A2.1 Origin of Cells

Higher Level only TO EDIT ONCE LEARNT ( A2.1.7-9 )

What conditions are thought to have existed on prebiotic earth ?

• atmosphere,

• temperature,

• UV radiation,

• volcanic activity

• asteroid bombardment.

What were the oxygen levels in prebiotic earth ?

Trace amounts of oxygen because it reacted with other elements

Why were methane concentrations high in prebiotic earth ?

They were higher than today due to intense volcanic activity and meteorite bombardment

Why were carbon dioxide concentrations high in prebiotic earth ?

Due to emissions from volcanoes

Why were temperatures higher in prebiotic earth ?

Carbon dioxide and methane are both heat trapping greenhouse gases Comet and asteroid impacts will raise temperatures despite the sun emitting 20% less energy

What is UV ?

A high energy form of radiation that provided the activation energy for chemical reactions

Outline the UV radiation conditions in prebiotic earth

The stratospheric ozone layer that currently protects the earth from radiation didn't exist ( due to lack of oxygen ) so UV radiation would've penetrated to the earth's surface.

What's an organic aerosol haze ?

When carbon compounds form in droplets of water in the atmosphere

They would've then been deposited into bodies of water

Why could carbon compounds spontaneously form ?

Due to the differences in temperature and the ozone layer.

How did the ozone layer form?

As O2 built up in the atmosphere due to the evolution of living organisms, these molecules reacted with each other to form ozone (O3)

Why are cells considered to be living ?

Individual cells use energy to maintain their state Cells can divide to produce more cells Cells can be taken from the body and cultured

Why are cells considered as the smallest unit of self sustaining life ?

The organelles within a cell cannot survive alone

What are the challenges in defining matter as living or non-living ?

Functions of life are commonly used however they declare things needed to maintain life rather than create life itself

LIving things use energy to keep themselves in an ordered state ( This would be difficult to achieve without living components )

Why are viruses not considered living?

They cannot reproduce by themselves and do not have all characteristics of life

Define spontaneous generation

The idea that living organisms can be spontaneously formed from non-living substances.

What did Robert Remak's studies discover ?

That every cell is formed by division of a pre-existing cell

What are the intermediate stage required for evolution of the first cells ?

Catalysis Self-assembly Compartmentalization Self- replication of molecules

Outline the catalysis stage

Provides control over which chemical reactions occur

Outline the self- assembly stage

Carbon compounds such as amino acids have to form polymers

Outline the compartmentalization stage

A membrane must develop to enclose cell contents

Outline the self replication of molecules stage

Molecules replicate to form the basis of inheritance and the persistence of successful variants

Discuss the limitations in testing hypothesis about the cells origin

Billions of years ago the conditions in earth were very different. Whilst scientists have attempted to model conditions on prebiotic earth it is not possible to replicate the conditions with certainty

What hypothesis did Miller and Urey's experiment test ?

A variety of carbon compounds could have formed in the pre-biotic ocean

• based on the assumption that atmosphere contained carbon dioxide, water vapour and ammonia

How was the Miller Urey experiment set up?

Five litre flask: mixture of methane, hydrogen and ammonia ( representative of prebiotic atmosphere )

• water vapour was added to mixture by boiling water in another flask

Electrical discharges - stimulate lighting Condenser: cooled the substances produced then the condensate was returned to the flask with boiling water

What were the results of the Miller- Urey experiment ?

Day 1: Pink water Week 1: Dark red water

• carbon compounds had been produced

What conclusions were drawn from the Miller-Urey experiments ?

That it was possible for carbon compounds to spontaneously form prior to the formation of life

• as long as the experiments stimulated conditions were accurate

What are vesicles?

membranous sacs that are used to transport materials in the cell

What are exosomes?

Small membrane bound extracellular vesicles released from cells

What's an amphithatic molecule?

A molecule comprised of both Hydrophilic and Hydrophobic components

What do modern cells use as genetic material ?

Modern cells use DNA as genetic material and enzymes are used as catalysts

What suggests that RNA was the first genetic material ?

The idea that they can store genetic information in the same way as DNA but it is self replicating

• Viruses also use RNA which supports the theory

Compare the genetic stability of DNA and RNA

RNA: has a high mutation rate because the polymerase enzyme that copies the base sequences are less accurate than the equivalent in DNA ( advantageous in viruses to evade host's immune system however in living organisms genetic stability is crucial )

DNA was a beneficial change as it provides stability to the organisms

What's convergent evolution?

similar structure to evolve in organisms that do not have a recent common ancestor

What is LUCA?

last universal common ancestor

Explain the use of deductive reasoning to predict what genes where present in LUCA cells ?

Researchers identified genes that were in bacteria and archaea ~( they originated in early life ). A wide distribution suggests that the genes were inherited from a common ancestor. If evolutionary trees for bacteria/ archaea and the shared gene matches it tells us that the gene has been inherited from a common ancestor of both. ( LUCA had the gene )

What are hydrothermal vents ?

Cracks in the earths surface that are characterized by gushing hot water carrying reduced inorganic chemicals.

What conditions were present at a white smoker hydrothermal vent ?

• emerge at temperatures of 60 to 90 degrees

• contained high concentrations of hydrogen, methane, ammonia and sulfides

What do the chemicals present in alkaline hydrothermal vents represent ?

They represent readily accessible supplies of energy which early cells would have needed to assemble carbon compounds into polymers

How can it be deduced that LUCA lived in similar conditions to hydrothermal vents ?

Researchers have discovered that of the 355 protein families that are likely to have been in LUCA's genome they are genes needed for anaerobic metabolism and for fixing carbon dioxide and nitrogen. It can then be deduced that LUCA lived in an environment with high concentrations of hydrogen, CO2 and iron. ( Hydrothermal vent conditions )

What's a stromatolite?

Fossils formed when mats of cyanobacteria in shallow seawater trap sediments and secrete calcium carbonate gradually building up a rocky mound

What's the strelley pool formation ?

earliest uncontested evidence for life

• large rocks that resemble fossilised stromatolites