BMS100 Central Dogma Pre-learning Video 1: DNA PDF

Central Dogma Pre-learning video 1: DNA Dr. Rhea Hurnik BMS100 Plan Pre-learning 1) DNA, Chromosomes, & genes 2) RNA In-class: Transcription Translation Nucleic acid • Which biomolecule is the basis for nucleic acid? • Types: § 1) DNA: deoxyribonucleic acid • forms the inherited genetic mater...

Central Dogma Pre-learning video 1: DNA Dr. Rhea Hurnik BMS100 Plan Pre-learning 1) DNA, Chromosomes, & genes 2) RNA In-class: Transcription Translation 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 righthanded 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 pyrimidinepyrimidine 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 § More on next slide • 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 Phosphodiester 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 it’s 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) § Which cell types in the human body are haploid (n), meaning they only contain 1 copy of each chromosome? 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 = noncoding 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 The end! 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/bysa/4.0>, via Wikimedia Commons. 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