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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