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 material inside ou...

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 , via Wikimedia Commons. Retrieved from: https://upload.wikimedia.org/wikipedia/commons/7/7e/Topological_ram ifications_of_DNA_replication_and_transcription.jpg