Central Dogma RNA Study Notes PDF

Central Dogma Pre-learning video 2: RNA Dr. Rhea Hurnik BMS100 Template strand • Like DNA, RNA is a polymer made of nucleotides linked by a phosphodiester bond. • RNA differs from DNA chemically in 2 main ways: ▪ 1) Ribose sugar vs deoxyribose sugar ▪ 2) Uracil (U) base rather than thymine (T) •...

Central Dogma Pre-learning video 2: RNA Dr. Rhea Hurnik BMS100 Template strand • Like DNA, RNA is a polymer made of nucleotides linked by a phosphodiester bond. • RNA differs from DNA chemically in 2 main ways: ▪ 1) Ribose sugar vs deoxyribose sugar ▪ 2) Uracil (U) base rather than thymine (T) • Still contains adenine, guanine, and cytosine RNA • Structurally RNA and DNA are also quite different ▪ DNA always occurs in a double-stranded helix ▪ RNA is single-stranded • Therefore can fold up into various shapes Types of RNA - mRNA • DNA is transcribed into RNA to serve as a template for protein translation ▪ In this case the RNA transcript is called messenger RNA (mRNA) • Initially it is termed pre-mRNA. • Pre-mRNA then undergoes processing into mature mRNA ▪ This is discussed further in class Types of RNA continued • Some sequences of DNA are transcribed into RNA than does not get translated into proteins ▪ This is called non-coding RNA ▪ Non-coding RNA serve as enzymatic, structural, and regulatory components of a wide variety of processes in the cell Non-coding RNA - snRNA • Small nuclear RNA (snRNA) functions in the spliceosome ▪ Preview: spliceosomes are needed to remove introns from pre-mRNA – aka splicing • snRNA associated with proteins subunits to form small nuclear ribonucleoproteins (snRNPs), which form the core of the spliceosome. Non-coding RNA - rRNA • Ribosomal RNA (rRNA) ▪ Needed for the basic structure of ribosome complex ▪ Involved in catalysis of the peptide bond between amino acids Check your knowledge Which of the following RNA molecules directly codes for proteins? A) mRNA B) tRNA C) rRNA D) snRNA Non-coding RNA - tRNA • Transfer RNA (tRNA) are needed in translation to carry the correct amino acid to the growing polypeptide chain • tRNA folds into a unique cloverleaf shape Non-coding RNA - tRNA • Two particular regions of the tRNA are particularly important to protein translation ▪ Anticodon: • 3 consecutive nucleotides that pairs with the complementary codon in an mRNA molecule ▪ Amino acid binding site: • Short single-stranded region at the 3’ end of the tRNA molecule • Binds the amino acid that corresponds to the anticodon on the tRNA Wobble Hypothesis • Despite 64 possible combinations of nucleotides in into a 3 nucleotide codon, there are only 20 amino acids ▪ This demonstrates the redundancy of the genetic code ▪ This implies that either: • There is more than 1 possible tRNA for many of the amino acids OR • Some tRNA molecule can base-pair with more than one codon ▪ Both are true! Wobble Hypothesis • Some tRNA are built to only require accurate base-pairing of only the first two positions of the codon & can tolerate mismatch (aka wobble) in the third position ▪ This explains why so many of the alternative codons for an amino acid differ only in their third nucleotide. Non-coding RNA - other • miRNA (micro RNA) ▪ Regulate gene expression via post-transcriptional silencing • Block/prevent translation of specific mRNAs & promote their degradation • siRNA (Small interfering RNA) ▪ Reduce gene expression • Direct degradation of specific mRNA • lncRNA (long non-coding RNA) ▪ Regulate gene expression • Can increase or decrease transcription ▪ Involved in X-chromosome inactivation Types of RNA - summary Types of RNA Name Function mRNA Messenger RNA Codes for proteins rRNA Ribosomal RNA Important constituents of ribosomes. Catalyzes protein synthesis tRNA Transfer RNA Adaptor between mRNA and amino acids snRNA Small nuclear RNA Splicing of pre-mRNA miRNA Micro RNA Regulate gene expression: block translation of specific mRNA & promote its degradation siRNA Small interfering RNA Regulate gene expression: direct specific mRNA degradation lncRNA Long non-coding RNA Regulate gene expression: can increase or decrease transcription Check your knowledge Which of the following RNA molecules are involved in gene regulation A) mRNA, tRNA, siRNA B) tRNA, rRNA, miRNA C) siRNA, miRNA, lncRNA D) snRNA, lncRNA, miRNA References • Abali, Emine E; Cline, Susan D; Franklin, David S; Viselli, Susan M. Lippincott Illustrated Reviews: Biochemistry (Lippincott Illustrated Reviews Series) (p. 105). Wolters Kluwer Health • Boron, W. and Boulpaep, E. Medical Physiology (3rd ed). Elsevier • Alberts et al. Molecular Biology of the Cell. Garland Science. • Betts et al. Anatomy and Physiology (2ed). OpenStax • Images: ▪ Kcneuman, CC BY-SA 4.0 <https://creativecommons.org/licenses/by-sa/4.0>, via Wikimedia Commons. Retrieved from: https://upload.wikimedia.org/wikipedia/commons/7/7e/Topo logical_ramifications_of_DNA_replication_and_transcription.j pg