|Concepts||denaturing proteins, lipids and their self assembly into bilayers, nucleic acids, DNA, and encoding information for protein synthesis, history of the discovery of DNA double helix structure|
|Keywords||denaturing, disulfide bond, triglyceride, zwitterion, aliphatic compound, cell wall, nucleotide, amphipathic, amine, base pairs, codon, Laue pattern, alpha helix, Oswald Avery, Erwin Chargaff, Rosalind Franklin, Francis Crick, James Watson, Maurice Wilkins, x-ray crystallography, biological replication|
|Chemical Substances||fats, oils, cholesterols, hormones, phospholipid, phosphatide, phosphatidylethanolamine, ribose, 2-deoxyribose, DNA, RNA, guanine, cytosine, adenine, thymine|
|Applications||cooking food, pickling food, hair styling, laundry detergent|
Before starting this session, you should be familiar with:
- Prior sessions in this Organic Materials module (starting with Session 27), and particularly the fundamentals of protein structure as described in Session 31:
- Composition (primary structure of amino acid chains)
- Packing (secondary structures of alpha helix, beta pleated sheet, and random coil),
- Conformation (tertiary structure or folding caused by R-group interactions)
- X-ray crystallography, as introduced in Session 18: X-Ray Diffraction Techniques
After completing this session, you should be able to:
- Describe several methods of denaturing proteins and provide practical examples of each method.
- List the characteristics and properties of lipids.
- List the characteristics and properties of nucleic acids.
- Draw the chemical structure of DNA, and indicate the role of hydrogen bonding in forming the structure.
- Describe how the chemical structure of DNA carries information and supports replication.
|[Saylor] 24.6, “The Molecules of Life.”||Overview of lipids and nucleic acids|
|[PB-EOC] 20-1 through 20-5 in Chapter 20, “Lipids.”||Fatty acids; waxes; fats and oils; soaps, detergents, and micelles; phospholipids|
|[PB-EOC] 21-2, 21-5, and 21-8 in Chapter 21, “Nucleosides, Nucleotides, and Nucleic Acids.”||Overview of nucleic acids; DNA and heredity; biosynthesis of proteins via translation|
After a quick review of the previous session, Prof. Sadoway begins with a discussion of denaturing proteins – disrupting protein secondary and tertiary structures. Examples of the denaturing process include:
- Changing temperature (frying an egg)
- Changing pH (pickling food)
- Introducing oxidizing/reducing agents to rearrange disulfide bonds (hair styling)
- Introducing detergents, which destabilize hydrophobic pockets
Next, the lecture introduces lipids.
- Lipids are defined by their properties, not by their chemical composition; they are soluble in solvents of low polarity.
- Examples include fats, oils, cholesterols, and hormones. Some lipids have a hydrophilic head and hydrophobic tail; arranged in two layers, tail to tail, they produce a lipid bilayer capable of self-assembly.
- The lipid bilayer is the basis of cell walls. It includes integral proteins that change conformation in response to certain conditions, creating dynamic physical responses in the cell wall – once again, chemistry as the animating force of life.
After lipids, the lecture proceeds with the structure of nucleic acids.
- Nucleic acids carry information that directs metabolic activity, including replication.
- They are macromolecules whose structural unit is the nucleotide, consisting of three building blocks: a sugar (ribose or 2-deoxyribose), a phosphate acting as a bridge and a ‘spacer,’ and an amine group (one from the set AGCU for RNA, and AGCT for DNA).
- The amine groups combine in pairs (A-T or C-G), and intermolecular spacing and hydrogen bonds lead to the double helix structure.
- The order of A-T and C-G pairs (“letters”) in chains creates “word” sequences of the genetic code.
This lecture ends with a history of the discovery of DNA’s double helix structure: early insights by Oswald, Chargaff’s rule, Franklin’s x-ray crystallography experiment and its subsequent controversial use by Watson and Crick.
For Further Study
Judson, Horace Freeland. The Eighth Day of Creation: Makers of the Revolution in Biology. 25th anniversary edition. Woodbury, NY: Cold Spring Harbor Laboratory Press, 1996. ISBN: 9780879694784.
Maddox, Brenda. Rosalind Franklin: The Dark Lady of DNA. New York, NY: HarperCollins, 2002. ISBN: 9780060184070.
Watson, James D. The Double Helix: A Personal Account of the Discovery of the Structure of DNA. New York, NY: Touchstone/Simon & Schuster, 2001 (original publication 1968). ISBN: 9780743216302.
“It’s a Chemical Reaction, That’s All.” Music and lyrics by Cole Porter. From Silk Stockings. Fred Astaire, Cyd Charisse; directed by Rouben Mamoulian and Roy Mack. Original film release MGM, 1957. DVD, Warner Home Video, 2003.
Hank Ballard and the Midnighters. “The Twist.” (B-side with “Teardrops on Your Letter.”) Original release: King Records, 1959. Available on many reissue compilations, such as Their Very Best: Hank Ballard & The Midnighters. K-Tel, 2007.
Other OCW and OER Content
|7.01SC Fundamentals of Biology||MIT OpenCourseWare||Undergraduate (first-year)||See Unit 1: Biochemistry|