Here is a cell, the basic unit of all living tissue. In most human cells there is a structure called the nucleus. The nucleus contains the genome. In humans, the genome is split between 23 pairs of chromosomes. Each chromosome contains a long strand of DNA, tightly packaged around proteins called histones.
Within the DNA are sections called genes. These genes contain the instructions for making proteins. When a gene is switched on, an enzyme called RNA polymerase attaches to the start of the gene.
It moves along the DNA, making a strand of messenger RNA out of free bases in the nucleus. The DNA code determines the order in which the free bases are added to the messenger RNA. This process is called transcription.
Before the messenger RNA can be used as a template for the production of proteins, it needs to be processed. This involves removing and adding sections of RNA. The messenger RNA then moves out of the nucleus into the cytoplasm.
Protein factories in the cytoplasm, called ribosomes, Bind to the messenger RNA. The ribosome reads the code in the messenger RNA to produce a chain made up of amino acids. There are 20 different types of amino acid.
Transfer RNA molecules carry the amino acids to the ribosome. The messenger RNA is read three bases at a time. As each triplet is read, A transfer RNA delivers the corresponding amino acid. This is added to a growing chain of amino acids.
Once the last amino acid has been added, the chain folds into a complex 3D shape to form the protein. Protein Synthesis Translation Inside the body, the process of translation occurs within every single cell. Each cell has a nucleus. After transcription, mRNAs move out of the nucleus and enter the cytoplasm. This mRNA strand acts as a template for protein synthesis.
Present in the cytoplasm is an enzyme aminoacyl-tRNA synthetase. The enzyme macromolecule has two binding sites. One site recognizes the amino acid, methionine.
This is followed by the binding of the ATP molecule and release of pyrophosphate, resulting in activation of amino acid. Finally, the tRNA and the activated amino acid bind together. This aminoacylated tRNA is known as met-tRNA and is released from the enzyme. This marks the commencement of first stage of protein synthesis, the initiation stage.
During the A initiation stage, a small subunit of a ribosome binds to the mRNA strand. The mRNA strand is made up of codons, which are sequences of three bases. Then the ribosome subunit moves along the mRNA in 5' to 3' direction, until it recognizes the AUG codon or the initiation codon.
At this point, met tRNA possessing the anticodon UAC pairs up with the AUG codon of the mRNA. Then, a large subunit of ribosome combines with a small ribosomal subunit. The large subunit shows three sites.
The acceptor site or the A site, the peptidyl site or the P site, the exit site or the E site. This whole unit forms the initiation complex. This is followed by the elongation stage.
During this stage, another tRNA-carrying molecule of an amino acid approaches the mRNA ribosome complex and fits in the A-site. Then, a bond is formed between methionine and the amino acid molecule on the tRNA. As a result, met tRNA becomes deacylated.
The ribosome then advances a distance of one codon and the deacylated tRNA shifts to the E site from where it dissociates. Meanwhile, another tRNA carrying an amino acid molecule attaches to the A site. This is followed by the binding of the amino acid molecules. Repetition of this process leads to the formation of an amino acid chain.
This event is called elongation. Finally, when the UAG codon or the stop codon reaches the A-site, elongation is terminated. Termination is the last stage of protein synthesis. The chain of amino acid molecules is released from the ribosome.
This released amino acid chain is the protein, and this part of protein synthesis is known as translation. Then, the tRNA detaches from the mRNA. Ribosome detaches and dissociates into its small and large subunits. Summary. Protein synthesis shows that the first stage involves the binding of MET-tRNA, 2mRNA, and the small subunit of the ribosome.
The larger subunit of ribosome then combines with the small subunit. Second stage is the elongation stage. In this stage, the incoming aminoacyl-tRNA fits in the A-site.
Then a bond is formed between the Methionine and the amino acid molecule on the tRNA. The process is repeated until a chain of amino acid molecules is formed. The last stage of protein synthesis is the termination stage.
When the ribosome reaches the stop codon, U-A-G, elongation stops and the newly formed amino acid chain which is the protein macromolecule, detaches from the ribosome. Subsequently, ribosomal subunits, along with the tRNA, dissociate from the mRNA. In order for our bodies to function, we need to supply them with a variety of nutrients we get from our diet.
Our bodies cannot use the food as it is when it enters our digestive system. The process of chemical digestion uses different proteins and enzymes to break down the food particles into usable nutrients our cells can absorb. And where are the instructions to manufacture these and all the different types of proteins we need to stay alive? The instructions to make proteins are contained in our DNA. DNA contains genes.
A gene is a continuous string of nucleotides containing a region that codes for an RNA molecule. This region begins with a promoter and ends in a terminator. Genes also contain regulatory sequences that can be found near the promoter or at a more distant location.
For some genes, the encoded RNA is used to synthesize a protein in a process called gene expression. For these genes, the gene expression is used to synthesize a protein in a process called gene expression. expression can be divided into two processes, transcription and translation.
In eukaryotic cells, transcription occurs in the nucleus. where DNA is used as a template to make messenger RNA. Then in translation, which occurs in the cytoplasm of the cell, the information contained in the messenger RNA is used to make a polypeptide. During transcription, the DNA in the gene is used as a template to make a messenger RNA strand with the help of the enzyme RNA polymerase.
This process occurs in three stages. initiation, elongation, and termination. During initiation, the promoter region of the gene functions as a recognition site for RNA polymerase to bind.
This is where the majority of gene expression is controlled, by either permitting or blocking access to this site by the RNA polymerase. Binding causes the DNA double helix to unwind and open. Then during elongation, The RNA polymerase slides along the template DNA strand.
As the complementary bases pair up, the RNA polymerase links nucleotides to the three prime end of the growing RNA molecule. Once the RNA polymerase reaches the terminator portion of the gene, the messenger RNA transcript is complete, and the RNA polymerase, the DNA strand, and the messenger RNA transcript dissociate from each other. The strand of messenger RNA that is made during transcription includes regions called exons that code for a protein and non-coding sections called introns. In order for the messenger RNA to be used in translation, the non-coding introns need to be removed and modifications such as a 5' cap and a 3' poly-A tail are added.
This process is called intron splicing and is performed by a complex made up of proteins and RNA called a spliceosome. This complex removes the intron segments and joins the adjacent exons to produce a mature messenger RNA strand that can leave the nucleus through a nuclear pore and enter the cytoplasm to begin translation. How is the information in the mature messenger RNA strand translated into a protein? The nitrogenous bases are grouped into three letter codes called codons. The genetic code includes 64 codons.
Most codons code for specific amino acids. There are four special codons, one that codes for start and three that code for stop. Translation begins with the messenger RNA strand binding to the small ribosomal subunit upstream of the start codon. Each amino acid is brought to the ribosome by a specific transfer RNA molecule. The type of amino acid is determined by the anticodon sequence of the transfer RNA.
Complementary base pairing occurs between the codon of the messenger RNA and the anticodon of the transfer RNA. After the initiator transfer RNA molecule binds to the start codon, the large ribosomal subunit binds to form the translation complex, and initiation is complete. In the large ribosomal subunit, there are three distinct regions, called the E, P, and A sites. During elongation, Individual amino acids are brought to the messenger RNA strand by a transfer RNA molecule through complementary base pairing of the codons and anticodons.
Each anticodon of a transfer RNA molecule corresponds to a particular amino acid. A charged transfer RNA molecule binds to the A site and a peptide bond forms between its amino acid and the one attached to the transfer RNA molecule at the P site. The complex slides down one codon to the right, where the now uncharged transfer RNA molecule exits from the E site, and the A site is open to accept the next transfer RNA molecule. Elongation will continue until a stop codon is reached.
A release factor binds to the A site at a stop codon, and the polypeptide is released from the transfer RNA in the P site. The entire complex dissociates and can reassemble to begin the process again at initiation. The purpose of translation is to produce polypeptides quickly and accurately.
After dissociation, the polypeptide may need to be modified before it is ready to function. Modifications take place in different organelles for different proteins. In order for a digestive enzyme to be secreted into the stomach or intestines, the polypeptide is translated into the endoplasmic reticulum. modified as it passes through the golgi, then secreted using a vesicle through the plasma membrane of the cell into the lumen of the digestive tract. Proteins are needed for most physiological functions of the body to occur properly, such as breaking down food particles in digestion, and the processes of transcription and translation make the production of proteins possible.
The job of this mRNA is to carry the gene's message from the DNA out of the nucleus to a ribosome for production of the particular protein that this gene codes for. There can be several million ribosomes in a typical eukaryotic cell. These complex catalytic machines use the mRNA copy of the genetic information to assemble amino acid building blocks into the three-dimensional proteins that are essential for life.
Let's see how it works. The ribosome is composed of one large and one small subunit that assemble around the messenger RNA, which then passes through the ribosome like a computer tape. The amino acid building blocks, that's the small glowing red molecules, are carried into the ribosome attached.
to specific transfer RNAs. That's the larger green molecules also referred to as tRNA. The small subunit of the ribosome positions the mRNA so that it can be read in groups of three letters known as a codon.
Each codon on the mRNA matches a corresponding anticodon on the base of a transfer RNA molecule. The larger subunit of the ribosome removes each amino acid and joins it onto the growing protein chain. As the mRNA is ratcheted through the ribosome, the mRNA sequence is translated into an amino acid sequence. There are three locations inside the ribosome, designated the A site, the P site, and the E site. The addition of each amino acid is a three-step cycle.
First, the tRNA enters the ribosome at the A-site and is tested for a codon-anticodon match with the mRNA. Next, provided there is a correct match, the tRNA is shifted to the P-site and the amino acid it carries is added to the end of the amino acid chain. The mRNA is also ratcheted on three nucleotides, or one codon.
Thirdly, the spent tRNA is moved to the e-site and then ejected from the ribosome to be recycled. As the protein synthesis proceeds, the finished chain emerges from the ribosome. It folds up into a precise shape determined by the exact order of amino acids.
Thus, the central dogma explains how the four-letter DNA code is, quite literally, turned into flesh and blood.