Q&A: Components of Protein Biosynthesis

Protein biosynthesis (or protein synthesis) is a core biological process, occurring inside cells, balancing the loss of cellular proteins (via degradation or export) through the production of new proteins. Proteins perform a variety of critical functions as enzymes, structural proteins or hormones and therefore, are crucial biological components. Protein synthesis is a very similar process for both prokaryotes and eukaryotes but there are some distinct differences.

This article is for Medical Students & Professionals

This is a Question & Answer revision article designed for medical students and professionals preparing for the PLAB, MRCP or USMLE examinations. They are based on actual questions from these examinations. You may find more useful one of our many articles on Diseases & Conditions, Medical Syndromes, Health & Wellness or Home Remedies.

In this article:
Protein synthesis
MCQ: clinical scenario
MCQ: answer
MCQ: explanation

Protein synthesis

Protein synthesis can be divided broadly into two phases - transcription and translation. During transcription, a section of DNA encoding a protein, known as a gene, is converted into a template molecule called messenger RNA. This conversion is carried out by enzymes, known as RNA polymerases, in the nucleus of the cell. In eukaryotes, this messenger RNA (mRNA) is initially produced in a premature form (pre-mRNA) which undergoes post-transcriptional modifications to produce mature mRNA. The mature mRNA is exported from the nucleus via nuclear pores to the cytoplasm of the cell for translation to occur. During translation, the mRNA is read by ribosomes which use the nucleotide sequence of the mRNA to determine the sequence of amino acids. The ribosomes catalyse the formation of covalent peptide bonds between the encoded amino acids to form a polypeptide chain.

Following translation the polypeptide chain must fold to form a functional protein, for example, to function as an enzyme the polypeptide chain must fold correctly to produce a functional active site.

MCA: clinical scenario

Protein synthesis is the process whereby DNA encodes for the production of amino acids and proteins. In this process what is a unit of three nucleotides on the mRNA called?

a) ribozyme
b) antiribozyme
c) base-pair
d) codon
e) anticodon

MCQ: answer

The correct answer is D

MCQ: explanation

The coding mRNA sequence can be described as a unit of three nucleotides called a codon. The ribosome binds to the mRNA at the start codon (AUG) that is recognized only by the initiator tRNA. The ribosome proceeds to the elongation phase of protein synthesis. During this stage, complexes composed of an amino acid linked to tRNA, sequentially bind to the appropriate codon in mRNA by forming complementary base pairs with the tRNA anticodon. The ribosome moves from codon to codon along the mRNA.

Amino acids are added one by one, translated into polypeptidic sequences dictated by DNA and represented by mRNA. At the end, a release factor binds to the stop codon, terminating translation and releasing the complete polypeptide from the ribosome.

Reference(s)
1). Alberts, Bruce (2015). Molecular biology of the cell (Sixth ed.). Abingdon, UK: Garland Science, Taylor and Francis Group. ISBN 978-0815344643.
2). O'Connor, Clare (2010). Essentials of Cell Biology. NPG Education: Cambridge, MA. Retrieved 3 March 2020. Available online: https://www.nature.com/scitable/ebooks/essentials-of-cell-biology-14749010/
3). Wang, Yu-Chieh; Peterson, Suzanne E; Loring, Jeanne F (2013). "Protein post-translational modifications and regulation of pluripotency in human stem cells". Cell Research. 24 (2): 143–160. doi:10.1038/cr.2013.151. PMC 3915910. PMID 24217768. Available online: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3915910