Central Dogma Study Notes PDF

Central Dogma Pre-learning video 1: DNA Dr. Rhea Hurnik BMS100 Plan • Pre-learning • 1) DNA, Chromosomes, & genes • 2) RNA Nucleic acid • Which biomolecule is the basis for nucleic acid? • Types: ▪ 1) DNA: deoxyribonucleic acid • forms the inherited genetic material inside our cells. ▪ Segment...

Central Dogma Pre-learning video 1: DNA Dr. Rhea Hurnik BMS100 Plan • Pre-learning • 1) DNA, Chromosomes, & genes • 2) RNA Nucleic acid • Which biomolecule is the basis for nucleic acid? • Types: ▪ 1) DNA: deoxyribonucleic acid • forms the inherited genetic material inside our cells. ▪ Segments of this DNA, called genes, code for protein & determine our physical traits ▪ 2) RNA: ribonucleic acid Central Dogma • DNA does not direct protein synthesis itself, but uses RNA as an intermediate: DNA Structure - nucleotides • Review: What are the 3 components of a nucleotide 2 types of nitrogenous bases: • Purines – double ring base • Which of the 4 bases are purines? • Pyrimidines – single ring base • Which of the 4 bases are pyrimidines? DNA structure – Double helix • The 3D structure of DNA is a double helix: ▪ The sugar-phosphate backbone forms a right-handed double helix to maximize efficiency of the base-pairing FYI - 1 complete turn for every 10 base pairs. DNA structure – base pair bonding • The 3D structure of DNA is a double helix: ▪ The two DNA strands are held together by H-bonds between bases • A pairs with T • G pairs with C DNA Structure – Thinking questions Why does A always pair with T & G always pair with C? Hint: try determining H-bonds that would form between A and C or G and T. Chargaff’s rule states that the number of purines must equal the number of pyrimidines. ▪ Why is this necessary to maintain the DNA double helix? • Hint: how would the shape of the DNA helix change with a purine-purine interaction vs a pyrimidine-pyrimidine interaction DNA Structure – Double helix cont. What forces are needed to stabilize the DNA double helix? 1. H-bonds between complementary base pairs 2. Sugar phosphate backbone 3. Base stacking DNA Structure – Phosphodiester bond 5’ end of chain • Nucleotides are joined together along the sugar phosphate backbone ▪ Phosphodiester bond Base H Base H Phosphodiest er bond Base H 3’ end of chain DNA Structure – Phosphodiester bond cont. 5’ end of chain • Consider the negative charge between phosphate groups within the sugar phosphate backbone ▪ Wouldn’t these adjacent negative charges repel one another & destabilize the helix? • Yes! • Positively charged magnesium ions help stabilize these negative charges Base H Base Mg2+ H Base H 3’ end of chain DNA Structure – Double helix cont. • What forces are needed to stabilize the DNA double helix? ▪ 1. H-bonds between complementary base pairs ▪ 2. Sugar phosphate backbone ▪ 3. Base stacking • Bases stack parallel to each other, ▪ This expels water (hydrophobic effects) Check your knowledge Which of the following bonds contribute to the stability of the DNA helix? Select all that apply A) Phosphodiester bond B) H-bonds C) Hydrophobic interactions D) Ionic interactions DNA Condensation - Nucleosomes • Nucleosomes are the structural unit for packaging DNA • Nucleosomes are composed of: ▪ 147 base pairs wrapped around a histone core • Octamer of H2A, H2B, H3 and H4 ▪ H1 linker protein DNA Condensation Chromatin Chromatin: complex of DNA + tightly bound protein ▪ It can be found either as densely packed heterochromatin or dispersed Euchromatin • Which form would be found when the cell is transcriptionally active? DNA Condensation Chromosomes • In its most condensed form, DNA is packaged into chromosomes. • Most humans cells have 23 pairs of chromosomes (46 total) ▪ 1 copy of each chromosomes come from each parent (2n; diploid) • The maternal and paternal chromosome pair are called homologous chromosomes (aka homologs) DNA Condensation Chromosomes • Autosomal chromosomes ▪ Chromosomes 1-22 ▪ Form homologous pairs • Sex chromosomes: determine biologic sex ▪ Non-homologous ▪ Female: • two X chromosomes ▪ Male: •1X,1Y Human male karyotype Genes • Chromosomes carry genes – the functional units of heredity ▪ Gene: segment of DNA containing the instructions for making a particular protein Genes • Exon = coding sequence of a gene • Intron = non-coding sequences of a gene ▪ Removed via splicing after transcription Non-coding DNA • 98.5% of the human genome does not encode protein ▪ A large majority of this non-coding DNA regulates gene expression. For example: • Promotor & enhancer regions – bind transcription factors • Binding sites for factors than organize chromatin structures • Non-coding regulatory RNA – eg. microRNA • Mobile genetic elements (“transposons”) ▪ Not well understood. Implicated in gene regulation & chromatin organization Check your knowledge What is the name of the non-coding sequence removed during splicing? A) Intron B) Promotor C) Exon D) heterochromatin 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