TEAS Ready🧬 Science · Biology · Lesson 6 of 7 · 6 min
Macromolecules: carbohydrates, lipids, proteins and nucleic acids
🍞 Bread, butter, eggs and DNA are all built from the same four kinds of big molecules. Learn their building blocks and you can answer most macromolecule questions.
💡 Key idea
Carbohydrates = monosaccharides, proteins = amino acids, nucleic acids = nucleotides, and a fat = glycerol + fatty acids.
🧠 The idea
Large biological molecules are POLYMERS built from smaller MONOMERS by dehydration synthesis (removing water) and broken apart by hydrolysis (adding water). CARBOHYDRATES are made of monosaccharides such as glucose; they supply quick energy, and starch, glycogen and cellulose are polysaccharides. LIPIDS (fats, oils, phospholipids, steroids) are not true polymers; a triglyceride is glycerol plus three fatty acids. Lipids store long-term energy, form cell membranes and act as hormones. PROTEINS are chains of amino acids joined by peptide bonds; their shape decides their job, such as structure, transport or acting as ENZYMES. Enzymes are biological catalysts that lower activation energy; each has an active site that fits a specific substrate, and high heat or wrong pH can denature it. NUCLEIC ACIDS (DNA and RNA) are made of nucleotides and store genetic information.
✏️ Worked example
A food-testing lab finds a molecule containing carbon, hydrogen, oxygen and nitrogen, built from 20 kinds of repeating units joined by peptide bonds. Step 1: nitrogen plus peptide bonds point to amino acids. Step 2: chains of amino acids are proteins. Step 3: if the lab heats it to 90 °C and it stops working, the protein has been denatured, which changes its shape, not its amino acid sequence.
📌 Takeaways
- Dehydration synthesis builds polymers; hydrolysis breaks them down.
- Enzymes are mostly proteins that speed reactions by lowering activation energy and are not used up.
- Glycogen stores sugar in animals; starch stores it in plants; cellulose builds plant cell walls.
📖 Terms in this lesson
Enzyme: A protein that speeds up a chemical reaction in the body without being used up; for example, amylase breaks down starch.
✅ Check yourself
Question 1 of 3
What are the monomers of proteins?
- Fatty acids
- Nucleotides
- Monosaccharides
- Amino acids
Show the answer and rationale
Answer: D
Proteins are polymers of amino acids linked by peptide bonds. Nucleotides build nucleic acids, monosaccharides build carbohydrates, and fatty acids are part of lipids.
Question 2 of 3
How does an enzyme speed up a chemical reaction?
- It is used up as a reactant
- It adds energy to the products
- It lowers the activation energy
- It raises the temperature of the cell
Show the answer and rationale
Answer: C
Enzymes lower the activation energy needed to start a reaction and are not consumed. They do not heat the cell or add energy to the products.
Question 3 of 3
Which molecule stores glucose in human liver and muscle?
- Glycogen
- Cholesterol
- Cellulose
- Starch
Show the answer and rationale
Answer: A
Animals store glucose as glycogen in the liver and skeletal muscle. Starch is the storage form in plants, cellulose builds plant cell walls, and cholesterol is a lipid.
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