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Protein synthesis
 
 
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Protein synthesis is the creation of proteins using DNA
DNA

Deoxyribonucleic acid is a nucleic acid that contains the genetics instructions used in the development and functioning of all known living organisms and some viruses....
 and RNA
RNA

Ribonucleic acid is a type of molecule that consists of a long chain of nucleotide units. Each nucleotide consists of a nucleobase, a ribose sugar, and a phosphate....
. Proteins can often be synthesized directly from genes by translating
Translation (genetics)

Translation is the first stage of protein biosynthesis . Translation is the production of proteins by decoding mRNA produced in Transcription ....
 mRNA. When a protein is harmful and needs to be available on short notice or in large quantities, a protein precursor
Protein precursor

A protein precursor, also called a pro-protein or pro-peptide, is an inactive protein that can be turned into an active form by posttranslational modification....
 is produced. A proprotein is an inactive protein containing one or more inhibitory peptide
Inhibitory peptide

An inhibitory peptide is a peptide, polypeptide, or amino acid sequence within a proprotein that contains an inhibitor. The proprotein is turned into an active form when the inhibitory sequence is removed by proteolysis during posttranslational modification....
s that can be activated when the inhibitory sequence is removed by proteolysis
Proteolysis

Proteolysis is the directed degradation of proteins by cellular enzymes called proteases or by intramolecular digestion....
 during posttranslational modification
Posttranslational modification

Posttranslational modification is the chemistry modification of a protein after its translation . It is one of the later steps in protein biosynthesis for many proteins....
. A preprotein is a form that contains a signal sequence (an N-terminal signal peptide
Signal peptide

A signal peptide is a short peptide chain that directs the post-translation transport of a protein.Signal peptides may also be called targeting signals, signal sequences, transit peptides, or localization signals....
) that specifies its insertion into or through membranes; i.e., targets them for secretion.






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Encyclopedia


Protein synthesis is the creation of proteins using DNA
DNA

Deoxyribonucleic acid is a nucleic acid that contains the genetics instructions used in the development and functioning of all known living organisms and some viruses....
 and RNA
RNA

Ribonucleic acid is a type of molecule that consists of a long chain of nucleotide units. Each nucleotide consists of a nucleobase, a ribose sugar, and a phosphate....
. Proteins can often be synthesized directly from genes by translating
Translation (genetics)

Translation is the first stage of protein biosynthesis . Translation is the production of proteins by decoding mRNA produced in Transcription ....
 mRNA. When a protein is harmful and needs to be available on short notice or in large quantities, a protein precursor
Protein precursor

A protein precursor, also called a pro-protein or pro-peptide, is an inactive protein that can be turned into an active form by posttranslational modification....
 is produced. A proprotein is an inactive protein containing one or more inhibitory peptide
Inhibitory peptide

An inhibitory peptide is a peptide, polypeptide, or amino acid sequence within a proprotein that contains an inhibitor. The proprotein is turned into an active form when the inhibitory sequence is removed by proteolysis during posttranslational modification....
s that can be activated when the inhibitory sequence is removed by proteolysis
Proteolysis

Proteolysis is the directed degradation of proteins by cellular enzymes called proteases or by intramolecular digestion....
 during posttranslational modification
Posttranslational modification

Posttranslational modification is the chemistry modification of a protein after its translation . It is one of the later steps in protein biosynthesis for many proteins....
. A preprotein is a form that contains a signal sequence (an N-terminal signal peptide
Signal peptide

A signal peptide is a short peptide chain that directs the post-translation transport of a protein.Signal peptides may also be called targeting signals, signal sequences, transit peptides, or localization signals....
) that specifies its insertion into or through membranes; i.e., targets them for secretion. The signal peptide is cleaved off in the endoplasmic reticulum
Endoplasmic reticulum

The endoplasmic reticulum is a eukaryote organelle that forms an interconnected network of tubules, vesicle , and cisternae within cell . The lacey membranes of the endoplasmic reticulum were first seen by Keith R....
.. Preproproteins have both sequences (inhibitory and signal) still present.

For synthesis of protein, a succession of tRNA molecules charged with their appropriate amino acids have to be brought together with an mRNA molecule and matched up by base-pairing through their anti-codons with each of its successive codons. The amino acids then have to be linked together to extend the growing protein chain, and the tRNAs, relieved of their burdens, have to be released. This whole complex of processes is carried out by a giant multimolecular machine, the ribosome, formed of two main chains of RNA, called ribosomal RNA (rRNA), and more than 50 different proteins. This molecular juggernaut latches onto the end of an mRNA molecule and then trundles along it, capturing loaded tRNA molecules and stitching together the amino acids they carry to form a new protein chain.

Process


Transcription

Protein synthesis starts in the nucleus, where the DNA is held. The DNA structure is two helixes made up of sugar and phosphate held together by the bases. The sugar and the phosphate are joined together by covalent bond. deoxyribonucleic acid, thymidine
Thymidine

Thymidine is a chemical Chemical compound, more precisely a pyrimidine deoxynucleoside. Deoxythymidine is the DNA nucleoside T, which pairs with deoxyadenosine in double-stranded DNA....
, and deoxycytidine
Deoxycytidine

Deoxycytidine is a deoxyribonucleoside. It is like cytidine, but with one oxygen atom removed....
. Similar to DNA replication, the DNA is "unzipped" by the enzyme helicase, leaving the single nucleotide chain open to be copied. RNA polymerase reads the DNA strand from 3 prime to 5 prime, while it synthsizes a single strand of messenger RNA from 5 prime to 3 prime.The first product of transcription differs in prokaryotic cells then that of Eukaryotic ones, as in prokaryotic cells the product is mRNA, which needs no post-transcriptional modification, while on the other hand, in Eukaryotic cells, the first product is called Primary transcript, that needs post-transcriptional modification (Capping with 7 methyl guanosine cap, tailing with a poly A tail) to give hnRNA (heterphil nuclear RNA). hnRNA then undergoes splicing of introns(non coding parts of gene) via splicosomes to give mRNA This single strand of mRNA leaves the nucleus through nuclear pores, and migrates into the cytoplasm where it joins with ribosomes, where protein synthesis occurs by the formation of peptide bonds and polypeptide chains.
  • Note: in the new RNA strand, the nucleotide Uracil
    Uracil

    Uracil is a common and naturally occurring pyrimidine derivative. Originally discovered in 1900, it was isolated by hydrolysis of yeast nuclein that was found in bovine thymus and spleen, herring, sperm, and wheat germ....
     takes the place of thymine
    Thymine

    Thymine is one of the four bases in the nucleic acid of DNA that make up the letters GCAT. The others are adenine, guanine, and cytosine. Thymine always pairs with adenine....
    .


Translation

Translation the process of converting the mRNA codon sequences into an amino acid polypeptide chain.

1. Initiation - A ribosome attaches to the mRNA and starts to code at the FMet codon (usually AUG, sometimes GUG or UUG).

2. Elongation - tRNA brings the corresponding amino acid (which has an anticodon that identifies the amino acid as the corresponding molecule to a codon) to each codon as the ribosome moves down the mRNA strand.

3. Termination - Reading of the final mRNA codon (aka the STOP codon), which ends the synthesis of the peptide chain and releases it.

See also

  • Protein biosynthesis
    Protein biosynthesis

    Protein synthesis is the process in which cell 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 ....
  • Peptide synthesis
    Peptide synthesis

    In organic chemistry, peptide synthesis is the production of peptides, which are organic compounds in which multiple amino acids are linked via peptide bonds which are also known as amide bonds....