Translation in Biology- Steps, Purpose, & Products

Introduction

Gene translation is how a nucleic acid sequence (mRNA) is converted into an amino acid sequence. Translation occurs in all organisms in archaea, prokaryotes, and eukaryotes.

The purpose of translation is to turn a nucleic acid sequence into an amino acid sequence. This process will create a protein that the cell can use to perform various functions.

Figure: Translation overview diagram

An Overview of Nuclei Acids-DNA and RNA

Figure: Nucleic acids

Nucleic acids are the building blocks for nucleoproteins. They both are made up of four nitrogenous bases: adenine, cytosine, guanine, and thymine joined by phosphate bonds. Nucleic acids come in two forms: deoxyribonucleic acid (DNA) and ribonucleic acid (RNA). DNA is a double-stranded molecule, while RNA is single-stranded. The difference between the two relies on the sugar group that they contain.

Ribonucleic acid (RNA) is a nucleic acid containing the genetic information needed to create proteins. RNA consists of three major regions: The 5′ cap, the 10s, and the 3′ trailer. These regions are located at both ends of the RNA molecule and control how it interacts with other molecules.

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Nucleic Acids and Translation

Figure: Nucleic acids in translation

A cap is present at the 5′ end of an RNA molecule and consists of seven to ten nucleotides. The cap acts as a binding site for enzymes that assist with the process of translation. The cap is recognized by an enzyme called cap-binding complex (CBC). This complex binds to the cap structure and recruits other proteins that assist the process of translation.

The DNA carries the genetic material that makes up proteins, where the translation process comes in. The nucleic acids are read three times to create codons that instruct the ribosome to add, remove or replace amino acids.

When the cell creates a protein, it determines which tRNA will match each amino acid and attaches the tRNA to the amino acid. The ribosome copies the codon into mRNA with each tRNA. After all three tRNAs have been inserted, the ribosome moves down to the next codon. In this way, a code is created to instruct the creation of a protein.

Each codon can be matched with several different tRNAs, depending on the sequence of bases in the mRNA and which tRNA the cell selects. This process, although complex, is very accurate and produces no errors in translation.

Amino Acids and Codons

Figure: Amino acids and corresponding codons

Protein synthesis starts with translation, where genetic information is read from the DNA and converted into a sequence of amino acids.

Amino acids are the building blocks of proteins and are used to make different types of amino acids. Twenty amino acids participate in protein synthesis, as well as others that are non-standard. The sequence of amino acids will determine the structure and function of a protein.

Proteins are defined by their amino acid sequence, which can vary from protein to protein. However, different types of proteins are characterized by a specific sequence of amino acids.

Codons are the reading frame of a nucleic acid sequence that has been translated. Some codons will code for specific amino acids (meaning if you read them in a protein, they will code for a particular amino acid).

The correlation between codons and amino acids in translation

There are 64 possible codons, but only 61 of them code for specific amino acids. The rest of the codons are stop codons, which will end protein synthesis. However, there is a redundancy in the genetic code, and if one amino acid is not present in a cell, the next amino acid can often be used instead.

For example, if there is no valine in the protein made, leucine can be used instead. This is a canon for amino acids. In translation, if no codon present can be read to produce the first amino acid in a protein, the second amino acid will be used.

Similarly, if no codons are present that can produce the third amino acid, then the fourth one will be used.

Thus, this redundancy exists in the genetic code of organisms so that translation errors do not lead to nonsense proteins. Usually, translation only uses codon aug to start the translation process. Thus, this is a common stop codon.

If the genetic sequence is put into a cell that does not contain the corresponding RNA, this will lead to nonsense proteins degraded by enzymes.

The Stages of Translation

Figure: The three stages of translation

Translation occurs in all cells, and at any given moment, there are thousands of different proteins being synthesized. It occurs in three stages initiation, elongation, and termination.

Initiation

Figure: The initiation stage

Initiation occurs before the elongation phase begins. Initiation marks the beginning of translation as well as when initiation factors are released from mRNAs.

In initiation, translation factors are loaded onto the messenger RNA before it is translated (the bond between the cap and coding region must be broken). The mRNA template is loaded onto the ribosome, and when the bond is broken, the factors are released.

A ribosome, a messenger RNA, and initiator tRNA come together to form an initiation complex during initiation. The formation of this complex begins the elongation process.

Initiation factors are proteins that help transport the mRNA to the ribosome, and they are all found in the nucleus. The initiator tRNA carries an aminoacyl tRNA group, which means an amino acid covalently attached to its 3′ end.

The ribosome recognizes this aminoacyl group, and because of this, it binds to a specific start codon. The initiator tRNA is charged with methionine, but when it reaches its appropriate start codon, and binds to it.

The methionine is released and is replaced with a formamidopyrimidine, which becomes N-formylmethioninamine. The initiator tRNA is now called formylmethionine-tRNA.

Elongation

Figure: The elongation step of translation

In the elongation phase, a polypeptide chain forms as the mRNA is translated into a polypeptide. Elongation occurs in two steps:

The first step

It involves each amino acid being bound to one tRNA. The tRNA is attached to the mRNA and is recognized by a specific codon. The tRNA molecules and mRNA molecules will pair with each other during this step.

Once it has been attached, the tRNA carries its aminoacyl group to the a-site on the ribosome. The ribosome then combines the aminoacyl group with the tRNA molecule. The amino acid is now attached to the tRNA and is known as a peptide bond. The tRNA is now called a peptide-tRNA.

The second step

This step involves the removal of the five-nucleotide, which are removed by the release factor.

The elongation process moves in a 3′ to 5′ direction, and when it reaches the end of an mRNA strand, it will fill in the appropriate stop codon. This causes a release factor to bind to the ribosome and release the completed polypeptide chain from the ribosome.

The completed polypeptide (a protein) leaves the cell in an assembly line called the endoplasmic reticulum. The protein will either be used by the cell or secreted out of the cell.

Elongation factors are the proteins that move the growing chain to the next codon. One example of an elongation factor is EF-G, which moves chains through eukaryotes. Another example is EF-Tu, which moves chains through prokaryotes.

Termination

Figure: The termination step of translation

End termination is the formation of the stop codon (UAA, UGA, or UAG) on an mRNA. It is a process that occurs at the end of translation. The factors that create a stop codon are release factors and termination factors (the same as initiators).

Release factors bind to an initiation factor, which makes the polypeptide fall off. The release factor immediately binds to the stop codon because it recognizes the sequence. Termination factors then bind to the e-site of the ribosome.

The process of termination involves three steps:

  1. Guanosine nucleotide dissociation from the ribosome
  2. Release factor binding to codon and stop signal
  3. Release factor binding to e-site of ribosome

A specific release factor recognizes the stop codon. This factor binds to the chain in its final position. The binding causes the protein to fall off the ribosome, releasing it from the endoplasmic reticulum. The ribosome then moves to a new position where it continues translation.

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What are the Purposes of Translation?

Figure: Growing a polypeptide chain

The purpose of translation is to produce a new protein, which the cell will then use. Each process involved in translation has a specific function.

  • Initiation factors are the factor that allows for the appropriate gene to be read in the correct place, correcting any mistakes.
  • Elongation factors are involved in the making of a polypeptide chain. Termination factors are necessary to stop translation at appropriate times.
  • The cell can either use or secrete the proteins made from translation. It might be attached to a lipid to make a cell membrane. A protein could also be used in the cytoskeleton or as an enzyme.
  • This process is essential for the growth and survival of a cell. Without translation, cells could not grow or reproduce proteins that are necessary to survive.
  • It is also essential for the survival of an organism because it makes proteins that are necessary for life. Proteins make up the enzymes that cells use to extract energy from nutrients.
  • Proteins also repair damaged molecules, they make up the cytoskeleton that keeps the cell in shape, and they are involved in the functioning of all living organisms.

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What are the Products of Translation?

  • The process of translation produces a polypeptide chain, which is a linear string of amino acids.
  • This amino acid chain serves in many different ways, but it always has one purpose: to be used by a cell. The new chain is also known as a nascent protein.
  • The products of translation are proteins. Proteins serve many functions in the cell, and they are essential for life.

Translation in Prokaryotes

Figure: An illustration of prokaryote translation

In prokaryotes, the genetic expression that leads to protein formation occurs in two places at once.

Transcription takes place inside of the nucleus, while translation occurs at ribosomes found in the cytoplasm.

The genetic code that is used by prokaryotic cells is also the same as in eukaryotes. Prokaryotes can be unicellular or multicellular, and they do not have differentiated tissues.

During protein synthesis, the genetic code in prokaryotes can be described as an open reading frame. The stop codons that are used by these cells are all the same.

A prokaryotic cell has three types of RNA: messenger RNA (mRNA), transfer RNA (tRNA), and ribosomal RNA (rRNA).

Molecules of mRNA have to be transported from the nucleus to the cytoplasm, where the ribosomes are. The cell uses a system to move mRNA through the nuclear membrane and into the cytoplasm. mRNA is then translated at the ribosomes.

Differences between Prokaryotes and Eukaryotes Translation

  • Eukaryotes have a simple RNA splicing system, while prokaryotes do not.
  • Prokaryotic cells use a faster translation than eukaryotic cells.
  • Eukaryotes use a wider range of stop codons than prokaryotes do.
  • Eukaryotes have a larger average genome length than prokaryotes.

How to Create an mRNA Template

Figure: mRNA Template

All cells have ribosomes. They are always at the start codon and stop codon while moving between to read the genetic code. The ribosome is the site of translation, where a protein will be made.

The mRNA template contains all of the information about the protein. The mRNA template could be compared to a blueprint. Every cell has its DNA so that it can make specific proteins and RNA for that cell.

The process of translation is speedy. It takes place in a matter of seconds, but the process requires different factors to come together simultaneously. It also requires more than one ribosome working at a time to read multiple mRNAs and produce various proteins.

The mRNA template is created in the nucleus. First, a DNA strand is formed by using one of two techniques:

  1. Polymerase chain reaction
  2. To create a complementary DNA strand with an RNA polymerase enzyme that binds to one DNA and then moves along the other DNA strand, copying the genetic code

When digested by different kinds of RNA enzymes, the DNA is separated into two strands. These are single-stranded RNAs, and the separated DNA becomes a single-stranded DNA (ssDNA).

After the transcription of an mRNA template, it is cut off when a stop codon is reached. Then, it is released from the nuclear membrane when a specific sequence in the mRNA template signals.

The ribosome binds to the mRNA template, which causes it to be cut shorter by a mechanism- RNaseH.

Explaining the Two “R”s in Translation

One of the essential parts of translation, as stated before, is initiation. It is how the cell knows which protein to produce.

The first “R” of translation is RNA polymerase. This enzyme goes along one DNA strand and makes an RNA strand that the cell can use. Two different DNA strands are made to combine for a new, single-stranded mRNA strand.

The second “R” is the ribosome, which helps translate from the mRNA strand to proteins through initiation and elongation. The ribosome is crucial in translation because it reads the genetic code and puts amino acids into proteins.

The Genetic Code in Translation

The genetic code is the set of rules that specify which amino acid is used in translation. The cell follows these rules when making proteins. This code is made of three-letter nucleotide sets called codons.

Some of the codon combinations are AAG, CGU, CGC, and UGG. These are the stop codons that tell the ribosome to stop reading the genetic code.

Since there are four letters in the genetic code, there are only 64 possible combinations of codons. The genetic code is universal to all organisms on Earth. This means that any organism, even a virus, would share the same genetic code.

The Genetic code Table

Figure: A genetic code table

The genetic code table shows a classification of each amino acid and its corresponding codon. The first letter represents the nucleotide set in the mRNA template, and the second letter represents the amino acid that is added to make a protein.

The next set of two letters in the genetic code table represents the amino acids added to build the protein. When adding an amino acid, it goes through a step called translocation. In this step, a tRNA transports the amino acid to the P site.

There are three stop codons: UAA, UAG, and UGA. These are called nonsense codons because if they were to be translated, they would make a stop signal that causes the ribosome to stop reading the genetic code.

The next two sets of letters in the genetic code table represent amino acids added together to add to the protein being built.

The last set of letters in the genetic code table represents the amino acid added to make a stop signal to the protein.

Transcription and Translation

Large amounts of DNA are not directly used to make proteins. To produce a protein, first, the DNA must undergo transcription: This is the process of copying genetic DNA information onto RNA molecules. The RNA is then used for translation.

Since a polypeptide chain is formed on a ribosome, it can be said that the DNA acts as a template for protein formation.

The process of translation is the synthesis of protein from RNA. The genetic code determines which amino acid corresponds to each base in the sequence, allowing the ribosome to create a protein.

Differences between Translation and Transcription

Figure: Translation vs Transcription
  • Transcription and translation are two processes that are part of the larger process of genetic expression. The function of both processes is to produce a polypeptide chain, but they work in different ways.
  • Transcription uses DNA and RNA to copy genetic information from one type of molecule to another. In translation, the cell reads mRNA to create a polypeptide chain.
  • Transcription occurs in the nucleus, while translation takes place at ribosomes found in the cytoplasm.
  • Transcription is a slow process involving mRNA synthesis, while translation occurs quickly and often many times within a cell. Transcription ends with forming a mature mRNA molecule, while translation involves the use of many proteins and enzymes.

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Bottom Line

Gene translation is an intricate process that involves the synthesis of proteins from mRNA. The genetic code is crucial to this process for telling the ribosome how to construct a polypeptide chain.

This process has recently shed light on genome sequencing because the DNA encodes many proteins in genes.

However, the genetic code is universal to all forms of life. It has allowed for breakthroughs in treating diseases that affect many different organisms, such as cancer.

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