The evolution of multicellular organisms allowed cell specialization and cell replacement. There is an unbroken chain of life from the first cells on Earth to all cells in organisms alive today.
General Understandings:
- According to the cell theory, living organisms are composed of cells.
- Organisms consisting of only one cell carry out all functions of life in that cell.
- Surface area to volume ratio is important in the limitation of cell size.
- Multicellular organisms have properties that emerge from the interaction of their cellular components.
- Specialized tissues can develop by cell differentiation in multicellular organisms.
- Differentiation involves the expression of some genes and not others in a cell’s genome.
- The capacity of stem cells to divide and differentiate along different pathways is necessary in embryonic development and also makes stem cells suitable for therapeutic uses.
- Cells can only be formed by division of pre-existing cells.
- The first cells must have arisen from non-living material.
- The origin of eukaryotic cells can be explained by the endosymbiotic theory.
What is the Cell Theory?
-All living things are made of one or more cells
-The cell is the smallest unit of life
-All cells come from pre-existing cells
Limitations of the Cell Theory:
-Muscles are elongated cells, which contain several nucleuses in one cell in order to control it (multi-nucleoid)
-Viruses: living or not? Cells or not?
-Fungal hyphae: acquires a continual cytoplasm, very large and multi-nucleoid.
-All living things are made of one or more cells
-The cell is the smallest unit of life
-All cells come from pre-existing cells
Limitations of the Cell Theory:
-Muscles are elongated cells, which contain several nucleuses in one cell in order to control it (multi-nucleoid)
-Viruses: living or not? Cells or not?
-Fungal hyphae: acquires a continual cytoplasm, very large and multi-nucleoid.
Louis Pasteur made a nutrient broth by boiling water containing yeast and sugar. He concluded that the germs in the air were able to fall unobstructed down the straight-necked flask and contaminate the broth. The other flask which had the “swan-neck”, trapped germs in its curved neck, preventing them from reaching the broth, which never changed color or became cloudy. This explains that spontaneous generation was not a real phenomenon since; the broth in the curved-neck flask would have eventually become re-infected because the germs would have spontaneously generated. But the curved-neck flask never became infected, indicating that the germs could only come from other germs.
Outline of the Miller Urey Experiment:
-About 4.6 billion years ago
-Conditions of pre-biotic Earth:
High Temperature
Lightning
Reducing Atmosphere
-The experiment simulates:
High-energy sources
Reducing Atmosphere
Result: Mixture of Amino Acids
The Miller Urey Experiment simulated the gases of:
CH4, NH3, N2
(HAM)
-Hydrogen
-Methane
-Ammonia
Why didn’t Peptide bonds formed?
Because there weren’t any enzymes and they were needed in order to from these Peptide bonds.
Relative Sizes of Cells
From Large to Small:
-Eukaryotic Cells: 100 µm
-Organelles: 10 µm
-Bacteria: 1 µm
-Viruses: 100nm
-Cell Membrane Thickness: 10nm
-Molecules: 1 nm
-About 4.6 billion years ago
-Conditions of pre-biotic Earth:
High Temperature
Lightning
Reducing Atmosphere
-The experiment simulates:
High-energy sources
Reducing Atmosphere
Result: Mixture of Amino Acids
The Miller Urey Experiment simulated the gases of:
CH4, NH3, N2
(HAM)
-Hydrogen
-Methane
-Ammonia
Why didn’t Peptide bonds formed?
Because there weren’t any enzymes and they were needed in order to from these Peptide bonds.
Relative Sizes of Cells
From Large to Small:
-Eukaryotic Cells: 100 µm
-Organelles: 10 µm
-Bacteria: 1 µm
-Viruses: 100nm
-Cell Membrane Thickness: 10nm
-Molecules: 1 nm
What is needed for the Spontaneous Origin of Life?
-The synthesis of simple organic molecules (amino acids) from inorganic molecules (water, carbon dioxide, ammonia)
-The assembly of these molecules into polymers (chains of amino acids)
-The formation of polymers that can self-replicate themselves to allow inheritance of characteristics.
-The development of membranes that have internal chemical differences from their surroundings.
Necessary Functions Cell Carry Out:
Growth: an irreversible increase in size
Homeostasis: keeping conditions inside the organisms within tolerable limits
Metabolism: chemical reactions inside the cell, including cell respiration to release energy
Nutrition: obtaining food, to provide energy and the materials needed for growth
Reproduction: producing offspring either sexually or asexually
Sensitivity: perceiving and responding to changes in the environment
Endosymbiotic Theory: Theory that chloroplasts and mitochondria were once free-living prokaryotes that were engulfed by larger prokaryotes and survived to evolve into modern organelles.
-The synthesis of simple organic molecules (amino acids) from inorganic molecules (water, carbon dioxide, ammonia)
-The assembly of these molecules into polymers (chains of amino acids)
-The formation of polymers that can self-replicate themselves to allow inheritance of characteristics.
-The development of membranes that have internal chemical differences from their surroundings.
Necessary Functions Cell Carry Out:
Growth: an irreversible increase in size
Homeostasis: keeping conditions inside the organisms within tolerable limits
Metabolism: chemical reactions inside the cell, including cell respiration to release energy
Nutrition: obtaining food, to provide energy and the materials needed for growth
Reproduction: producing offspring either sexually or asexually
Sensitivity: perceiving and responding to changes in the environment
Endosymbiotic Theory: Theory that chloroplasts and mitochondria were once free-living prokaryotes that were engulfed by larger prokaryotes and survived to evolve into modern organelles.
Mitochondria and Chloroplast:
-Both have a double membrane (the second outer membrane from the host, the eater)
-Have a look of naked DNA, lacking histone proteins
-Divide by binary fission
-Small 70S ribosomes (not 80S eukaryotic ribosomes)
Why is Cells Small?
-Surface area determines rate of exchange
-Volume determines metabolism
-The smaller the surface are to volume ratio, the faster rate of exchange and metabolism; “As cell size increases, volume increases proportionally faster than SA => SA: V ratio decreases”
-Both have a double membrane (the second outer membrane from the host, the eater)
-Have a look of naked DNA, lacking histone proteins
-Divide by binary fission
-Small 70S ribosomes (not 80S eukaryotic ribosomes)
Why is Cells Small?
-Surface area determines rate of exchange
-Volume determines metabolism
-The smaller the surface are to volume ratio, the faster rate of exchange and metabolism; “As cell size increases, volume increases proportionally faster than SA => SA: V ratio decreases”
Stem cells: Cells that retain capacity to divide and differentiate along different pathways.
Differentiation of Cells
-Each specialized to carry out a subset of functions; greater efficiency
-Achieved through differential gene expression
-All cells in an organism have identical DNA
Reductionism: reduce phenomenon to its constituent parts.
-Smallest parts are predictable then the system as a whole is predictable.
-No new properties will arise from the sum of the parts
-Each specialized to carry out a subset of functions; greater efficiency
-Achieved through differential gene expression
-All cells in an organism have identical DNA
Reductionism: reduce phenomenon to its constituent parts.
-Smallest parts are predictable then the system as a whole is predictable.
-No new properties will arise from the sum of the parts
There is a difference between the living and the non-living environment. How are we able to know the difference?
Due to the cell theory that all living things are made up of one or more cells, the difference between living and non-living organisms is that although both contain atoms, living organisms have cells a within them and non-living organisms only contain atoms. In order to test a living organism experiments can be done in which cellular substances are taken from the organism, and test if there is DNA or not within it.
Biology is the study of life, yet life is an emergent property. Under what circumstances is a systems approach productive in biology and under what circumstances is a reductionist approach more appropriate? How do scientists decide between competing approaches?
Depending on the experiment, it should be approached as reductionist or not. Usually in the biological world, experiments are approached to with the scientific method or a system in which steps are to be followed. In experiments such as analyzing new data or experiments that were never talked about before, reductionist approachs should be considered since there is no other method to do so.
Due to the cell theory that all living things are made up of one or more cells, the difference between living and non-living organisms is that although both contain atoms, living organisms have cells a within them and non-living organisms only contain atoms. In order to test a living organism experiments can be done in which cellular substances are taken from the organism, and test if there is DNA or not within it.
Biology is the study of life, yet life is an emergent property. Under what circumstances is a systems approach productive in biology and under what circumstances is a reductionist approach more appropriate? How do scientists decide between competing approaches?
Depending on the experiment, it should be approached as reductionist or not. Usually in the biological world, experiments are approached to with the scientific method or a system in which steps are to be followed. In experiments such as analyzing new data or experiments that were never talked about before, reductionist approachs should be considered since there is no other method to do so.