Transcript Little bit of history

Introduction to Biophysics
Lecture 6
Physical carriers of genetic information
Central Dogma of Molecular Biology
Formation of double helix is highly cooperative process
Pitch 3.4 nm
Chemically, DNA consists of two long polymers of units called nucleotides, with
backbones made of sugars and phosphate groups joined by ester bonds. These two
strands run in opposite directions to each other and are therefore anti-parallel.
The two strands of DNA in a double helix can therefore be pulled apart like a zipper,
either by a mechanical force or high temperature.
Main function – information storage
DNA polymers can be enormous molecules
containing millions of nucleotides. For instance,
the largest human chromosome, chromosome
number 1, is approximately 220 million base
pairs long (calculate length).
Stabilization:
Stacking interaction between the
aromatic bases (dispersion forces).
H-bonds in Watson-Crick base pairs
Electrostatic interaction between
charged phosphates
Little bit of history
Gregor Mendel (1822-1884)– monk trained in physics and
mathematics.
Model system – flowering pea plant, Pisum sativum
7 heritable features: flower position, seed color, seed shape, ripe
pod shape, unripe pod color, flower color, stem length.
2 option for each.
Observation: sufficiently simple traits are inherited in a discrete,
yes/no manner. Genetic code = collection of switches (factors).
Alleles – the various available option for one factor.
Conclusions: Each somatic cell carries 2 copies of each factor but
germ cell – carries one copy. Meiosis chooses each factor randomly.
Dominant versus
recessive
Glossary:
Meiosis is a process of reduction division in which the number of chromosomes
per cell is cut in half. In animals, meiosis always results in the formation of
gametes. Meiosis is essential for sexual reproduction and therefore occurs in all
eukaryotes (including single-celled organisms) that reproduce sexually.
Mitosis is the process by which a eukaryotic cell separates the chromosomes in
its cell nucleus, into two identical sets in two daughter nuclei.
Classical genetic
Cell Biology
By this time role of nucleus in the passing of genetic information has been
recognized.
Nucleus organizes itself into threadlike chromosome just before division.
Just before division each chromosome double.
1900 – H. de Vries, K. Correns, E. von Tshermak rediscovered Mandel’s work.
Mendel’s genetic “factors” = are physical objects = genes locate on chromosome
But what are chromosomes???
Not all traits assorted independently.
Certain pairs of traits seemed to be linked.
T.H. Morgan (1909) – model- fruit fly Drosophila - patiense to look for subtle
statistical patterns.
Very really linked traits would separate.
Chromosome pairs were observed to wrapping around each other.
Breakage and exchange of chromosome pieces??
If chromosome is a threadlike then genetic factors must be in a fixed sequences.
4 unlinked groups
Classical genetics and cell biology – no further progress on understanding chromosomes.
Schrödinger –gene - nearly perfect fidelity of their information storage despite their
miniature size.
Object of molecular scale
Single molecule???
Exposure to X-rays induces
mutations
Ones formed they spread
in population by same
rules as normal genes.
Gene is a single molecule
Probability of mutation = P1c* = P1Kcion
P1 – chance for gene to suffer particular mutation if it is located in the volume .
Transmission of order from one organism to it’s descendants
The major advance in understanding the nature of gene mutation and gene structure.
The work was a keystone in the formation of molecular genetics.
Repeat Central Dogma of Molecular Biology with movie
http://www.youtube.com/watch?v=yqESR7E4b_8
Reading: finish Nelson Chapter 3.
Homework: Problems 3.3 and 3.4 page 105