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Chapter 16 Molecular Basis of Inheritance Power. Point Lectures for Campbell Biology: Concepts & Connections, Seventh Edition Reece, Taylor, Simon, and Dickey © 2012 Pearson Education, Inc. Lecture by Edward J. Zalisko
Figure 10. 0_1 Chapter 16: Big Ideas The Structure of the Genetic Material DNA Replication The Flow of Genetic Information from DNA to RNA to Protein The Genetics of Viruses and Bacteria
THE STRUCTURE OF THE GENETIC MATERIAL © 2012 Pearson Education, Inc.
SCIENTIFIC DISCOVERY: Experiments that showed that DNA is the genetic material § In 1928, Frederick Griffith discovered that a “transforming factor” could be transferred into a bacterial cell. He found that – when he exposed heat-killed pathogenic bacteria to harmless bacteria, some harmless bacteria were converted to disease-causing bacteria and – the disease-causing characteristic was inherited by descendants of the transformed cells. – Used two strains of Strepcoccus pneumoniae Rough (R) coat = harmless and Smooth (S) coat = harmful © 2012 Pearson Education, Inc.
SCIENTIFIC DISCOVERY: Experiments that showed that DNA is the genetic material Conclusion: The rough strain was transformed to smooth strain in the mouse body. How? ?
SCIENTIFIC DISCOVERY: Experiments that showed that DNA is the genetic material § Avery, Mc. Carty and Mac. Leod § Separated and purified the S cell contents § Mixed with live R cells and injected into mice § Only the mice with DNA extract died
SCIENTIFIC DISCOVERY: Experiments that showed that DNA is the genetic material § Until the 1940 s, the case for proteins serving as the genetic material was stronger than the case for DNA. – Proteins are made from 20 different amino acids. – DNA was known to be made from just four kinds of nucleotides. § Scientists were still skeptical about these results © 2012 Pearson Education, Inc.
SCIENTIFIC DISCOVERY: Experiments showed that DNA is the genetic material § In 1952, Alfred Hershey and Martha Chase used bacteriophages to show that DNA is the genetic material of T 2, a virus that infects the bacterium Escherichia coli (E. coli). – Bacteriophages (or phages for short) are viruses that infect bacterial cells. – Phages were labeled with radioactive sulfur to detect proteins or radioactive phosphorus to detect DNA. – Bacteria were infected with either type of labeled phage to determine which substance was injected into cells and which remained outside the infected cell. © 2012 Pearson Education, Inc.
Figure 10. 1 A Life cycle of the bacteriophage Head Tail fiber DNA
Figure 10. 1 C 1 A phage attaches itself to a bacterial cell. 2 The phage injects 3 The phage DNA directs its DNA into the bacterium. the host cell to make more phage DNA and proteins; new phages assemble. 4 The cell lyses and releases the new phages.
10. 1 SCIENTIFIC DISCOVERY: Experiments showed that DNA is the genetic material – The sulfur-labeled protein stayed with the phages outside the bacterial cell, while the phosphorus-labeled DNA was detected inside cells. – Cells with phosphorus-labeled DNA produced new bacteriophages with radioactivity in DNA but not in protein. Animation: Hershey-Chase Experiment Animation: Phage T 2 Reproductive Cycle © 2012 Pearson Education, Inc.
Figure 10. 1 B_1 Phage Empty protein shell Radioactive protein Bacterium DNA Batch 1: Radioactive protein labeled in yellow 2 1 Batch 2: Radioactive DNA labeled in green Phage DNA Radioactive DNA
Figure 10. 1 B_2 Empty protein shell The radioactivity is in the liquid. Phage DNA Centrifuge Pellet 3 4 Centrifuge Pellet The radioactivity is in the pellet.
Figure 10. 1 B Phage Empty protein shell Radioactive protein Bacterium Centrifuge Pellet 1 Batch 2: Radioactive DNA labeled in green Phage DNA Batch 1: Radioactive protein labeled in yellow The radioactivity is in the liquid. 2 3 4 Radioactive DNA Centrifuge Pellet The radioactivity is in the pellet.
Figure 10. 0_2
DNA is the genetic material What does DNA look like and how does it work as genetics material? § DNA and RNA are nucleic acids. § One of the two strands of DNA is a DNA polynucleotide, a nucleotide polymer (chain). § A nucleotide is composed of a – nitrogenous base, – five-carbon sugar, and – phosphate group. © 2012 Pearson Education, Inc.
Figure 10. 2 A_3 Nitrogenous base (can be A, G, C, or T) Thymine (T) Phosphate group Sugar (deoxyribose) DNA nucleotide
Figure 10. 2 B Thymine (T) Cytosine (C) Pyrimidines Guanine (G) Adenine (A) Purines
DNA are polymers of nucleotides § Each type of DNA nucleotide has a different nitrogencontaining base: § Chargaff isolated and quantified the amount of A, T, G, C from cells and found – adenine (A), § Quantity of A=T – cytosine (C), § Quantity of G=C – thymine (T), and – guanine (G). § Known as Chargaff’s rules Animation: DNA and RNA Structure © 2012 Pearson Education, Inc.
DNA are polymers of nucleotides § More evidence for DNA as the genetic material – DNA doubles in cells getting ready for cell division – A haploid cell has half as much DNA as a diploid cell § Race to discover the DNA structure was on! – Contenders: – Wilkins and Franklin of England – Linus Pauling of USA – Watson and Crick of ……
Discovery of DNA Structure § World renowned X- ray crystallography expert § X-rays of DNA § Information can be used to find out the width of molecule § Spacing between bases §
10. 3 SCIENTIFIC DISCOVERY: DNA is a double-stranded helix § In 1953, James D. Watson and Francis Crick deduced the secondary structure of DNA, using – X-ray crystallography data of DNA from the work of Rosalind Franklin and Maurice Wilkins and – Chargaff’s observation that in DNA, – the amount of adenine was equal to the amount of thymine and – the amount of guanine was equal to that of cytosine. © 2012 Pearson Education, Inc.
10. 3 SCIENTIFIC DISCOVERY: DNA is a double-stranded helix § Watson and Crick reported that DNA consisted of two polynucleotide strands wrapped into a double helix. – The sugar-phosphate backbone is on the outside. – The nitrogenous bases are perpendicular to the backbone in the interior. – Specific pairs of bases give the helix a uniform shape. – A pairs with T, forming two hydrogen bonds, and – G pairs with C, forming three hydrogen bonds. – The two strands are anti-parallel © 2012 Pearson Education, Inc.
Figure 10. 3 B
Watson and …. . Circa 2004
Figure 10. 2 A T A C T G Sugar-phosphate backbone A C G T A C G A G T T Covalent bond joining nucleotides T C A C A A G Phosphate group Nitrogenous base Sugar Nitrogenous base (can be A, G, C, or T) C G T A A DNA double helix DNA nucleotide T Thymine (T) T Phosphate group G G Two representations of a DNA polynucleotide Sugar (deoxyribose) DNA nucleotide
Figure 10. 2 A_2 Sugar-phosphate backbone A A Covalent bond joining nucleotides C DNA nucleotide T Nitrogenous base Sugar C T G G Two representations of a DNA polynucleotide Phosphate group
Figure 10. 3 D_2 Hydrogen bond G T C A A C T G Partial chemical structure
Figure 10. 3 C Twist
10. 3 SCIENTIFIC DISCOVERY: DNA is a double-stranded helix § In 1962, the Nobel Prize was awarded to – James D. Watson, Francis Crick, and Maurice Wilkins. – Rosalind Franklin probably would have received the prize as well but for her death from cancer in 1958. Nobel Prizes are never awarded posthumously. § The Watson-Crick model gave new meaning to the words genes and chromosomes. The genetic information in a chromosome is encoded in the nucleotide sequence of DNA. © 2012 Pearson Education, Inc.
DNA REPLICATION © 2012 Pearson Education, Inc.
10. 4 DNA replication depends on specific base pairing § In their description of the structure of DNA, Watson and Crick noted that the structure of DNA suggests a possible copying mechanism. § DNA replication follows a semiconservative model. – The two DNA strands separate. – Each strand is used as a pattern to produce a complementary strand, using specific base pairing. – Each new DNA helix has one old strand with one new strand. Animation: DNA Replication Overview © 2012 Pearson Education, Inc.
How does the DNA make a copy of itself - Replication A. Conservative: The parent DNA strands remain together after replication and the daughter DNA consists of new strands B. Semi-conservative: Each new DNA consists of a parent and a new strand C. Dispersive: Each daughter DNA consists of a mixture of parent and daughter DNA
Meselson and Stahl Experiment with Light and Heavy Nitrogen Grew E. coli in heavy nitrogen N 15 till all DNA showed as a heavy band when centrifuged Grew for second generation in N 14 § Transferred to N 14 and grew for one generation Grew for the third generation in N 14 § Prediction? Prediction for each type of § Prediction? replication?
Meselson and Stahl Experiment with Light and Heavy Nitrogen
Figure 10. 4 A_s 1 A T C G G C A T T A A parental molecule of DNA
Figure 10. 4 A_s 2 A T A C G C G A T A T A parental molecule of DNA T A G C T G C C A Free nucleotides The parental strands separate and serve as templates T A
Figure 10. 4 A_s 3 A T A C G C G A T A T A parental molecule of DNA T A G C C A Free nucleotides The parental strands separate and serve as templates T A T G C G C G C T A T A T A Two identical daughter molecules of DNA are formed
Figure 10. 4 B A T G A A T Parental DNA molecule T A G C Daughter strand T C G T C A G C C Parental strand G C G G T C C T A G T A C C T A T G A T A A C A T G T Daughter DNA molecules
10. 5 DNA replication proceeds in two directions at many sites simultaneously § DNA replication begins at the origins of replication where – DNA unwinds at the origin to produce a “bubble, ” – replication proceeds in both directions from the origin, and – replication ends when products from the bubbles merge with each other. © 2012 Pearson Education, Inc.
Figure 10. 5 A Parental DNA molecule Origin of replication “Bubble” Two daughter DNA molecules Parental strand Daughter strand
10. 5 DNA replication proceeds in two directions at many sites simultaneously § DNA replication occurs in the 5 to 3 direction. – Replication is continuous on the 3 to 5 template. – Replication is discontinuous on the 5 to 3 template, forming short segments. © 2012 Pearson Education, Inc.
Figure 10. 5 B 3 end 5 end P 4 3 P 5 2 1 2 A T 5 C P P G C P P T 3 end 3 4 G P OH 1 HO A P 5 end
10. 5 DNA replication proceeds in two directions at many sites simultaneously § Proteins are involved in DNA replication. 1. DNA ligase joins small fragments into a continuous chain. 2. DNA polymerase I and III – adds nucleotides to a growing chain and – proofreads and corrects improper base pairings. 3. Helicase – unwinds DNA at replication fork 4. Single stranded binding protein – stabilizes unwound DNA 5. Topoisomerase – corrects overwinding ahead of DNA fork by breaking and joining DNA © 2012 Pearson Education, Inc.
10. 5 DNA replication proceeds in two directions at many sites simultaneously § DNA polymerases and DNA ligase also repair DNA damaged by harmful radiation and toxic chemicals. § DNA replication ensures that all the somatic cells in a multicellular organism carry the same genetic information. © 2012 Pearson Education, Inc.
DNA Replication Process § Helicase unwinds the DNA double helix § Single stranded binding proteins stabilize the unwound DNA
DNA Replication § Primase synthesizes a small section of RNA on each 5’ end § Nucleotides pair up § DNA Pol III joins the backbone together
Figure 10. 5 C DNA polymerase molecule 5 3 Parental DNA Replication fork 5 3 DNA ligase Overall direction of replication 3 5 This daughter strand is synthesized continuously This daughter strand is 3 synthesized 5 in pieces
DNA Replication § DNA Pol I removes the primer and replaces with DNA nucleotides A gap formed is sealed with DNA Ligase
Molecular process of DNA replication
You should now be able to 1. Describe the experiments of Griffith, Hershey, and Chase, which supported the idea that DNA was life’s genetic material. 2. Explain the structure of DNA. 3. Explain how the structure of DNA facilitates its replication. 4. Describe the process of DNA replication. © 2012 Pearson Education, Inc.