How Mutations Affect Protein Synthesis

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In order to understand how mutations affect protein synthesis, it is important to understand the process by which proteins are made (synthesized) and what a mutation is. Both of these occur on the cellular level of all living beings.

Steps of Protein Synthesis

There are three major protein synthesis steps:

1. Transcription
2. Transferal
3. Translation

Every activity carried out by living cells uses one or more proteins. Proteins are made inside the nucleus of cells within a chromosome made of DNA, the spiral-shaped two-stranded structure that stores the genes, or “recipes,” that cells use to make proteins. When the section of DNA that contains the recipe is copied or transcribed, the two strands of DNA separate. Then, free nucleotides pair with their complementary DNA bases, forming a new molecule called RNA.

The RNA spins off, and the DNA spirals up again. The new RNA strand is called messenger RNA. It carries the genetic message out from the nucleus of the cell to a cell structure called a ribosome. The ribosome is the “construction site” where the protein is synthesized. Every cell in a mammal contains about 10 million ribosomes.

The messenger RNA, with its protein “blueprint,” joins to a ribosome. The bases of the messenger RNA are grouped into sets of three nucleotides called codons. Each codon matches an anticodon on another kind of RNA called transfer RNA. Each transfer RNA carries one of 20 amino acids. The ribosomes gather the amino acids together into a polypeptide chain, and that is what makes up a protein. The order of amino acids on the chain is what determines which protein it will be.

Each transfer RNA floats away from the ribosome after bringing along its own amino acid. Once the amino acids are gathered one by one in the proper order to form a polypeptide chain, the process of protein synthesis reaches a “stop” codon signaling completion. The ribosome then releases the messenger RNA as well as the polypeptide.

Here is where mutations can come into the picture and cause problems. A mutation is some sort of change or defect in a gene. It can be caused by many different factors, such as environmental conditions, viruses, inherited diseases, exposure to radiation or a mistake in the DNA replication process. A mutation alters one of the three nucleotides in the codon, causing the “recipe” to be transcribed differently from the way it should have been translated.

When the codon and anticodon attempt to match up on the transfer RNA, the sequencing of amino acids on the polypeptide chain goes wrong and produces the wrong protein. It is like attempting to spell the word “pot” but spelling the word “top” instead. It has the same three letters, but since they are in the wrong order, the meaning is completely different. Likewise, the protein made from the “recipe” of a mutated gene will not be the correct protein.

Many small gene mutations do not cause major problems. But other mutations can have very serious health consequences because of how they affect protein synthesis.

An example of a mutation is the sickle cell gene. This abnormally shaped gene may have mutated for a good reason because one sickle cell gene protects its carrier from the deadly parasitic disease malaria. However, if someone inherits a sickle cell gene from each parent, resulting in two copies, it damages the protein synthesis of the hemoglobin cells that carry oxygen through the blood. The hemoglobin loses its oxygen and turns rigid, blocking blood vessels. This causes pain, fever and tissue damage from a disease called sickle cell anemia.

Fortunately, not every mutation will result in damage to the protein synthesis process, however, it is estimated that about 70 percent of mutations have negative effects on the process.

Resources about Protein Synthesis

Images of protein synthesis

Maricopa.edu information about protein synthesis

NIH.gov What is a gene mutation and how do mutations occur?

Resource by F.Rosseti

I am a teacher in Michigan. I grew up in Florida and have lived here in MI for close to 15 years. I enjoy writing and skiing in my spare time.

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