Lecture 2Monday, January 26, 2004

• Survey

• Introduction continued :CSK, tensegrity.

• Basic cellular components

Geodesic- Buckminster Fuller

A geodesic dome uses a pattern of self-bracing triangles in a pattern that gives maximum structural advantage, thus theoretically using the least material possible. (A "geodesic" line on a sphere is the shortest distance between any two points.)

Nucleus connected to the CSK, modeledwith straws.

Ten

segr

ity

How does the CSK provide structure?

Some results are not compatible with tensegrity model

Signals travel at speed of sound, as expected for a tensegrity model.

With or without microtubules

Percolation: an alternate theory

LA NY

Figure 1.9 Hypothetical telephonenetwork in the U.S.

Malines, Belgium

Fibroblast

Pulling out the chromosomes

A micropipet can suck up the end of a chromosome and then the entire 23 Can be pulled out, indicating they are all connected.

Cells incorporate intoNano-fabricated devices

Attaching to needles

Stretching on a cantilever

Growing on electrodes

The generic cell

Basic structureAnd components

Building blocks

• Water• Cl, Na, K, Ca, Mg (50) - Electrolytes• Fatty acids-lipids- (200) Phospholipids• Amino Acids- (115) Proteins• Sugars- (100) Carbohydrates• Sugars + Bases (200) Nucleotides

• 30-200 Daltons 103 -106 Daltons• I.e number of aa’s for spectrin = 230,000 D• 115

H2O

Compound Fraction in Cell(%)

Relative Size of molecule

Polarity of molecule

Water 70-80 Small Polarized

Protein (Polypeptide)

10-20 Large Regionally polarized

Lipid(Fat)

2-20 Medium Non-Polarized

Carbohydrate(Sugars)

1-2 Medium to large

Regionally polarized

Salts(Electrolytes)

1 Small Polarized

Lipid vesicles are ghost-like

3. Vesicles pass through each other.

2. Pipet pushes vesicle out.

1. Vesicles make contact

H2O

Hydrophobic core

Polar Phosphate Heads

70 A

H2O

H2O

Proteins

• Primary, secondary, tertiary, quaternary structures

• Make filaments: rods, tubes,

• Flexural Stiffness

4RI

IYK f

Rod Bending

Polymer Length-stiffness

• Persistence length

• Acid-base reactions determine charge, that determines mechanical properties .

• HA

• pKa=pH +log[HA]• [A-]

H+ + A-

Cartilage

Swelling pressure = osmotic pressure-elastic (compressive) pressure

H20

Polymer-polymerIntra-polymerosmosis

FactorsCa++, pH

Cell inside is a gel : a state of matter whereby electro-osmosis produced by charged polymers causes water pressure inside.

Structure by light & immunofluorescence

PMT

Filter

Fibroblasts are stained with Phallacidin green for F actin,Texas red for microtubules, and DAPI for nucleic acid.

F actin microtubules

F actin is green with Phalloidin, G actin is red with Texasred. Nucleus has fewer stress fibers, but is thicker thanrest of cell, so red is diffuse.

F actin G actin

Studying the CSK: “Knock-out” methods

• Spectrin• Actin• Microtubules• Intermediate

Filaments

• Heat• Cytochalasin• Nocodazole• Acyrlamide

Swelling and Lysis to measure membrane strength

• RBCs

Muscle

3%

50%

Frog

Pipet Aspiration

Neutrophils are WBCs involved in immune response.The source of cortical tension is unknown, but may befrom actin tangential to surface.

Cells are Wiggly and Soft

New ways to describe softness- difference between cookedand uncooked noodles: thermal fluctuations.

Neutrophils are WBCs involved in immune response.The source of cortical tension is unknown, but may befrom actin tangential to surface.

Fibroblast dividing