Transcript Brief Important Events in the Development of the Cell - Varga

Spontaneous Generation
Where do cells come from?
Abiogenesis
Early scientists believed that living things
formed from non-living things
spontaneously.
These early scientists
believed that frogs and
fish fell from the sky with
the rain.
Aristotle proposed that fish and frogs
came from the mud and that flies came
from rotting meat.
He introduced his theory of
ABIOGENESIS  theory which states that
nonliving things can be transformed into
living things spontaneously.
 This theory was accepted for more than
2000 years.
Jean van Helmont believed that mice
came from grains of wheat and dirty shirts.
Redi
Redi, in 1668, did an experiment to prove
that flies did not come from rotting meat.
- He had four jars each with a different
kind of meat (eel, fish, veal, and snake).
He put these meats in four other jars but
put lids on the jars.
- After time maggots were all over the
meat in the uncovered jars.
Redi
- Critics claimed that the difference was
fresh air.
- Redi repeated his experiment but this
time he put wire mesh over the jars. This
time no maggots were found.
- Redi concluded that flies do not come
from rotting meat.
Needham
In 1745 Needham boiled chicken broth
then put it into a flask
He wanted to see if microorganisms would
grow. He only boiled the broth for a short time,
so the microorganisms grew.
He supported spontaneous generation
Spallanazani
Spallanzani
He put the broth in a flask, sealed it, drew out
any air, he then boiled the broth.
Critics said that he only disproved that
spontaneous generation cannot occur
without air
Pasteur
 1859 Pasteur
He boiled a meat broth in a flask
Heated the flask’s neck until he could bend it into
an S shape. (Therefore air could enter the flask but
not airborne microorganisms, these organisms
would settle in the neck of the flask).
He found no microorganisms to grow in the broth.
When he tilted the flask so that the airborne
microorganisms could enter the flask, he found
growth in the flask.
http://www.youtube.com/watch?v=WNByRg
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Brief Important Events in the
Development of the
Cell Theory
Hooke (1635-1703): viewed pieces of cork through a microscope,
and described ‘cells’ in 1665.
 Leeuwenhoek (1632-1723): viewed small organisms, protozoa and
single celled organisms, under a microscope, which he called
‘animalicules’. He was the first person to observe bacteria.
 Lorenz Orken : He stated “all living organisms originate and
consist of cells”.
 Brown : first to coin the term nucleus, which he discovered in a
plant cell.
 Schwann and Schleiden : concluded that animals and plants
are made up of cells
Modern Cell Theory
All Living things are composed of cells.
The cell is the basic unit of life.
All cells arise from pre-existing cells. Cells
do not spontaneously arise or come from
non-living things.
Biogenesis

Is the idea that living things only arise
from other living things of the same type.
What did the first cells ‘look’ like?
Prokaryotes
Characteristics of a Prokaryotic Cell
Simple cells
Smaller than Eukaryotic cells
Lack a cell nucleus
Organelles lack membranes
Majority are unicellular (one cell)
Two Domains: archaea and bacteria
Prokaryotic Cell
Reproduce asexually usually by budding or binary
fission
Prokaryotic Cell
Structure:
cell wall
plasma membrane
nucleoid ( DNA (deoxyribonucleic acid) material)
ribosomes (function in protein synthesis)
plasmids (extra genetic material that is able to
replicate independently)
Pili
Cytoplasm
flagellum
One strand of DNA, usually circular
Eukaryotic Cells
Characteristics of a Eukaryotic Cell
Found in all 5 kingdoms EXCEPT monera
(bacteria)
Membrane bound organelles
Has a true nucleus
Unicellular and multi-cellular
Contains many strands of DNA
Larger than prokaryotic cells; 10-100 µm (1
micrometer = 0.000 1 centimeter)
 Structure of cell:
 Cytoplasm – gel like
 Mitochondria - energy source
 Cell membrane
 Nucleus ( the ‘control center’) – contains all the
cell’s genetic material.
Eukaryotic Cell
Vacuole (mostly in plant cells) - is a fluid
filled sac that stores materials
Ribosomes (can be attached to the ER or
are free) - are the site of protein synthesis
Eukaryotic Cell
Lysosomes (contain enzymes) - engulf
molecules
Chloroplasts (mostly in plant cells) - site of
photosynthesis
Eukaryotic Cells
Endoplasmic reticulum [ER] (made up of
heavily folded membranes) - is important
in protein and lipid synthesis
Golgi apparatus (is a stack of membranes)
- involved in packaging of proteins
Eukaryotic Cell
Cytoskeleton - supports and shapes the
cell
Centriole (made up of protein tubes) – aids
in mitosis
May or may not have flagellum.
Similarities between Prokaryotic and
Eukaryotic Cells
Which came first…..
Prokaryotic or Eukaryotic???
Endosymbiont Hypothesis
The idea that prokaryotic cells developed
into eukaryotic cells.
Endosymbiont or Endosymbiosis
Hypothesis
Endosymbiosis Hypothesis
endo = “within” sym = together biosis = “way of life”
The idea that mitochondria and
chloroplasts were at one time simple
bacteria (prokaryotic cells) that were taken
in by a larger prokaryotic cell about 1.5
billion years ago
These smaller bacteria gave the larger cell
energy and sugars (via photosynthesis)
The larger cell gave the smaller cell a safe
place to live.
Both cells benefitted.
Eventually the smaller cell became an
organelle apart of the larger cell.
Evidence
Mitochondria and chloroplasts have their
own DNA (deoxyribonucleic acids) and
ribosomes. Their DNA is circular and
similar to prokaryotes.
Mitochondria and chloroplasts are about
the same size as prokaryotes.
 Mitochondria and chloroplasts are able to
copy themselves within the cell.