Protein Synthesis: Translation and Mutation

Biology Index

Where are we going with this? The information on this page should increase understanding related to this standard:  Demonstrate how DNA sequence information is decoded through transcriptional and translational processes within the cell in order to synthesize proteins. Examine the relationship of structure and function of various types of RNA and the importance of this relationship in these processes.

Article includes ideas, images, and content from Troy Smigielski (2022-01)

Protein Synthesis: Translation and Mutation

(So, this seems like a thing…)

The goal of protein synthesis is to make a protein. In other places, we have discussed that proteins do a wide variety of functions in the body and/or are expressed as a trait. We have also explored how the protein synthesis process begins in the nucleus of a cell with the transcription process.

But, let's start with a quick review…

Okay, thanks!

In the nucleus of a cell, the first thing that happens is that the DNA elongates and opens up to make room for the RNA nucleotides to come in. The DNA is composed of a coding strand (which carries the code the mRNA will need to make the proteins) and a template strand made up of the complementary nucleotides found in the coding strand…

You know…

So… 

To summarize:

1. Transcription is the step in protein synthesis where DNA makes mRNA.

2. This process takes place in the nucleus.

3. After transcription, the cell has a long strand of mRNA that serves as a messenger between the nucleus (DNA) and the ribosome (protein).

4. But, before translation, the cell edits the mRNA sequence.

4a. Introns are the sequences that were cut out. (The invaders, intruders, the invasive code…)

4b. Exons are the sequences that were left in. (The expected code that will be expressed in the protein.)

5. When the strand has been edited, the cell splits up the bases into groups of three.

6. Each group of three bases is called a codon.

7. Each codon codes for an individual amino acid.

7a. When these are put together (in a specific order), they make up a specific protein.

That's pretty much it! But… Let's look at it again with pictures and more words! 

After transcription, it is time to begin the process called translation. 

You can think of it this way… in transcription, the DNA code is copied—transcribed. Then, the code has to be translated from the letters (A, U, C, and G) into a specific sequence of amino acids.

Okay… at the end of transcription, the cell has an edited strand of mRNA. Translation is the step that takes the mRNA code and turns it into a protein.

Translation occurs at the ribosome. (Sometimes, you'll see it described as "on" the ribosome.)

Wazzat?

1. mRNA travels to the ribosome to wait for tRNA.
2. tRNA transfers the anticodon and the appropriate amino acid to the mRNA sequence.
3. Amino acids are joined together with peptide bonds by the ribosome to make a protein.
   (Amino acids make up a protein)

tRNA acts as a molecular “bridge” that connects mRNA codons to the appropriate amino acid. One end has an anticodon and the other has the matching amino acid.

An anticodon is the complementary codon of the original mRNA codon. It is used to match up to the correct part of the sequence. Anticodons are like placeholders that allow tRNA to bind to the mRNA.

Hold on… What?

The mRNA is the important sequence that codes for the amino acid. It is the RNA version of the DNA coding strand. The tRNA has one job: to transfer the appropriate amino acid (that the mRNA coded for) to the ribosome. The ribosome then puts those amino acids together and creates a protein.

Hmm… could you be more specific?

Since the mRNA has a specific sequence of codons, then tRNA MUST line up in a specific sequence dragging their specific amino acid along with them. The result is that the amino acids line up in a specific sequence. And… that specific sequence determines which protein is made.

Woo… how about another picture?

Mutations

Do you think the correct base pair is brought every single time without error? Or that each codon is translated perfectly every time? A mutation is when the DNA sequence is changed.

Uh oh… this shoulds bad!

The DNA sequence makes the mRNA, which provides the instructions to make a protein. Therefore, a change in the DNA sequence can completely change the protein being made.

For instance… 

Having used the analogy that a protein is a sentence and the amino acids are the alphabet, you can imagine what might happen if you switch some of the letters around.

Who is the girl going to marry?
How is the girl going to marry?

The boy was forced to give up his file.
The boy was forced to give up his life. 

In the cases above, the two "proteins" made are not the same!

Mutations can occur from environmental factors such as overexposure to:

• Chemicals
• Pollutants
• Radiation
• Sunlight

Mutations can also occur during:

• DNA replication
• protein synthesis.

Mutations can be classified in different ways.

Point Mutations

A point mutation is when one nucleotide is swapped out for another.

A point mutation can be a silent mutation if the resulting amino acid does not change as a result of the mutation.

Source, 2022-02

Silent Mutation Example

If the DNA sequence “GGT” gets changed to “GGG.” 

The mRNA sequence would change from “CCA” to “CCC.” 

“CCA” and “CCC” both code for Proline, so no harm would be done. 

A point mutation can also be a missense mutation if the amino acid changes as a result of the mutation.

If the DNA sequence “GGT” gets changed to “CGT.”

The mRNA sequence would change from “CCA” to “GCA.”

“CCA” codes for Proline; “GCA” codes for Alanine.

This changes the entire protein.

Frameshift Mutations

A frameshift mutation is when a nucleotide is either inserted or deleted in the DNA sequence.

Ex: ABCDEF       ABBCDEF

Ex: ABCDEF            ACDEF

Inversion Mutations

An inversion mutation is when a DNA sequence gets reversed.

Ex: ABCDEF          ABCFED

Hey… Could mutations be GOOD?

Sometimes, mutations help an organism out. 

Mutations can help increase an organism’s fitness and helps increase genetic variability within a species.