General Biology: Core Concepts and Macromolecules Study Guide

Scientific Method and Process of Science

Characteristics of Life

Living things share several defining characteristics that distinguish them from non-living matter.

• Key characteristics: Composed of cells, capable of replication/reproduction, contain/process/respond to information, acquire and use energy, and evolve.

• Evolution: The process by which populations of organisms change over generations.

Scientific Method

The scientific method is a systematic approach to understanding the natural world through observation, hypothesis formation, experimentation, and analysis.

• Hypothesis: A testable and falsifiable statement that explains observations.

• Theory: A broad explanation based on extensive evidence; more comprehensive than a hypothesis.

• Laws: Descriptions of observed phenomena, often mathematical, but do not explain why phenomena occur.

• Predictions: Logical outcomes expected if the hypothesis is correct.

• Variables: Factors that can be changed or controlled in an experiment.

• Independent variable: The factor manipulated by the experimenter.

• Dependent variable: The factor measured in response to changes in the independent variable.

Experimental Design

Good experimental design includes controls, replication, and minimizing confounding variables.

• Control group: A group not exposed to the experimental treatment, used for comparison.

• Placebo: An inert treatment given to control groups in medical studies.

• Double-blind experiment: Neither participants nor experimenters know who receives the treatment, reducing bias.

• Sample size: Larger sample sizes increase confidence in results.

• Confounding variables: Other factors that may affect the dependent variable.

Statistical significance is used to determine whether observed results are likely due to chance.

Atoms, Bonds, and Water

Atomic Structure and Chemical Bonds

Atoms are the basic units of matter, consisting of protons, neutrons, and electrons.

• Covalent bonds: Atoms share electrons equally or unequally.

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

• Nonpolar covalent bonds: Electrons are shared equally (e.g., in O2 or CH4).

• Ionic bonds: Electrons are transferred from one atom to another, creating ions.

Properties of Water

Water's unique properties are essential for life and result from its polar covalent bonds and hydrogen bonding.

• Cohesion: Water molecules stick to each other.

• Adhesion: Water molecules stick to other substances.

• High specific heat: Water resists temperature changes.

• High heat of vaporization: Water requires a lot of energy to evaporate.

• Solvent properties: Water dissolves many substances, especially polar and ionic compounds.

Hydrophilic vs. Hydrophobic

• Hydrophilic: Molecules that interact well with water (e.g., ions, polar molecules).

• Hydrophobic: Molecules that do not interact well with water (e.g., nonpolar molecules, oils).

Macromolecules: Structure and Function

Carbohydrates

Carbohydrates are organic molecules composed of carbon, hydrogen, and oxygen, typically in a 1:2:1 ratio. They serve as energy sources and structural components.

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

• Disaccharides: Two monosaccharides joined by glycosidic linkages (e.g., sucrose, lactose).

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

• Glycosidic linkage: Covalent bond joining monosaccharides.

Functions: Energy storage (starch in plants, glycogen in animals), structural support (cellulose in plants, chitin in fungi and insects).

Proteins

Proteins are polymers of amino acids and perform a wide variety of functions in cells.

• Amino acids: Building blocks of proteins, each with a central carbon, amino group, carboxyl group, hydrogen atom, and R group (side chain).

• Peptide bond: Covalent bond linking amino acids.

• Levels of protein structure:

  • Primary: Sequence of amino acids.

  • Secondary: Local folding (α-helix, β-sheet) due to hydrogen bonding.

  • Tertiary: 3D shape due to interactions among R groups.

  • Quaternary: Association of multiple polypeptide chains.

• Denaturation: Loss of protein structure (and function) due to heat, pH, or chemicals.

• Enzymes: Proteins that catalyze biochemical reactions by lowering activation energy.

Nucleic Acids

Nucleic acids (DNA and RNA) store and transmit genetic information. They are polymers of nucleotides.

• Nucleotide: Consists of a phosphate group, a five-carbon sugar (deoxyribose in DNA, ribose in RNA), and a nitrogenous base.

• Nitrogenous bases: Adenine (A), guanine (G), cytosine (C), thymine (T, in DNA), uracil (U, in RNA).

• Phosphodiester bond: Covalent bond linking nucleotides.

• Base pairing: A pairs with T (or U in RNA), G pairs with C.

• ATP (adenosine triphosphate): Main energy currency of the cell.

Functions: Storage and transmission of genetic information, energy transfer (ATP).

Lipids

Lipids are hydrophobic molecules that include fats, phospholipids, and steroids. They are not true polymers.

• Fats (triglycerides): Glycerol + 3 fatty acids. Used for energy storage.

• Saturated fatty acids: No double bonds, solid at room temperature.

• Unsaturated fatty acids: One or more double bonds, liquid at room temperature.

• Phospholipids: Glycerol + 2 fatty acids + phosphate group. Major component of cell membranes. Amphipathic (hydrophilic head, hydrophobic tails).

• Steroids: Four fused carbon rings (e.g., cholesterol).

Biological Membranes

Phospholipids form bilayers in water, creating selectively permeable membranes.

• Selective permeability: Some substances cross more easily than others.

• Fluid mosaic model: Membranes are dynamic, with proteins and lipids moving laterally.

• Cholesterol: Modulates membrane fluidity.

Summary Table: Macromolecules

Macromolecule	Monomer	Bond Type	Main Functions	Examples
Carbohydrates	Monosaccharide	Glycosidic linkage	Energy storage, structure	Starch, glycogen, cellulose
Proteins	Amino acid	Peptide bond	Catalysis, structure, transport	Enzymes, hemoglobin
Nucleic acids	Nucleotide	Phosphodiester bond	Genetic information, energy (ATP)	DNA, RNA, ATP
Lipids	Fatty acids, glycerol	Ester bond	Energy storage, membranes, signaling	Triglycerides, phospholipids, steroids

Key Equations and Concepts

• pH calculation: $\text{pH} = -\log_{10}[\text{H}^+]$

• Base pairing in DNA: $\text{A} = \text{T}, \text{G} = \text{C}$

• ATP hydrolysis: $\text{ATP} + \text{H}_2\text{O} \rightarrow \text{ADP} + \text{P}_i + \text{energy}$

Additional Info

• Be able to identify macromolecules based on structure and function.

• Understand the directionality of nucleic acids (5' to 3').

• Recognize the importance of membrane fluidity and selective permeability.