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DNA→RNA → PROTEINS Chapters 16 & 17 http://faculty.uca.edu/~johnc/mbi1440.htm http://www.wappingersschools.org/RCK/staff/teacherhp/johnson/visualvocab/mRNA.gif Scientists originally thought PROTEINS had to be the genetic material 1928- GRIFFITH’s EXPERIMENT 12 A Images from: http://microvet.arizona.edu/Courses/vsc610/mic205/griffith.jpg 1943- EXPERIMENTS BY OSWALD AVERY, MACLYN McCARTY, & COLIN MACLEOD WITH LIPIDS, POLYSACCHARIDES, OR PROTEINS THERE’S NO TRANSFORMATION ONLY NUCLEIC ACIDS CHANGE THE BACTERIA SO . . . NUCLEIC ACIDS CARRY THE INFORMATION ! http://www.synapses.co.uk/genetics/dnastruc.html http://oceanworld.tamu.edu/resources/oceanography-book/Images/BacteriophageCartoon.jpg 1952-Alfred Hershey and Martha Chase Bacteriophages are viruses that infect bacteria Phages are made of DNA surrounded by a protein coat http://www.mun.ca/biology/scarr/Chase_&_Hershey_1953.jpg HERSHEY CHASE BLENDER EXPERIMENT http://www.mun.ca/biology/scarr/hersheychase-experiment.jpg ROSALIND FRANKLIN and MAURICE WILKINS Analyzed DNA with X-ray crystallography to try and determine structure of DNA 1953 - JAMES WATSON & FRANCIS CRICK used Rosalind Franklin’s X-ray crystallography images (PHOTO 51) to come up with alpha helix model for the structure of DNA http://en.wikipedia.org/wiki/Rosalind_Franklin http://www.time.com/time/time100/scientist/profile/watsoncrick.html DOUBLE HELIX Linus Pauling's Triple helix model http://www.biosciences.bham.ac.uk/labs/minchin/tutorials/lgdna.html Arrow from: http://www.harrythecat.com/graphics/b/arrow48d.gif STRUCTURE OF NUCLEIC ACIDS Built from NUCLEOTIDE SUBUNITS NITROGEN BASES CAN BE: ADENINE GUANINE CYTOSINE THYMINE URACIL Sugar can be DEOXYRIBOSE (DNA) RIBOSE (RNA) Image by: Riedell DNA has no URACIL RNA has no THYMINE PURINES (A & G) have 2 RINGS PYRIMIDINES (T, C, & U) have 1 RING http://student.ccbcmd.edu/courses/bio141/lecguide/unit6/genetics/DNA/DNA/fg4.html http://student.ccbcmd.edu/~gkaiser/biotutorials/dna/fg29.html Subunits come in as TRIPHOSPHATES Splitting of nucleotide triphosphates provides the energy to link the nucleotides See animation http://www.cat.cc.md.us/~gkaiser/biotutorials/energy/adpan.html DNA • DOUBLE STRANDED • Strands run ANTIPARALLEL • Backbone = sugars and phosphates • Rungs of ladder = nitrogen bases • Hydrogen bonds hold sides of ladder together http://staff.jccc.net/pdecell/proteinsynthesis/antiparralell.gif RNA • SINGLE STRANDED • Folds into 3D shape • Backbone = sugars and phosphates • Rungs of ladder = nitrogen bases http://tigger.uic.edu/classes/phys/phys461/phys450/ANJUM04/ 5’ and 3’ ENDS • 5’ and 3’ ends named for the CARBON Erwin Chargaff analyzed DNA from different organisms and found CHARGAFF’s RULES: A = T G = C Now know its because: A always bonds with T G always bonds with C A Purine always bonds to a Pyrimidine SemiConservative Conservative Dispersive MESELSON & STAHL Images from: http://instruct1.cit.cornell.edu/courses/biog105/pages/demos/106/unit01/6.dnareplicationmodels.html Grew bacteria for many generations in radioactive (heavy) 15N . . . so all DNA is heavy Then grow in 14N, centrifuge as generations divide, and check to see where heavy DNA ends up http://www.sumanasinc.com/webcontent/animations/content/meselson.html MESELSON & STAHL Can tell which model it is by the banding patterns of DNA molecules SO WHAT ? Proved SEMI-CONSERVATIVE REPLICATION MODEL http://www.sumanasinc.com/webcontent/animations/content/meselson.html Chromosome Structure in Prokaryotes Approximately 5 million base pairs 3,000 genes Chromosome E. coli bacterium Bases on the chromosome DNA molecule in bacteria single circular loop © Pearson Education Inc, publishing as Pearson Prentice Hall. All rights reserved CENTRAL DOGMA OF MOLECULAR BIOLOGY (How information passes in cells) http://www.emunix.emich.edu/~rwinning/genetics/pics/dogma.jpg http://student.ccbcmd.edu/~gkaiser/biotutorials/dna/fg12.html Starting place = ORIGIN OF REPLICATION Bacteria have one Eukaryotes-multiple spots DNA REPLICATION FORK HOW NUCLEOTIDES ARE ADDED DURING DNA REPLICATION DNA REPLICATION FORK http://bio.usuhs.mil/biochem4.html TELOMERES & TELOMERASE Each replication shortens DNA strand Primer removed but can’t be replaced with DNA because no 3’ end available for DNA POLYMERASE Image from: AP BIOLOGY by Campbell and Reese 7th edition • TELOMERES-repetitive sequences added to ends of genes to protect information in code • TELOMERASE can add to telomere segments in cells that must divide frequently • Ex: Cells that give rise to sperm & eggs • Shortening of telomeres may play a role in aging • Cancer cells may have increased telomerase activity which allows them to keep dividing ANIMATION http://stemcells.nih.gov/info/scireport/appendixC.asp PROOFREADING & REPAIR • Mistakes in final DNA: 1 in 10 billion • Mistakes in initial base pairing during replication: 1 in 100,000 • DNA POLYMERASE proofreads each base as it’s added & fixes errors • Errors can come from: 1. “proofreading mistakes” that are not caught 2. Environmental damage from CARCINOGENS (Ex: X-rays, UV light, cigarette smoke, etc) NUCLEOTIDE EXCISION REPAIR • Cells continually monitor DNA and make repairs • NUCLEASES-DNA cutting enzyme removes errors • DNA POLYMERASE AND LIGASE can fill in gap and repair using other strand • Xeroderm pigmentosum- genetic disorder – mutation in DNA enzymes that repair UV damage in skin cells – can’t go out in sunlight – increased skin cancers/cataracts DNA →RNA TRANSCRIPTION RNA- the Other Nucleic Acid Made of NUCLEOTIDES Sugar = ribose URACIL NOT THYMINE Single stranded http://tigger.uic.edu/classes/phys/phys461/phys450/ANJUM04 http://images2.clinicaltools.com/images/gene/dna_versus_rna_reversed.jpg 3 KINDS OF RNA HELP WITH INFO TRANSFER FOR PROTEIN SYNTHESIS RIBOSOMAL RNA (rRNA) Made in nucleolus 2 subunits (large & small) Combine with proteins to form ribosomes Bacterial ribosomes different size than eukaryotic ribosomes • Evidence for ENDOSYMBIOTIC THEORY • Medically significant-some antibiotics target bacterial ribosomes w/o harming host rRNA and t-RNA images from Image from: Biology; Miller and Levine; Pearson Education publishing as Prentice Hall; 2006 mRNA image from http://wps.prenhall.com/wps/media/tmp/labeling/1140654_dyn.gif 3 KINDS OF RNA HELP WITH INFO TRANSFER FOR PROTEIN SYNTHESIS TRANSFER RNA (tRNA) ANTICODON sequence matches CODON on mRNA to add correct amino acids during protein synthesis AMINOACYL-tRNA SYNTHETASE Enzyme attaches a specific amino acid using energy from ATP http://www-math.mit.edu/~lippert/18.417/lectures/01_Intro/ 3 KINDS OF RNA HELP WITH INFO TRANSFER FOR PROTEIN SYNTHESIS MESSENGER RNA (mRNA) carries code from DNA to ribosomes TRANSCRIPTION See a video clip about TRANSCRIPTION • Prokaryotes- mRNA functional as soon as transcribed • Eukarytoes-mRNA is processed before use SEE PROCESSING VIDEO Image from AP BIOLOBY by Campbell and Reese mRNA’s require EDITING before use • Message in NOT CONTINUOUS • INTRONS are removed Image by Riedell mRNA EDITING snRNPs (small nuclear ribonucleoproteins) Made of proteins and RNA Role in the SPLICEOSOME (Complex that cuts out the INTRONS and joins EXONS to make the final mRNA) RIBOZYMES-RNA molecules that function as enzymes (pre-RNA can remove its own introns) INTRONS & EXONS • PROTEIN DOMAINS • Modular • Ex: – Active site, – site to attach to membrane • In many proteins, different exons code for different domains • May facilitate evolution of new proteins (EXON SHUFFLING) • Increased Crossing over • Mix & match exons Image from AP BIOLOGY by Campbell and Reese GTP "cap" put on 5’ end- stability and used to bind mRNA to ribosome • PolyA "tail" put on 3’ end (AAA)- stability and movement through the nuclear membrane Image from AP BIOLOBY by Campbell and Reese TRANSLATION (Protein synthesis) Section 12-3 64 possible codons Code is REDUNDANT “WOBBLES” Some amino acids have more than one codon. START=AUG (Methionine is 1st) 3 codons for STOP Image from: Biology; Miller and Levine; Pearson Education publishing as Prentice Hall; 2006 http://www.biologycorner.com/bio4/notes/codon.html Image from: Biology; Miller and Levine; Pearson Education publishing as Prentice Hall; 2006 Section 12-3 Translation Figure 12–18 Translation (continued) Section 12-3 Image from: Biology; Miller and Levine; Pearson Education publishing as Prentice Hall; 2006 TRANSLATION How translation works SEE ANOTHER Translation Animation REGULATION & MODIFICATION DURING TRANSCRIPTION • Proteins affect ability of RNA polymerase to bind to DNA AFTER TRANSCRIPTION • Speed of editing introns/exons • access to transport proteins or speed of transport out • Control amount of mRNA degradation by RIBONUCLEASES DURING TRANSLATION • Polyribosomes (polysomes) • Availability of enzymes • POST-TRANSLATIONAL MODIFICATION • Alter protein (add phosphates, sugars, etc) • Cut and join peptide chains COMPLETING PROTEINS • POLYRIBOSOMES (POLYSOMES) – Numerous ribosomes translate same mRNA at same time – 3-D folding (1’, 2’, 3’ structure) – Chaparonins POST-TRANSLATIONAL MODIFICATIONS – Some amino acids modified by addition of sugars, lipids, phosphate groups, etc – Enzymes can modify ends, cleave into pieces join polypeptide strands (4’ structure) Ex: Made as proinsulin then cut Final insulin hormone made of two chains connected by disulfide bridges http://www.vivo.colostate.edu/hbooks/pathphys/endocrine/pancreas/insulin.html ARCHIBALD GARROD 1902 • • • • • 1st to suggest genes dictate phenotypes through enzymes that catalyze specific chemical reactions Postulated that the symptoms of an inherited disease are due to inability to make a specific enzyme Coined term “inborn errors of metabolism” to describe such diseases Beginning of “One gene-one enzyme” hypothesis ALCAPTONURIA- “black urine” disease- defect in enzyme that breaks down amino acid tyrosine http://www.personal.psu.edu/faculty/w/x/wxm15/Online/Molecular%20Biology/media/phenylalanine.gif http://www.nature.com/bjp/journal/v147/n1s/images/0706466f5.jpg Mutations • Point mutations – single base change – base-pair substitution • silent mutation – no amino acid change – redundancy in code • missense – change amino acid • nonsense – change to stop codon Slide from Explore Biology by Kim Foglia Point mutation leads to Sickle cell anemia What kind of mutation? Slide from Explore Biology by Kim Foglia Sickle cell anemia Slide from Explore Biology by Kim Foglia Mutations • Frameshift – shift in the reading frame • changes everything “downstream” – insertions • adding base(s) – deletions • losing base(s) – More damaging at beginning of gene than at end Slide modified from: Explore Biology by Kim Foglia XERODERMA PIGMENTOSUM • UV light damage causes THYMINE DIMERS • Usually repaired (Nucleotide Excision repair) – – – – Repair enzymes defective Increased skin cancer severe burns in sunlight Must avoid sunlight AP BIOLOGY by Campbell and Reese http://www.shadeshort.com/ REPLICATION DNA → DNA ____________ TRANSCRIPTION DNA → RNA ____________ RNA→ Protein TRANSLATION ___________