Origin of Cells

Macromolecules are used

in cells 

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. 

 

Organic Compounds

Carbon-containing molecules and have C-C and C-H bonds 

Exceptions of Organic Compounds

Oxides, cyanides (HCN) and carbonates (eg, HCO₃) 

Inorganic Compounds:

All the other compounds that are not organic 

Oparin and Haldane suggest that the

prebiotic Earth’s atmosphere was significantly different than today.

Evidence suggests that Earth’s prebiotic atmosphere was primarily composed of

Nitrogen, Carbon Dioxide, Methane and Hydrogen

The Carbon Dioxide Resulted from

volcanic eruptions and water vapour

The methane resulted from

volcanic eruptions

There was no oxygen gas or ozone (O₃) present in the atmosphere, as

oxygen gas was first released into the atmosphere by photo synthesis  

Elements Present:

CO₂, CH₄, H₂O, N 

Aleksandr Ivanovich Oparin

1894 - 1990

John Burton S. Haldane

1892 - 1964

Carbon dioxide and methane

are heat-trapping greenhouse gases.

The high concentration of CO₂ resulted in

high temperature.  

The lack of ozone layer resulted in

high levels of ultraviolet light entering the atmosphere 

Oparin and Haldane proposed that the

energy available from ultraviolet light and higher temperatures (as well as lightening and volcanic activity) on the prebiotic Earth allowed the spontaneous generation of organic compounds.

Over time, the organic molecules became more

complex eventually leading to self-replicating structures (RNA) and to the first cells.  

Once living organisms had evolved they caused

enormous changes to conditions on Earth. Oxygen levels started increasing.

This lead to formation of the

ozone layer so the greenhouse effect decreased.  

The Cell theory states that:  

1. Cells are the basic unit of life 

2. All Organisms are composed of at least one cells 

• 3. All cells come from pre-existing cells 

1. Cells are the

1. basic unit of life 

1. All Organisms are

1. composed of at least one cells 

• 1. All cells come from

pre-existing cells 

Characteristics of Life 

movement, respiration, sensitivity, homeostasis, growth, reproduction, excretion, nutriotion

Movement

an actions by an organism or part of an organism causing a change of position or place.  

Respiration (metabolism)

the chemical reactions in cells that break down nutrient molecules and release energy for metabolism.  

Sensitivity (Response to stimuli):

the ability to detect and respond to changes in the internal or external environment.  

Homeostasis:

process of maintaining a constant internal environment

Growth:

a permanent increase in size and dry mass 

Reproduction:

the processes that make more of the same kind of organism  

Excretion:

the removal of the waste products of metabolism and substances in excess of requirements  

Nutrition:

the taking of materials for energy, growth and development + made up at least once cell that contain genetic information in the form of DNA. 

 

Viruses are

not Alive 

Living organisms should possess

all of the characteristics of life.

Viruses do have genetic material (DNA or RNA) however they

do not possess most of the characteristics of life.  

Viruses do not have

cells which carry out metabolism and homeostasis.

Viruses cannot

respond to stimuli, and they do not grow 

Viruses are not capable of

reproducing themselves. They are replicated by host cells. 

Cells are

highly complex structures that can currently only be produced by division of pre-existing cells.

Requirements for the development of the first cells. 

catalysis, self-replication, self-assembly, compartemntaliaztion

Catalysis:

controlling which chemical reactions occur by speeding up specific reactions.  

Self-replication of molecules as a

basic for inheritance and persistence of successful variants 

Self-assembly:

carbon compounds must assemble to from polymers 

The emergence of compartmentalization a membrane must

develop to enclose cell contents

Miller and Urey carried out an experiment to

test Haldane and 

Oparin's hypothesis that the macromolecules of life could have 

spontaneously generated on a prebiotic Earth. 

Miller and Urey attempted to

simulate the conditions on a prebiotic Earth in a laboratory setting. 

The gases used in the experiment were

methane, ammonia, and hydrogen along with water vapor represented the prebiotic atmosphere. 

Water was used to

model the oceans. 

A condenser allowed water vapor to

 

return to the liquid water. 

In the experiment energy was supplied through

electrical sparks, simulating lightning, and a heat source to evaporate the water. 

After one week of the experiment the water became a

brownish black. 

Analysis of the water showed that

many complex organic molecules, including amino acids, had been produced. 

The experiment showed that at least some of the organic molecules required for life could be

spontaneously generated under certain conditions. 

Evaluate Miller and Urey's Experiment: Strengths

• Modelled prebiotic Earth and its atmosphere. 

• Demonstrated that molecules such as amino acids can be generated spontaneously under certain conditions. 

• • The design of the experiment allow it to be replicated by other scientists. 

Strength: Modelled

prebiotic Earth and its atmosphere. 

Strength: Demonstrated that  

molecules such as amino acids can be generated spontaneously under certain conditions.

Strength: The design of the experiment allow it to

be replicated by other scientists. 

Evaluate Miller and Urey's Experiment: Limitations

• There remains debate on the actual atmosphere of prebiotic 
   Earth. 

• The experiment did not produce all of the organic molecules required for life. 

• • The simulation could not account for all conditions on the prebiotic Earth. 

Limitation: There remains debate on the

actual atmosphere of prebiotic 
 Earth. 

Limitation: The experiment did not

produce all of the organic molecules required for life. 

Limitation: The simulation could not

account for all conditions on the prebiotic Earth. 

Formation of a membrane-bound compartment is

needed to allow internal chemistry to become different from that outside the compartment. 

 

Cell metabolism requires the separation of the

cytoplasm from the external environment. Cell membranes serve this function in modern cells. 

 

Cell membranes are formed of

phospholipid bilayers. 

Phospholipids are

amphipathic, with hydrophilic phosphate heads, and hydrophobic fatty acid tails. 

hydrophilic

attracted to water

hydrophilic phosphate heads, and hydropho

repulsed to water

 Phospholipids have formed spontaneously in

experiments similar to Miller and Urey's experiment. 

Phospholipids spontaneously coalesce to form

spherical bilayers (vesicles) when mixed with water. 

spherical bilayers

vesicles - the form of membrane

It has been hypothesized that the first genetic material was

trapped within a phospholipid vesicle forming a protocell.

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.  

RNA is hypothesized to the first genetic material because: 

RNA is capable of self-replication 

RNA can store genetic information 

RNA can catalyse reactions 

inpdendently

RNA can store genetic information  - evidence

 some viruses use RNA as their genetic information. 

RNA can catalyse reactions  - evidence

 Ribozymes (RNA Molecules) in the ribosome catalyse the formation of peptide bonds during protein synthesis.  

 The last universal common ancestor (LUCA) is the

most recent common ancestor all organisms on Earth.  

There may have been other forms of life at the same time as LUCA, but these forms of life became

extinct as LUCA and its descendants outcompeted them (natural selection) 

 

There are no fossil remains for

the last universal common ancestor (LUCA) 

However, the fact that all organisms share the same genetic code, strongly

suggests that all organisms have evolved from LUCA. 

All living things share a number of genes which are  

assumed to have been inherited from LUCA

Those parts of that are shared are

key parts of structures within cells such as ribosome and enzymes that synthesize DNA and RNA are essentially the same in all organisms.)

Cladisitics allow scientists to

estimate the age of common ancestor by analyzing changes in the genetic cod

Cladisitics

method of biological classificaiton, organism into group based on their evolutionary ancestor

The Earth is

4.6 billion years old 

LUCA appeared

4 billion years ago

Life has continued to evolve for the

last 4-billion-year producing biodiversity currently found on our planet 

Biodiversity

huge variety of all living things on earth.  

Estimating the Age of the First Living Cells 

Fossils, Chemical Evidence, Biomarkers and Genetic Evidence

Fossil Evidence: The oldest fossils of cells (of cyanobacteria) are

approximately 3.5 billion years old. 

Chemical Evidence: The minerals and rocks around

the earliest fossils have been dated using radioactive dating 

 Carbon isotope or uranium isotope depending on

how ancient the rocks are 

Biomarkers: molecular fossil of lipids and other organic compounds persevered  

in sediments.  

Genetic Evidence:  

Molecular Clocks: Comparing the number of mutations in genes between specie allows scientists to

estimate when the two species diverged into separate species

Molecular Clocks: The fewer the mutation, the more

recently they shared a common ancestor

Scientists have used this technique to

estimate that LUCA existed approximately 4 billion years ago.