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3.3: Protein Synthesis and Gene Expression

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How do you build a protein?

Your body needs proteins to create muscles, regulate chemical reactions, transport oxygen and perform other important tasks in your body. But how are these proteins built? They are made up of units called amino acids. Just like there are only a few types of blocks in a set, there are a limited number of amino acids. But there are very many different ways in which they can be combined.

Introduction to Protein Synthesis

The DNA sequence contains the instructions to place units called amino acids into a specific order. When these amino acid are assembled in that specific order, proteins are made. In short, DNA contains the instructions to create proteins. Each strand of DNA has many separate sequences that code for a specific protein. Insulin is an example of a protein made by your cells (Figure below). Units of DNA that contain code for the creation of a protein are called genes.

Insulin. Each blue or purple bead represents a different amino acid.

Cells Can Turn Genes On or Off

There are about 22,000 genes in every human cell. Does every human cell have the same genes? Yes. Does every human cell make the same proteins? No. In a multicellular organism, such as us, cells have specific functions because they have different proteins. They have different proteins because different genes are expressed in different cell types.

Imagine that all of your genes are "turned off." Each cell type only "turns on" (or expresses) the genes that have the code for the proteins it needs to use. So different cell types "turn on" different genes, allowing different proteins to be made. This gives different cell types different functions.


  • amino acid: The building blocks of proteins.
  • gene: Unit of DNA that contains code for the creation of one protein.
  • gene expression: The process of using a gene to make a gene product.


  • DNA contains the instructions to assemble amino acids in a specific order to make protein.
  • Each cell type only "turns on" (or expresses) the genes that have the code for the proteins it needs to use.


Use the resource below to answer the questions that follow.

  1. What is the molecule that assembles the protein?
  2. What is the molecule that delivers the amino acids?
  3. What initiates protein synthesis?


  1. What is a gene?
  2. If every human cell has the same genes, how can they look so different?

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6 , 7

Date Created:

Nov 29, 2012

Last Modified:

Apr 11, 2014
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