Biochemistry connects chemistry to living systems by showing how atoms and molecules build cells, store energy, and control life processes. This cheat sheet covers the four major classes of biological macromolecules: carbohydrates, lipids, proteins, and nucleic acids. Students need these patterns to identify molecule structure, predict function, and understand reactions in cells.
It is especially useful for reviewing before biology, chemistry, or health science assessments.
The core idea is that many large biomolecules are polymers made from smaller monomers. Dehydration synthesis joins monomers by removing water, while hydrolysis breaks polymers apart by adding water. Carbohydrates and lipids are major energy molecules, proteins perform most cell functions, and nucleic acids store genetic information.
Enzymes are proteins that lower activation energy and speed reactions without being used up.
Key Facts
- Carbohydrates are made mainly of carbon, hydrogen, and oxygen in an approximate ratio of , often written as .
- Monosaccharides such as glucose, , are carbohydrate monomers used for quick cellular energy.
- Dehydration synthesis joins monomers by removing water, so the general pattern is .
- Hydrolysis breaks polymers by adding water, so the general pattern is .
- Lipids are mostly nonpolar molecules with many bonds, which makes them useful for long-term energy storage and cell membranes.
- Proteins are polymers of amino acids joined by peptide bonds, and their function depends on their three-dimensional shape.
- Nucleic acids are polymers of nucleotides, and DNA stores genetic information using the bases , , , and .
- Enzymes lower activation energy, written as , which increases reaction rate without changing the overall reaction products.
Vocabulary
- Macromolecule
- A large biological molecule made from smaller units and used by living organisms for structure, energy, information, or chemical reactions.
- Monomer
- A small repeating molecular unit that can bond with other similar units to form a polymer.
- Polymer
- A large molecule made of many bonded monomers, such as starch, protein, or DNA.
- Dehydration synthesis
- A chemical reaction that builds a larger molecule by joining smaller molecules and releasing .
- Hydrolysis
- A chemical reaction that breaks a larger molecule into smaller molecules by adding .
- Enzyme
- A biological catalyst, usually a protein, that speeds up a reaction by lowering without being consumed.
Common Mistakes to Avoid
- Confusing monomers with polymers is wrong because monomers are the small building blocks, while polymers are the large molecules made from many monomers.
- Saying dehydration synthesis uses water is wrong because dehydration synthesis releases when a bond forms between monomers.
- Saying hydrolysis removes water is wrong because hydrolysis adds to break bonds in a polymer.
- Assuming all lipids are polymers is wrong because many lipids, such as triglycerides and phospholipids, are large biomolecules but are not true repeating-unit polymers.
- Thinking enzymes are used up in reactions is wrong because enzymes are catalysts that are reused after helping convert substrates into products.
Practice Questions
- 1 A carbohydrate has the formula . Does it match the approximate carbohydrate ratio , and what is ?
- 2 A student joins glucose monomers into one starch fragment using dehydration synthesis. How many molecules are released?
- 3 A protein fragment contains amino acids in one chain. How many peptide bonds connect the amino acids?
- 4 Explain why changing the shape of an enzyme can stop it from working even if the enzyme is still present in the cell.
Understanding Biochemistry & Macromolecules
The behavior of a biomolecule comes from its atoms, bonds, and shape. Carbon can form four strong bonds, so it makes chains, rings, and branching structures. Small changes in a structure can change what a molecule does.
Glucose and fructose contain the same kinds and numbers of atoms, yet their atoms are arranged differently. Their properties are therefore not identical. Water is important because it is polar.
Polar or charged parts of biomolecules tend to interact with water, while nonpolar parts avoid it. This helps phospholipids form cell membranes. Their water friendly heads face the watery surroundings, while their water avoiding tails point inward and create a barrier.
Cells handle energy in different ways depending on the time scale. Sugars can be broken down relatively quickly during cellular respiration. Plants link many glucose units into starch for storage.
Animals store glucose units as glycogen, mainly in the liver and muscles. These storage polymers can release glucose when demand rises. Fats store more energy per gram because their long hydrocarbon sections contain many high energy electron bonds.
They are useful for long term reserves, insulation, and protection around organs. Energy is not created when food is broken down.
Chemical reactions transfer energy from food molecules into smaller usable energy carriers, especially ATP. Cells spend ATP to power transport, movement, building molecules, and other work.
Protein function depends on several levels of structure. The order of amino acids is set by genetic information. That order controls how the chain folds through attractions between different side groups.
A folded protein may have a pocket that fits a particular molecule. In an enzyme, this pocket is the active site. Binding can position reactants correctly, strain certain bonds, or provide a suitable chemical environment.
Temperature and pH matter because they can disrupt the weak attractions that maintain protein shape. Extreme conditions can denature a protein, meaning it loses its working shape. A denatured enzyme may no longer bind its substrate.
Students should distinguish denaturation from breaking every peptide bond. Often the amino acid chain remains intact even when the protein stops working.
DNA stores instructions as a sequence of bases, but cells usually use RNA to carry or interpret those instructions during protein production. The base sequence in a gene helps determine the amino acid sequence of a protein. A change in DNA can alter one amino acid, many amino acids, or sometimes no amino acids at all.
The effect depends on where the change occurs and how it affects folding. These ideas connect macromolecules to inherited traits, genetic disorders, medicine, digestion, and nutrition.
When studying diagrams, pay close attention to the bond being made or broken, the role of water, and the direction of energy transfer. It helps to connect each molecule class to a structure, a main job, and a real cell example rather than memorizing isolated lists.