Protein biosynthesis, although very similar, is different for prokaryotes and eukaryotes. QUESTION 28 Which of the following is the correct sequence of events in protein synthesis a. 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. The following is the correct sequence of events. 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. 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. Ribosomes: The eukaryotic ribosome has two subunits: a 40S small subunit and a 60S large subunit. Preproproteins have both sequences (inhibitory and signal) still present.įor 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. Fundamentals Protein synthesis involves a complex interplay of many macromolecules. The signal peptide is cleaved off in the endoplasmic reticulum. 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. 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. When a protein is harmful and needs to be available on short notice or in large quantities, a protein precursor is produced. Proteins can often be synthesized directly from genes by translating mRNA. RNA is needed to help carry out the instructions in DNA. The last version is used as a template in synthesis of a polypeptide chain. Events in the order of synthesis of a protein: A small subunit binds to the mRNA The activated amino acid tRNA complex attaches the initiation codon on mRNA The large subunit attaches to the small subunit and the initiator tRNA fits in the P-site A tRNA matches its anticodon to the codon in the A- site A peptide bond forms. Key terms Structure of RNA DNA alone cannot account for the expression of genes. The cistron DNA is transcribed into a variety of RNA intermediates. 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. Protein synthesis is the process in which cells build proteins.
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