Question

describe in your own words process of transcription and translation. No less than 100 words

Answer 1

Genes provide information for building proteins. They don’t however directly create proteins. The production of proteins is completed through two processes: transcription and translation.

Transcription and translation take the information in DNA and use it to produce proteins. Transcription uses a strand of DNA as a template to build a molecule called RNA.

The RNA molecule is the link between DNA and the production of proteins. During translation, the RNA molecule created in the transcription process delivers information from the DNA to the protein building machines.

DNA → RNA → Protein

DNA and RNA are similar molecules and are both built from smaller molecules called nucleotides. Proteins are made from a sequence of amino acids rather than nucleotides. Transcription and translation are the two processes that convert a sequence of nucleotides from DNA into a sequence of amino acids to build the desired protein.

These two processes are essential for life. They are found in all organisms – eukaryotic and prokaryotic. Converting genetic information into proteins has kept life in existence for billions of years.

TRANSCRIPTION

Transcription is the process of producing a strand of RNA from a strand of DNA. Similar to the way DNA is used as a template in DNA replication, it is again used as a template during transcription. The information that is stored in DNA molecules is rewritten or ‘transcribed’ into a new RNA molecule.

Each nitrogenous base of a DNA molecule provides a piece of information for protein production. A strand of DNA has a specific sequence of bases. The specific sequence provides the information for the production of a specific protein.Through transcription, the sequence of bases of the DNA is transcribed into the reciprocal sequence of bases in a strand of RNA. Through transcription, the information of the DNA molecule is passed onto the new strand of RNA which can then carry the information to where proteins are produced. RNA molecules used for this purpose are known as messenger RNA (mRNA).

A gene is a particular segment of DNA. The sequence of bases in for a gene determines the sequence of nucleotides along an RNA molecule.Only one strand of a DNA double helix is transcribed for each gene. This strand is known as the ‘template strand’. The same template strand of DNA is used every time that particular gene is transcribed. The opposite strand of the DNA double helix may be transcribed for other genes.

An enzyme called ‘RNA polymerase’ is responsible for separating the two strands of DNA in a double helix. As it separates the two strands, RNA polymerase builds a strand of mRNA by adding the complementary nucleotides (A, U, G, C) to the template strand of DNA.A specific set of nucleotides along the template strand of DNA indicates where the gene starts and where the RNA polymerase should attach and begin unravelling the double helix. The section of DNA or the gene that is transcribed is known as the ‘transcription unit’.

In prokaryotic cells, such as bacteria, once a specific sequence of nucleotides has been transcribed then transcription is completed. This specific sequence of nucleotides is called the ‘terminator sequence’.In eukaryotic cells, transcription of a DNA strand must be complete before translation can begin. The two processes are separated by the membrane of the nucleus so they cannot be performed on the same strand at the same time as they are in prokaryotic cells.

If a certain protein is required in large numbers, one gene can be transcribed by several RNA polymerase enzymes at one time. This makes it possible for a large number of proteins to be produced from multiple RNA molecules in a short time.

TRANSLATION

Translation is the process where the information carried in mRNA molecules is used to create proteins. The specific sequence of nucleotides in the mRNA molecule provide the code for the production of a protein with a specific sequence of amino acids.Much like how RNA is built from many nucleotides, a protein is formed from many amino acids. A chain of amino acids is called a ‘polypeptide chain’ and a polypeptide chain bends and folds on itself to form a protein.During translation, the information of the strand of RNA is ‘translated’ from RNA language into polypeptide language i.e. the sequence of nucleotides is translated into a sequence of amino acids.

Ribosomes are small cellular machines that control the production of proteins in cells. They are made from proteins and RNA molecules and provide a platform for mRNA molecules to couple with complimentary transfer RNA (tRNA) molecules.Each tRNA molecule is bound to an amino acid and delivers the necessary amino acid to the ribosome. The tRNA molecules bind to the complementary bases of the mRNA molecule.

Ribosomes have three sites for different stages of interaction with tRNA and mRNA: the P site, A site and E site. The P site is where the ribosome holds the polypeptide chain and where the tRNA adds its amino acid to the growing chain.

Translation begins when a ribosome binds to a mRNA strand and an initiator tRNA. The initiator tRNA delivers an amino acid called ‘methionine’ directly to the P site and keeps the A site open for the second tRNA molecule to bind to.The strand of mRNA moves through the ribosome from the A site to the P site and exits at the E site. Molecules of tRNA bind to the codons of the mRNA at the A site before moving to the P site where their amino acid is attached to the end of the growing polypeptide chain.Once tRNA molecules have released their amino acids they move into the E site and are released from the mRNA and ribosome. As one tRNA molecule moves from the P site into the E site another tRNA molecule moves from the A site into the P site and delivers the next amino acid to the polypeptide chain.

Translation ends when a stop codon on the mRNA strand reaches the A site in the ribosome. The stop codon doesn’t have a complementary tRNA or anticodon.

Instead, a protein called a ‘release factor’ binds to the stop codon and adds a water molecule to the polypeptide chain when it moves into the P site. Once the water molecule is added to the polypeptide, the polypeptide is released from the ribosome.

It is common for multiple strands of mRNA to be translated simultaneously by multiple ribosomes. This greatly increases the rate of protein production.A polypeptide chain must fold on itself to create its final shape as a protein. As the polypeptide is being made it is already folding into a protein. Other proteins are used to guide the polypeptide to fold into the correct shape.

Often a polypeptide chain will need to be modified before it is able to perform properly. A range of molecules, such as sugars and lipids, can be added to the polypeptide. Likewise, the polypeptide chain may be split into smaller chains or have amino acids removed.