ucleic Acids DA RA PRTEIS 1 The book of you 2 ucleic Acids Function: genetic material stores information genes blueprint for building proteins DA DA RA proteins transfers information blueprint for new cells blueprint for next generation proteins 3
4 G T A A C C T C A A G G T 5 6
ucleic Acids Examples: RA (ribonucleic acid) single helix A-U C-G DA (deoxyribonucleic acid) double helix A-T C-G Structure: monomers = nucleotides RA DA 7 ucleotides 3 parts nitrogen base (C- ring) pentose sugar (5C) ribose in RA deoxyribose in DA phosphate (P 4 ) group T A C G 8 Types of nucleotides 2 types of nucleotides different nitrogen bases purines double ring base adenine (A) guanine (G) pyrimidines single ring base cytosine (C) thymine (T) uracil (U) Purine = AG Pure silver! 9
H H CH 3 Sugar H A with T Adenine (A) Thymine (T) Sugar H H H C with G Sugar H Sugar Figure 16.8 H Guanine (G) Cytosine (C) 10 Pairing of nucleotides ucleotides bond between DA strands Hydrogen bonds purine :: pyrimidine A :: T 2 H bonds G :: C 3 H bonds H bonds? Why is this important? 11 Scientific History of DA http://www.dnai.org/timeline/ March to understanding that DA is the genetic material Friedrich Miescher (1869) discovery of nuclein (DA) in cell nucleus T.H. Morgan (1908) genes are on chromosomes Frederick Griffith (1928) a transforming factor can change phenotype Erwin Chargaff (1947) Chargaff rules: A = T, C = G Hershey & Chase (1952) confirmation that DA is genetic material Watson & Crick (1953) determined double helix structure of DA 12
Discovery of uclein Friedrich Miescher working with human leukocytes (white blood cells) isolated nuclei from pus discovered phosphorous rich macromolecule named nuclein 1869 13 Genes are on chromosomes 1908 Thomas Morgan s conclusions genes are on chromosomes but is it the protein or the DA of the chromosomes that are the genes? initially proteins were thought to be genetic material Why? 14 The Transforming Principle 1928 Frederick Griffith Streptococcus pneumonia bacteria was working to find cure for pneumonia harmless live bacteria ( rough ) mixed with heat-killed pathogenic bacteria ( smooth ) causes fatal disease in mice a substance passed from dead bacteria to live bacteria to change their phenotype Transforming Principle 15
Transformation 16 The Transforming Principle live pathogenic strain of bacteria live non-pathogenic strain of bacteria heat-killed pathogenic bacteria mix heat-killed pathogenic & non-pathogenic bacteria A. B. C. D. mice die mice live mice live mice die Transformation = change in phenotype something in heat-killed bacteria could still transmit disease-causing properties 17 Confirmation of DA 1952 Why use Sulfur vs. Phosphorus? Hershey & Chase classic blender experiment worked with bacteriophage viruses that infect bacteria grew phage viruses in 2 media, radioactively labeled with either 35 S in their proteins 32 P in their DA infected bacteria with labeled phages 18
19 Hershey & Chase Protein coat labeled with 35 S T2 bacteriophages are labeled with radioactive isotopes S vs. P DA labeled with 32 P Which radioactive marker is found inside the cell? bacteriophages infect bacterial cells Which molecule carries viral genetic info? bacterial cells are agitated to remove viral protein coats 35 S radioactivity found in the medium 32 P radioactivity found in the bacterial cells 20 Blender experiment Radioactive phage & bacteria in blender 35 S phage radioactive proteins stayed in fluid supernatant therefore viral protein did T enter bacteria 32 P phage radioactive DA stayed in bacterial pellet therefore viral DA did enter bacteria Confirmed DA is transforming factor 21
1952 Hershey & Chase Martha Chase Alfred Hershey 22 1947 Chargaff DA composition: Chargaff s rules varies from species to species all 4 bases not in equal quantity bases present in characteristic ratio humans: A = 30.9% T = 29.4% G = 19.9% C = 19.8% s Rule T A = G C = That s interesting! What do you notice? 23 1953 Structure of DA developed double helix model of DA Watson & Crick other leading scientists working on question: Rosalind Franklin Maurice Wilkins Linus Pauling Franklin Wilkins Pauling 24
Rosalind Franklin (1920-1958) 25 Watson and Crick 1953 article in ature Watson Crick 26 Watson and Crick 27
DA replication It has not escaped our notice that the specific pairing we have postulated immediately suggests a possible copying mechanism for the genetic material. James Watson Francis Crick 1953 28 When does a cell copy DA? When does DA have to be copied? To make new cells grow, repair, replace mitosis reproduction meiosis 29 But how is DA copied? Replication of DA base pairing suggests that it will allow each side to serve as a template for a new strand It has not escaped our notice that the specific pairing we have postulated immediately suggests a possible copying mechanism for the genetic material. Watson & Crick 30
Directionality of DA You need to number the carbons! it matters! P 4 nucleotide base CH 2 4ʹ ribose 1ʹ H 2ʹ 31 The DA backbone Putting the DA backbone together refer to the and ends of the DA the last trailing carbon P 4 CH 2 4ʹ C P CH 2 4ʹ 2ʹ base 1ʹ base 1ʹ H 2ʹ 32 Anti-parallel strands ucleotides in DA backbone are bonded from phosphate to sugar between & carbons DA molecule has direction complementary strand runs in opposite direction 33
Bonding in DA hydrogen bonds covalent bonds.strong or weak bonds? How do the bonds fit the mechanism for copying DA? 34 DA Replication Large team of enzymes coordinates replication 35 DA replication 36
Replication: 1st step Unwind DA helicase enzyme unwinds part of DA helix stabilized by single-stranded binding proteins helicase single-stranded binding proteins replication fork 37 Replication: 2nd step DA Polymerase III Build daughter DA strand add new complementary bases Primase creates a start region of RA bases DA polymerase III adds new bases according to the pairing rules Must add on to 3 end of growing chain. (built in 5 to 3 direction) 38 Leading & Lagging strands Limits of DA polymerase III can only build onto end of an existing DA strand kazaki fragments ligase Lagging strand growing replication fork Lagging strand kazaki fragments joined by ligase spot welder enzyme Leading strand DA polymerase III Leading strand continuous synthesis 39
Starting DA synthesis: RA primers Limits of DA polymerase III can only build onto end of an existing DA strand growing replication fork DA polymerase III primase RA RA primer built by primase serves as starter sequence for DA polymerase III 40 Replacing RA primers with DA DA polymerase I removes sections of RA primer and replaces with DA nucleotides DA polymerase I ligase growing replication fork RA But DA polymerase I still can only build onto end of an existing DA strand 41 DA replication ucleotides can only be added to 3 end helicase unwinds and binding proteins hold apart. primase creates a primer for polymerase to start. leading strand replicated in the direction of the replication fork can be copied continuously lagging strand replicated in direction away from replication fork therefore it is copied in kazaki fragments ligase enzyme connects fragments DA polymerase I replaces RA primers with DA bases 42
DA replication 43 Replication Review DA polymerase I DA polymerase III lagging strand kazaki primase fragments 5 ligase 3 5 SSB 3 3 helicase 5 5 3 leading strand direction of replication DA polymerase III SSB = single-stranded binding proteins 44 G...T...C...A! 45
Editing & proofreading DA 1000 bases/second = lots of typos! uclease, DA polymerase I, & Ligase proofreads & corrects typos repairs mismatched bases removes abnormal bases repairs damage throughout life reduces error rate from 1 in 10,000 to 1 in 100 million bases 46