dna → rna → proteins chapters 16 & 17 johnc/mbi1440.htm
TRANSCRIPT
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DNA→RNA → PROTEINSChapters 16 & 17
http://faculty.uca.edu/~johnc/mbi1440.htm
http://www.wappingersschools.org/RCK/staff/teacherhp/johnson/visualvocab/mRNA.gif
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1928- GRIFFITH’s EXPERIMENT
Scientists originally thought PROTEINS had to be the genetic material
Images from: http://microvet.arizona.edu/Courses/vsc610/mic205/griffith.jpg
12 A
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1943- EXPERIMENTS BY OSWALD AVERY, MACLYN McCARTY, & COLIN MACLEOD
http://www.synapses.co.uk/genetics/dnastruc.html
WITH LIPIDS, POLYSACCHARIDES, OR PROTEINSTHERE’S NO TRANSFORMATION
ONLY NUCLEIC ACIDS CHANGE THE BACTERIA SO . . .
NUCLEIC ACIDS CARRY THEINFORMATION !
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1952-Alfred Hershey and Martha Chase
Bacteriophages are viruses that infect bacteria
Phages are made ofDNA surrounded by a protein coat
http://www.mun.ca/biology/scarr/Chase_&_Hershey_1953.jpg
http://oceanworld.tamu.edu/resources/oceanography-book/Images/BacteriophageCartoon.jpg
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HERSHEY CHASE BLENDER EXPERIMENT
http://www.mun.ca/biology/scarr/hersheychase-experiment.jpg
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http://en.wikipedia.org/wiki/Rosalind_Franklin http://www.time.com/time/time100/scientist/profile/watsoncrick.html
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 helixmodel for the structure of DNA
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DOUBLE HELIX
http://www.biosciences.bham.ac.uk/labs/minchin/tutorials/lgdna.html
Linus Pauling's Triple helix model
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STRUCTURE OF NUCLEIC ACIDS
Image by: Riedell
Sugar can be DEOXYRIBOSE (DNA) RIBOSE (RNA)
Built from NUCLEOTIDE SUBUNITS
NITROGEN BASES CAN BE:
ADENINEGUANINECYTOSINETHYMINEURACIL
Arrow from: http://www.harrythecat.com/graphics/b/arrow48d.gif
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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.htmlhttp://student.ccbcmd.edu/~gkaiser/biotutorials/dna/fg29.html
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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
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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
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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/
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5’ and 3’ ENDS
• 5’ and 3’ ends named for the CARBON
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Erwin Chargaff analyzed DNA from different organisms and found
CHARGAFF’s RULES: A = T G = C
Now know its because:A always bonds with TG always bonds with C
A Purine always bonds to a Pyrimidine
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Semi-
Conservative
Conservative
Dispersive
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MESELSON & STAHLGrew 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
Images from: http://instruct1.cit.cornell.edu/courses/biog105/pages/demos/106/unit01/6.dnareplicationmodels.html
http://www.sumanasinc.com/webcontent/animations/content/meselson.html
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MESELSON & STAHL
Can tell which model it is by the bandingpatterns of DNA
molecules
SO WHAT ?
http://www.sumanasinc.com/webcontent/animations/content/meselson.html
Proved SEMI-CONSERVATIVE REPLICATION MODEL
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Chromosome
E. coli bacterium
Bases on the chromosome
Chromosome Structure in Prokaryotes
© Pearson Education Inc, publishing as Pearson Prentice Hall. All rights reserved
DNA molecule in bacteriasingle circular loop
Approximately 5 million base pairs3,000 genes
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CENTRAL DOGMA OF MOLECULAR BIOLOGY
(How information passes in cells)
http://www.emunix.emich.edu/~rwinning/genetics/pics/dogma.jpg
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http://student.ccbcmd.edu/~gkaiser/biotutorials/dna/fg12.html
DNA REPLICATION FORK
Starting place = ORIGIN OF REPLICATION
Bacteria have one
Eukaryotes-multiple spots
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HOW NUCLEOTIDES ARE ADDED DURING DNA REPLICATION
http://bio.usuhs.mil/biochem4.html
DNA REPLICATION FORK
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TELOMERES & TELOMERASE
Image from: AP BIOLOGY by Campbell and Reese 7th edition
Primer removed butcan’t be replaced withDNA because no3’ end available forDNA POLYMERASE
Each replicationshortens DNA strand
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• 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
http://stemcells.nih.gov/info/scireport/appendixC.asp
ANIMATION
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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)
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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
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DNA →RNATRANSCRIPTION
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RNA- the Other Nucleic Acid
Made of NUCLEOTIDESSugar = riboseURACIL NOT THYMINESingle stranded
http://images2.clinicaltools.com/images/gene/dna_versus_rna_reversed.jpg http://tigger.uic.edu/classes/phys/phys461/phys450/ANJUM04
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3 KINDS OF RNA HELP WITH INFO TRANSFER FOR PROTEIN SYNTHESIS
RIBOSOMAL RNA (rRNA)Made in nucleolus2 subunits (large & small)Combine with proteins to
form ribosomesBacterial 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; 2006mRNA image from http://wps.prenhall.com/wps/media/tmp/labeling/1140654_dyn.gif
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3 KINDS OF RNA HELP WITH INFO TRANSFER FOR PROTEIN SYNTHESIS
TRANSFER RNA (tRNA)
ANTICODON sequence matches CODON on mRNA to add correctamino 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/
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3 KINDS OF RNA HELP WITH INFO TRANSFER FOR PROTEIN SYNTHESIS
MESSENGER RNA (mRNA)carries code from DNA to ribosomes
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TRANSCRIPTION
See a video clip aboutTRANSCRIPTION
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• Prokaryotes- mRNA functional as soon as transcribed
• Eukarytoes-mRNA is processed before use
Image from AP BIOLOBY by Campbell and Reese
SEE PROCESSING VIDEO
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mRNA’s require EDITING before use
• Message in NOT CONTINUOUS
• INTRONS are removed
Image by Riedell
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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)
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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
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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
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TRANSLATION(Protein synthesis)
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Section 12-3 64 possible codons
Code is REDUNDANT“WOBBLES”
Some amino acidshave more than onecodon.
START=AUG(Methionine is 1st)3 codons for STOP
Image from: Biology; Miller and Levine; Pearson Education publishing as Prentice Hall; 2006
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http://www.biologycorner.com/bio4/notes/codon.html
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TranslationSection 12-3
Image from: Biology; Miller and Levine; Pearson Education publishing as Prentice Hall; 2006
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Figure 12–18 Translation (continued)Section 12-3
Image from: Biology; Miller and Levine; Pearson Education publishing as Prentice Hall; 2006
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TRANSLATION
SEE ANOTHERTranslation Animation
How translation works
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REGULATION & MODIFICATIONDURING 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
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COMPLETING PROTEINS• POLYRIBOSOMES (POLYSOMES)
– Numerous ribosomes translate same mRNA at same time
– 3-D folding (1’, 2’, 3’ structure)– Chaparonins
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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 hormonemade of two chains connected by disulfide bridges
http://www.vivo.colostate.edu/hbooks/pathphys/endocrine/pancreas/insulin.html
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• 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 tyrosinehttp://www.personal.psu.edu/faculty/w/x/wxm15/Online/Molecular%20Biology/media/phenylalanine.gifhttp://www.nature.com/bjp/journal/v147/n1s/images/0706466f5.jpg
ARCHIBALD GARROD1902
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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
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Point mutation leads to Sickle cell anemia
What kind of mutation?
Slide from Explore Biology by Kim Foglia
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Sickle cell anemia
Slide from Explore Biology by Kim Foglia
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Mutations • Frameshift
– shift in the reading frame
• changes everything “downstream”
– insertions• adding base(s)
– deletions• losing base(s)
– More damaging atbeginning of gene than at end
Slide modified from: Explore Biology by Kim Foglia
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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/
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DNA → DNA ____________
DNA → RNA ____________
RNA→ Protein ___________
REPLICATION
TRANSCRIPTION
TRANSLATION