Lecture #2: StuffBE/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 leafmorphology?

Why do/don’t trees fall down?

Lecture #2: Stuff

Why/How do kangaroos hop on two legs…?

when wombats don’t.

How is locomotionof 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

lengthstuff

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

squarebeam

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 cellulosevirtually indigestable

gut symbiont (Trychonympha)

termite

Part 2: What is biological stuff made from?

2. Lipids = Fats

polarhydrophilic region

non-polarhydrophobic 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’

aminoacidchains

NH2

helix sheet turn

structuralmotifs

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 saltsCalcium-based crystals are essential for making hard bits.

e.g. CaCo3 calciteCa2(PO4)3(OH) hydroxyapatite CaMg(CO3)2 dolomiteSiO2(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 lengthHooke’s Law of elasticity

F= k1 x Lk1 = spring constant

Units: M T-2

= SOLID (elastic material)

force

length

slope=k

2. Force = constant x rate of length change

F= k2 x d(L)/dt k2 = viscosity or damping constant

k2 = M T-1

= FLUID (viscous material)

force

d(length)/dt

slope=k

Part 3: How do we mechanically classify stuff?

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

force

length

hysteresis

timelength

force

initially stiff

force decaysover 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 expandto fill any arbitrary volume

liquid molecules will remain within cohesive mass

Why is it hard to ‘pull’ a vacuum ?

lowpressure

highpressure

= 1 atmosphere

pushing against atmosphere,

not pulling against vacuum

Lecture #2: Stuff

Things have materialproperties and structural properties.

Biological materials are composed of carbohydrates, lipids, proteins and inorganic crystals.

force

lengthstuff

Materials can be divided into solids, liquids, and gases.

Lecture #3: Jumping Fleas