Lecture #2: Stuff BE/Bio 105 Central question: how do things work? Why is oak tree shaped like this? Why is alder shaped like this? What is role of leaf morphology? Why do/don’t trees fall down?

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 length stuff

Part 1: From whence come mechanical properties of stuff? For any structure (e.g. I-beam, tree) we can define and measure mechanical properties: e.g. stiffness, strength, toughness, resiliance But how do these structures ‘get’ these properties? It is convenient to separate material properties from structural properties: I -beam tree steel wood materials We will define material properties solid cylinder square beam structures We will define structural properties

This dichotomy is sometime absurd when considering biological structures. consider wood: Cellulose is a polymer of the sugar hexose Part 1: From whence come mechanical properties of stuff?

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

1. Carbohydrates = sugars, often as polymers e.g. chitin – structure molecule of arthropods and fungi e.g. cellulose – structure molecule of plants both chitin and cellulose virtually indigestable gut symbiont (Trychonympha) termite 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’ amino acid chains NH 2 helixsheetturn structural motifs 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. CaCo 3 calcite Ca 2 (PO 4 ) 3 (OH)hydroxyapatite CaMg(CO 3 ) 2 dolomite SiO 2 (H2O) N silicas calcite hydroxyapatite dolomite Many biological materials are composites of carbos, proteins, lipids, and inorganics! Part 2: What is biological stuff made from?

force length ‘stuff’ tester stuff Three general types of responses: 1. Force = constant x length Hooke’s Law of elasticity F= k 1 x L k 1 = spring constant Units: M T -2 = SOLID (elastic material) force length slope=k 2. Force = constant x rate of length change F= k 2 x d(L)/dt k2 = viscosity or damping constant k 2 = M T -1 = FLUID (viscous material) force d(length)/dt slope=k Part 3: How do we mechanically classify stuff?

3. Force = constant x length + constant x rate of length change F= k 1 x L + k 2 x d(L)/dt = Viscoelastic material force length hysteresis time length force initially stiff force decays over time length force time Hookian

Part 3: How do we mechanically classify stuff? Difference between gas and liquid (both are fluids): modified ‘stuff’ tester stuff compression extension Liquids will resist both compression and extension Gas will resist compression, but it always ‘trying’ to expand. Gas molecules will expand to fill any arbitrary volume liquid molecules will remain within cohesive mass Why is it hard to ‘pull’ a vacuum ? low pressure high pressure = 1 atmosphere pushing against atmosphere, not pulling against vacuum

Lecture #2: Stuff Things have material properties and structural properties. Biological materials are composed of carbohydrates, lipids, proteins and inorganic crystals. force length stuff Materials can be divided into solids, liquids, and gases.

Lecture #3: Jumping Fleas