what is the correct order of molecules involved in protein synthesis from beginning to end?

6.4: Protein Synthesis

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The Central Dogma of Biological science

Your DNA, or deoxyribonucleic acid, contains the genes that determine who you lot are. How can this organic molecule control your characteristics? Dna contains instructions for all the proteins your torso makes. Proteins, in turn, determine the structure and function of all your cells. What determines a poly peptide'southward structure? It begins with the sequence of amino acids that make up the protein. Instructions for making proteins with the correct sequence of amino acids are encoded in Deoxyribonucleic acid.

Figure \(\PageIndex{1}\): Transcription and translation (Protein synthesis) in a jail cell.

Dna is found in chromosomes. In eukaryotic cells, chromosomes always remain in the nucleus, but proteins are made at ribosomes in the cytoplasm or on the rough endoplasmic reticulum (RER). How exercise the instructions in Deoxyribonucleic acid become to the site of protein synthesis outside the nucleus? Some other type of nucleic acid is responsible. This nucleic acid is RNA or ribonucleic acid. RNA is a small molecule that can squeeze through pores in the nuclear membrane. It carries the data from DNA in the nucleus to a ribosome in the cytoplasm so helps gather the protein. In short:

Deoxyribonucleic acid → RNA → Protein

Discovering this sequence of events was a major milestone in molecular biology. It is called the central dogma of biological science. The 2 processes involved in the central dogma are transcription and translation.

Figure \(\PageIndex{2}\): An overview of transcription and translation. The top panel shows a gene. A factor is composed of the open reading frame (aka coding sequence) that is flanked by regulatory sequences. At the beginning of the factor, the regulatory sequence contains a promoter where RNA polymerase attaches and starts transcription. At the end of the open reading frame, the regulatory sequence contains a terminator (not shown.)The eye panel shows a pre mRNA which is modified by excising introns and keeping exons. This is called mail service transcription modification. A mature mRNA contains a 5' cap and poly-A tail. The bottom panel shows a synthesis of protein via translation.

Transcription

Transcription is the get-go office of the fundamental dogma of molecular biology: Deoxyribonucleic acid → RNA. Information technology is the transfer of genetic instructions in Deoxyribonucleic acid to mRNA. Transcription happens in the nucleus of the cell. During transcription, a strand of mRNA is made that is complementary to a strand of Dna called a factor. A cistron tin can easily be identified from the DNA sequence. A gene contains the basic three regions, promoter, coding sequence (reading frame), and terminator. There are more than parts of a gene which are illustrated in Figure \(\PageIndex{three}\).

Figure \(\PageIndex{3}\): The major components of a gene. ane. promoter, ii. transcription initiation, three. 5' upstream untranslated region, 4. translation start codon site, 5. protein-coding sequence, six. translation stop codon region, seven. three' downstream untranslated region, and viii. terminator.

Steps of Transcription

Transcription takes place in 3 steps, called initiation, elongation, and termination. The steps are illustrated in Figure \(\PageIndex{4}\).

1. Initiation is the commencement of transcription. Information technology occurs when the enzyme RNA polymerase binds to a region of a gene called the promoter. This signals the Deoxyribonucleic acid to unwind so the enzyme can "read" the bases in one of the DNA strands. The enzyme is ready to make a strand of mRNA with a complementary sequence of bases. The promoter is not role of the resulting mRNA
2. Elongation is the addition of nucleotides to the mRNA strand.
3. Termination is the ending of transcription. As RNA polymerase transcribes the terminator, it detaches from Deoxyribonucleic acid. The mRNA strand is complete afterwards this pace.

   

   Figure \(\PageIndex{4}\): Transcription occurs in the three steps - initiation, elongation, and termination

Processing mRNA

In eukaryotes, the new mRNA is not yet ready for translation. At this stage, it is called pre-mRNA, and information technology must go through more processing earlier it leaves the nucleus as mature mRNA. The processing may include the addition of a v' cap, splicing, editing, and 3' polyadenylation (poly-A) tail. These processes modify the mRNA in various means. Such modifications allow a single gene to exist used to brand more than than i protein. See Figure \(\PageIndex{5}\) as yous read below:

• 5' cap protects mRNA in the cytoplasm and helps in the attachment of mRNA with the ribosome for translation.
• Splicing removes introns from the poly peptide-coding sequence of mRNA. Introns are regions that do non code for the protein. The remaining mRNA consists merely of regions chosen exons that do code for the protein.
• Editing changes some of the nucleotides in mRNA. For example, a human being poly peptide called APOB, which helps transport lipids in the blood, has 2 dissimilar forms because of editing. One form is smaller than the other because editing adds an earlier finish signal in mRNA.
• Polyadenylation adds a "tail" to the mRNA. The tail consists of a cord of Equally (adenine bases). It signals the end of mRNA. Information technology is as well involved in exporting mRNA from the nucleus, and it protects mRNA from enzymes that might break it downwardly.

Figure \(\PageIndex{five}\): Splicing removes introns from mRNA. Mature mRNA is translated to poly peptide.

Translation

The translation is the second function of the fundamental dogma of molecular biological science: RNA --> Protein. Information technology is the procedure in which the genetic code in mRNA is read to make a protein. The translation is illustrated in Figure \(\PageIndex{6}\). After mRNA leaves the nucleus, it moves to a ribosome, which consists of rRNA and proteins. Translation happens on the ribosomes floating in the cytosol, or on the ribosomes attached to the crude endoplasmic reticulum. The ribosome reads the sequence of codons in mRNA, and molecules of tRNA bring amino acids to the ribosome in the correct sequence.

To understand the part of tRNA, y'all need to know more about its structure. Each tRNA molecule has an anticodon for the amino acid it carries. An anticodon is complementary to the codon for an amino acrid. For example, the amino acrid lysine has the codon AAG, and then the anticodon is UUC. Therefore, lysine would be carried by a tRNA molecule with the anticodon UUC. Wherever the codon AAG appears in mRNA, a UUC anticodon of tRNA temporarily binds. While bound to mRNA, tRNA gives up its amino acid. With the help of rRNA, bonds form between the amino acids as they are brought 1 by one to the ribosome, creating a polypeptide concatenation. The concatenation of amino acids keeps growing until a stop codon is reached.

Ribosomes, which are simply fabricated out of rRNA (ribosomal RNA) and poly peptide, take been classified as ribozymes because the rRNA has enzymatic activity. The rRNA is important for the peptidyl transferase activity that bonds amino acids. Ribosomes have two subunits of rRNA and protein. The large subunit has three active sites called E, P, and A sites. These sites are important in the catalytic activity of ribosomes.

Merely as with mRNA synthesis, poly peptide synthesis can be divided into three phases: initiation, elongation, and termination. In add-on to the mRNA template, many other molecules contribute to the process of translation, such as ribosomes, tRNAs, and various enzymatic factors

Translation Initiation: The small-scale subunit binds to a site upstream (on the 5' side) of the start of the mRNA. It proceeds to scan the mRNA in the 5'-->3' direction until it encounters the Commencement codon (AUG). The large subunit attaches and the initiator tRNA, which carries methionine (Met), binds to the P site on the ribosome.

Translation Elongation: The ribosome shifts one codon at a time, catalyzing each process that occurs in the three sites. With each stride, a charged tRNA enters the complex, the polypeptide becomes i amino acid longer, and an uncharged tRNA departs. The energy for each bail betwixt amino acids is derived from GTP, a molecule similar to ATP. Briefly, the ribosomes interact with other RNA molecules to brand chains of amino acids called polypeptide bondage, due to the peptide bond that forms between private amino acids. Inside the ribosome, three sites participate in the translation procedure, the A, P, and E sites. Amazingly, the East. coli translation appliance takes merely 0.05 seconds to add each amino acid, meaning that a 200-amino acid polypeptide could be translated in only 10 seconds.

Translation Termination: Termination of translation occurs when a stop codon (UAA, UAG, or UGA) is encountered (meet Effigy \(\PageIndex{7}\). When the ribosome encounters the stop codon, the growing polypeptide is released with the help of diverse releasing factors and the ribosome subunits dissociate and go out the mRNA. Afterwards many ribosomes have completed translation, the mRNA is degraded so the nucleotides tin can exist reused in another transcription reaction.

Figure \(\PageIndex{6}\): At the initiation phase, the initiator tRNA carrying methionine with its anticodon encounters the AUG beginning codon at the P-site of the ribosome. During elongation, the ribosome translocates in the 5' to 3' direction of the mRNA, at which point the amino acids of tRNA in P-site and amino acid of tRNA in the A-site of the large subunit bond to each other via a peptide bail. This repeated movement of the ribosome creates a long amino acid concatenation based on the codons in the mRNA. As the ribosome translocates, the tRNA leaves the ribosome through the E-site, while new tRNA enters the A-site in guild to continue elongating the amino acid chain.

Effigy \(\PageIndex{vii}\). Summary of protein translation. During initiation, both ribosomal subunits, mRNA, and initiator tRNA come together. The initiator anticodon of initiator tRNA hydrogen bond with the start codon. During elongation, tRNA brings amino acids one by one to add together to the polypeptide concatenation. During termination, the release factor recognizes end codon, all components dissociate, and the completed polypeptide is released.

What Happens Next?

After a polypeptide concatenation is synthesized, it may undergo additional processes. For instance, it may assume a folded third shape due to interactions amongst its amino acids. It may as well bind with other polypeptides or with dissimilar types of molecules, such every bit lipids or carbohydrates. Many proteins travel to the Golgi apparatus within the cytoplasm to be modified for the specific job they will do.

Summary of Primal Dogma

Effigy \(\PageIndex{eight}\): The fundamental dogma: Instructions on DNA are transcribed onto messenger RNA. Ribosomes are able to read the genetic information inscribed on a strand of messenger RNA and utilise this information to string amino acids together into a protein.

Review

1. Relate poly peptide synthesis and its two major phases to the central dogma of molecular biology.
2. Identify the steps of transcription, and summarize what happens during each pace.
3. Explain how mRNA is candy before it leaves the nucleus.
4. Describe what happens during the translation phase of poly peptide synthesis.
5. What additional processes may a polypeptide chain undergo subsequently it is synthesized?
6. Where does transcription take place in eukaryotes?
7. Where does translation have identify?
8. Which type of RNA (mRNA, rRNA, or tRNA) best fits each of the statements below? Choose only one type for each.
   1. Contains the codons
   2. Contains the anticodons
   3. Makes up the ribosome, along with proteins
9. If the DNA has a triplet lawmaking of CAG in one strand (the strand used equally a template for transcription),
   1. What is the complementary sequence on the other Deoxyribonucleic acid strand?
   2. What is the complementary sequence in the mRNA? What is this sequence called?
   3. @lid is the resulting sequence in the tRNA? What is this sequence called? What do you lot notice about this sequence compared to the original DNA triplet on the template strand?
10. The promoter is a region located in the:
    1. Deoxyribonucleic acid
    2. mRNA
    3. tRNA
    4. Both A and B
11. Truthful or False. Introns in mRNA demark to tRNA at the ribosome.
12. True or Faux. tRNAs tin be thought of equally the link between amino acids and codons in the mRNA.

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Source: https://bio.libretexts.org/Bookshelves/Human_Biology/Book:_Human_Biology_%28Wakim_and_Grewal%29/06:_DNA_and_Protein_Synthesis/6.04:_Protein_Synthesis

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