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Chapter 10 Molecular Biology of the Gene PowerPoint Lectures for Campbell Biology: Concepts & Connections, Seventh Edition Reece, Taylor, Simon, and Dickey © 2012 Pearson Education, Inc. Lecture by Edward J. Zalisko THE STRUCTURE OF THE GENETIC MATERIAL © 2012 Pearson Education, Inc. Experiments showed that DNA is the genetic material Requirements for the genetic material: Must be able to code for unlimited amount of information Must be stable Yet able to change (everyone has a unique genetic sequence) Until the 1940s, 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. © 2012 Pearson Education, Inc. Experiments showed that DNA is the genetic material Frederick Griffith discovered that a “transforming factor” could be transferred into a bacterial cell. Hershey and Chase experiment Only radio-labeled DNA entered bacteria cell Animation: Hershey-Chase Experiment Animation: Phage T2 Reproductive Cycle © 2012 Pearson Education, Inc. LE 16-2 Living S cells (control) Living R cells (control) Heat-killed S cells (control) Mixture of heat-killed S cells and living R cells RESULTS Mouse dies Mouse healthy Mouse healthy Mouse dies Living S cells are found in blood sample LE 16-3 Phage head Tail Tail fiber Bacterial cell 100 nm DNA Figure 10.1A Head Tail Tail fiber DNA Radioactive Sulfur used to label protein Phage Empty protein shell Radioactive protein Bacterium Phage DNA DNA Batch 1: Radioactive protein labeled in yellow The radioactivity is in the liquid. Centrifuge Pellet 1 Batch 2: Radioactive DNA labeled in green 2 3 4 Radioactive DNA Centrifuge Pellet Radioactive Phosphorous used to label DNA The radioactivity is in the pellet. 10.2 DNA and RNA are polymers of nucleotides 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. The nucleotides are joined to one another by a COVALENT BOND between sugar-phosphate backbone. Animation: DNA and RNA Structure © 2012 Pearson Education, Inc. Thymine (T) Cytosine (C) Pyrimidines Guanine (G) Adenine (A) Purines Nitrogenous base (can be A, G, C, or T) Thymine (T) Phosphate group Sugar (deoxyribose) DNA nucleotide RNA RNA (ribonucleic acid) is unlike DNA in that it – uses the sugar ribose (instead of deoxyribose in DNA) and Nitrogenous base (can be A, G, C, or U) Phosphate group Uracil (U) – RNA has the nitrogenous base uracil (U) instead of thymine. – RNA is a single, linear strand © 2012 Pearson Education, Inc. Sugar (ribose) Figure 10.2D Cytosine Uracil Adenine Guanine Ribose Phosphate The nucleotides are joined to one another by a COVALENT BOND between sugar-phosphate backbone. T A C T G Sugar-phosphate backbone A C G T A C G A G T Covalent bond joining nucleotides T C A C A C A A G T Phosphate group Nitrogenous base Nitrogenous base (can be A, G, C, or T) Sugar C G T A A DNA double helix DNA nucleotide T Thymine (T) T Phosphate group G G G G Sugar (deoxyribose) DNA nucleotide Two representations of a DNA polynucleotide Sugar–phosphate backbone Nitrogenous bases 5 end Thymine (T) The nucleotides are joined to one another by a COVALENT BOND between sugarphosphate backbone. Adenine (A) Cytosine (C) Phosphate Sugar (deoxyribose) 3 end DNA nucleotide Guanine (G) Figure 10.3B LE 16-6 Rosalind Franklin Franklin’s X-ray diffraction photograph of DNA 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. Chargaff’s Rule: Equal proportion of A:T and G:C 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. Animation: DNA Double Helix © 2012 Pearson Education, Inc. Figure 10.3C Twist Nucleotides in opposing strands are connected by HYDROGEN bonds 5 end Hydrogen bond 3 end 1 nm 3.4 nm 3 end 0.34 nm Key features of DNA structure 5 end Partial chemical structure Space-filling model Notice the two nucleotide strands run anti-parallel (opposite) of each other! LE 16-8 Sugar Adenine (A) Sugar Thymine (T) Sugar Sugar Guanine (G) Cytosine (C)