#AP Biology: Chemical Bonds & Macromolecules - The Night Before Review

Hey! Let's get you totally prepped for your AP Bio exam. We're going to make sure all the key concepts are crystal clear. Let's dive in!

#Chemical Bonds: The Foundation of Life

# Covalent Bonds: Sharing is Caring 🤝

• Definition: Electrons are shared between atoms. These are strong bonds that form molecules.

• Single Bond: One pair of electrons shared (represented by a single line, e.g., H-H).

• Double Bond: Two pairs of electrons shared (represented by a double line, e.g., O=O).

• Electronegativity: An atom's pull on electrons in a bond. The bigger the difference, the more polar the bond.

Examples: * Methane (CH4) * Carbon Monoxide (CO) * Iodine Monobromide (IBr)

# Ionic Bonds: Opposites Attract ➕➖

• Definition: Electrons are transferred, creating ions with opposite charges that attract each other. Forms ionic compounds (salts).
• Process: One atom loses electrons (becomes positive), and another gains electrons (becomes negative).
• Result: Electrostatic attraction holds the ions together.

Examples: * Sodium Chloride (NaCl) * Lithium Fluoride (LiF)

Image courtesy of Surfguppy.

# Metallic Bonds: The Electron Sea 🌊

• Definition: Attraction between metal ions and a 'sea' of delocalized (free) electrons.
• Properties: Explains why metals are good conductors of electricity and heat.

Examples: * Iron (Fe) * Copper (Cu) * Gold (Au)

#Polymers & Monomers: Building Blocks of Life

# Polymers: Many Units Together

• Definition: Large molecules made of many repeating smaller units (monomers) linked by covalent bonds. Think of it like a train (polymer) made of many train cars (monomers).
• Key Point: Most biological macromolecules (carbohydrates, proteins, nucleic acids) form polymers, but lipids generally do not.

# Monomers: Single Units

• Definition: Small building block molecules that combine to form a polymer.
• Analogy: Monomers are like LEGO bricks; when you put many together, you get a larger structure (polymer).

#Covalent Bond Polarity: Uneven Sharing

# Nonpolar Covalent Bonds: Equal Sharing

• Definition: Electrons are shared equally, resulting in no partial charges.
• Cause: Occurs when electronegativity differences between atoms are small.

# Polar Covalent Bonds: Unequal Sharing

• Definition: Electrons are shared unequally, creating partial positive (δ+) and partial negative (δ-) charges.
• Cause: Occurs when there's a significant difference in electronegativity between atoms.

#Intra vs. Intermolecular Bonds: Within and Between

# Intramolecular Bonds: Within Molecules

• Definition: Bonds that hold atoms together within a molecule.
• Example: Covalent bonds (like the ones in H2O).

# Intermolecular Bonds: Between Molecules

• Definition: Weak attractions between molecules.

• Example: Hydrogen Bonds - A hydrogen atom bonded to a highly electronegative atom (F, N, or O) is attracted to another electronegative atom. These are weak but crucial for life!

#Dehydration Synthesis & Hydrolysis: Building and Breaking

# Dehydration Synthesis: Building Polymers

• Definition: Monomers combine to form polymers by removing water (H2O).
• Process: One monomer provides an OH-, and another provides H+, forming H2O.
• Type of Reaction: Condensation reaction, endergonic (requires energy), and anabolic (builds complexity).
• Enzymes: Required to facilitate the reaction.

# Hydrolysis: Breaking Down Polymers

• Definition: Polymers are broken down into monomers by adding water (H2O).
• Process: Water is split into H+ and OH-, which break the bond between monomers.
• Type of Reaction: Exergonic (releases energy) and catabolic (reduces complexity).
• Enzymes: Required to facilitate the reaction.

Image courtesy of WikiMedia Commons.

#Final Exam Focus

• High-Priority Topics:
  • Covalent vs. Ionic Bonds (and their properties)
  • Polarity of Bonds and Molecules
  • Hydrogen Bonds (and their importance in water and biological molecules)
  • Dehydration Synthesis and Hydrolysis (and their role in polymer formation and breakdown)
• Common Question Types:
  • MCQs on identifying bond types and their characteristics
  • FRQs on explaining the role of water in biological processes (hydrogen bonds)
  • FRQs requiring you to describe dehydration synthesis and hydrolysis
• Last-Minute Tips:
  • Time Management: Quickly identify the question type and focus on answering what the question is asking.
  • Common Pitfalls: Confusing covalent and ionic bonds, missing the importance of hydrogen bonds, not understanding the role of enzymes in synthesis and hydrolysis.
  • Strategies: Read each question carefully, underline key terms, and plan your answers before writing.

# Practice Questions

Practice Question

#Multiple Choice Questions

1. Which of the following best describes the primary function of hydrogen bonds in biological systems? (A) They form the backbone of DNA molecules. (B) They provide the strong bonds that hold proteins together. (C) They are responsible for the high surface tension of water. (D) They are the bonds that link monomers to form polymers.

2. A researcher is studying a newly discovered molecule. They find that the molecule is composed of many repeating subunits linked together by covalent bonds. This molecule is best classified as a: (A) Monomer (B) Polymer (C) Lipid (D) Salt

#Free Response Question

Question:

Water is essential to all living organisms. Describe the unique properties of water that result from its polarity and hydrogen bonding. Explain how these properties contribute to the processes of dehydration synthesis and hydrolysis. Additionally, discuss why lipids do not form polymers in the same way that carbohydrates, proteins, and nucleic acids do.

Scoring Breakdown:

• Water Properties (3 points):
  • 1 point for mentioning water's polarity (unequal sharing of electrons).
  • 1 point for mentioning hydrogen bonding between water molecules.
  • 1 point for describing at least one property of water resulting from hydrogen bonding (e.g., high surface tension, high specific heat).
• Dehydration Synthesis and Hydrolysis (3 points):
  • 1 point for explaining how water is removed during dehydration synthesis to form polymers.
  • 1 point for explaining how water is added during hydrolysis to break down polymers.
  • 1 point for mentioning that both processes are facilitated by enzymes.
• Lipids and Polymers (2 points):
  • 1 point for stating that lipids generally do not form polymers.
  • 1 point for providing a valid reason (e.g., lipids are primarily composed of nonpolar molecules, they are not formed by repeating monomeric subunits).