Structure and Function of Biological Macromolecules

Elijah Ramirez
6 min read
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Study Guide Overview
This study guide covers the four main macromolecules: nucleic acids, carbohydrates, proteins, and lipids. It emphasizes the relationship between structure and function, detailing monomers, bonds, and key examples for each macromolecule. Specific topics include DNA/RNA structure, levels of protein structure (including denaturation), types of carbohydrates (mono-, di-, and polysaccharides), and lipid functions. Practice questions and exam tips are also provided.
AP Biology: Macromolecules - Your Night-Before-the-Exam Guide
Hey there, future biologist! Let's make sure you're totally prepped for the AP Biology exam. This guide is designed to be your go-to resource, hitting all the key points and making those connections you need to ace this thing. Let's dive in!
The Four Giants: Macromolecules
These are the big players in the biological world. Understanding them is crucial. Let's break them down:
- Nucleic Acids ๐งฌ: Genetic info carriers.
- Carbohydrates ๐ฉ: Energy and structure.
- Proteins ๐ฅฉ: Workhorses of the cell.
- Lipids ๐: Energy storage and membranes.
Structure Determines Function
Remember, the shape of a molecule dictates what it does. The monomers (building blocks) and their arrangement are key. Think of it like LEGOs โ different arrangements, different structures, different functions!
๐งฌ Nucleic Acids
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Monomers: Nucleotides (sugar, phosphate, nitrogenous base).
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Types: DNA (stores genetic info) and RNA (carries out instructions).
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Directionality: 5' to 3' (important for replication & transcription).
- New nucleotides are added to the 3' end during polymerization.
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DNA Structure: Double helix, antiparallel strands.
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A pairs with T (2 hydrogen bonds).
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C pairs with G (3 hydrogen bonds).
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This base pairing ensures stability and accurate genetic info transfer.
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Image courtesy of Lumen Learning
Image courtesy of BioNinja
๐ฅฉ Proteins
- Monomers: Amino acids.
- Bonds: Peptide bonds (formed by dehydration synthesis).
- Functions: Structural, catalytic (enzymes), signaling, defense, transport.
Levels of Protein Structure
- Primary: Sequence of amino acids.
- Secondary: Alpha helices and beta-pleated sheets (hydrogen bonds).
- Tertiary: 3D structure (interactions between R-groups).
- Quaternary: Multiple polypeptide chains.
Image courtesy of Lumen Learning.
Primary = "The letter sequence", Secondary = "Local folding", Tertiary = "Overall 3D shape", Quaternary = "Multiple subunits"
Denaturation
- Loss of tertiary structure due to heat, pH, etc.
- Leads to loss of function.
- Different from hydrolysis (breaking down into smaller pieces).
Sickle-cell disease: A single amino acid change in hemoglobin can have huge consequences. This highlights the importance of protein structure!
Species with common ancestors often have similar protein structures.
๐ฉ Carbohydrates
- Monomers: Monosaccharides (simple sugars).
- Functions: Energy source, structural support.
- Types: Linear or branched.
Image courtesy of ResearchGate
Disaccharides and Polysaccharides
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Disaccharide: Two monosaccharides linked by a glycosidic bond (formed by dehydration synthesis).
- Maltose: Glucose + Glucose
- Sucrose: Glucose + Fructose
- Lactose: Glucose + Galactose
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Polysaccharides: Polymers of sugars.
- Starch: Energy storage in plants.
- Glycogen: Energy storage in animals.
- Cellulose: Structural in plant cell walls.
- Chitin: Structural in arthropod exoskeletons and fungal cell walls.
Think of Starch and Cellulose as plant-based, and Glycogen as animal-based. Chitin helps with structure in bugs and fungi.
๐ Lipids
- Key Functions: Energy storage, cell membrane structure.
- Examples: Fats, oils, phospholipids.
Final Exam Focus
Okay, you're almost there! Here's what to really focus on:
- High-Yield Topics: Protein structure (especially denaturation), nucleic acid structure and base pairing, carbohydrate types and functions.
- Common Question Types: MCQs on identifying monomers, FRQs on relating structure to function, and questions combining multiple concepts.
Time Management: Don't get bogged down on one question. If you're stuck, move on and come back later. You got this!
Don't confuse: Denaturation with hydrolysis. Denaturation is a change in shape, hydrolysis is a breakdown.
Practice Question
Practice Questions
Multiple Choice Questions
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Which of the following best describes the primary structure of a protein? a) The overall 3D shape of the protein b) The sequence of amino acids c) The alpha-helices and beta-pleated sheets d) The interactions between multiple polypeptide chains
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What type of bond holds together the two strands of a DNA molecule? a) Peptide bonds b) Glycosidic bonds c) Hydrogen bonds d) Covalent bonds
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Which polysaccharide is used for energy storage in animals? a) Cellulose b) Starch c) Glycogen d) Chitin
Free Response Question
Question:
Describe the four levels of protein structure. Explain how changes in the primary structure can affect the overall function of a protein. Provide an example of a disease caused by a change in protein structure.
Scoring Breakdown:
- Level 1 (1 point): Correctly identifies and describes the primary structure as the sequence of amino acids.
- Level 2 (1 point): Correctly identifies and describes the secondary structure as alpha helices and beta-pleated sheets formed by hydrogen bonds.
- Level 3 (1 point): Correctly identifies and describes the tertiary structure as the overall 3D shape formed by interactions between R-groups.
- Level 4 (1 point): Correctly identifies and describes the quaternary structure as the arrangement of multiple polypeptide chains.
- Effect of primary structure (2 points): Explains that changes in the primary structure (amino acid sequence) can alter the folding of the protein, leading to changes in secondary, tertiary, and quaternary structures, which can affect the protein's function.
- Example (1 point): Provides an example of a disease caused by a change in protein structure, such as sickle cell anemia (caused by a single amino acid substitution in hemoglobin).

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Question 1 of 13
Ready to dive in? ๐ Which of the following is NOT one of the four major classes of biological macromolecules?
Nucleic acids
Proteins
Carbohydrates
Vitamins