What plausible hypothesis could account for the origin of life?
What intermediate stages could there have been between non-living matter and the first living cells?
What are the 3 principles of cell theory?
A2.1 Origin of Cells
Guiding Questions
A2.1 Origin of Cells
Can science explain the origin of life?
Guiding question
A2.1.1—Conditions on early Earth and the pre-biotic formation of carbon compounds | Include the lack of free oxygen and therefore ozone, higher concentrations of carbon dioxide and methane, resulting in higher temperatures and ultraviolet light penetration. The conditions may have caused a variety of carbon compounds to form spontaneously by chemical processes that do not now occur |
A2.1.2—Cells as the smallest units of self-sustaining life | Discuss the differences between something that is living and something that is non-living. Include reasons that viruses are considered to be non-living. |
A2.1.3—Challenge of explaining the spontaneous origin of cells | Cells are highly complex structures that can currently only be produced by division of pre-existing cells. Students should be aware that catalysis, self-replication of molecules, self-assembly and the emergence of compartmentalization were necessary requirements for the evolution of the first cells. |
A2.1.4—Evidence for the origin of carbon compounds | Evaluate the Miller–Urey experiment. |
A2.1.5—Spontaneous formation of vesicles by coalescence of fatty acids into spherical bilayers | Formation of a membrane-bound compartment is needed to allow internal chemistry to become different from that outside the compartment |
A2.1.6—RNA as a presumed first genetic material | RNA can be replicated and has some catalytic activity so it may have acted initially as both the genetic material and the enzymes of the earliest cells. Ribozymes in the ribosome are still used to catalyse peptide bond formation during protein synthesis |
A2.1.7—Evidence for a last universal common ancestor | Students should develop an appreciation of the immense length of time over which life has been evolving on Earth |
A2.1.8—Approaches used to estimate dates of the first living cells and the last universal common ancestor | Students should develop an appreciation of the immense length of time over which life has been evolving on Earth |
A2.1.9—Evidence for the evolution of the last universal common ancestor in the vicinity of hydrothermal vents | Include fossilized evidence of life from ancient seafloor hydrothermal vent precipitates and evidence of conserved sequences from genomic analysis. |
So… what came first…?
A2.1 Origin of Cells
Justify your answer
A2.1.4 Evidence for the origin of carbon compounds
List things we would need to create life on Mars
A2.1 Origin of Cells
Can we live on Mars? Justify your answer
A2.1.4 Evidence for the origin of carbon compounds
Challenge: What processes and/or molecules would need to be present? How do we create life?
A2.1 Origin of Cells
What are the principles of cell theory?
A2.1.2—Cells as the smallest units of self-sustaining life
1. All living things are composed of cells (or cell products)
2. Cells are the smallest unit of life
3. Cells only arise from pre-existing cells
Challenge: What are the exceptions to the cell theory and why?
Challenge: Why are viruses consdered to be non-living?
All cells have:
A2.1 Origin of Cells
What do we know about cells?
A2.1.1—Conditions on early Earth and the pre-biotic formation of carbon compounds
A2.1 Origin of Cells
What are the principles of cell theory?
A2.1.2—Cells as the smallest units of self-sustaining life
1. Cells are highly complex structures and no mechanism has been found for producing cells from simpler subunits.
What are the principles of cell theory?
2. All known examples of growth be it of a tissue, an organism or a population, are all a result of cell division.
A2.1 Origin of Cells
A2.1.2—Cells as the smallest units of self-sustaining life
What are the principles of cell theory?
3. Viruses are produced from simpler subunits, but they do not consist of cells, and they can only be produced inside the host cells that they have infected.
A2.1 Origin of Cells
A2.1.2—Cells as the smallest units of self-sustaining life
What are the principles of cell theory?
4. Genetic code is universal each of the 64 codons (a codon is a combination of 3 DNA bases) produces the same amino acid in translation, regardless of the organism
The logical deduction is that all cells have arisen as the result of cell division from a single common ancestor.
A2.1 Origin of Cells
A2.1.6—RNA as a presumed first genetic material
A2.1 Origin of Cells
Can we live on Mars? Justify your answer
A2.1.4 Evidence for the origin of carbon compounds
A2.1 Origin of Cells
What was early Earth like 4.7 billion years ago?
A2.1.4 Evidence for the origin of carbon compounds
A2.1 Origin of Cells
What was early Earth like 4.7 billion years ago?
A2.1.4 Evidence for the origin of carbon compounds
Ozone (O3) is a form of oxygen that is found in the stratosphere, a region of the atmosphere located approximately 10 to 50 kilometers.
The ozone is controlled by the presence (or lack) of oxygen molecules.
A2.1 Origin of Cells
Suggest reasons why the presence of oxygen has affected life on Earth.
A2.1.4 Evidence for the origin of carbon compounds
A2.1 Origin of Cells
Suggest reasons why the presence of oxygen has affected life on Earth.
A2.1.4 Evidence for the origin of carbon compounds
1. The non-living synthesis of simple organic molecules (from inorganic compounds) such as sugars and amino acids
2. The assembly of these organic molecules into polymers
3. The formation of plasma membranes
4. DNA and enzymes (RNA can replicate, catalyse reactions and act as instructions)
A2.1 Origin of Cells
Four processes needed for spontaneous life on Earth
A2.1.1—Conditions on early Earth and the pre-biotic formation of carbon compounds
Chemical Evolution
A2.1 Origin of Cells
From these 4 requirements for life.. which came first? why?
A2.1.3—Challenge of explaining the spontaneous origin of cells
Plasma membranes (Protocells)
Genes RNA can replicate
Metabolism catalyse reactions
Organic synthesis requires the presence of a range of inorganic molecules and an energy source to combine them into organic forms
A2.1 Origin of Cells
Where did the inorganic molecules and energy come from?
A2.1.4 Evidence for the origin of carbon compounds
A2.1 Origin of Cells
A2.1.4 Evidence for the origin of carbon compounds
Hydrothermal vents: Regions of the ocean floor where superheated water is released from the Earth's crust
A2.1 Origin of Cells
A2.1.4 Evidence for the origin of carbon compounds
Volcanoes: Intensive volcanic activity could provide sufficient thermal activity either on land or under the seabed
A2.1 Origin of Cells
A2.1.4 Evidence for the origin of carbon compounds
Extraterrestrial locations: Other planets (e.g. Mars) may have been subjected to appropriate conditions (compound transfer via meteorites)
A2.1 Origin of Cells
A2.1.4 Evidence for the origin of carbon compounds
Miller and Urey recreated the conditions of pre-biotic Earth in a closed system consisting of a series of flasks and tubes
A2.1 Origin of Cells
What did Miller and Urey do?
A2.1.4—Evidence for the origin of carbon compounds
Methane & Ammonia
Water (Ocean)
Organic Molecules were synthesised
Amino Acids, Lipids and Sugars
Miller and Urey’s experiment:�- used high levels of methane (CH4) which was actually in relatively low abundance
-used Electrical discharges instead of UV light
A2.1 Origin of Cells
What did Miller and Urey do?
A2.1.4—Evidence for the origin of carbon compounds
Weak Hydrophobic Interactions enables the cell membrane to be fluid and flexible.
B2.1.13—Membrane fluidity and the fusion and formation of vesicles
B2.1 Membranes and Membrane Transport
Breaking and building the cell membrane requires ATP.
B2.1.13—Membrane fluidity and the fusion and formation of vesicles
B2.1 Membranes and Membrane Transport
Endocytosis
Exocytosis
Pinocytosis - Microvilli
Phagocytosis - Immune Response
RM Endocytosis - Cholesterol for Membrane Synthesis
B2.1.13—Membrane fluidity and the fusion and formation of vesicles
B2.1 Membranes and Membrane Transport
B2.2.9—Structure and function of vesicles in cells
B2.2 Organelles and compartmentalization
Clathrin
Membrane curvature
Clathrin Lattice Formed
Clathrin Coated Vesicle
Clathrin Uncoating
Transport vesicles, lysosomes and peroxisomes usually contain a single membrane. Phagolysosomes are usually double-membrane.
B2.2.9—Structure and function of vesicles in cells
B2.2 Organelles and compartmentalization
4. Formation of membranes to package the organic molecules
Experiments have shown that phospholipids natural assemble into bilayers, if conditions are correct.
Formation of the bilayer creates an isolated internal environment.
The formation of an internal environment means that optimal conditions, e.g. for replication or catalysis can be maintained.
A2.1 Origin of Cells
Four processes needed for spontaneous life on Earth
A2.1.5—Spontaneous formation of vesicles by coalescence of fatty acids into spherical bilayers
Coalescence is the process where two or more oil droplets merge together to form a larger oil droplet.
A2.1 Origin of Cells
How do vesicles interact?
A2.1.5—Spontaneous formation of vesicles by coalescence of fatty acids into spherical bilayers
A2.1 Origin of Cells
What is the central dogma?
A2.1.6—RNA as a presumed first genetic material
Ribozymes - | | act as catalysts |
Proteins (enzymes) | contains genetic material and catalyst to make more proteins | |
RNA | RNA molecules that have catalytic properties |
A2.1 Origin of Cells
A2.1.7—Evidence for a last universal common ancestor (LUCA)
A2.1 Origin of Cells
A2.1.8—Approaches used to estimate dates of the first living cells and the last universal common ancestor
A2.1 Origin of Cells
A2.1.9—Evidence for the evolution of the last universal common ancestor in the vicinity of hydrothermal vents
A2.1 Origin of Cells
A2.1.9—Evidence for the evolution of the last universal common ancestor in the vicinity of hydrothermal vents
Watch to 1 min 40 secs:
A2.1 Origin of Cells
Spontaneous Generation
1.5.U2 The first cells must have arisen from non-living material.
But when Pasteur broke the swan neck off the bottle microorganisms soon grew in the broth.
A2.1 Origin of Cells
Pasteur’s Swan Neck Flask Experiment
Estimating the dates of the first living cells and the Last Universal Common Ancestor (LUCA) is a challenging task due to the limited availability of direct evidence from the distant past.
A2.1 Origin of Cells
What did Miller and Urey do?
A2.1.8 Approaches used to estimate dates of the first living cells and the last universal common ancestor