Cech Discovered the First Catalytic RNA Molecule

 For many years after their discovery it was assumed that all enzymes were proteins. However, while examining the processing of ribosomal RNA (rRNA) molecules in the ciliated protozoan Tetrahymena in the early 1980s, Thomas Cech and his coworkers observed that processing of the 26S rRNA proceeded smoothly in vitro even in the total absence of protein. They subsequently traced the source of this splicing activity to a 413 bp catalytic segment of the RNA, which they termed a ribozyme —a discovery that earned Cech a Nobel Prize.

Several other ribozymes have since been discovered. The vast majority catalyze nucleophilic displacement reactions that target the phosphodiester bonds of the RNA backbone. In small self-cleaving RNAs, such as hammerhead or hepatitis delta virus RNA, the attacking nucleophile is water and the result is hydrolysis. For the large group I intron ribozymes, the attacking nucleophile is the 3′-hydroxyl of the terminal ribose of another segment of RNA and the result is a splicing reaction.

The Ribosome—The Ultimate Ribozyme

The ribosome was the first example of a “molecular machine” to be recognized. A massive complex comprised of scores of protein subunits and several large ribosomal RNA molecules, the ribosome performs the vitally important and highly com plex process of synthesizing long polypeptide chains following the instructions encoded in messenger RNA (mRNA) molecules. For many years, it was assumed that rRNAs played a passive, structural role, or perhaps assisted in the recognition of cognate mRNAs through a base pairing mechanism. It was thus somewhat surprising when it was discovered that rRNAs were both necessary and sufficient for catalyzing peptide synthesis.

The RNA World Hypothesis

The discovery of ribozymes has had a profound influence on evolutionary theory. For many years, scientists had hypothesized that the first biologic catalysts were formed when amino acids contained in the primordial soup coalesced to form simple proteins. With the realization that RNA could both carry information and catalyze chemical reactions, a new “RNA World” hypothesis emerged in which RNA constituted the first biologic macromolecule. Eventually, a more chemically stable oligonucleotide, DNA, superseded RNA for long-term information storage, while proteins, by virtue of their greater chemical functional group and conformational diversity dominated catalysis. If one assumes that some sort of RNA protein hybrid was formed as an intermediate in the transition from ribonucleotide to polypeptide catalysts, one needs to look no further than the ribosome to find the presumed missing link.

Why did not proteins take over all catalytic functions? Presumably, in the case of the ribosome the process was both too complex and too essential to permit much opportunity for possible competitors to gain a foothold. In the case of the small self-cleaving RNAs and self-splicing introns, they may represent one of the few cases in which RNA autocatalysis is more efficient than development of a new protein catalyst.

اخر الاخبار

اخبار العتبة العباسية المقدسة

قسم صناعة الشبابيك يواصل أعمال تصنيع بابٍ لحرم مرقد الإمامين الجوادين (عليهما السلام)

قسم العلاقات ينظّم برنامجًا ثقافيًّا لوفد من طلبة مجموعة العميد

قسم الشؤون الفكرية وجامعة العميد يصدران العدد 37 من مجلة تسليم المحكمة

متحف الكفيل يواصل أعمال تركيب عارضات مقتنيات متحف العتبة العسكرية المقدسة

المزيد

الآخبار الصحية

علاج طبيعي لمشكلات البشرة وحب الشباب

اكتشاف ارتباط عنصر شائع في نظامنا الغذائي بحصوات المرارة

كل ليلة.. 11 دقيقة إضافية من النوم لها مفعول السحر

علاج طبيعي يخفف أعراض سكري الحمل

المزيد

الآخبار التكنلوجية

قمر وردي ومذنب يلامس الشمس.. 8 ظواهر فلكية تزين السماء طوال شهر أبريل

تفسير حديث لتحيز التوحد بين الجنسين.. هل تمتلك الإناث "درعا جينيا" ضد المرض؟

الجلوس الذهني النشط.. مفتاح تقليل خطر الخرف لدى كبار السن

خسائر غير مسبوقة للجليد في أيسلندا وسواحل المحيط الهادئ خلال 2025

المزيد

مواضيع ذات صلة

The Catalytic Activity of Enzymes Facilitates Their Detection

Chymotrypsin & Fructose-2,6-Bisphosphatase Illustrate Covalent Catalysis

Iron Metabolism

Biochemistry and Biosynthesis of Adrenal Steroids and Testosterone Steroids

Enzymes Employ Multiple Mechanistic Strategies to Facilitate Catalysis

The Oxygen Dissociation Curves for Myoglobin & Hemoglobin Suit Their Physiologic Roles

Heme & Ferrous Iron Confer the Ability to Store & Transport Oxygen

Control of Heme Biosynthesis

Protein Folding

X-Ray Crystallography

Tertiary & Quaternary Structure of proteins

Proteomics & the Proteome