Unit 1: Chemistry of Life – General Biology Study Guide

Unit 1: Chemistry of Life

Scientific Method Review

The scientific method is a systematic approach to understanding the natural world through observation, experimentation, and logical reasoning. It is foundational to all scientific inquiry.

• What is Science? Science is a method of gaining knowledge about the natural world through observation and experimentation.

• Observations: Can be qualitative (descriptive) or quantitative (numerical).

• Reasoning: Inductive reasoning draws generalizations from specific observations; deductive reasoning applies general principles to predict specific results.

• Hypothesis: A testable explanation for an observation or phenomenon.

• Null Hypothesis (H0): States there is no significant effect or difference.

• Alternative Hypothesis (Ha): States there is a significant effect or difference.

• Variables: Independent variable is manipulated; dependent variable is measured.

• Controls: Positive control produces a known result; negative control produces no result.

• Constants: Factors kept the same across all groups.

• Number of Trials: Multiple trials increase reliability and statistical significance.

Statistics in Biology

Statistics help biologists summarize, describe, and analyze experimental data to draw conclusions about biological phenomena.

• Normal Distribution: Data often form a bell-shaped curve (normal distribution).

• Central Tendencies:

  • Mean (Average): $\text{Mean} = \frac{\sum x}{n}$

  • Median: Middle value in ordered data.

  • Mode: Most frequently occurring value.

• Range: Difference between highest and lowest values.

• Standard Deviation (SD): Measures spread of data around the mean.

  • $SD = \sqrt{\frac{\sum (x_i - \bar{x})^2}{n-1}}$

  • ~68% of data within 1 SD, ~95% within 2 SDs, ~99.7% within 3 SDs (normal distribution).

• Standard Error (SE): Indicates how close the sample mean is to the true population mean.

  • $SE = \frac{SD}{\sqrt{n}}$

• Error Bars: Graphical representations of variability (SD or SE) on charts.

• Chi-Square Test ($\chi^2$): Determines if observed results differ significantly from expected results.

  • $\chi^2 = \sum \frac{(O - E)^2}{E}$

  • Compare to critical value based on degrees of freedom ($df = n - 1$).

Chemistry Review

Understanding matter, elements, and compounds is essential for studying biological molecules and processes.

• Matter: Anything that has mass and takes up space.

• Element: Pure substance consisting of one type of atom.

• Compound: Substance formed from two or more elements in a fixed ratio.

• Essential Elements: Needed in large amounts (e.g., C, H, O, N).

• Trace Elements: Needed in small amounts (e.g., Fe, Zn).

• Atomic Number: Number of protons in an atom.

• Atomic Mass: Average mass of an element’s atoms.

• Bohr Model: Electrons orbit nucleus in fixed energy levels.

• Lewis Dot Model: Shows valence electrons as dots.

• Octet Rule: Atoms gain, lose, or share electrons to achieve 8 in their outer shell.

• Electronegativity: Atom’s ability to attract electrons in a bond.

Types of Chemical Bonds

• Covalent Bonds: Electrons shared between atoms.

  • Nonpolar: Shared equally (e.g., H2).

  • Polar: Shared unequally (e.g., H2O).

  • Double/Triple Bonds: Two or three pairs shared.

• Ionic Bonds: Electrons transferred, forming charged ions (e.g., NaCl).

• Hydrogen Bonds: Weak bonds between hydrogen and electronegative atoms (important in water and DNA).

Acids, Bases, and pH

• Acids: Increase H+ concentration (e.g., HCl).

• Bases: Decrease H+ concentration (e.g., NaOH).

• pH Scale: 0–14; 7 is neutral, <7 acidic, >7 basic.

• Buffers: Maintain stable pH by absorbing/releasing H+ or OH-.

• Importance: Enzyme activity, cellular respiration, and homeostasis depend on proper pH.

Properties of Water

Water’s unique properties are essential for life and result from its molecular structure and hydrogen bonding.

• Polarity: Water is a polar molecule with partial charges.

• Cohesion: Water molecules stick to each other (surface tension).

• Adhesion: Water molecules stick to other substances.

• Capillary Action: Water moves in narrow spaces (important in plants).

• High Specific Heat: Water absorbs/releases heat with little temperature change.

• Evaporative Cooling: Water evaporation cools surfaces.

• Density: Ice is less dense than liquid water (floats).

• Water as a Solvent: Dissolves many substances, facilitating biological reactions.

Chemistry of Life

Life is based on organic compounds, primarily carbon-based molecules, and a few key inorganic compounds.

• Organic Compounds: Contain carbon and hydrogen (e.g., glucose, DNA).

• Inorganic Compounds: Do not contain both carbon and hydrogen (e.g., water, CO2).

• Key Elements: Nitrogen (proteins, nucleic acids), phosphorus (DNA, ATP), sulfur (proteins).

The Versatility of Carbon

• Tetravalency: Carbon forms four covalent bonds.

• Bonding Capacity: Can form single, double, triple bonds; chains and rings.

• Hydrocarbon Chains: Chains of carbon and hydrogen; foundation for many biomolecules.

• Functional Groups: Specific groups of atoms that confer chemical properties (e.g., hydroxyl, carboxyl, amino, phosphate).

Biological Macromolecules

Macromolecules are large, complex molecules essential for life, including carbohydrates, proteins, nucleic acids, and lipids.

Monomers and Polymers

• Monomers: Small, basic units (e.g., monosaccharides, amino acids, nucleotides).

• Polymers: Large molecules made of repeating monomers (e.g., polysaccharides, proteins, nucleic acids).

• Dehydration Reaction: Joins monomers by removing water.

• Hydrolysis: Breaks polymers into monomers by adding water.

Carbohydrates

• Monosaccharides: Simple sugars (e.g., glucose, fructose).

• Disaccharides: Two monosaccharides joined (e.g., sucrose).

• Polysaccharides: Long chains (e.g., starch, glycogen, cellulose, chitin).

Proteins

• Amino Acids: 20 types; building blocks of proteins.

• Peptide Bonds: Link amino acids.

• Protein Structure:

  1. Primary: Sequence of amino acids.

  2. Secondary: Alpha helices and beta sheets.

  3. Tertiary: 3D shape of polypeptide.

  4. Quaternary: Multiple polypeptides together.

• Functions: Enzymes, antibodies, hormones, structure.

Nucleic Acids

• DNA: Stores genetic information; double-stranded.

• RNA: Transmits genetic information; single-stranded.

• Nucleotides: Monomers; consist of sugar, phosphate, nitrogenous base.

• Phosphodiester Linkage: Bonds between nucleotides.

• Sequence: Order of nucleotides encodes information.

Lipids

• Fats (Triglycerides): Glycerol + 3 fatty acids; energy storage.

• Saturated Fats: No double bonds; solid at room temperature.

• Unsaturated Fats: Double bonds; liquid at room temperature.

• Phospholipids: Glycerol + 2 fatty acids + phosphate; form cell membranes.

• Steroids: Four fused rings; hormones and membrane components (e.g., cholesterol).

Additional info: This guide covers foundational topics from the first unit of a General Biology course, including the scientific method, statistics, chemistry, water properties, and biological macromolecules. It is suitable for exam preparation and review.