Download Topic 1.5 Cell Biology

Cell Biology
Topic 1.5
Origin of Cells
• According to the cell theory, all cells come
from pre-existing cells
• Sperm and egg join to make a zygote
• Zygote divides repeatedly to form embryo
• What about the first cell??
• They would need to have arisen from nonliving material
Origin of Cells
• Spontaneous generation is the formation of
living thins from non-living matter
• Theophratus- Silphium plant
• Aristotle-insects from dew or hair
• Paracelus-mice from decaying matter
• Francesco Redi-rotting meat and flies
Origin of cells
Origin of Cells
• Louis Pasteur
spontaneous generation
experiments
• Boiled (control) and
unboiled
(experimental)broth in
long necked flasks
Origin of cells
• Cells may have formed over hundreds of
millions of years of evolution
• In a series of stages:
1. Production of carbon compounds such as amino acids
and sugars
2. Assembly of carbon compounds into polymers
3. Formation of membranes
4. Development of a mechanism of inheritance
Origin of cells
• Miller and Urey
simulated the earth’s
early atmosphere
• They were able to
produce amino acids
and other carbon
compounds needed for
life
Origin of cells
• Deep ocean vents also
simulate the early earth
• Provide and energy
source for the
formation of carbon
compound polymers
• Iron sulfide
• chemosynthesis
Origin of cells
• Formation of membranes
• Creates an inside environment different from
the outside
• Phospholipids behave this way naturally
• Show video!
Origin of cells
• Mechanism of inheritance
• In order for DNA to replicate it needs
enzymes(catalysts) , but enzymes are coded
by genes
• “chicken and the egg”
• May have been an earlier stage where RNA
was the genetic material
• It can act as genetic material and a catalyst
Origin of cells
Endosymbiotic theory
• Supports the evolution of some prokaryotes
into eukaryotes
• Theory that mitochondria and chloroplasts
were once free living prokaryotes
• Larger anerobic prokaryotes took them in by
Endocytosis (engulfing) but did not eat them!
• They were instead used for energy production
Endosymbiotic theory
• Symbiotic relationship/mutualism
• Large prokaryote provides food and small
prokaryote provides energy
Endosymbiotic theory
Evidence that supports the theory:
• Both chloroplasts and mitochondria contain their
own DNA (circular piece of DNA similar to other
prokaryotes)
• They also contain ribosomes that are similar to
the ribosome found in prokaryotes (70s subunits)
• They also produce some of their own proteins
• They can only be produced by division of preexisting mitochondria/chloroplasts
Endosymbiotic theory