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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?