Transcript Slide 1
BE/Bio 105 Lecture #2: Stuff Central question: how do things work? Why is oak tree shaped like this? Why is alder shaped like this? Why do/don’t trees fall down? What is role of leaf morphology? Lecture #2: Stuff Why/How do kangaroos hop on two legs…? when wombats don’t. How is locomotion of kangaroos & wombats related to their skeletal structure? All these questions basically asking, ‘how do these things work?’ or ‘how can I build one?’ = REVERSE ENGINEERING Lecture #2: Stuff Outline: Part 1: From whence come mechanical properties of stuff? Part 2: What is biological stuff made from? Part 3: How do we mechanically classify stuff? force stuff length Part 1: From whence come mechanical properties of stuff? I-beam For any structure (e.g. I-beam, tree) we can define and measure mechanical properties: e.g. stiffness, strength, toughness, resiliance tree But how do these structures ‘get’ these properties? It is convenient to separate material properties from structural properties: steel materials We will define material properties wood square beam solid cylinder structures We will define structural properties Part 1: From whence come mechanical properties of stuff? This dichotomy is sometime absurd when considering biological structures. consider wood: Cellulose is a polymer of the sugar hexose Part 2: What is biological stuff made from? Biological entities composed of 4 components: 1. Carbohydrates • bun, lettuce, onion, tomato 2. Lipids • cheese, mayo 3. Proteins • burger 4. Inorganic crystals • salt Part 2: What is biological stuff made from? 1. Carbohydrates = sugars, often as polymers e.g. chitin – structure molecule of arthropods and fungi e.g. cellulose – structure molecule of plants termite both chitin and cellulose virtually indigestable gut symbiont (Trychonympha) Part 2: What is biological stuff made from? 2. Lipids = Fats polar hydrophilic region non-polar hydrophobic region form stable, but fluid Bi-lipid membranes Highest energy-to-weight ratio. Thus best energy storage material Part 2: What is biological stuff made from? 3. Proteins = encode amino acid chains ‘central dogma’ NH2 amino acid chains helix structural motifs sheet turn Part 2: What is biological stuff made from? Proteins can function like little machines: Myosin (molecular motor) Note also: genome can only encode proteins. Therefore enzymatic role of proteins is critical for synthesizing lipids and carbohydrates. Part 2: What is biological stuff made from? 4. inorganic crystals and salts Calcium-based crystals are essential for making hard bits. e.g. CaCo3 Ca2(PO4)3(OH) CaMg(CO3)2 SiO2(H2O)N dolomite calcite hydroxyapatite dolomite silicas calcite hydroxyapatite Many biological materials are composites of carbos, proteins, lipids, and inorganics! Part 3: How do we mechanically classify stuff? Three general types of responses: 1. Force = constant x length Hooke’s Law of elasticity force stuff length slope=k force F= k1 x L k1 = spring constant Units: M T-2 length = SOLID (elastic material) slope=k 2. Force = constant x rate of length change ‘stuff’ tester F= k2 x d(L)/dt k2 = viscosity or damping constant k2 = M T-1 = FLUID (viscous material) force d(length)/dt Part 3: How do we mechanically classify stuff? 3. Force = constant x length + constant x rate of length change F= k1 x L + k2 x d(L)/dt = Viscoelastic material Hookian hysteresis initially stiff force force decays over time force force length length length time time Part 3: How do we mechanically classify stuff? Difference between gas and liquid (both are fluids): Liquids will resist both compression and extension extension Gas will resist compression, but it always ‘trying’ to expand. compression Why is it hard to ‘pull’ a vacuum ? stuff Gas molecules will expand to fill any arbitrary volume modified ‘stuff’ tester high pressure = 1 atmosphere low pressure liquid molecules will remain within cohesive mass pushing against atmosphere, not pulling against vacuum Lecture #2: Stuff force stuff Things have material properties and structural properties. Biological materials are composed of carbohydrates, lipids, proteins and inorganic crystals. length Materials can be divided into solids, liquids, and gases. Lecture #3: Jumping Fleas