Carbohydrates: Structure, Function, and Reactions

Dehydration Synthesis

• A reaction where two molecules join by removing a water molecule
• One molecule loses a hydrogen (H), the other a hydroxyl group (OH), forming a covalent bond and releasing H₂O
• Used to build polymers from monomers

Hydrolysis

• Reaction where water (H₂O) breaks a bond between two molecules
• A water molecule is added, with H attaching to one part and OH to the other, effectively splitting the molecule
• Used to break down polymers into monomers for energy or other cellular functions

Photosynthesis

• Process by which plants, algae, and some bacteria convert light energy into glucose, occurring in chloroplasts with chlorophyll
• Overall chemical reaction: 6CO₂ + 6H₂O + light energy → C₆H₁₂O₆ + 6O₂
• Reactants include carbon dioxide (CO₂), water (H₂O), and light energy
• Products include glucose (C₆H₁₂O₆) and oxygen (O₂)

Monomer

• A small molecular unit that joins with similar units to form a polymer
• Building blocks of biological molecules

Polymer

• A large molecule made of repeating monomer units bonded together
• Can be natural or synthetic

Macromolecule

• A molecule containing a very large number of atoms, such as a protein, nucleic acid, or synthetic polymer

Polymerization

• The process to create polymers

Dimer

• A polymer formed from two monomers

Glycosidic Bonds

• Alpha 1-4 glycosidic bonds link alpha glucose molecules (starch, glycogen)
• Beta 1-4 glycosidic bonds link beta glucose molecules (cellulose, chitin)

Isomers

• Glucose, fructose, and galactose are structural isomers
• Maltose, sucrose, and lactose are disaccharide isomers

Carbohydrates: General

• Organic molecules made of carbon, hydrogen, and oxygen in a 1:2:1 ratio
• General formula: (CH₂O)ₙ
• Classified into monosaccharides, disaccharides, and polysaccharides

Carbohydrates: Foods

• Simple carbs: Fruits, honey, milk
• Complex carbs: Bread, rice, pasta, potatoes, legumes, whole grains, vegetables

Carbohydrates: Functions

• Primary energy source (glucose used in cellular respiration)
• Energy storage (glycogen in animals, starch in plants)
• Structural support (cellulose in plants, chitin in fungi & arthropod exoskeletons)

Monosaccharides

• Three monosaccharides are glucose, fructose, and galactose

Disaccharides

• Sucrose = Glucose + Fructose
• Lactose = Glucose + Galactose
• Maltose = Glucose + Glucose

Polysaccharides

• Starch (amylose): Found in plants, stores energy
• Glycogen: Found in animals, stores energy
• Chitin: Found in fungi and arthropod exoskeletons, provides structural support
• Cellulose: Found in plants, provides structural support

Indigestible Polysaccharides

• Cellulose and chitin are indigestible

Fiber/Roughage

• Cellulose is dietary fiber

Fiber in Diet

• Aids digestion by adding bulk to stool and preventing constipation
• Lowers cholesterol and regulates blood sugar

Cellulose Digestion

• Bacteria and fungi in herbivore digestive tracts produce cellulase to break down cellulose

Glucose Types

• Alpha glucose: -OH group on carbon 1 (C1) is below the ring
• Beta glucose: -OH group on carbon 1 (C1) is above the ring

Alpha Glucose Bonds

• α-1,4 glycosidic bond links two alpha glucose molecules
• Amylase and maltase break it down (digestible)

Alpha Glucose Polysaccharides

• Starch (Amylose) is a long chain of alpha glucose
• Glycogen is a long chain of alpha glucose

Beta Glucose Bonds

• β-1,4 glycosidic bond links beta glucose molecules

Beta Glucose Polysaccharides

• Cellulose is composed of long chains of beta glucose
• Chitin is composed of long chains of beta glucose

Hydrolysis

• Breaks down polymers into monomers by adding water
• Example: Breaking down starch into glucose or proteins into amino acids

Glucose vs Glycogen

• Both are carbohydrates and provide energy
• Both contain glucose monomers
• Glucose: Simple sugar (monosaccharide), used immediately for energy
• Glycogen: Polysaccharide, stored in the liver and muscles for later energy use

Lipid Definition

• Hydrophobic organic molecules composed mainly of carbon, hydrogen, and oxygen

Triglycerides: Foods

• Body fat is composed of triglycerides
• Butter, oils, nuts, avocados, and fatty fish are all rich in fat

Triglycerides: Composition

• Made of glycerol and three fatty acids, linked by ester bonds
• Three water molecules are produced from the dehydration synthesis with the glycerol and 3 fatty acid chains

Triglycerides: Functions

• Energy storage, insulation, and protection of organs

Glycerol

• Three-carbon molecule that is polar
• Consists of 8 hydrogen and 3 oxygen

Fatty Acids

• Long hydrocarbon chains with a carboxyl (-COOH) group.

Saturated vs. Unsaturated Fats

• Saturated fats have no double bonds; unsaturated fats have one or more
• Saturated fats are solid at room temperature, while unsaturated fats are liquid
• 2n+1 saturated general formula for the hydrogen of a fatty acid chain
• 2n-1 unsaturated general formula for the hydrogen of a fatty acid chain

Cis vs. Trans Fats

• Cis fats are natural; trans fats are processed and increase heart disease risk
• Cis has hydrogen on the same side whereas trans has it on the opposite

Hydrogenation

• Converts unsaturated fats into saturated fats by adding hydrogen
• Partial hydrogenation only converts some of the double bonds by adding hydrogen

Natural Fats

• Saturated fat: butter, ice cream, fried foods, processed meat
• Monounsaturated fat: avocado, flax seed, rapeseed
• Polyunsaturated fat: fish, sunflower seeds, corn oil

Omega-3 Fatty Acids

• Reduce triglycerides, lowering the risk of heart disease
• Lower blood pressure, especially in people with hypertension
• Anti-inflammatory properties, reducing chronic inflammation linked to atherosclerosis
• Prevent blood clots that could lead to heart attacks or strokes

Fat vs. Oil

• Fat: Solid at room temperature, usually from animals, high in saturated fatty acids
• Oil: Liquid at room temperature, usually from plants or fish, high in unsaturated fatty acids
• Saturated fats are linked to higher cholesterol and cardiovascular risk (when consumed in excess)
• Unsaturated fats (especially omega-3 and omega-6) are generally healthier for heart health

Phospholipids: Composition

• Glycerol backbone
• Two fatty acid tails (hydrophobic)
• Phosphate group with a polar head (hydrophilic)
• Polar head can be modified by different molecules like choline, ethanolamine, or serine

Phospholipids: Properties

• Hydrophilic (polar) head attracted to water, interacts with the aqueous environment
• Hydrophobic (non-polar) tails repel water but interact with other hydrophobic molecules

Phospholipids: Locations

• Cell membranes, forming the phospholipid bilayer
• Lung surfactant, reducing surface tension
• Lipoproteins, transporting lipids in the bloodstream

Phospholipids: Cell Membranes

• Hydrophilic heads face outward toward the extracellular fluid and cytoplasm
• Hydrophobic tails face inward, forming a non-polar interior

Steroids: Structure

• Share a four-ring structure (three six-carbon rings and one five-carbon ring)

Steroids: Examples

• Cholesterol: Maintains cell membrane fluidity and is a precursor for steroid hormones, vitamin D, and bile salts
• Cortisol: Regulates metabolism and stress response
• Aldosterone: Maintains blood pressure and electrolyte balance
• Sex Hormones (e.g., estrogen, testosterone): Regulate reproduction and secondary sexual characteristics
• Anabolic Steroids: Synthetic variants of testosterone used to build muscle mass

Steroids: Vitamin D and Bile

• Vitamin D is made from cholesterol in the skin upon sunlight exposure, aiding calcium absorption
• Bile salts are made from cholesterol in the liver, aiding fat digestion

Steroids: Cholesterol

• HDL (High-Density Lipoprotein): "Good" cholesterol, removes excess cholesterol and transports it to the liver
• LDL (Low-Density Lipoprotein): "Bad" cholesterol, delivers cholesterol to cells, but high levels can lead to plaque buildup

Atherosclerosis

• Plaque (fat, cholesterol, and other substances) builds up on artery walls, leading to narrowing and hardening of arteries
• Reduces blood flow, increases blood pressure, and can lead to heart attacks and strokes

Waxes

• Fatty acid combined with an alcohol
• Plants: Produce coatings on leaves to prevent water loss
• Bees: Create beeswax to build honeycombs
• Marine Organisms: Produce waxes for buoyancy and waterproofing
• Humans: Produce earwax to protect the ear canal

Explore carbohydrates, their role in dehydration synthesis and hydrolysis, and their function in the body. Understand glycosidic bonds, isomers, and the breakdown of disaccharides like lactose. Match polysaccharides with their definitions.