PROTEIN SYNTHESIS







Proteins are crucial chemicals. Proteins are one of the most diverse chemicals in the body. Proteins are synthesized within cells. The raw material for protein synthesis includes amino acids which are derived from catabolic digestive processes.







PROTEIN SYNTHESIS DILEMMA


DNA “speaks nucleotide language”


but


Protein “speaks amino acid language”


and


DNA is confined to the nucleus


but


Protein synthesis occurs in the cytoplasm


the solution


Copy and then transport the nucleotide code out of the nucleus and into the cytoplasm


This process is called Transcription




So, once the nucleotide code has been copied and transported out of the nucleus, the next major phase of protein synthesis may commence. The nucleotide code carried by the mRNA must now be translated into “amino acid language.” This phase is called Translation.





Once synthesized, ribosomes leave the nucleus as separate large and small subunits. The large unit interacts with the mRNA and then the small subunit helps to hold the mRNA in place.









Once the mRNA molecule is secure within the assembled ribosome. The nucleotide code is “read” 3 bases at a time.

Each 3-base sequence is referred to as a codon.

As each codon is “read,” the mRNA is moved on the ribosome to the next codon.

Transfer RNA molecules circulate in the cytoplasm.

One end of the tRNA molecule has a sequence of three nitrogenous bases. These bases are collectively called the anticodon.

Each anticodon codes for a particular amino acid that binds to the other end of the tRNA molecule.

Anticodons match up with mRNA codons based on compatible base pairing (A-U, G-C)

As the matches are made peptide bonds between the amino acids are formed and the nucleotide language has now been translated to an amino acid (protein) language






After Translation, protein synthesis may continue with processing occurring in two organelles, the endoplasmic reticulum, and the Golgi apparatus.





The endoplasmic reticulum (ER) is a network of tubes and sacs in the cytoplasm of a cell that plays many important roles in the cell's transportation system. The ER is continuous with the nuclear envelope at the pores to allow for the transport of substances in and out of the nucleus. Several chemical reaction occur inside of the ER.

Rough ER is studded with ribosomes.

Smooth ER does not have ribosomes


Newly formed proteins may be released from the ribosomes into the rough endoplasmic reticulum where some level of processing may occur


After processing, the newly formed protein may attach to the wall of the ER and get pinched off


The protein and surrounding ER derived membrane is called a transport vesicle.

The transfer vesicle may circulate in the cytoplasm until coming in contact with another organelle called the Golgi apparatus


The Golgi apparatus, is a cell organelle that appears as a series of stacked membranes. Its function is to help process and package proteins and lipid molecules, especially proteins destined to be exported from the cell.

Protein processing may continue in the Golgi apparatus. If a protein has quaternary structure, it is likely achieved in the Golgi apparatus.

The finished protein may embed in the Golgi wall and pinch off forming the secretory vesicle.

The secretory vesicle blends into the plasma membrane and releases the protein from the cell in a process known as exocytosis