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Feb 18, 2008 · What is dehydration synthesis
Each amino acid has a carboxyl group and an amine group, and amino acids link to one another to form a chain by a dehydration reaction by joining the amine group of one amino acid to the carboxyl group of the next. Thus polypeptide chains have an end with an unbound carboxyl group, the C-terminus, and an end with an amine group, the N-terminus. Proteins are synthesized starting from the N-terminus and ending at the C-terminus.
Organic chemistry: “Amino acid and polypeptide synthesis”. Amino acid synthesis--Gabriel synthesis; synthesis. degradation. Polypeptide synthesis-- () and () amino-protecting groups; protection of the terminus via ester formation; DCC () -activating reagent. An example of calculating and charge at a specific pH for a long polypeptide
The synthesis of proteins requires ..
The N-terminal signal peptide is recognized by the signal recognition particle (SRP) and results in the targeting of the protein to the secretory pathway. In eukaryotic cells, these proteins are synthesized at the rough endoplasmic reticulum. In prokaryotic cells, the proteins are exported across the cell membrane. In chloroplasts, signal peptides target proteins to the thylakoids.
A peptide bond is a chemical bond formed between two molecules when the carboxyl group of one molecule reacts with the amino group of the other molecule, releasing a molecule of water (H2O). This is a dehydration synthesis reaction (also known as a condensation reaction), and usually occurs between amino acids. The resulting CO-NH bond is called a peptide bond, and the resulting molecule is an amide. The four-atom functional group -C(=O)NH- is called an amide group or (in the context of proteins) a peptide group. Polypeptides and proteins are chains of amino acids held together by peptide bonds, as is the backbone of PNA. Polyamides, such as nylons and aramids, are synthetic molecules (polymers) that possess peptide bonds.
(an example of dehydration synthesis reaction)
Plants are a rich source of cyclic peptides, with the vast majority of these molecules being produced via non-ribosomal biosynthetic pathways. In contrast, the cyclotides are gene-coded products generated via processing of a larger precursor protein (2). The gene for the first such precursor is Oak1 (Oldenlandia affinis kalata clone number 1), which was shown to be responsible for the synthesis of kalata B1 (7). Figure 2 illustrates the generic configuration of the precursor protein, which consist of an endoplasmic reticulum signal sequence, a non-conserved pro-region, a highly conserved region known as the N-terminal repeat (NTR), the mature cyclotide domain and finally a short hydrophobic C-terminal tail. The cyclotide domain may contain either one cyclotide sequence, as in the case of Oak1, or multiple copies separated by additional NTR sequences as seen for Oak2 and Oak4. In precursor proteins containing multiple cyclotide domains these can either be all identical sequences, as is the case for Oak4, or they can be different cyclotides as in Oak2 which contains sequences corresponding to kalata B3 and B6.
The remarkable stability of cyclotides means that they have an exciting range of potential applications centred on either their intrinsic biological activities or the possibility of using the CCK motif as a scaffold for stabilizing biologically active epitopes (16). Interest in these has recently intensified with the publications of a chemical methodology capable of synthetically producing cyclotides with high yields (17), and the amenability of the CCK framework to amino-acid substitutions (18). But for molecules to be useful in a therapeutic setting they require useful biopharmaceutical characteristics such as resistance to proteolysis and membrane permeability. A recent study on related cystine knot proteins as drug candidates showed that cystine knots do permeate well through rat small intestinal mucosa relative to non-cystine knot peptide drugs such as insulin and bacitracin (19). Furthermore, enzymatic digestion of cystine knot peptide drugs was associated with only a few proteases and it was suggested that this limitation may be overcome by mutating out particular cleavage sites. Thus, certain cystine knot proteins satisfy the basic criteria for drug delivery and represent exciting novel candidates as scaffolds for peptide drug delivery (19). The diverse range of intrinsic activities of cyclotides also continues to hold promise for a wide range of applications in the agricultural fields.
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or proteins via dehydration synthesis
The N-terminus is the first part of the protein that exits the ribosome during protein biosynthesis. It often contains sequences that act as targeting signals, basically intracellular zip codes, that allow for the protein to be delivered to its designated location within the cell. The targeting signal is usually cleaved off after successful targeting by a processing peptidase.
What is dehydration synthesis and hydrolysis? | Yahoo …
The amino acid sequences of signal peptides direct proteins (which are synthesized in the cytosol) to certain organelles such as the nucleus, mitochondrial matrix, endoplasmic reticulum, chloroplast, apoplast and peroxisome. Some signal peptides are cleaved from the protein by signal peptidase after the proteins are transported.
Synthesis of Biological Macromolecules | Boundless …
An endoplasmic reticulum signal peptide is the best characterised signal peptide. It exists at the amino terminal of a protein. The protein is guided to the ER by a signal-recognition particle, which moves between the ER and the cytoplasm. It binds to the signal peptide. The SRP binds to the signal peptide as soon as it is synthesised and extruded from the ribosome. This causes a pause in protein synthesis, most probably allowing the ribosome-SRP complex time to bind to the SRP receptor on the target ER membrane. The SRP protein is thought to be a regulatory GTP protein. Conformational changes may therefore lead to the SRP release. The protein may then be threaded through the ER membrane by a translocator pore.
Synthesis of Biological Macromolecules
Synthetic peptide nucleic acid oligomers have been used in recent years in molecular biology procedures, diagnostic assays and antisense therapies. Due to their higher binding strength it is not necessary to design long PNA oligomers for use in these roles, which usually require oligonucleotide probes of 20-25 bases. The main concern of the length of the PNA-oligomers is to guarantee the specificity. PNA oligomers also show greater specificity in binding to complementary DNAs, with a PNA/DNA base mismatch being more destabilizing than a similar mismatch in a DNA/DNA duplex. This binding strength and specificity also applies to PNA/RNA duplexes. PNAs are not easily recognized by either nucleases or proteases, making them resistant to enzyme degradation. PNAs are also stable over a wide pH range.
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