Chapter 1: Bio Primer

Transcription

1 Chapter 1: Bio Primer 1.1 Cell Structure; DNA; RNA; transcription; translation; proteins Prof. Yechiam Yemini (YY) Computer Science Department Columbia University COMS Overview Cell structure and mechanisms DNA; RNA; Transcription; Regulation Translation; protein; sequence & structure References: B. Alberts et al, Molecular Biology of The Cell, 4 th edition, Garland Science. R. Horton et al, Principles of Biochemistry, 3 rd Edition, Prentice Hall. J.D. Watson et al, Molecular Biology of The Gene, 5 th edition, Pearson Benjamin Cummings. NCBI Introductory overview: Animation sites: o o COMS

2 Organisms Are Made of Cells COMS Prokaryotes & Eukaryotes Have Different Cells Prokaryotes: single cell organisms without nucleus E.g., Bacteria: E-coli, H-Pylori Eukaryotes: single/multi-cell organisms with nucleus E.g., Yeast, plants, drosophila, humans Earth formed -4.5B yrs Prokaryotic bacteria -3.5B yrs Nucleated cells Multi-cellular eukaryotes -1.5B yrs -0.5B yrs Pearson; Benjamin COMS Cummings

3 Single cell; size 0.2-2µm Single or multi cell; cell size µm No nucleus Nucleus Structure One membrane at cell boundarymultiple membranes/compartments No organelles Organelles: mitochondria, Golgi, chloroplasts No cytoskeleton Cytoskeleton DNA Proteins Prokaryotes Eukaryotes Single circular DNA Two or more chromosomes Genes code proteins Genes have large non-coding regions (introns) 90% of DNA encodes proteins 95-97% non-coding DNA ~ base pairs ~ base pairs DNA is loosely organized DNA is tightly packed (chromatin + histones) Cell division through fission Mitosis 1-2k protein species 5-20k protein species ~10 6 proteins per cell ~10 9 proteins per cell COMS Cells Are Made of Macromolecules Small molecules: 3% Macromolecules: 26% Sugars Fatty Acids Amino Acids Nucleotides Polysaccharides Fats, Lipids, Membranes Proteins Nucleic Acids (DNA, RNA) Molecules % weight Water 70% Inorganic ions 1% Sugars 1% Amino acids 0.4% Nucleotides 0.4% Fatty acids 1% Other small molecules 0.2% Macromolecules (proteins, DNA, RNA, polysaccharides) 26% COMS

4 DNA Structure COMS The Central Dogma of Biology DNA Transcription RNA Translation Protein DNA stores hereditary information DNA is transcribed into RNA RNA is translated into proteins Proteins perform the key functions of cells COMS

5 DNA Consists of Sequences of Nucleotides DNA strands are sequences of nucleotides Backbone + Sugar Phosphate T T Base Nucleotide A C T T A C G C Bases: Adenine, Guanine, Thymine, Cytosine DNA is organized in complementary double strands Hydrogen bonds hybridize complementary pairs: A T, C G 5 -end Hydrogen bonds 3 -end T G A T T G A C T A A C G C C G COMS DNA Forms A Double Helix Helix full turn: 10.5bp Vertical hydrogen bonds support the structure Major and minor grooves provide access by proteins (e.g., transcription factors) COMS

6 DNA is 2m long; needs to fold into 10-6 m nucleus Chromatin beads fold around 4 histones Transcription needs to unpack the DNA to copy it DNA Is Tightly Packed COMS Sample Bioinformatics Challenges Sequencing the genome Discovering sequence similarity Discovering genes Analyzing evolutionary relationships Discovering other important structures Distinguishing exons from introns Regulatory structures: (promoters & transcription factors) Regions expressing micro RNA. COMS

7 Transcription COMS Schematics DNA Transcription mrna Translation Protein COMS

8 Overview A. Assembling transcription complex B. Transcribing DNA to mrna C. Removing introns COMS Animation The Transcription Process COMS

9 Transcription Details From PDB COMS Transcription Factors TFs bind to promoters regions and to RNA polymerases TFs regulate the rate of transcription (up/down) Regulation is yet to be well understood COMS

10 Transcription Is Regulated COMS Example The Lac Operon Lac consists of 3 genes; commonly transcribed Used by bacteria to transport and metabolize lactose camp activates transcription to initiate transport & metabolism of lactose COMS

11 Lac Activation Low-level sugar generate camp camp binds with CRP; adjusts its alpha helix to fit the DNA grooves and binds with it CRP-cAMP accelerates polymerase binding Lac Lac COMS Splicing The Introns COMS

12 From Genes To Networks Regulation is organized in networks Top: gene network regulating the body development of sea urchin Middle: a promoter region Bottom: interaction of two modules COMS Regulatory Networks Can Be Complex Genetic regulatory network controlling the development of the body plan of the sea urchin embryo Davidson et al., Science, 295(5560): COMS

13 Sample Bioinformatics Challenges Discovering and analyzing transcription factors Evolutionary analysis; motifs finding Discovering the structure of regulatory networks Analyzing the operations of regulatory networks Designing synthetic regulatory networks COMS Translation COMS

14 RNA Encodes Protein Sequences DNA Transcription RNA Translation Protein Proteins are sequences of amino-acids (AA) Translation uses RNA sequence as a template to construct AA sequence The coding problem: Code sequence of 20 amino-acids using 4 nucleic acids 2 nucleic acids can code only 4 2 =16 amino-acids Codon: sequence of 3 nucleic acids; encodes amino acid Translation: translate mrna codons to amino acids Start/Stop codons define an open reading frame(orf) Translation requires reading/identifying codons and forming a respective protein sequence COMS The Genetic Code U C A G U UUU Phenylalanine UUC Phe UUA Leucine UUG Leu UCU Serine UCC Ser UCA Ser UCG Ser UAU Tyrosine UAC Ty UAA Stop UAG Stop UGU Cysteine UGC Cys UGA Stop UGG Tryptophan C CUU Leu CUC Leu CUA Leu CUG Leu CCU Proline CCC Pro CCA Pro CCG Pro CAU Histidine CAC His CAA Glutamine CAG Gln CGU Arginine CGC Arg CGA Arg CGG Arg A AUU Isoleucine AUC Ile AUA Ile AUG Methionine ACU Threonine ACC Thr ACA Thr ACG Thr AAU Asparagine AAC Asn AAA Lysine AAG Lys AGU Serine AGC Ser AGA Arg AGG Arg G GUU Valine GUC Val GUA Val GUG Val GCU Alanine GCC Ala GCA Ala GCG Ala GAU Aspartate GAC Asp GAA Glutamate GAG Glu GGU Glycine GGC Gly GGA Gly GGG Gly COMS

15 trna Provides Translation Units Anticodon 3 CGA 5 binds to codon 5 GCU 3 of mrna It translates GCU to Alanine COMS Translation Basics Initiation: Ribosome binds to mrna; moves in 5 3 until it finds Start codon AUG Elongation Ribosome recruits trna to match next codon trna binds its AA into peptide bond with protein Ribosome releases trna and moves to next codob Termination Until a Stop codon is reached Release factor releases polypeptide from ribosome COMS

16 Animation Translation of RNA into proteins COMS Proteins Are Sequences of Amino Acids Proteins are constructed through peptide bonds Proteins are folded into complex conformations Proteins perform functions by binding Transcription factors and polymerase bind to DNA Enzymes bind to molecules to accelerate their reactions Globins bind to oxygen to transport it Antibodies bind to pathogens COMS

17 Example: Hemoglobin COMS Sickle-Cell Anemia: A Single Nucleotide Change Codon 6 in β-globin Sickle structure COMS

18 Evolution of β-globin (α-globin cluster is coded by chromosome 16 ) COMS The Evolution of α-globin Across Species COMS

19 Protein Structures COMS Protein Structure Is Of Central Importance Structure is found through complex crystallography X-ray diffraction; NMR The holy-grail: compute structure from sequence Ab-initio: compute structure directly from sequence Homology techniques: use similarity to known proteins Structure is conserved across wide variations Small number of fold families (α-helix, β-sheets ) There are rules (e.g., hydrophobic AA are packed inside) Nature folds proteins very fast So why is it so difficult to predict structure? COMS

20 SwissProt vs. PDB Statistics PDB ~30k structures COMS Proteins Interact Via Active Sites Protein interactions are defined by active sites E.g., antibody with pathogen E.g., drug design Proteins use geometry: ligands latch with holes Proteins use physics: electrical fields How can protein-protein interactions be computed? COMS

21 Sample Bioinformatics Challenges Analyzing protein sequence similarity Evolutionary conservation/changes Computing structure from sequences Analyzing structure homologies Analyzing protein-2-protein interactions Inferring function from structure COMS The Cell Cycle COMS

22 Cells Operate In Cycles G0 Phase cell is at rest G1 Phase (4hrs) Cell either progresses into synthesis or leaves cell cycle to differentiate S Phase (10hrs) DNA Synthesis Checkpoint determines integrity of DNA G2 Phase (4hrs) Cell prepares for Mitosis Checkpoint determines integrity of DNA DNA is repaired or cell dies (Apoptosis) Mitosis (2hrs) Chromosomes are separated Cell divides COMS The Cell Cycle is Regulated Transition among phases is controlled by a regulatory network Checkpoints are used to assure quality COMS

23 Evolution COMS Optimizing Functionality DNA is substantially conserved through evolution Evolution = mutation + selection Mutation = single nucleotide polymorphism (SNP); duplication of entire DNA segments mating; recombination Selection = optimize fitness of species Examples Metabolic nets learn to optimize energy budget (Alon 05) Functional similarity Sequence similarity COMS