3.3 Biochemical Compounds

Created by: CK-12/Adapted by Christine Miller

Figure 3.3.1 Carbo-licious!

Carbs Galore

What do all of these foods have in common? All of them consist mainly of large compounds called , often referred to as “carbs.” Contrary to popular belief, carbohydrates are an important part of a healthy diet. They are also one of four major classes of biological .

Chemical Compounds in Living Things

Image shows scattered beads and a beaded bracelet.
Figure 3.3.2 The individual beads represent monomers, and when the beads are connected to form the bracelet, it represents a polymer.

The compounds found in living things are known as biochemical compounds or biological molecules. Biochemical compounds make up the  and other structures of organisms. They also carry out life processes. Carbon is the basis of all biochemical compounds, so carbon is essential to life on Earth. Without carbon, life as we know it could not exist.

Carbon is so basic to life because of its ability to form stable bonds with many elements, including itself. This property allows carbon to create a huge variety of very large and complex molecules. In fact, there are nearly 10 million carbon-based compounds in living things!

Most biochemical compounds are very large molecules called polymers. A  is built of repeating units of smaller compounds called . Monomers are like the individual beads on a string of beads, and the whole string is the polymer. The individual beads (monomers) can do some jobs on their own, but sometimes you need a larger molecule, so the monomers can be connected to form polymers.


Classes of Biochemical Compounds

Although there are millions of different biochemical compounds in Earth’s living things, all biochemical compounds contain the elements carbon, hydrogen, and oxygen. Some contain only these elements, while others contain additional elements, as well. The vast number of biochemical compounds can be grouped into just four major classes: , and .


Image shows a glucose molecule. The molecule contains 6 carbons fused into a ring with several hydroxide groups.
Figure 3.3.3 Glucose is a common monosaccharide which can form large polymers including starch, glycogen and cellulose.

include sugars and starches. These compounds contain only the elements carbon, hydrogen, and oxygen. In living things, carbohydrates provide  to cells, store energy, and form certain structures (such as the cell walls of plants). The that makes up large carbohydrate compounds is called a monosaccharide. The sugar glucose, represented by the chemical model in Figure 3.3.2, is a monosaccharide. It contains six carbon atoms (C), along with several atoms of hydrogen (H) and oxygen (O). Thousands of glucose molecules can join together to form a polysaccharide, such as starch.



Image shows a bar of butter, two bottles of cooking oil, and a jar of coconut oil.
Figure 3.3.4 Fats and oils are examples of lipids

include fats and oils. They primarily contain the elements carbon, hydrogen, and oxygen, although some lipids contain additional elements, such as phosphorus. Lipids function in living things to store , form cell membranes, and carry messages. Lipids consist of repeating units that join together to form chains called fatty acids. Most naturally occurring fatty acids have an unbranched chain of an even number (generally between 4 and 28) of carbon atoms.


Image shows chicken breasts, eggs, nuts and lentils.
Figure 3.3.5 There are many sources of dietary protein.

 include , antibodies, and many other important compounds in living things. They contain the elements carbon, hydrogen, oxygen, nitrogen, and sulfur. Functions of proteins are very numerous. They help cellsno post keep their shape, compose muscles, speed up , and carry messages and materials. The monomers that make up large protein compounds are called . There are 20 different amino acids that combine into long chains (called polypeptides) to form the building blocks of a vast array of proteins in living things.

Nucleic Acids

 include the molecules  (deoxyribonucleic acid) and (ribonucleic acid). They contain the elements carbon, hydrogen, oxygen, nitrogen, and phosphorus. Their functions in living things are to encode instructions for making proteins, to help make proteins, and to pass instructions between parents and offspring. The monomer that makes up nucleic acids is the nucleotide.  All nucleotides are the same, except for a component called a nitrogen base. There are four different nitrogen bases, and each nucleotide contains one of these four bases. The sequence of nitrogen bases in the chains of nucleotides in DNA and RNA makes up the code for protein synthesis, which is called the genetic code. The animation in Figure 3.3.5 represents the very complex structure of DNA, which consists of two chains of nucleotides.

A rotating model of DNA. It contains long strands of nucleotides. Each nucleotide consists of a deoxyribose sugar, a phosphate group, and a nitrogenous base. The sugar and phosphate groups linking in long chains. Two complementary strands of DNA are bound by hydrogen bonds holding complementary nitrogenous base pairs together.
Figure 3.3.6 DNA is a polymer made of many monomers called nucleotides. DNA carries all the instructions a cell needs to carry out metabolism.

3.3 Summary

  • Biochemical compounds are carbon-based compounds found in living things. They make up cellsno post and other structures of organisms and carry out life processes. Most biochemical compounds are large molecules called that consist of many repeating units of smaller molecules, which are called .
  • There are millions of biochemical compounds, but all of them fall into four major classes: , lipids, , and .
  • Carbohydrates include sugars and starches. They provide cells with energy, store energy, and make up organic structures, such as the cell walls of plants.
  • Lipids include fats and oils. They store energy, form cell membranes, and carry messages.
  • Proteins include enzymes, antibodies, and numerous other important compounds in living things. They have many functions — helping cells keep their shape, making up muscles, speeding up chemical reactions, and carrying messages and materials.
  • Nucleic acids include  and RNA. They encode instructions for making proteins, help make proteins, and pass encoded instructions from parents to offspring.

3.3 Review Questions

  1. Why is carbon so important to life on Earth?
  2. What are biochemical compounds?
  3. Describe the diversity of biochemical compounds and explain how they are classified.
  4. Identify two types of carbohydrates. What are the main functions of this class of biochemical compounds?
  5. What roles are played by lipids in living things?
  6. The enzyme amylase is found in saliva. It helps break down starches in foods into simpler sugar molecules. What type of biochemical compound do you think amylase is?
  7. Explain how DNA and RNA contain the genetic code.
  8. What are the three elements present in every class of biochemical compound?
  9. Classify each of the following terms as a monomer or a polymer:
    1. Nucleic acid
    2. Amino acid
    3. Monosaccharide
    4. Protein
    5. Nucleotide
    6. Polysaccharide
  10. Match each  of the above monomers with its correct polymer and identify which class of biochemical compound is represented by each monomer/polymer pair.
  11. Is glucose a monomer or a polymer? Explain your answer.
  12. What is one element contained in proteins and nucleic acids, but not in carbohydrates?
  13. Describe the relationship between proteins and nucleic acids.
  14. Why do you think it is important to eat a diet that contains a balance of carbohydrates, proteins, and fats?
  15. Examine the picture of the meal in Figure 3.3.6.  What types of biochemical compounds can you identify?
Image shows four bowls of food, each containing noodles, a type of meat, green leafy vegetables and green onions in a broth. Each bowl has chopsticks resting on the side, and there are two smaller bowls in the centre holding lime and chilis.
Figure 3.3.7 Which biomolecules do you see represented here?

3.3 Explore More

Biomolecules (updated), by the Amoeba Sisters, 2016.


Figure 3.3.1

Figure 3.3.2
jewellery_beads_stones_necklace-1200668 on Pxhere, is used under a CC0 1.0 universal public domain dedication license (https://creativecommons.org/publicdomain/zero/1.0/).

Figure 3.3.3
Glucose; Structure of beta-D-glucopyranose (Haworth projection), by NEUROtiker on Wikimedia Commons, has been released into the public domain (https://en.wikipedia.org/wiki/Public_domain).

Figure 3.3.4
Lipid Examples; Butter and Oil, by Bill Branson (photographer), on Wikimedia Commons is released into the public domain (https://en.wikipedia.org/wiki/Public_domain).

Figure 3.3.5
Protein-rich_Foods, by Smastronardo on Wikimedia Commons, is used under a CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0) license.

Figure 3.3.6
Bdna_cropped [gif], by Jahobr on Wikimedia Commons, is released into the public domain (https://en.wikipedia.org/wiki/Public_domain) (This is a derivative work from Bdna.gif by Spiffistan.)

Figure 3.3.7Dinner by Quốc Trung [@boeing] on Unsplash is used under the Unsplash License (https://unsplash.com/license).


Amoeba Sisters. (2016, February 11).  Biomolecules (updated). YouTube. https://www.youtube.com/watch?v=YO244P1e9QM&feature=youtu.be


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Human Biology by Christine Miller is licensed under a Creative Commons Attribution-NonCommercial 4.0 International License, except where otherwise noted.

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