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27 Dec 2025

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21 pages

Understanding Biological Molecules: Key Biochemistry Concepts

Maja Szulczynska

@majaszulczynska

Ever wondered why water droplets stick together or how your... Show more

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Date: 3/10 ha

Waler
- is a porar moleulle; the oxyger end of the molecule nas a
negative charge + the hydrogen atoms have a pasive charge.

Water's Structure and Bonding

Water might seem simple, but it's actually a polar molecule with some pretty amazing tricks up its sleeve. The oxygen end carries a negative charge whilst the hydrogen atoms are positively charged, creating what scientists call a dipole.

When water molecules get close together, these opposite charges attract each other, forming hydrogen bonds. Think of it like molecular magnets - individually weak, but together they create a strong lattice framework that gives water its unique properties.

This attraction between water molecules is called cohesion, and it's absolutely crucial for life. It's what allows water to travel up tall trees and helps create that bouncy surface tension you see on ponds.

Key Point: Water's polar nature makes it an excellent solvent - the positive and negative parts attract other charged particles like ions and polar molecules (such as glucose), allowing them to dissolve easily.

Water's Life-Supporting Properties

Water has some incredible properties that make it perfect for supporting life. Its high specific heat capacity means it takes loads of energy to change its temperature, keeping aquatic environments stable and allowing enzymes to work efficiently.

The high latent heat of vaporisation makes water brilliant for cooling - that's why sweating works so well! When water evaporates from your skin, it takes heat energy with it, cooling you down effectively.

Water serves as the body's ultimate transport medium. Blood is mostly water and carries dissolved substances around your body, whilst in plants, minerals dissolved in water travel from roots to leaves through the xylem.

Fascinating Fact: Water is less dense when frozen, so ice floats! This insulates the water below, keeping aquatic life safe during winter whilst allowing sunlight through for photosynthesis.

Carbohydrates: The Building Blocks

Carbohydrates are organic molecules made from carbon, hydrogen, and oxygen that serve as life's main energy currency. They come in three sizes: monosaccharides (single units), disaccharides (two units), and polysaccharides (many units).

Monosaccharides are grouped by their carbon count - trioses (3 carbons) are vital for respiration and photosynthesis, pentoses (5 carbons) form the backbone of DNA and RNA, whilst hexoses (6 carbons) like glucose provide energy for cellular respiration.

The star of the show is glucose, which exists in two forms: alpha and beta. This might seem like a small difference, but it completely changes how glucose molecules can link together to form larger carbohydrates.

Remember: When glucose bonds are broken during respiration, the released energy is captured to make ATP - your cells' energy currency.

Disaccharides: Sweet Partnerships

Disaccharides form when two monosaccharides join together through a condensation reaction, eliminating water and creating a glycosidic bond. It's like molecular handholding that creates something entirely new.

Maltose forms when two alpha-glucose molecules join with an α(1-4) glycosidic bond - you'll find this in germinating seeds. The bond forms between carbon 1 of the first glucose and carbon 4 of the second.

This process is completely reversible through hydrolysis - just add water and the bond breaks, splitting maltose back into two glucose molecules. Other important disaccharides include sucrose $glucose + fructose$ found in plants, and lactose $glucose + galactose$ in mammalian milk.

Test Tip: Remember that condensation removes water to form bonds, whilst hydrolysis adds water to break them - opposite processes that are fundamental to biology.

Testing for Sugars: Laboratory Skills

There are two types of sugars you can test for: reducing sugars and non-reducing sugars. Reducing sugars (like glucose and fructose) donate electrons in chemical reactions, whilst non-reducing sugars (like sucrose) don't.

Benedict's test is your go-to method for detecting reducing sugars. Heat equal volumes of Benedict's reagent and your test solution to 100°C. If reducing sugars are present, you'll see a colour change from blue through green, yellow, and orange to a brick-red precipitate.

For non-reducing sugars like sucrose, you need an extra step. First, break them down by heating with hydrochloric acid, then add alkali to neutralise before doing the Benedict's test. If it turns red, non-reducing sugars were originally present.

Lab Success: The intensity of the colour change in Benedict's test indicates the concentration of reducing sugars - the redder it gets, the more sugar is present.

Starch and Glycogen: Energy Storage Champions

Starch is how plants store glucose, found in high concentrations in seeds and storage organs like potato tubers. It's made of two polymers: amylose and amylopectin, both built from alpha-glucose molecules.

Amylose forms long, unbranched chains with α(1-4) glycosidic bonds, creating a linear molecule that coils into a helix. Amylopectin has the same backbone but includes α(1-6) bonds every 25-30 glucose units, creating branch points.

Glycogen is the animal equivalent of starch, serving as our main energy store in the liver and muscles. It has the same bonding pattern as amylopectin but with much shorter chains and more frequent branching, making it more compact and efficient.

Smart Design: The branched structure of glycogen and amylopectin provides more sites for enzymes to attack, allowing for rapid glucose release when energy is needed quickly.

Cellulose and Chitin: Structural Superstars

Cellulose is the most abundant organic molecule on Earth, forming the structural framework of plant cell walls. Unlike starch, it's made from beta-glucose units joined by β(1-4) glycosidic bonds.

The beta linkage rotates adjacent glucose molecules by 180°, allowing hydrogen bonds to form between parallel chains. This creates incredibly strong microfibrils - bundles of 60-70 cellulose molecules tightly cross-linked together.

Chitin is similar to cellulose but found in insect exoskeletons and fungal cell walls. It has amino acid groups attached, making it a heteropolysaccharide that's strong, waterproof, and lightweight - perfect biological armour.

Engineering Marvel: Cell walls have several layers of fibres running at different angles, creating a laminated structure that's incredibly strong yet still permeable to water and solutes.

Lipids: The Versatile Molecules

Lipids are non-polar molecules made of carbon, hydrogen, and oxygen that won't dissolve in water but love organic solvents like ethanol. The most common type is triglycerides - the fats and oils in your diet.

Fatty acids are long-chain carboxylic acids, usually 14-22 carbons long. They can be saturated (no double bonds), monounsaturated (one double bond), or polyunsaturated (multiple double bonds). More double bonds mean lower melting points.

Triglycerides form when glycerol (a type of alcohol) joins with three fatty acids through condensation reactions, creating ester bonds and releasing three water molecules. They're perfect for long-term energy storage, insulation, and waterproofing.

Health Connection: Understanding saturated vs unsaturated fats helps explain why some fats are solid at room temperature (butter) whilst others are liquid (olive oil).

Saturated vs Unsaturated Fats

The difference between saturated and unsaturated fatty acids lies in their chemical bonds. Saturated fats have no double bonds between carbon atoms, meaning they're "saturated" with hydrogen atoms and tend to be solid at room temperature.

Unsaturated fatty acids contain one or more C=C double bonds, which creates kinks in the molecular chain. These kinks prevent the molecules from packing tightly together, making them liquid at room temperature - that's why most plant oils are liquid.

Animal fats tend to be saturated, whilst plant oils are usually unsaturated. This has major health implications - diets high in saturated fats are linked to heart disease, whilst unsaturated fats (especially from sources like olive oil) are generally healthier.

Memory Trick: Think "saturated = solid" and "unsaturated = usually liquid" to remember which fats are which at room temperature.

Lipids and Heart Disease

Heart disease primarily results from fatty deposits in coronary arteries (atherosclerosis) and high blood pressure. Diets consistently high in saturated fats, smoking, lack of exercise, and ageing all contribute to this process.

When you digest food, lipids and proteins combine to form lipoproteins that travel through your bloodstream. These can deposit on the smooth inner walls of arteries, gradually building up atherosclerotic plaques.

As these fatty deposits accumulate, they reduce the available space for blood flow. If a plaque completely blocks an artery supplying the heart muscle, it causes a myocardial infarction - commonly known as a heart attack.

Prevention Focus: Understanding how dietary fats affect your cardiovascular system empowers you to make informed choices about nutrition and lifestyle for long-term health.

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Biology

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115

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27 Dec 2025

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21 pages

Understanding Biological Molecules: Key Biochemistry Concepts

Maja Szulczynska

@majaszulczynska

Prevention Focus: Understanding how dietary fats affect your cardiovascular system empowers you to make informed choices about nutrition and lifestyle for long-term health.