Molecules of Life Lesson: Carbs, Proteins, Lipids & DNA

Lesson Overview

• Carbohydrates 
• Proteins – Building Blocks and Workhorses of the Cell
• Lipids – Fats, Oils, and More
• Nucleic Acids – The Genetic Information Molecules

Living organisms depend on four major biological molecules for survival: carbohydrates, proteins, lipids, and nucleic acids. These molecules are essential for energy production, structural support, information storage, and regulation of biological processes. 

Each type of molecule has a unique structure and function that contributes to the overall functioning of cells and organisms. A clear understanding of these molecules helps explain how life operates at the molecular level and provides the foundation for studying biological systems.

Carbohydrates 

Carbohydrates (often called "carbs") are the body's primary quick energy source. They include sugars and starches in your diet. Let's explore what carbs are made of and the different kinds of carbs you should know:

• Types of Carbohydrates: There are three main categories of carbohydrates: monosaccharides, disaccharides, and polysaccharides. These words describe how many sugar units are linked together:
  
  • Monosaccharide – "one sugar." This is the simplest type of carb: a single sugar molecule. Example: glucose (blood sugar) is a monosaccharide. Monosaccharides are building blocks for larger carbs.
    
  • Disaccharide – "two sugars." Two monosaccharides bonded together make a disaccharide. Example: sucrose (table sugar) is a disaccharide made of glucose + fructose.
    
  • Polysaccharide – "many sugars." Long chains of sugar units make polysaccharides. Examples: starch (plants) and glycogen (animals) store energy, while cellulose (plant cell walls) provides structure – all are polysaccharides made of many glucose units.
    
• Elements in Carbohydrates: All carbohydrates are made of the elements carbon (C), hydrogen (H), and oxygen (O). Nitrogen is not found in carbohydrates – that sets them apart from proteins.
  
• Functions of Carbohydrates: Carbs have a few key jobs in living organisms:
  
  • Immediate energy: Carbohydrates provide an immediate source of fuel. When you eat carbs, your body breaks them down into glucose, which your cells use for energy right away.
    
  • Energy storage: Some carbohydrates store energy for later use. Plants store energy in starch (for example, potatoes are rich in starch), and animals store it in glycogen (we keep glycogen in our liver and muscles). These polysaccharides can be broken down when the body needs extra fuel.
    
  • Structural support: Certain carbs provide structure to cells. For example, cellulose in plant cell walls gives plants rigidity. (Cellulose is a type of fiber – we can't digest it for energy, but it's crucial for plant structure.)
    
  • What about growth? You might wonder if carbohydrates "trigger growth of cells". Carbs provide the energy needed for growth, but they don't directly cause cells to grow or divide. That's mainly the job of proteins and growth hormones.

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DNA: The Molecule of Life! Trivia Quiz

Proteins – Building Blocks and Workhorses of the Cell

Proteins are the multitaskers of biology. They form much of your body's structure (muscles, skin, hair) and also do lots of work inside cells (as enzymes, antibodies, etc.). Let's break down what proteins are made of and how they function:

• Elements in Proteins: Proteins are made of carbon, hydrogen, oxygen, and nitrogen (C, H, O, N). Nitrogen is the extra element here that carbohydrates and lipids don't have.
  
• Amino Acids – the Building Blocks of Proteins: Proteins are long chains of smaller molecules called amino acids.
  
  1. Peptide bonds: Amino acids link together via peptide bonds, forming a chain (a polypeptide).
     
  2. Building tissues: These amino acid chains are the building material for body structures. For example, muscles are made of proteins, and those proteins are built from amino acids. So yes, amino acids are the "basic building blocks" of muscle and other tissues.
     
  3. Primary structure: The sequence of amino acids in a chain is called a protein's primary structure – the first level of its structure.
     
• Four Levels of Protein Structure: Proteins fold into complex shapes. Here are the four levels of structure to know:
  
  1. Primary structure: amino acid sequence
     
  2. Secondary structure: local helices or sheets
     
  3. Tertiary structure: overall 3D folding of one chain
     
  4. Quaternary structure: multiple chains together (one protein)

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Molecules, Building Blocks of Life

Lipids – Fats, Oils, and More

Lipids are a diverse group of hydrophobic (water-fearing) molecules, including fats, oils, waxes, and steroids. They don't mix with water (think of oil in water) and they're great for energy storage and for building cell membranes. Here's what to know about lipids:

• Composition of Lipids: Lipids are made up of carbon, hydrogen, and oxygen (C, H, O), just like carbs. However, they have a lot more hydrogen relative to oxygen than carbohydrates do. This makes lipids nonpolar (they won't dissolve in water). Importantly, basic lipids do not include nitrogen. Some complex lipids contain phosphorus (phospholipids in cell membranes have a phosphate group), but typical fats and oils are just C, H, O.
  
• Building Blocks of Lipids: Lipids aren't long chains of a single repeating monomer like proteins or polysaccharides. A typical fat (triglyceride) consists of one glycerol molecule attached to three fatty acid chains. In other words, glycerol + 3 fatty acids = a fat molecule. This is different from a carbohydrate polymer (which might be a chain of many glucose units) – instead, lipids are built by combining a few smaller components together.
  
• Functions of Lipids: Lipids serve several important functions:
  
  • Long-term energy storage & insulation: Fats store a lot of energy for the long term. That fat also insulates the body (helps keep you warm).
    
  • Cell membranes: A special type of lipid called a phospholipid makes up cell membranes. Phospholipids form a double layer (the lipid bilayer) that acts as a barrier around cells, controlling what goes in and out. Every cell membrane in your body relies on lipids.
    
  • Hormones (chemical signals): Many hormones are lipids, specifically steroid hormones like testosterone and estrogen. These are derived from cholesterol (another lipid), and they help send signals around the body.

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Biology Molecules of Life

Nucleic Acids – The Genetic Information Molecules

Nucleic acids are the molecules that store and transmit genetic information in living things. The two main examples are DNA and RNA. These molecules essentially tell the cell how to build proteins, which in turn carry out most life functions. Here's what to know:

• Composition of Nucleic Acids: Nucleic acids are made of carbon, hydrogen, oxygen, nitrogen, and phosphorus (C, H, O, N, P). The element phosphorus is a giveaway – the other types don't have P.
  
• Building Blocks: Nucleotides: The monomers of nucleic acids are called nucleotides. Each nucleotide has three parts: a sugar, a phosphate group, and a nitrogenous base. These nucleotides link together in long chains to form a nucleic acid strand. (DNA is double-stranded; RNA is usually single-stranded.)
  
• Function of Nucleic Acids: DNA stores the genetic instructions (genes) for making proteins, and RNA helps carry out those instructions (for example, mRNA brings the code from DNA to ribosomes to build a protein). In short, DNA is the long-term information storage, and RNA is the working copy used to produce proteins. Life wouldn't be possible without these molecules, since they allow traits to be passed on and let cells make the things they need.

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4 Molecules of Life