MECHANISM OF PROTEIN SYNTHESIS
Protein synthesis occurs on ribosomes in the cytoplasm of a cell but is controlled by DNA located in the nucleus....
Fig. 8.16 Translation process of protein synthesis in prokaryotes.
The enthalpy of transfer of polar groups from the protein interior into water is positive at low temperatures and negative at higher temperatures . This is due to the polar groups creating their own ordered water, which generates a negative enthalpy change due to the increased molecular interactions. Balanced against this is the positive enthalpy change as the pre-existing water structure and the polar interactions within the protein both have to be broken. As water naturally has more structure at lower temperatures, the breakdown of the water structure makes a greater positive contribution to the overall enthalpy at lower temperatures.
In contrast, the enthalpy of transfer of non-polar groups from the protein interior into water is negative below about 25 °C and positive above . At lower temperatures, non-polar groups enhance pre-existing order such as the clathrate-related structure , discussed , generating enthalpy but this effect is lost with increasing temperature, as any pre-existing order is also lost. At higher temperatures, the creation of these clathrate structures requires an enthalpic input. Thus, there is an overall positive enthalpy of unfolding at higher temperatures. An equivalent but alternative way of describing this process is that at lower temperatures the clathrate-type structure optimizes its multiple molecular interactions whereas at higher temperatures such favorable structuring is no longer available.
The actual site of protein synthesis
Although the native state of a protein resides at a minimum on the potential energy surface, there is no reason to suppose that this structure is the global minimum free energy structure as its folding route is a guided, rather than random, process. It is clear that other structures with lower minima exist, such as those often irreversibly produced on denaturation, for example on heating followed by cooling, which utilizes other intermolecular interactions .
9-13)Withf-met-tRNA in the P-site and the next acylated-tRNA in the A-site ---- apeptidyl transferase forms a peptide bond between the two amino acids.F-metis cleaved from its tRNA and the tRNA leaves, leaving the P-site open.Thesecond tRNA “translocates” into the P-site from the A-site.Anew acylated tRNA moves into the empty A-site to base-pair with the codon inthat site.Thisprocess repeats over and over until a nonsense codon is presented in theA-site. TerminationReleasefactors cleave everything is the A-site is unoccupied for too long. Inpolycistronic mRNA, the next AUG is not too far away and the ribosomereinitiates to synthesize the next protein. What are polysomes? Read about Antibiotics and ribosomes on page 188.
information from DNA to the site of protein synthesis
Overall, protein stability depends on the balance between these enthalpic and entropic changes. For globular proteins, the ΔG of unfolding has a maximum 10-30 °C, decreasing both colder and hotter through zero with the thermodynamic consequences of both cold and heat denaturation. The hydration of the internal non-polar groups is mainly responsible for cold denaturation as their energy of hydration is greatest when cold. Thus, it is the increased natural structuring of water at lower temperatures that causes cold destabilization of proteins in solution (that is, the entropic cost of denaturation, due to the structuring of the water molecules around the exposed groups, is reduced) . An equivalent alternative view is that the increase as the temperature is raised from a low value, such that the extended polypeptide chain, present at very low temperatures, folds up to produce an active globular protein so releasing water molecules to the bulk environment.
Although indicated as such in the cartoons, there is no one 'minimum' structure but a collection of substates with small energetic differences. Jumps between these substates, eased by hydration, allows and determines the flexibility that the protein needs for its biological actions.
09/03/2015 · Protein synthesis is one of the most ..
where the actual the process of protein synthesis take ..
The first part of the process of protein synthesis is transcription - the creation of RNA based on the DNA template....
MECHANISM OF PROTEIN SYNTHESIS | Biology …
Protein synthesis or translation has an observed fidelity of 1 error in 10 3 ..
MECHANISM OF PROTEIN SYNTHESIS
05/05/2010 · Much of what is currently understood about eukaryotic protein synthesis represents ..
site of protein synthesis smooth ER ..
5. After initiation of the translation process, elongation process for the formation of dipeptide and ultimately the polypeptide chain is started by the attachment of AA2-tRNAAA2 (amino acyl tRNA or second amino acid attached with its specific tRNA) at its respective codon at the empty A-site with the help of the elongation factors EFTu (temperature unstable elongation factor) and EFTs (temperature stable elongation factor). This process also requires GTP. (In eukaryotes the elongation factors eEF1 and eEF2 are involved in the elongation process).
The actual site of protein synthesis is ..
Fig 8.14 Initiation of translation in eukaryotes.
4. The ribosomes have two sites, the A-site (amino acyl site) for the location of new amino acyl-tRNA (except for the fmet-tRNAfmet) and a P-site (peptidyl site) for locating the tRNA attached with newly synthesizing amino acid chain (di and polypeptide). The fmet-tRNAfmet after binding withIF2, is located on the initiation codon AUG at the P-site of the 30S subunit of ribosome which requires energy in the form of GTP. The role of IF1 is not
known. (In eukaryotes more initiation factors i.e., eIF1 to e1F6, are involved in nitiation).
carry ribosomes to the site of protein synthesis c
7. Thereafter, the naked tRNA at the P-site is removed with the help of the elongation factor EFG and the energy GTP as the ribosome moves by 3 nucleotides along the mRNA in 5’→ 3′ direction. Now, the P-site carries the fmet-AA2-tRNAAA2 (tRNA attached with a dipeptide).
actual synthesis of a polypeptide, ..
The process of synthesis of proteins from mRNA (translation of language of nucleic acids into the language of proteins) is called translation. There are 20 different types of amino acids, which constitute various proteins, and these amino acids themselves cannot recognize their respective codons in the mRNA. Different amino acids are carried by their specific tRNA molecules at the
site of protein synthesis (mRNA). There are about 55 types of tRNA molecules available in the cytoplasm, so that one amino acid may have more than one tRNAs.
15/01/2018 · Protein Synthesis Within the nuclei of ..
In eukaryotes, the termination sites in DNA are present far away from the corresponding actual 3′ end of mRNA, thus, to produce HnRNA (heterogeneous nuclear RNA). The 3′ end of the mRNA is generated after the processing of HnRNA by snurp (small nuclear RNA-protein complex). In addition to these extra nucleotides at 3′ end, the HnRNA may also contain extra nucleotide sequences at the 5′ end and at the internal positions. These extra nucleotide sequences at internal positions are called introns, whereas, the nucleotide sequences in between the introns
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