Download HPS211 - Lecture 11

HPS211!
Lecture 11!
Cells!
!
• Concepts were new, but there were similar ideas
floating around previously!
• Laboratory methods introduced to life sciences!
• Previously known as natural history.!
• More observational!
• Now became more experimental and relied
increasingly on laboratory experiments!
!
!
Agenda!
• Transformation of life science in 19th c.!
• Schleiden's and Schwann's cell theory!
• Founders of modern cell theory!
• Remak's and Virchow's theory of cell formation: cell
division!
• New directions of researches and thoughts!
!
Prior Cell Study!
• Studies of living organisms before the late 18th c!
• Natural history: field work, observe, collect,
classify species!
• Naturalists (eg. Darwin)!
Medicine:
form and functions of the human
•
body + internal organs!
• Studies of animals and plants as byproducts
for medical needs!
• Plants provide useful medicines!
• Animals for anatomical lessons (eg.
dissections)!
• Major Places for Biological Study: Faculties of
medicine, private collections!
!
The studies were before into two big sections: natural
history and medicine.!
!
• Transformation in the late 18th c!
• They started coming back from the fields and
took their work into their own collections and
"laboratories"!
• Shift focus from species in wild to the bodies of
organisms!
• Rise of morphology (eg. Cuvier's comparative
anatomy)!
• Museums of natural history as research centers!
• Prestigious science workers like Lamarck
worked as professors at the museums!
• Less renown scientists went into the field!
!
Transformation in the 19th c!
• Shifted from morphology (study of forms of plants
and animals) to study of function of the structures
(physiology)!
• Physiology became distinct from medicine!
• It was more of a science (like philosophy, study
for knowledge's sake), as opposed to the
practicality of medicine!
• Emphasis on experimental method, with advent of
new techniques: laboratory science!
• (eg. microscope, vivisection, tissue culture)!
• Vivisection was very controversial: dissection of
organisms while they are still alive!
• Animals and plant tissues were cultivated out of
nutrient solutions or solid nutrient materials!
• Very important for cellular research!
• New institutions in France & Germany!
• College de France: Francois Magendie &
Claude Bernard!
• Focus of developments in France!
• Major teaching and research institution. But
didn't offer degrees.!
• Offered positions for leading physiological
researchers!
• German Teaching laboratories at research
universities!
• University of Berlin: Johannes Muller!
• Trained a whole generation of German
physiologists!
!
• Carl Ludwig!
• Emil DuBois-Reymond!
• Hermann Helmholtz!
It was no longer loose form, in people's own homes.
It was now biology and life sciences.!
!
Microscope!
• Published Micrographia (1665)!
• Robert Hooke!
!
• Hooke Invented the microscope, observed many
things under it, published findings in his book.!
• He saw small boxes in cork (dried plant matter)!
• He called them "cells" => small rooms!
!
Many other researchers used the microscope too.!
Most famous after Hooke: Antonic van Leeuwenhoek!
• Made microscopes, first to observe living cells!
!
Back then, cells were just part of the structure. They
did not play any physiological role in the organisms.!
!
Robert Brown observed nucleus inside the cell.!
• Cells are more significant than just empty boxes.!
!
Karl Ernst von Baer!
• Identified ovum under microscope!
• Suggested cells played parts in the birth of
individual living beings!
!
!
Schleiden and Schwann came up with cell theory
mostly independently.!
!
Cell Theory!
• Observed that cells are present in almost all plant
and animal tissues!
• Still found traces of cells in nails, nerves, etc.
Places where cells were unlikely to be found!
• Believed cells are universal structural feature
among all living tissues!
Found
that cells comprises a body and a nucleus
•
within!
!
1838 - 1839!
Based on their observations, they concluded:!
1. All tissues of living beings are made of cells
(structural claim)!
2. Cells are the basic units of life; they are lively
themselves and are responsible for lively
phenomena of an organism (functional claim)!
!
Their Theory on Cell Formation!
• A new cell emerges from its mother cell!
• Chemical substance of mother's cell's nucleus spills
out to form a granule in the mother cell body!
• Granule grows as more nuclear substance deposits
on it!
• When the granule is large enough, it separates
from mother cell and grows further into a full cell!
• A process similar to crystallization; inorganic
chemical reaction!
• Free cell formation!
!
!
This Free Cell Formation theory was rejected by
many researchers in Europe.!
Robert Remak and Rudolph Virchow from Berlin
were especially vocal about their opposition.!
Were both students and assistance of Johannes
Muler.!
At that time, Jews weren't allowed paid positions at
universities, so he took up an unpaid position under
Muler.!
!
Remak and Virchow's Theory of
Cell DIvision!
• New cell is formed through division from an existing
cell!
• Only way of cell formation!
• Cell formation is not inorganic, not through
crystallization!
• Virchow's slogan in 1855: omnis cellula e cellula!
• Every cell is from a preexisting cell!
!
Rejected the inorganic process. All cells MUST come
from preexisting cells.!
!
Vitalism vs. Materialism!
Materialism!
• Organisms are like machines!
• Life can be reduced to physical and chemical
effects!
!
• Became quite popular among mechanical
philosophers!
• DesCartes!
• Boerhaave!
• Buffon!
• Helmholtz!
• Schleiden!
• Free cell formation was part of this!
!
Vitalism!
• Organisms require some vital forces or agents!
• Life cannot be reduced to physical & chemical
effects!
• Even by putting the required chemicals together,
you still need to "blow" some liveliness into the
mass in order to make it live!
!
• Backers included:!
• Stahl!
• Linnaeus!
• Muller!
• Remak!
!
Spontaneous Generation was at the center of this
debate!
• Many materialists supported the idea of
spontaneous generation!
• Free cell formation was considered spontaneous
generation!
• It's replacement with cell division was
considered a victory of vitalism over materialism!
!
Cells with a Simple Structure!
• Hooke believed cells were just empty boxes!
• Then Schwann believed cells have nucleus, stuff
inside (cytoplasm), and the cellular membrane!
!
Second half of 19th c.!
• Biologists found a variety of entities within the cells!
• Cell structure is much more complicated then that
of Schwann and Schleiden!
!
Improvements in Microscope Techniques!
• Compound lens microscopes to overcome spherical
and chromatic aberrations!
• Staining techniques!
• Microtome techniques (thin sections of tissue)!
• Tissue cultures!
!
Theory of Cell State!
• A sociological metaphor of life: an organism as a
"state" of individual cellular organisms!
• "Division of labor" developed as number multiplies!
• The whole organism is reduced to the sum of
individual cells!
!
• Counterpoint!
• holism, the whole is more than the sum of
individuals!
• Organisms as a complex integrated system!
• Homeostatis & teleology!
!
Embryology & Heredity!
• Cell theory and microscopy enabled biologists to
follow the development of an organism from a
fertilized ovum to an embryo and eventually to an
adult!
• Significance of nucleus in cell division!
• Often started with nucleus!
• Chromatin forms chromosomes!
• Chromosomes remain same )meiosis) or halved
(meitosis) after division!
!
Embryology!
Study of the development of animals (also sometimes
plants)!
!
Weismann's Theory!
• Heredity pass down through germ cells (sperm &
ovum)!
• Hereditary substance in a cell is in it's nucleus!
• Chromosomes are likely the carriers of heredity