Download Le Louis - LaPazChirripoColegio2016-2017

Louis Pasteur (1822-1885)
“LE LOUIS”
Unit 1.5
Application: evidence from Louis Pasteur’s
experiments that spontaneous generation of cells
and organisms does not NOW occur on earth
What is a theory?
What is a theory?
• Statement to represent a well-substantiated explanation of a natural
phenomenon that incorporates tested hypothesis and laws.
• What theory have we looked at recently?
Louis Pasteur: evidence for our cell theory
Louis Pasteur: evidence for our cell theory
• all organisms are composed of
one or more cells
• Cells are the smallest unit of life
• Cells come from pre-existing
cells
What is a theory?
• Statement to represent a well-substantiated explanation of a natural
phenomenon that incorporates tested hypothesis and laws.
• Can there be exceptions to the rules?
• Are there exceptions to our cell theory?
Exceptions to current cell theory
cells always function as
autonomous units
living structures are
composed of discrete
cells
larger organisms are
always made of many
microscopic cells
Grandest exception: Where did the first cells
come from?
• Of course not known at this point
• To start to form an understanding we look at how cells could progress
from a simple non compartmentalized prokaryote to a complex highly
compartmentalized eukaryote.
• ENDOSYMBIOTIC THEORY
• Margulis, 1981
2B, PE, ?, E < P, E no <P, E L P, P ∆, EP
IN this exchange the eukaryote helped the bacteria by
providing protection and carbon compounds. After changing
the bacteria became an ATP specialist
• Evidence for mitochondria as evolved bacteria
• Size, about that of bacteria
• Division? BF
• Divide independently? yes
• Have their own ribosomes? 70s
• Have their own DNA which resembles the DNA of prokaryotic more
than that of the eukaryotic?
• Have 2 membranes on exterior, consistent with engulfing?
More evidence for endosymbiosis:
chloroplasts in plant cells
• Protist called Hatena
• Normally ingests organic matter as
a consumer to meet nutritional
requirements
• However, when it has the
opportunity it ingests algae, it
switches to using the algae to
create energy by photosynthesis,
the 2 organisms thrive as one
symbiotically
More: elysia chlorotica
• Slug
• Juvenile brown mobile stage it
behaves as a consume r taking
nutrients from its environment
• If it comes into contact with
green algae and consumes it, it
incorporates the algae in its
digestive and becomes a green
sedentary adult slug
Further evidence: DNA Barcoding
• The mitochondrial DNA is used
why?
• In plants the DNA of chloroplasts
are used, why?
The PBL
The fluid-mosaic model (PBL) was not the first accepted model to
describe membrane structure
The first model to describe the position of proteins within the bilayer
was proposed by Hugh Davson and James Danielli in 1935
• DD proposed a “lipid-protein” sandwich model whereby two layers of
protein surrounded a central phospholipid bilayer
• 2 layers were identified (wrongly) as being two protein layers
Evidence that lead to the singer-nicholson
• There were a number of problems with the lipo-protein sandwich
model proposed by DD
• Not all membranes are identical or symmetrical, as the DD implied
• Membranes with different functions have different structure, can be
seen with microscope
• A protein layer is not likely because it would be mostly non polar and
would not be able to form a uniform and continuous layer around the
outer surface of a membrane
Falsification Evidence:
Membrane proteins were discovered to be insoluble in water (indicating
hydrophobic surfaces) and varied in size
• Such proteins would not be able to form a uniform and continuous layer around
the outer surface of a membrane
Fluorescent antibody tagging of membrane proteins showed they were mobile and
not fixed in place
• Membrane proteins from two different cells were tagged with red and green
fluorescent markers respectively
• When the two cells were fused, the markers became mixed throughout the
membrane of the fused cell
• This demonstrated that the membrane proteins could move and did not form a
static layer (as per Davson-Danielli)
Why o why no DD?
Osmolality lab: Plasmolysis
• Plasmolysis is the process in which cells lose water in a hypertonic
solution. The reverse process, cytolysis, can occur if the cell is in a
hypotonic solution resulting in a lower external osmotic pressure and
a net flow of water into the cell.