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DNA → RNA → PROTEINS Chapters 16 & 17

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Presentation on theme: "DNA → RNA → PROTEINS Chapters 16 & 17"— Presentation transcript:

1 DNA → RNA → PROTEINS Chapters 16 & 17

2 1928- GRIFFITH’s EXPERIMENT Scientists originally thought PROTEINS had to be the genetic material Images from: 12 A

3 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 !

4 1952-Alfred Hershey and Martha Chase Bacteriophages are viruses that infect bacteria Phages are made of DNA surrounded by a protein coat

5 HERSHEY CHASE BLENDER EXPERIMENT

6 ROSALIND FRANKLIN and MAURICE WILKINS Analyzed DNA with X-ray crystallography to try and determine structure of DNA 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

7 DOUBLE HELIX Linus Pauling's Triple helix model

8 STRUCTURE OF NUCLEIC ACIDS Image by: Riedell Sugar can be DEOXYRIBOSE (DNA) RIBOSE (RNA) Built from NUCLEOTIDE SUBUNITS NITROGEN BASES CAN BE: ADENINE GUANINE CYTOSINE THYMINE URACIL Arrow from:

9 DNA has no URACILRNA has no THYMINE PURINES (A & G) have 2 RINGS PYRIMIDINES (T, C, & U) have 1 RING

10 Subunits come in as TRIPHOSPHATES Splitting of nucleotide triphosphates provides the energy to link the nucleotides See animation

11 DNA DOUBLE STRANDED Strands run ANTIPARALLEL Backbone = sugars and phosphates Rungs of ladder = nitrogen bases Hydrogen bonds hold sides of ladder together

12 RNA SINGLE STRANDED Folds into 3D shape Backbone = sugars and phosphates Rungs of ladder = nitrogen bases

13 5’ and 3’ ENDS 5’ and 3’ ends named for the CARBON

14 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

15 Semi- Conservative Dispersive

16 MESELSON & STAHL Grew bacteria for many generations in radioactive (heavy) 15 N... so all DNA is heavy Then grow in 14 N, centrifuge as generations divide, and check to see where heavy DNA ends up Images from:

17 MESELSON & STAHL Can tell which model it is by the banding patterns of DNA molecules SO WHAT ? Proved SEMI-CONSERVATIVE REPLICATION MODEL

18 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 bacteria single circular loop Approximately 5 million base pairs 3,000 genes

19 CENTRAL DOGMA OF MOLECULAR BIOLOGY (How information passes in cells)

20 DNA REPLICATION FORK Starting place = ORIGIN OF REPLICATION Bacteria have one Eukaryotes-multiple spots

21 HOW NUCLEOTIDES ARE ADDED DURING DNA REPLICATIONHOW NUCLEOTIDES ARE ADDED DURING DNA REPLICATION DNA REPLICATION FORK

22 TELOMERES & TELOMERASE Image from: AP BIOLOGY by Campbell and Reese 7 th edition Primer removed but can’t be replaced with DNA because no 3’ end available for DNA POLYMERASE Each replication shortens DNA strand

23 TELOMERES-repetitive sequences added to ends of genes to protect information in codeTELOMERES 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

24 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)

25 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

26 DNA → RNA TRANSCRIPTION

27 RNA- the Other Nucleic Acid Made of NUCLEOTIDES Sugar = ribose URACIL NOT THYMINE Single stranded

28 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

29 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

30 3 KINDS OF RNA HELP WITH INFO TRANSFER FOR PROTEIN SYNTHESIS MESSENGER RNA (mRNA) carries code from DNA to ribosomes

31 TRANSCRIPTION See a video clip about TRANSCRIPTION

32 Prokaryotes- mRNA functional as soon as transcribed Eukarytoes-mRNA is processed before use Image from AP BIOLOBY by Campbell and Reese SEE PROCESSING VIDEO

33 mRNA’s require EDITING before use Message in NOT CONTINUOUS INTRONS are removed Image by Riedell

34 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)

35 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

36 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

37 TRANSLATION (Protein synthesis)

38 Section possible codons Code is REDUNDANT “WOBBLES” Some amino acids have more than one codon. START=AUG (Methionine is 1 st ) 3 codons for STOP Image from: Biology; Miller and Levine; Pearson Education publishing as Prentice Hall; 2006

39

40 Translation Section 12-3 Image from: Biology; Miller and Levine; Pearson Education publishing as Prentice Hall; 2006

41 Figure 12–18 Translation (continued) Section 12-3 Image from: Biology; Miller and Levine; Pearson Education publishing as Prentice Hall; 2006

42 TRANSLATION SEE ANOTHER Translation Animation How translation works

43 REGULATION 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

44 COMPLETING PROTEINS POLYRIBOSOMES (POLYSOMES) –Numerous ribosomes translate same mRNA at same time –3-D folding (1’, 2’, 3’ structure) –Chaparonins

45 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

46 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 ARCHIBALD GARROD 1902

47 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

48 Point mutation leads to Sickle cell anemia What kind of mutation? Slide from Explore Biology by Kim Foglia

49 Sickle cell anemia Slide from Explore Biology by Kim Foglia

50 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

51 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

52 DNA → DNA ____________ DNA → RNA ____________ RNA → Protein ___________ REPLICATION TRANSCRIPTION TRANSLATION


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