Macromolecules Lecture Review

Macromolecules

Nutrition Labels and Energy

• Food Energy Measurement: Measured in Calories (capital C).

  • $1 \text{ Calorie} = 1000 \text{ calories}$ (lowercase c)

  • $1 \text{ Calorie} = 1 \text{ kilocalorie (kcal)}$

• Definition of 1 calorie (lowercase c): The energy needed to raise the temperature of $1 \text{ gram}$ of water through $1 \text{ °C}$.

• Understanding Nutrition Facts (Cheerios example):

  • Serving Size: $1 \text{ cup (28g)}$ for adults; $\frac{3}{4} \text{ cup (21g)}$ for children under 4.

  • Calories: $100$ for cereal alone, $140$ with skim milk.

  • Calories from Fat: $15$ for cereal alone, $20$ with skim milk.

  • Total Fat: $2\text{g}$ ($3\%$ Daily Value).

    • Saturated Fat: $0\text{g}$ ($0\%$ Daily Value).

    • Trans Fat: $0\text{g}$.

    • Polyunsaturated Fat: $0.5\text{g}$.

    • Monounsaturated Fat: $0.5\text{g}$.

  • Cholesterol: $0\text{mg}$ ($0\%$ Daily Value).

  • Sodium: $190\text{mg}$ ($8\%$ Daily Value).

  • Potassium: $170\text{mg}$ ($5\%$ Daily Value).

  • Total Carbohydrate: $20\text{g}$ ($7\%$ Daily Value).

    • Dietary Fiber: $3\text{g}$ ($11\%$ Daily Value).

      • Soluble Fiber: $1\text{g}$.

    • Sugars: $1\text{g}$.

    • Other Carbohydrate: $16\text{g}$.

  • Protein: $3\text{g}$.

  • Vitamins and Minerals: Significant percentages of daily values for Vitamin A, C, Calcium, Iron, Vitamin D, Thiamin, Riboflavin, Niacin, Vitamin $B<em>6$, Folic Acid, Vitamin $B</em>{12}$, Phosphorus, Magnesium, Zinc are present.

Introduction to Macromolecules

• Definition: Large molecules composed of smaller molecules.

• Characteristics:

  • Complex in their structures.

  • Exhibit emergent properties, such as the ability to form large structures, catalyze chemical reactions, and signal and record information.

Four Major Classes of Biological Macromolecules

1. Carbohydrates

2. Lipids

3. Proteins

4. Nucleic Acids

• Organic Molecules: All biological macromolecules contain carbon.

  • They may also contain hydrogen, oxygen, nitrogen, and some other minor elements.

Polymers and Monomers

• Polymers: Most macromolecules are polymers, built from repeating smaller units called monomers.

  • Monomers are linked together by covalent bonds.

• Exceptions: Lipids are an exception; they are not typically polymers of repeating monomer units.

• Classes that are Polymers: Carbohydrates, Proteins, and Nucleic Acids are polymers of specific monomers.

Synthesis of Polymers: Dehydration Reactions

• Process: Monomers form polymers through condensation reactions also known as dehydration reactions.

• Mechanism: A water molecule ($H_2O$) is removed, forming a new covalent bond between two monomers.

• Example (General): An -OH group from one monomer and an -H atom from another monomer are removed, combining to form water ($H_2O$), and the two monomers link.

• Example (Amino Acids): In muscles, amino acids (monomers) are joined via dehydration synthesis reactions to form proteins (polymers).

• Example (Glucose to Maltose): Two glucose monomers are linked by a covalent bond, forming maltose and a water molecule.

Disassembly of Polymers: Hydrolysis Reactions

• Process: Polymers disassemble back into monomers through hydrolysis reactions.

  • Hydro- means water, -lysis means breaking.

• Mechanism: A water molecule ($H_2O$) is added, breaking a covalent bond in the polymer chain.

• Example (General): The water molecule splits, with one monomer receiving an -H and the other receiving an -OH, effectively breaking the bond between them.

• Example (Digestive System): In the digestive system, protein-rich food (polymers) undergoes hydrolysis reactions to break down into amino acids (monomers) that can be transported through the circulatory system.

• Example (Maltose to Glucose): Maltose is broken down into two glucose monomers by the addition of water, reversing the synthesis reaction.

Diversity of Polymers

• Specificity: Each class of polymers is formed from a specific set of monomers.

• Limited Monomers, Vast Diversity: Organisms share a relatively limited number of common monomer types (around $40-50$).

• Source of Diversity: The immense variety of polymers arises from the different arrangements and combinations of these small set of monomers.

Reactions Catalyzed by Enzymes

• Enzymes: Biological molecules that catalyze (speed up) both hydrolysis and dehydration reactions.

  • Most enzymes are composed of proteins.

• Specificity: Specific enzymes exist for each macromolecule class:

  • Carbohydrates: Broken down by amylase, sucrase, lactase, maltase.

  • Lipids: Broken down by lipases.

  • Proteins: Broken down by pepsin, trypsin, and peptidase.

Carbohydrates

• AKA: Sugars.

• Sources: Found in grains, fruits, and vegetables.

• Primary Function: Provide immediate energy to the body in the form of glucose; also serve as a short-term energy storage and provide structural support.

• General Formula: $(CH<em>2O)</em>n$

• Naming Convention: Names typically end with -ose.

• Composition Ratio: Carbon:Hydrogen:Oxygen ratio is $1:2:1$.

  • Example: Glucose has the formula $C<em>6H</em>{12}O_6$.

• Energy Content: Provide $4 \text{ Calories/g}$.

• Three Main Subtypes (saccharide = sugar):

  1. Monosaccharides

  2. Disaccharides

  3. Polysaccharides

Monosaccharides

• Definition: Simplest water-soluble sugars.

• Carbon Count: Usually have $3-7$ carbons.

• Functions:

  • Can be used directly for fuel (energy).

  • Can be converted into other organic molecules.

  • Can be combined to form larger polymers.

• Structural Isomers of a Hexose ($C<em>6H</em>{12}O_6$):

  1. Glucose: Important source of energy for cells.

  2. Galactose: A component of lactose (milk sugar).

  3. Fructose: A component of sucrose (fruit sugar).

• Structure in Aqueous Solutions:

  • May exist in linear form, but are mostly found as rings in aqueous (water-based) solutions.

  • Ring Formation: For glucose, carbon $1$ bonds to the oxygen attached to carbon $5$. Chemical equilibrium heavily favors ring formation.

• Stereoisomers: The ring forms can be locked into an $\alpha$ or $\beta$ position depending on the orientation of the hydroxyl group on carbon $1$.

  • Fructose and ribose also form rings, typically 5-membered rings (as opposed to the 6-membered ring of glucose).

Disaccharides

• Definition: Consist of two monosaccharides (di = two).

• Linkage: The two monosaccharides are joined by a glycosidic linkage (glyco = sugar), formed via a dehydration reaction.

• Common Examples:

  • Maltose: Glucose + Glucose (linked by an $\alpha$ $1-4$ glycosidic linkage). Used in brewing and malted milk candy.

  • Lactose: Galactose + Glucose (linked by a $\beta$ $1-4$ glycosidic linkage). Also known as milk sugar.

  • Sucrose: Glucose + Fructose (linked by an $\alpha$ $1-2$ glycosidic linkage). Common table sugar.

• High-Fructose Corn Syrup (HFCS):

  • Found in most sodas and fruit drinks.

  • Produced by rearranging glucose atoms to form its isomer, fructose.

Polysaccharides

• Definition: Long chains of monosaccharides joined by glycosidic linkages.

• Structure: May be branched or unbranched; may consist of multiple types of monosaccharides.

• Molecular Weight: Can be very large, often greater than $10,000 \text{ daltons}$.

• Distinction: Polysaccharides are distinguished by their glycosidic linkages and branching patterns.

Storage Polysaccharides

• In Plants: Starch

  • Composition: Composed of amylose and amylopectin.

  • Function: Major storage form of glucose in plants.

  • Linkage Types:

    1. $\alpha \ 1-4$ glycosidic bonds: Found in both amylose and amylopectin.

    2. $\alpha \ 1-6$ glycosidic bonds: Responsible for branching in amylopectin.

  • Amylose: Unbranched glucose monomers primarily via $\alpha \ 1-4$ glycosidic bonds.

  • Amylopectin: Branched glucose monomers via both $\alpha \ 1-4$ and $\alpha \ 1-6$ glycosidic bonds.

• In Animals: Glycogen

  • Composition: Consists of glucose monomers.

  • Function: The major storage form of glucose in animals, stored primarily in the liver and muscles.

  • Structure: Highly branched, similar to amylopectin but more extensively branched, which allows for rapid mobilization of glucose.

Structural Polysaccharides

• In Plants: Cellulose

  • Composition: A polymer of glucose, but with different glycosidic linkages compared to starch.

  • Linkage Type: Features $\beta \ 1-4$ glycosidic linkages.

  • Structure: The $\beta$ linkage causes cellulose to form straight, unbranched chains that can hydrogen bond with each other, leading to strong microfibrils.

  • Function: Major component of the tough cell walls that enclose plant cells, providing structural rigidity.

  • Starch vs. Cellulose: Both are polymers of glucose; the critical difference lies in the orientation of the hydroxyl group on carbon $1$. Starch uses $\alpha$-glucose, leading to helical structures, while cellulose uses $\beta$-glucose, leading to linear structures. This small difference has a profound impact on their properties and digestibility.

  • Digestion: Most organisms cannot digest cellulose because they lack enzymes to break the $\beta \ 1-4$ glycosidic linkages. However, they can digest starch due to the presence of enzymes that break $\alpha \ 1-4$ linkages.

    • Example: Cows have symbiotic microbes in their stomachs that possess the necessary enzymes to break down cellulose.

• In Arthropods and Fungi: Chitin

  • Definition: Another important structural polysaccharide.

  • Composition: Polymer of nitrogen-containing glucose derivative (N-acetylglucosamine).

  • Function: Found in the exoskeletons of arthropods (e.g., insects, crustaceans) and in the cell walls of fungi.

  • Other Uses: Can be used as surgical thread due to its strength and biodegradability.

Lipids

• Characteristics: A diverse group of non-polar hydrocarbons without repeating monomer units.

  • Dominated by non-polar hydrocarbon regions, making them hydrophobic (water-fearing).

• Functions:

  • Long-term energy storage.

  • Insulation from the environment for plants and animals.

  • Serve as building blocks for some hormones.

  • Important component of cellular membranes.

• Major Types:

  • Triglycerides (Fats)

  • Phospholipids

  • Steroids

  • Waxes

Triglycerides (Fats)

• Definition: A large lipid made from two kinds of smaller molecules: glycerol and fatty acids.

• Structure:

  • Glycerol: A three-carbon alcohol with a hydroxyl group attached to each carbon.

  • Fatty Acid: Consists of a long carbon chain (hydrocarbon tail) with a carboxyl group (COOH) at one end.

• Synthesis: Formed by dehydration reactions where each fatty acid attaches to glycerol via an ester linkage.

  • A fat molecule is also called a triacylglycerol (three fatty acids + glycerol).

• Diversity: Fatty acids vary in their length and the number and locations of double bonds they contain.

  • Ester Compounds: General formula $\text{RCOOR'}$. Often fragrant and/or flavorful (e.g., citronella, banana oil, aspirin).

Saturated Fatty Acids

• Structure: Have the maximum number of hydrogen atoms possible.

  • No double bonds between carbon atoms in the hydrocarbon chain.

• Physical Properties: Fatty acid chains are straight, allowing them to pack tightly together.

  • Typically solid at room temperature (e.g., butter, animal fat).

  • Example: Stearic acid.

Unsaturated Fatty Acids

• Structure: Have one or more double bonds between carbon atoms in the hydrocarbon chain.

• Physical Properties: Double bonds create

Yes, an ester linkage is indeed a covalent bond formed between a hydroxyl group (from an alcohol like glycerol) and a carboxyl group (from a carboxylic acid like a fatty acid). This reaction typically involves the removal of a water molecule, which is why it's a dehydration synthesis.