The Molecular Dance

Lecture 5Lecture 5Biophys Demystified Ch5

Biophys Nelson Ch3

To gain orderTo gain order….

• Cool down….

Question: Why is the nanoworld so different f th ld?from the macroworld?

Probabilistic FactsProbabilistic Facts

• “Random” • MeasurementMeasurement• Distribution

Class scoreClass score

• Student number 100• Midterm average =70Midterm average 70

• Did you pass?

A realistic worldA realistic world

• One atom• Two atomsTwo atoms• 10 atoms• 10^25 atoms

Discrete DistributionDiscrete Distribution

• Probability of observing xi is P(xi)• Ni/N P(xi) for large NNi/N P(xi) for large N

• Normalization

Continuous DistributionContinuous Distribution

A Lesson from HeredityA Lesson from Heredity

• A puzzle of life…• Generic InheritanceGeneric Inheritance• A story need some physicists…

Small man in a SpermSmall man in a Sperm

• What are purpose of ‘sperm’ and ‘egg’?

What is the ‘information carrier’What is the information carrier

• A CD contains about 1010 bits• A sperm contains about the sameA sperm contains about the same

information but only a micrometer long…

• Please don’t make mistakes during ease do t a e sta es du gcopying…

1865 Mendel1865 Mendel

• System: Flowering Pea plant• Good training in Physics and MathGood training in Physics and Math• Clear results….almost

• But fell into obscurity• But fell into obscurity….

Mendel’s ConclusionsMendel s Conclusions

• The cell making up most of an individual each carry two copies of each factor. y p

• Germ cells (sperm, pollen and eggs) are exceptional They contain only one copy ofexceptional. They contain only one copy of each factor.

• Meiosis chooses each factor randomly and independently of the others.independently of the others.

The color of LabradorThe color of Labrador

• Labrador Retrievers: Black, Yellow, and Chocolate. • Color is determined primarily by two genes. • The first gene (the B locus) determines the density of the

coat's pigment granules: dense granules result in a blackcoat s pigment granules: dense granules result in a black coat (B), sparse ones give a chocolate coat (b).

• The second (E) locus determines whether the pigment is d d t ll A d ith th i ( ) ll l illproduced at all. A dog with the recessive (e) allele will

produce little pigment and will be yellow regardless of its genotype at the B locus.

• For example, BBEE(Black), BBee(Yellow), bbEe(Chocolate))

• Please estimate the number ratio of puppies’ color if theirPlease estimate the number ratio of puppies color if their parents both have the BbEe genes.

ChromosomesChromosomes

Genetic LinkageGenetic Linkage

• System: Fruit Fly Drosophila melanogaster

From fruit fly studyFrom fruit fly study

• The physical carrier of genetic information are chromosomes.

• They are chains, 1-D informations.

SchrodingerSchrodinger

• In 1944, ‘What is life?’

Max Delbrück

The X ray golden ageThe X-ray golden age

• What is the ‘carrier’?• What are inside ‘chromosome’What are inside chromosome proteins, DNA, and RNA

Double HelixDouble Helix

• When Watson meets Crick…1950s

• Some facts…• # : A ~ T, C~G• X-ray data suggests helical structure• X-ray data suggests helical structure…(Data from Rosalind Franklin)• But how can they arrange into this?