Information about Protein Biosynthesis
Protein biosynthesis (synthesis) is the process in which cells build proteins. The term is sometimes used to refer only to protein translation but more often it refers to a multi-step process, beginning with amino acid synthesis and transcription which are then used for translation. Protein biosynthesis, although very similar, differs between prokaryotes and eukaryotes.
Amino acids are the monomers which are polymerized to produce proteins. Amino acid synthesis is the set of biochemical processes (metabolic pathways) which build the amino acids from carbon sources like glucose. Not all amino acids may be synthesised by every organism, for example adult humans have to obtain 9 of the 20 amino acids from their diet.
The amino acids are then loaded onto tRNA molecules for use in the process of translation.
Transcription is the process by which an mRNA template, carrying the sequence of the protein, is produced for the translation step from the genome. Transcription makes the template from one strand of the DNA double helix, called the template strand. Transcription takes place in 3 stages: Initiation, Elongation and Termination.
The DNA strand is read in the 3' to 5' direction and the mRNA is transcribed in the 5' to 3' direction by the RNA polymerase.
Protein translation involves the transfer of information from the mRNA into a peptide, composed of amino acids. This process is mediated by the ribosome, with the adaptation of the RNA sequence into amino acids mediated by transfer RNA. Numerous initation and elongation factors also play a role.
Translation requires a lot of energy, with the hydrolysis of approximately 4 NTP → NDP per amino acid added. (This includes the aminoacylation of the tRNA. Thus, gene expression is highly regulated to ensure that only proteins that are required are translated.
Translation involves 3 processes: initiation, elongation, and termination.
Many proteins undergo post-translational modification. This may include the formation of disulfide bridges or attachment of any of a number of biochemical functional groups, such as acetate, phosphate, various lipids and carbohydrates. Enzymes may also remove one or more amino acids from the leading (amino) end of the polypeptide chain, leaving a protein consisting of two polypeptide chains connected by disulfide bonds.
Gene expression is the process by which the inheritable information in a gene, such as the DNA sequence, is made into a functional gene product, such as protein or RNA.
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Amino acid synthesis
Amino acids are the monomers which are polymerized to produce proteins. Amino acid synthesis is the set of biochemical processes (metabolic pathways) which build the amino acids from carbon sources like glucose. Not all amino acids may be synthesised by every organism, for example adult humans have to obtain 9 of the 20 amino acids from their diet.
The amino acids are then loaded onto tRNA molecules for use in the process of translation.
Transcription
Transcription is the process by which an mRNA template, carrying the sequence of the protein, is produced for the translation step from the genome. Transcription makes the template from one strand of the DNA double helix, called the template strand. Transcription takes place in 3 stages: Initiation, Elongation and Termination.
The DNA strand is read in the 3' to 5' direction and the mRNA is transcribed in the 5' to 3' direction by the RNA polymerase.
Translation
Protein translation involves the transfer of information from the mRNA into a peptide, composed of amino acids. This process is mediated by the ribosome, with the adaptation of the RNA sequence into amino acids mediated by transfer RNA. Numerous initation and elongation factors also play a role.
Translation requires a lot of energy, with the hydrolysis of approximately 4 NTP → NDP per amino acid added. (This includes the aminoacylation of the tRNA. Thus, gene expression is highly regulated to ensure that only proteins that are required are translated.
Translation involves 3 processes: initiation, elongation, and termination.
Initiation in prokaryotes
The initiation of protein translation involves the assembly of the ribosome and addition of the first amino acid, methionine.- The 30S ribosomal subunit attaches to the mRNA, mediated by IF-1 and IF-3 (initiation factors). The 30S ribosome brings with it the P and A site, but the A site is blocked by IF-1 to prevent binding of tRNA. It aligns to the Shine-Dalgarno sequence, which positions the first codon (AUG) in the P site.
- Next, the specific aminoacyl-tRNA for N-formylmethionine (F-Met) is brought into the P site by IF-2. The anticodon of this tRNA will bind to the AUG codon on the mRNA. Note: this is the only tRNA brought into the P site; all successive aminoacyl-tRNAs will be brought to the A site for peptide elongation.
- The 50S ribosomal subunit is then brought in to complete the ribosome, and with it, IF-1, IF-2, and IF-3 come off the complex. The A and P site are completed, and the 50S subunit also brings the E (exit) site.
Initiation in eukaryotes
The initiation of protein translation in eukaryotes is similar to that of prokaryotes with some modifications.- A complex of proteins will connect the 5'cap and 3'PolyA tail, and this complex will recruit the ribosome subunits.
- There is no Shine-Dalgarno sequence in eukaryotes. Instead, the ribosome scans along the mRNA for the first methionine codon. Similarly, there is no N-formylmethionine in eukaryotic cells.
Elongation
Elongation of protein biosynthesis is fairly similar between prokaryotes and eukaryotes. The following is a description of elongation in prokaryotes.- Elongation proceeds after initiation with the binding of an aminoacyl-tRNA to the A site, which is the next codon in the mRNA. The aminoacyl-tRNA is brought to the ribosome through a series of interactions with EF-Tu (an elongation factor). This step involves the hydrolysis of GTP: EF-Tu-GTP --> EF-Tu-GDP (The hydrolyzed GDP is switched for GTP through another series of reactions with EF-Ts.)
- The next aminoacyl-tRNA binds to the codon, and the C-terminus of the F-Met undergoes nucleophilic attack by the N-terminus of the second amino acid. The F-Met is now connected to the second amino acid through a peptide bond.
- The first tRNA (for F-Met) is now uncharged. The entire ribosome complex moves along the mRNA through the action of another elongation factor (EF-G) and the hydrolysis of GTP --> GDP.
- The first tRNA is now in the E site and comes off from the ribosome, while the second tRNA, with the nascent peptide chain, is in the P site. Step 1-4 will repeat as successive amino acids are added.
Termination
Termination of protein biosynthesis occurs when the ribosome comes across a stop codon, for which there is no tRNA. At this point, protein biosynthesis halts and one of three release factors will bind to the stop codon. (Note: In eukaryotes, there is only one release factor that will bind to all three stop codons.) This induces a nucleophilic attack of the C-terminus of the nascent peptide by water - this hydrolysis releases the peptide from the ribosome. The ribosome, release factor, and uncharged tRNA then dissociate and translation is complete.Events following protein translation
The events following biosynthesis include post-translational modification and protein folding. During and after synthesis, polypeptide chains often fold to assume, so called, native secondary and tertiary structures. This is known as protein folding.Many proteins undergo post-translational modification. This may include the formation of disulfide bridges or attachment of any of a number of biochemical functional groups, such as acetate, phosphate, various lipids and carbohydrates. Enzymes may also remove one or more amino acids from the leading (amino) end of the polypeptide chain, leaving a protein consisting of two polypeptide chains connected by disulfide bonds.
See also
External links
- Science aid:Protein synthesis For high school
- Protein Synthesis
- Transcription
- : Translation
- Protein Synthesis Animation Wesleyan University Learning Objects animation of protein synthesis.
- Interactive Java simulation of transcription initiation. From Center for Models of Life at the Niels Bohr Institute.
Protein biosynthesis |
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Biochemical Processes: Amino acid synthesis - tRNA synthesis
Molecular Biology Processes: Transcription - Post-transcriptional modification - Translation
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Proteins are large organic compounds made of amino acids arranged in a linear chain and joined together by peptide bonds between the carboxyl and amino groups of adjacent amino acid residues.
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Translation is the second process of protein biosynthesis (part of the overall process of gene expression). Translation occurs in the cytoplasm where the ribosomes are located. Ribosomes are made of a small and large subunit which surrounds the mRNA.
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Amino acid synthesis is the set of biochemical processes (metabolic pathways) by which the various amino acids are produced from other compounds. The substrates for these processes are various compounds in the organism's diet or growth media.
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Transcription is the process through which a DNA sequence is enzymatically copied by an RNA polymerase to produce a complementary RNA. So to say, it is the transfer of genetic information from DNA into RNA.
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Translation is the second process of protein biosynthesis (part of the overall process of gene expression). Translation occurs in the cytoplasm where the ribosomes are located. Ribosomes are made of a small and large subunit which surrounds the mRNA.
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Prokaryotes (IPA: /prəʊˈkæriəʊtiz/) are a group of organisms that lack a cell nucleus (= karyon), or any other membrane-bound organelles.
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Amino acid synthesis is the set of biochemical processes (metabolic pathways) by which the various amino acids are produced from other compounds. The substrates for these processes are various compounds in the organism's diet or growth media.
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polymer is a substance composed of molecules with large molecular mass composed of repeating structural units, or monomers, connected by covalent chemical bonds. The word is derived from the Greek, πολυ, polu, "many"; and μέρος, meros,
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Biochemistry is the study of the chemical processes in living organisms.[1] The word "biochemistry" comes from the Greek word βιοχημεία biochēmeia, which means "the chemistry of life.
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In biochemistry, a metabolic pathway is a series of chemical reactions occurring within a cell. In each pathway a principal chemical is modified by chemical reactions. These reactions are accelerated, more accurately catalyzed, by enzymes.
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Glucose (Glc), a monosaccharide (or simple sugar), is an important carbohydrate in biology. The living cell uses it as a source of energy and metabolic intermediate.
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Translation is the second process of protein biosynthesis (part of the overall process of gene expression). Translation occurs in the cytoplasm where the ribosomes are located. Ribosomes are made of a small and large subunit which surrounds the mRNA.
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Transcription is the process through which a DNA sequence is enzymatically copied by an RNA polymerase to produce a complementary RNA. So to say, it is the transfer of genetic information from DNA into RNA.
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Messenger Ribonucleic Acid (mRNA) is a molecule of RNA encoding a chemical "blueprint" for a protein product. mRNA is transcribed from a DNA template, and carries coding information to the sites of protein synthesis: the ribosomes.
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In biology the genome of an organism is its whole hereditary information and is encoded in the DNA (or, for some viruses, RNA). This includes both the genes and the non-coding sequences of the DNA.
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The template strand (also known as the antisense strand or the anticoding strand or the noncoding strand) is the strand of DNA that the RNA polymerase uses as a guide to build complementary mRNA. This is the reverse complement of the coding strand.
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Translation is the second process of protein biosynthesis (part of the overall process of gene expression). Translation occurs in the cytoplasm where the ribosomes are located. Ribosomes are made of a small and large subunit which surrounds the mRNA.
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Peptides (from the Greek πεπτίδια, "small digestibles") are short polymers formed from the linking, in a defined order, of α-amino acids.
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amino acid is a molecule that contains both amine and carboxyl functional groups. In biochemistry, this term refers to alpha-amino acids with the general formula H2NCHRCOOH, where R is an organic substituent.
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A ribosome is a small, dense, functional structure found in most known cells that assemble proteins and polypeptides used in cell division. It catalyses the assembly of individual amino acids into polypeptide chains by reading messenger RNAs and binding amino acids that are
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Transfer RNA (abbreviated tRNA), first hypothesized by Francis Crick, is a small RNA chain (73-93 nucleotides) that transfers a specific amino acid to a growing polypeptide chain at the ribosomal site of protein synthesis during translation.
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Aminoacylation is the process of adding an aminoacyl group to a compound.
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See also
- Acylation
- Transfer RNA#Aminoacylation
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- For vocabulary, see Glossary of gene expression terms
Gene expression is the process by which the inheritable information in a gene, such as the DNA sequence, is made into a functional gene product, such as protein or RNA.
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Initiation factors are proteins that bind to the small subunit of the ribosome during the initiation of protein synthesis.
They are divided into two major groups:
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They are divided into two major groups:
- Prokaryotic initiation factors
- Eukaryotic initiation factors
External links
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The Shine-Dalgarno sequence, proposed by Australian scientists John Shine and Lynn Dalgarno,[1] is a ribosomal binding site generally located 6-7 nucleotides upstream of the start codon AUG.
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genetic code is the set of rules by which information encoded in genetic material (DNA or RNA sequences) is translated into proteins (amino acid sequences) by living cells.
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Aminoacyl-tRNA is tRNA (also known as transfer ribonucleic acid) to which its cognated amino acid is adhered. Their role is to deliver the amino acid to the ribosome where it will be incorporated into the polypeptide chain that is being produced.
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