus. The first shell holds 2 electrons, the second and third hold up to 8 each.
Isotopes: Atoms of the same element with different numbers of neutrons. Some isotopes are radioactive and used as tracers in medicine and research.

Example: Carbon-12 and Carbon-14 are isotopes of carbon; Carbon-14 is used in radiocarbon dating.

Electron Orbitals and Chemical Reactivity

Electron Arrangement and Stability

Orbitals: Three-dimensional regions where electrons are likely to be found 90% of the time.
Valence Electrons: Electrons in the outermost shell; determine chemical reactivity.
Stable Atoms: Atoms with full outer shells are nonreactive (inert).
Unpaired Electrons: Atoms with unpaired electrons in their outer shell are reactive and tend to form bonds.

Elements in the Human Body

Major and Trace Elements

The human body is composed primarily of a few key elements, with others present in trace amounts.

Element	Symbol	Percentage of Body Mass
Oxygen	O	65.0%
Carbon	C	18.5%
Hydrogen	H	9.5%
Nitrogen	N	3.3%
Calcium	Ca	1.5%
Phosphorus	P	1.0%
Potassium	K	0.4%
Sulfur	S	0.3%
Sodium	Na	0.2%
Chlorine	Cl	0.2%
Magnesium	Mg	0.1%
Trace Elements	-	<0.01%

Additional info: Trace elements include iron, zinc, copper, iodine, and others, which are essential in small amounts for various biological functions.

Chemical Bonds

Types of Chemical Bonds

Ionic Bonds: Formed when electrons are transferred from one atom to another, resulting in oppositely charged ions that attract each other.
Covalent Bonds: Formed when two atoms share one or more pairs of electrons. Can be single, double, or triple bonds depending on the number of shared electron pairs.
Polar Covalent Bonds: Electrons are shared unequally, resulting in partial charges on the atoms.
Hydrogen Bonds: Weak attractions between a slightly positive hydrogen atom and a slightly negative atom (often oxygen or nitrogen) in another molecule.

Example: In water (H2O), the oxygen atom is more electronegative than hydrogen, creating a polar molecule with hydrogen bonds between molecules.

Chemical Reactions

Making and Breaking Bonds

Reactants: Starting substances in a chemical reaction.
Products: Substances formed as a result of a chemical reaction.
Chemical Equilibrium: The point at which the forward and reverse reactions occur at the same rate, so the concentrations of reactants and products remain constant.
Photosynthesis Example:

Carbon dioxide and water (reactants) are converted to glucose and oxygen (products) using light energy.

Properties of Water

Unique Characteristics and Biological Importance

Cohesion: Water molecules stick to each other due to hydrogen bonding, leading to high surface tension.
Adhesion: Water molecules stick to other polar or charged substances, aiding processes like capillary action in plants.
High Specific Heat: Water resists temperature changes, helping to stabilize environments and organisms.
High Heat of Vaporization: Evaporation of water cools surfaces, important for temperature regulation.
Density of Ice: Ice is less dense than liquid water, so it floats, insulating aquatic life in winter.
Solvent Properties: Water dissolves many polar and ionic substances, making it the universal solvent in biological systems.

Example: Water's high specific heat helps moderate Earth's climate and maintain stable temperatures in organisms.

Solutions, Concentrations, and the Mole Concept

Measuring and Preparing Solutions

Percent Solutions: Grams of solute per 100 mL of water (mass/volume).
Molarity (M): Moles of solute per liter of solution.
Mole: The amount of substance containing molecules (Avogadro's number). The mass of one mole equals the molecular mass in grams.

Example: 1 mole of sucrose (C12H22O11) weighs 342 g.

Acids, Bases, and pH

pH Scale and Biological Buffers

Acids: Substances that donate H+ ions in solution.
Bases: Substances that accept H+ ions or donate OH- ions.
pH Scale: Measures the concentration of H+ ions; defined as .
Neutral Solution: [H+] = [OH-], pH = 7.
Acidic Solution: pH < 7.
Basic Solution: pH > 7.
Buffers: Substances that minimize changes in pH by accepting or donating H+ ions.

Example: The bicarbonate buffer system in blood:

This system helps maintain a stable pH in the body.

Environmental and Biological Relevance of Water

Water Scarcity and Global Distribution

Water Usage: Average Americans use about 100 gallons of water per person per day; in some regions, people have access to less than 5 gallons per day.
Global Water Distribution: The Great Lakes contain 20% of Earth's fresh surface water.
Water Scarcity: Over 1 billion people lack access to safe water; by 2025, two-thirds of the world's population may face water shortages.

Example: Acid rain and increased atmospheric CO2 lower the pH of oceans, affecting marine life and coral reefs.

Summary Table: Properties of Water and Their Biological Importance

Property	Description	Biological Importance
Cohesion	Water molecules stick together	Enables transport in plants
Adhesion	Water sticks to other substances	Helps water move through vessels
High Specific Heat	Resists temperature change	Stabilizes climate and body temperature
High Heat of Vaporization	Requires much energy to evaporate	Evaporative cooling (sweating)
Lower Density of Ice	Ice floats on water	Insulates aquatic life in winter
Solvent Ability	Dissolves many substances	Facilitates biochemical reactions