AP Biology Macromolecules Flashcards: Carbohydrates, Lipids, Proteins, & Nucleic Acids
Page 1 - AP Biology: Unit 1 Macromolecules overview.
This unit covers the four major classes of macromolecules essential for life: Carbohydrates, Lipids, Proteins, and Nucleic Acids. Understanding their basic units, how they link together, and their structures and functions is crucial for your test.
Page 2 - Carbohydrates & Lipids (Module 3)
Carbohydrates: These are your primary energy sources. They're built from carbon, hydrogen, and oxygen, usually in a 1:2:1 ratio (C_nH_2nO_n). Their basic units are monosaccharides (simple sugars like glucose, fructose, galactose, all sharing the formula C6H{12}O_6). These monosaccharides can be linear, ring-shaped, or branched, and their specific structure dictates their function. Functional groups like hydroxyl (-OH) and carbonyl are key to their polarity.
Bonds: Monosaccharides link together via glycosidic bonds, which are covalent bonds formed through dehydration synthesis (removing a water molecule (OH + H)). This creates larger carbohydrates called polysaccharides.
Examples & Roles: Think of glycogen (animal energy storage), starch (plant energy storage), cellulose (plant cell walls for structure), and chitin (insect exoskeletons). All are complex carbohydrates with distinct roles.
Lipids: Unlike other macromolecules, lipids aren't typically polymers. Their defining characteristic is being hydrophobic (water-fearing) due to their nonpolar nature. They're vital for energy storage, membrane structure, and hormones.
Types of Lipids:
Triacylglycerols (Triglycerides): Efficient energy storage, made of a glycerol molecule attached to 3 fatty acids. Fatty acids are long hydrocarbon chains with a carboxyl end.
Saturated Fats: Have no double bonds between carbon atoms, meaning they're 'saturated' with hydrogen atoms. They have straight chains and are usually solid at room temperature (e.g., butter).
Unsaturated Fats: Contain one or more double bonds, which create kinks or bends in the chains. These kinks prevent tight packing, making them typically liquid at room temperature (e.g., oils).
van der Waals forces contribute to the packing of fatty acids, affecting their physical state.
Steroids: Like cholesterol, they're important components of cell membranes and precursors for hormones.
Phospholipids: Crucial for cell membranes. They have a hydrophilic (water-loving) head and hydrophobic (water-fearing) tails. In aqueous environments, they spontaneously form a bilayer, which is the fundamental structure of biological membranes. The hydrophobic tails face inward, shielded from water, while the hydrophilic heads face outward.
Page 3 - Proteins (Module 4)
Proteins: These are incredibly diverse and perform most of the work in cells. Their basic building blocks are amino acids. There are 20 different amino acids, each characterized by a central alpha carbon (\alpha-carbon) bonded to:
An amino group (NH_2)
A carboxyl group (COOH)
A hydrogen atom (H)
A unique R-group (side chain). The R-group determines the amino acid's properties (polar, nonpolar, acidic, basic).
Bonds: Amino acids link together via peptide bonds, which are covalent bonds formed by dehydration synthesis between the amino group of one amino acid and the carboxyl group of another.
Structure and Function: A protein's specific 3-D shape is critical for its function. This shape develops through four levels of structure:
Primary Structure: The unique, linear sequence of amino acids in the polypeptide chain. This sequence is determined by DNA and is the foundation for all higher-order structures. Even a small change here can drastically alter function.
Secondary Structure: Localized folding patterns formed by hydrogen bonds between the carbonyl group of one amino acid and the amino group (N-H) of another in the polypeptide backbone (not the R-groups). The two main types are the \alpha-helix (a coiled shape) and the \beta-sheets (folded, pleated segments).
Tertiary Structure: The overall 3-D shape of a single polypeptide chain. This is determined by interactions between the R-group side chains, including hydrogen bonds, ionic bonds, disulfide bridges, and hydrophobic interactions. This level is where the protein truly becomes functional. Incorrect folding (denaturation) can destroy function.
Quaternary Structure: Occurs when two or more polypeptide chains (each with its own primary, secondary, and tertiary structure) come together to form a larger, functional protein complex. Examples include hemoglobin (four chains) or many enzymes.
Page 4 - Nucleic Acids (Module 5)
Nucleic Acids: These macromolecules store and transmit genetic information. Their basic building blocks are nucleotides.
Nucleotide Structure: Each nucleotide has three parts:
A nitrogenous base: Purines (double ring) like Adenine (A) and Guanine (G), or Pyrimidines (single ring) like Cytosine (C), Thymine (T), and Uracil (U).
A five-carbon sugar: Deoxyribose in DNA or Ribose in RNA.
One or more phosphate groups.
Bases: A key difference is that DNA uses T, while RNA uses U to pair with A.
Bonds: Nucleotides link together via phosphodiester bonds (a covalent bond between the phosphate of one nucleotide and the sugar of the next). This forms the sugar-phosphate backbone of a nucleic acid strand, which has a specific directionality: a 5' phosphate end and a 3' hydroxyl end.
DNA Directionality: DNA synthesis always proceeds in the 5' \to 3' direction, meaning new nucleotides are added to the 3' end.
DNA Structure: DNA typically forms a double helix, consisting of two antiparallel strands. The bases pair specifically: A pairs with T (forming 2 hydrogen bonds), and C pairs with G (forming 3 hydrogen bonds). This precise pairing is crucial for accurate genetic information storage.
DNA vs. RNA Summary:
DNA:
Sugar: Deoxyribose (2'H on the sugar).
Bases: A, T, G, C (Thymine).
Structure: Usually double-stranded, typically long.
Main Role: Information storage and transmission.
RNA:
Sugar: Ribose (2'OH on the sugar).
Bases: A, U, G, C (Uracil).
Structure: Usually single-stranded, typically short.
Main Role: Involved in protein synthesis and many other cellular functions (e.g., mRNA, tRNA, rRNA).