Medical research

Normally harmless cell molecule triggers neuron death

A vital intermediate in normal cell metabolism is also, in the right context, a trigger for cell death, according to a new study from Wanli Liu and Yonghui Zhang of Tsinghua University, and Yong Zhang of Peking University ...

Medical research

New clues to how muscle wasting occurs in people with cancer

Muscle wasting, or the loss of muscle tissue, is a common problem for people with cancer, but the precise mechanisms have long eluded doctors and scientists. Now, a new study led by Penn State researchers gives new clues ...

Psychology & Psychiatry

Scientists unpack how the brain separates present from past dangers

A team of neuroscientists has identified processes the brain undergoes to distinguish real and present dangers from those linked to past experiences in mice. The findings, which appear in the journal Nature, have implications ...

Neuroscience

Discovery of a new key player in long-term memory

A McGill-led multi-institutional research team has discovered that during memory consolidation, there are at least two distinct processes taking place in two different brain networks—the excitatory and inhibitory networks. ...

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Protein biosynthesis

Protein synthesis is the process in which cells build proteins. The term is sometimes used to refer only to protein translation but more often it refers to a multi-step process, beginning with amino acid synthesis and transcription of nuclear DNA into messenger RNA which is then used as input to translation.

The cistron DNA is transcribed into a variety of RNA intermediates. The last version is used as a template in synthesis of a polypeptide chain. Proteins can often be synthesized directly from genes by translating mRNA. When a protein is harmful and needs to be available on short notice or in large quantities, a protein precursor is produced. A proprotein is an inactive protein containing one or more inhibitory peptides that can be activated when the inhibitory sequence is removed by proteolysis during posttranslational modification. A preprotein is a form that contains a signal sequence (an N-terminal signal peptide) that specifies its insertion into or through membranes; i.e., targets them for secretion. The signal peptide is cleaved off in the endoplasmic reticulum.. Preproproteins have both sequences (inhibitory and signal) still present.

For synthesis of protein, a succession of tRNA molecules charged with appropriate amino acids have to be brought together with an mRNA molecule and matched up by base-pairing through their anti-codons with each of its successive codons. The amino acids then have to be linked together to extend the growing protein chain, and the tRNAs, relieved of their burdens, have to be released. This whole complex of processes is carried out by a giant multimolecular machine, the ribosome, formed of two main chains of RNA, called ribosomal RNA (rRNA), and more than 50 different proteins. This molecular juggernaut latches onto the end of an mRNA molecule and then trundles along it, capturing loaded tRNA molecules and stitching together the amino acids they carry to form a new protein chain.

Protein biosynthesis, although very similar, is different for prokaryotes and eukaryotes.

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