Unit 1 Chemistry Of Life Ap Biology Exam Review

Unit 1: Chemistry of Life - AP Biology Exam Review

The AP Biology exam's Unit 1, focusing on the Chemistry of Life, lays the groundwork for understanding all subsequent biological concepts. A strong grasp of this foundational unit is crucial for success. This comprehensive review covers key topics, providing a detailed overview to help you ace the exam.

I. Water: The Solvent of Life

Water's unique properties are essential for life. Its polarity, resulting from the unequal sharing of electrons between oxygen and hydrogen atoms, leads to several critical features:

A. Polarity and Hydrogen Bonding

Polarity: The slightly negative oxygen atom and slightly positive hydrogen atoms allow water molecules to form hydrogen bonds with each other and other polar molecules. This is fundamental to many of water's properties.

Hydrogen Bonds: These relatively weak bonds are constantly forming and breaking, giving water its unique properties. They are responsible for water's high cohesion and adhesion.

B. Cohesion and Adhesion

• Cohesion: Water molecules stick to each other due to hydrogen bonding. This contributes to surface tension, allowing insects to walk on water. It also facilitates water transport in plants through xylem vessels.

• Adhesion: Water molecules stick to other polar substances. This property is crucial for capillary action, the movement of water against gravity in narrow tubes like plant xylem.

C. High Specific Heat Capacity

Water resists temperature changes. This high specific heat capacity means it takes a significant amount of energy to raise its temperature. This helps regulate temperature fluctuations in organisms and aquatic environments, maintaining relatively stable internal temperatures.

D. High Heat of Vaporization

Water requires a large amount of energy to change from a liquid to a gas (evaporation). This high heat of vaporization allows for evaporative cooling, a crucial mechanism for temperature regulation in organisms (e.g., sweating in humans).

E. Density Anomaly of Ice

Ice is less dense than liquid water, allowing it to float. This density anomaly insulates aquatic life during winter, preventing bodies of water from freezing solid.

II. Carbon: The Backbone of Life

Carbon's unique ability to form four covalent bonds makes it the central element of organic molecules. Its versatility allows for the creation of a vast array of diverse molecules with different shapes and functions.

A. Carbon Skeletons

Carbon atoms can bond to each other in chains, rings, and branched structures, forming the carbon skeletons of organic molecules. These skeletons can be modified by adding functional groups, dramatically altering the molecule's properties.

B. Functional Groups

These groups of atoms attached to carbon skeletons are responsible for the characteristic chemical properties of organic molecules. Understanding the properties of common functional groups is essential. Key functional groups include:

• Hydroxyl (-OH): Alcohols; polar, hydrophilic
• Carbonyl (C=O): Ketones (internal C=O), aldehydes (terminal C=O); polar
• Carboxyl (-COOH): Carboxylic acids; acidic, polar
• Amino (-NH2): Amines; basic, polar
• Phosphate (-PO4): Organic phosphates; acidic, polar
• Sulfhydryl (-SH): Thiols; can form disulfide bridges

C. Isomers

Molecules with the same molecular formula but different structures are called isomers. Three main types are:

• Structural isomers: Differ in the arrangement of atoms.
• Geometric isomers (cis-trans isomers): Differ in the spatial arrangement around a double bond.
• Enantiomers (optical isomers): Mirror images of each other that are non-superimposable. These can have vastly different biological activities.

III. Macromolecules: The Building Blocks of Life

Four main classes of macromolecules – carbohydrates, lipids, proteins, and nucleic acids – are essential for life. Each is composed of smaller monomer units linked together through dehydration reactions.

A. Carbohydrates

Carbohydrates are composed of carbon, hydrogen, and oxygen in a 1:2:1 ratio. Their primary function is energy storage and structural support. Types include:

• Monosaccharides: Simple sugars (e.g., glucose, fructose).
• Disaccharides: Two monosaccharides linked by a glycosidic linkage (e.g., sucrose, lactose).
• Polysaccharides: Long chains of monosaccharides (e.g., starch, glycogen, cellulose, chitin). Starch and glycogen are energy storage polysaccharides, while cellulose and chitin provide structural support.

B. Lipids

Lipids are diverse hydrophobic molecules, primarily composed of carbon and hydrogen. They are insoluble in water. Key types include:

• Triglycerides: Composed of glycerol and three fatty acids. They serve as energy storage molecules. Fatty acids can be saturated (no double bonds) or unsaturated (one or more double bonds).
• Phospholipids: Essential components of cell membranes. They have a hydrophilic head and two hydrophobic tails.
• Steroids: Four fused carbon rings (e.g., cholesterol, hormones). Cholesterol is a crucial component of animal cell membranes.

C. Proteins

Proteins are polymers of amino acids linked by peptide bonds. They have a vast array of functions, including:

• Enzymes: Catalyze biochemical reactions.
• Structural proteins: Provide support (e.g., collagen).
• Transport proteins: Carry molecules (e.g., hemoglobin).
• Hormones: Chemical messengers (e.g., insulin).
• Antibodies: Part of the immune system.

Amino Acid Structure: Each amino acid has a central carbon atom bonded to an amino group (-NH2), a carboxyl group (-COOH), a hydrogen atom, and a variable R group (side chain). The R group determines the amino acid's properties.

Protein Structure: Proteins have four levels of structure:

• Primary structure: The linear sequence of amino acids.
• Secondary structure: Local folding patterns (alpha-helices and beta-pleated sheets) stabilized by hydrogen bonds.
• Tertiary structure: The overall three-dimensional shape of a polypeptide chain, stabilized by various interactions (hydrogen bonds, disulfide bridges, ionic bonds, hydrophobic interactions).
• Quaternary structure: The arrangement of multiple polypeptide chains in a protein complex.

D. Nucleic Acids

Nucleic acids store and transmit genetic information. Two main types exist:

• DNA (deoxyribonucleic acid): The genetic material in most organisms. It is a double helix composed of two strands of nucleotides.
• RNA (ribonucleic acid): Plays various roles in protein synthesis. It is usually single-stranded.

Nucleotide Structure: Nucleotides are composed of a sugar (deoxyribose in DNA, ribose in RNA), a phosphate group, and a nitrogenous base (adenine, guanine, cytosine, thymine in DNA; adenine, guanine, cytosine, uracil in RNA).

IV. Chemical Reactions and Energy

Chemical reactions are essential for life processes. Understanding the principles of energy transfer and reaction rates is crucial.

A. Energy Changes in Chemical Reactions

• Endergonic reactions: Require energy input (ΔG > 0).
• Exergonic reactions: Release energy (ΔG < 0).
• Gibbs Free Energy (ΔG): A measure of the energy available to do work.

B. Enzymes

Enzymes are biological catalysts that speed up chemical reactions by lowering the activation energy. They are highly specific for their substrates (reactants). Enzyme activity is influenced by factors such as temperature, pH, and substrate concentration.

C. Enzyme-Substrate Complex

The enzyme and substrate temporarily bind to form an enzyme-substrate complex, allowing the reaction to occur. The enzyme is unchanged after the reaction.

D. Factors Affecting Enzyme Activity

• Temperature: Enzymes have an optimal temperature for activity. High temperatures can denature the enzyme.
• pH: Enzymes have an optimal pH for activity. Extremes of pH can denature the enzyme.
• Substrate concentration: Enzyme activity increases with increasing substrate concentration until saturation is reached.

V. Important Considerations for the AP Biology Exam

This review covers the key concepts, but remember to delve deeper into each topic using your textbook and class notes. Practice is essential for mastering this material. Consider the following:

• Practice multiple-choice questions: Familiarize yourself with the question format and types of questions asked.
• Practice free-response questions: Develop your ability to write clear and concise answers that address the prompt completely.
• Understand the connections: The concepts within Unit 1 are interconnected. Understanding these relationships will enhance your overall understanding of biology.
• Review diagrams and figures: Visual representations are crucial for understanding complex biological processes.
• Use flashcards and other study aids: These can help reinforce key concepts and vocabulary.

By diligently reviewing these topics and engaging in active learning techniques, you will build a solid foundation in the Chemistry of Life and significantly increase your chances of succeeding on the AP Biology exam. Remember to focus on understanding the underlying principles rather than simply memorizing facts. Good luck!