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Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings PowerPoint Lectures for Biology: Concepts and Connections, Fifth Edition – Campbell,

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Presentation on theme: "Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings PowerPoint Lectures for Biology: Concepts and Connections, Fifth Edition – Campbell,"— Presentation transcript:

1 Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings PowerPoint Lectures for Biology: Concepts and Connections, Fifth Edition – Campbell, Reece, Taylor, and Simon Lectures by Chris Romero Chapter 12 and 13 DNA, RNA and Protein Synthesis

2 Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings A Frederick Griffith discovers transformation in bacteria : * discovered that “something” was able to transform harmless (non – virulent) bacteria into harmful (virulent) Discovery of the Role of DNA

3 Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings B Oswald Avery and colleagues show that DNA can transform bacteria C Alfred Hershey and Martha Chase use bacteriophage to confirm that DNA is the genetic material Discovery of the Role of DNA (cont’d)

4 Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings 1 Hershey-Chase Experiment: Infected cells make more virus by injecting their DNA animation

5 Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings D James Watson and Francis Crick propose a structural model for the DNA molecule Discovery of the Role of DNA (cont’d) 1. X-Ray crystallography images prepared by Maurice Wilkins and Rosalind Franklin 2.Chargraff’s Rule: # of Adenines = # of Thymines # Guanines = # of Cytosines Based On:

6 Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings DNA and RNA are Polymers of Nucleotides Both are nucleic acids made of long chains of nucleotide monomers A nucleotide (building block of a nucleic acid) has 3 parts: 1.A phosphate (PO 4 - ) group that is negatively charged 2.A 5-Carbon sugar (deoxyribose in DNA or ribose in RNA) 3.A nitrogen- containing base

7 Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings DNA ( deoxyribonucleic acid ) bases: Pyrimidines: single ring bases Purines: double ring bases Complimentary binding pattern: Adenine + Thymine (share 2 hydrogen bonds) Cytosine + Guanine (share 3 hydrogen bonds) Thymine (T) Cytosine (C) Adenine (A) Guanine (G) pyrimidines purines

8 Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings Similar to DNA except: Sugar in RNA = ribose Base “uracil” instead of thymine Single stranded Figure 10.2C, D RNA: ribonucleic acid

9 Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings The Structure of DNA Two polynucleotide strands wrapped around each other in a double helix A sugar-phosphate backbone Steps made of hydrogen-bound bases (A=T, C = G) Twist

10 Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings DNA REPLICATION : Starts with the separation of DNA strands Enzymes use each strand as a template to assemble new nucleotides into complementary strands…“semi-conservative” (Meselson & Stahl 1958) Portions to be replicated must untwist first

11 Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings DNA replication begins at specific sites on double helix 1.DNA segments unwind 2. Helicase splits H bonds between bases, unzip DNA 3. Binding proteins keep unzipped DNA apart (Single Stranded Binding Proteins) 4. Primase makes a short RNA primer because DNA polymerase can only extend a nucleotide chain, not start one. 5. DNA polymerase adds new nucleotides to the 3’ end of daughter strand that are complimentary to the parent strand 6. RNase H cuts out original primers 7. DNA polymerase fills in gap of removed primers 8. DNA ligase glues S/P backbone where needed Topoisomerase: prevents further coiling at replication fork replication forks Animation/tutorial 9. Two identical double helices

12 Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings Each strand of the double helix is oriented in the opposite direction (“anti-parallel”) “prime” #’s refer to carbons in the sugar At one end, the 3’ carbon has an (OH) and at the opposite, a 5’ carbon has the PO 4 - Why does this matter? DNA polymerase can only add nucleotides to the 3’ end. A daughter strand can only grow from 5’  3’ Therefore, only one daughter strand is made continuously (leading strand) The other strand (lagging strand) is made in a series of short pieces (Okazaki fragments), later connected by DNA ligase A Structural Problem with DNA Replication animation Animation/tutorial

13 Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings When DNA can repair mistakes and when it can’t DNA Repair enzymes work like a spell checker Cut out wrong sequences Undamaged strand is template Only 2 or 3 stable changes per year : some severe, others are not Mutations Inheritable changes occur in gametogenesis Now the “wrong” sequences are copied – Ex: cystic fibrosis (CF): a deletion of 3 nucleotides in a certain gene – Ex: sickle cell anemia: one nucleotide substitution in the hemoglobin gene Mutagen: a mutation causing substance (can break DNA) – Ex: X-Rays, radioactivity, nicotine

14 Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings Protein Synthesis: the transfer of information from: DNA  RNA  Proteins “gene expression”: A gene is a linear sequence of many nucleotides. 3 Types: 1.Structural genes: have info to make proteins 2.Regulatory genes: are on/off switches for genes 3.Genes that code for tRNA, rRNA, histones double stranded A T C G deoxyribose sugar single stranded A U C G ribose sugar 3 types of RNA: messenger, transfer, ribosomal DNA vs. RNA mRNA (messenger): copies DNA’s message in nucleus  brings it to cytoplasm tRNA (transfer): carries amino acids to mRNA so protein can be made rRNA (ribosomal): major part of the ribosome. Helps link amino acids from tRNA’s together  assemble protein

15 Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings 1.Transcription: The DNA of the gene is transcribed into mRNA 2.Translation: decoding the mRNA and assembling the protein Protein Synthesis is Two Steps:

16 Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings Transcription : Eukaryote DNA sequence (message for protein) is transcribed by mRNA Only one strand (non-coding strand) is needed as a template Steps: 1.RNA polymerase splits H bonds in DNA section 2.RNA polymerase travels along non-coding strand of DNA. RNA nucleotides join in a complimentary pattern (A=U, C=G) 3.A termination signal is reached, transcription is over 4.mRNA strip detaches from DNA, DNA helix closes up 5.mRNA is processed: Introns are cut out, Exons are glued together, cap and tail are added. 6.Mature mRNA leaves nucleus through pores  cytoplasm for next step

17 Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings Translation: the synthesis of proteins using mRNA, tRNA and ribosomes The Genetic Code: the language in which instructions for proteins are written in the base sequences Each triplet of mRNA bases is a “codon” because it will “code” for 1 amino acid – Ex: AUG GUC CCU AAU CCU Met – Val – Pro – Asn – Pro – Original coding strand of DNA (the actual gene): ATG GTC CCT AAT CCT Only difference: U is substituted for T – Use the Genetic Code chart to “decode” mRNA message

18 Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings – – Nearly all organisms use exactly the same genetic code – More than one codon for most amino acids = degenerate nature…a change (mutation) in gene does not always mean a different amino acid. – what does CAU code for? ACU? UAU? GCC? – how many codons for Leu? – what is special about AUG and it’s amino acid, Methionine? – what is special about UAA, UAG, and UGA? The Genetic Code is the Rosetta Stone of Life

19 Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings An exercise in translating the genetic code: A AG T A G TTTA GT Step 1: fill in corresponding DNA bases to dark blue strand (non-coding) Step 2: Transcribe the dark blue strand into mRNA (pink) Step 3: Translate the codons into correct amino acids (use chart) Coding strand (gene) transcription translation

20 Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings An exercise in translating the genetic code: answers Step 1: fill in corresponding DNA bases to dark blue strand (non-coding) Step 2: Transcribe the dark blue strand into mRNA (pink) Step 3: Translate the codons into correct amino acids (use chart)

21 Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings Need: tRNAs and ribosomes (rRNA) tRNA: single stranded RNA, folded up – 2 parts: anticodon and aa attachment site How Does Translation Happen? Ribosome: 2 protein subunits and ribosomal RNA allows aa’s to attach by making peptide bonds travels along mRNA strip, tRNA’s join and bring correct amino acids 3 sites on ribosome: A site – where new tRNA’s and amino acids join P site – where protein is growing E site – where empty tRNA’s exit ribosome Translocation: as ribosome moves, tRNA’s move from A site to P site. “A” site is now open for new tRNA with attached amino acid to join animation

22 Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings Put It All Together:

23 Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings Mutations can change the message of genes Mutations: changes in DNA base sequence caused by errors in DNA replication, recombination, or by mutagens substituting, inserting, or deleting nucleotides also alters a gene “frame-shift mutation”…most devastating to protein structure “point mutation”…may or may not alter amino acid sequence

24 Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings MUTANTS – Mutant Animals!


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