Fig. 8.16 Translation process of protein synthesis in prokaryotes.

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Protein biosynthesis - Wikipedia

The major milk proteins, including the caseins, ß-lactoglobulin and -lactalbumin, are synthesized in the mammary epithelial cells and are only produced by the mammary gland. The immunoglobulin and serum albumin in milk are not synthesized by the epithelial cells. Instead, they are absorbed from the blood (both serum albumin and the immunoglobulins). An exception to this is that a limited amount of immunoglobulin is synthesized by lymphocytes which reside in the mammary tissue (called plasma cells). These latter cells provide the mammary gland with local immunity.

Protein synthesis is the process whereby biological ..

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Molecules of tRNA are formed in the nucleus and migrate into the cytoplasm. There are twenty different types of tRNA, one for each type of amino acid. Each type of tRNA can grab one kind of amino acid molecule. Each tRNA has a three-base segment called an which is complementary to a codon on the mRNA. In protein synthesis, a tRNA molecule carrying an amino acid molecule becomes attached briefly to the mRNA at a codon complementary to its anticodon. Then a tRNA complementary to the adjacent codon attached on the mRNA. A peptide bond forms between the two amino acid molecules carried by the tRNAs. Amino acids are added one at a time to the growing chain as the mRNA strand is "read." This continues until a termination (stop) codon is encountered. After each peptide bond is formed, the tRNA is released to go and pick up a new amino acid in the cytoplasm. Determine the anticodon for each codon below. Write it in the space provided.

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i.RNA polymerase I (or A) found in nucleolus for the synthesis of rRNAs (28S and 18S).

ii.RNA polymerase II (or B) found in nucleoplasm for the synthesis of HnRNA (heterogeneous nuclear RNA) which, after processing gives rise to mRNA.

iii.RNA polymerase III (C) found in nucleoplasm for the synthesis of tRNA and 5S rRNA.

iv.Organeller RNA polymerase found in organelles, mitochondria and chloroplasts, (in photosynthetic organisms) and resembles the prokaryotic RNA polymerase.

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What Is The Purpose Of Protein Synthesis

+1 Frameshift at the RF2 recoding site. The AGG GGG in the mRNA interacts with the ribosomal RNA. The CUU at codon position 25 is a ‘slippery’ codon where the slippage of the reading frame occurs. UGACUA is a weak stop signal, which favours a frameshift into the +1 frame at the site, rather than efficient termination of protein synthesis. The amino acid sequence in the new frame is shown below.

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Protein synthesis termination is the process by which a completed polypeptide is released from the ribosome after the coding information within a messenger ribonucleic acid (mRNA) has been successfully translated.

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i.ρ-dependent Termination: In some prokaryotes, the termination of transcription is helped by a ρ (rho) protein that gets attached at the 5′ end of the newly synthesizing mRNA. The ρ then moves along the mRNA and induces the formation of hairpin loop near the 3′ end of mRNA due to the presence of inverted repeated sequences. This helps in the detachment of mRNA from the DNA (Fig. 8.9).

protein synthesis - from mRNA to protein - chemguide

The structural basis for TnaC-mediated translational stalling wasaddressed by obtaining a 5.8-Å cryo-EM map of the ribosome stalled byTnaC and high concentrations of tryptophan (Fig. 8). The cryo-EM datashows that the nascent chain adopts a distinct conformation in the exittunnel. We applied MDFF to obtain an atomic model of the entire ribosomeand the stalling nascent chain (Fig. 8F). The model allowed us to mapthe contacts between TnaC and the exit tunnel, as well as proposepossible communication pathways that would lead to inactivation of thecatalytic center of the ribosome (the so-called peptidyltransferasecenter, or PTC). One of the main findings was that two criticalribosomal residues at the PTC adopt conformations that are incompatiblewith cohabitation by release factors, which catalyze termination ofprotein synthesis.

Protein Synthesis/Translation ..

Similar to TnaC described above, the peptide SecM exists solely to stallthe ribosome synthesizing it. But unlike TnaC, which also requires thepresence of high levels of trytophan, SecM has an intrinsic stallingcapability. Stalling of the ribosome synthesizing SecM provides time fora downstream RNA helix on the same mRNA strand to unwind. Unwinding ofthis helix then allows for a new ribosome to bind and synthesize anew protein, SecA, a bacterial ATP-driven translocase that aids the passage ofnascent proteins across membranes in conjunction with SecY (see also ). When sufficient levels of SecA have been reached,SecA interacts with the SecM-stalled ribosome to pull on SecM, freeingit and allowing translation to resume (illustrated schematically inFig. 13). SecM, which serves no otherpurpose than to stall the ribosome, is released into the cell anddegraded.