The origin of life on earth

Question 1

Features of the cell popular definitions of life include?

Answer 1

Composed of cells/compartments
Systems that maintain homeostasis
Metabolism
Adapt to their environment,
Respond to stimuli
Can grow
Reproduce
Evolve
Communication
Genetic exchange

Question 2

NASA’s definition of life?

Answer 2

A self-sustaining chemical system capable of Darwinian evolution

Question 3

What must all simple cells have? And what can they have?

Answer 3

All cells have:
Compartment/growth
Metabolism (limited homeostasis)
Genetics/Evolution

Some cells have:
Differentiation of cells
Communication
Genetic exchange
Motility/react to stimuli
Complex homeostasis

Question 4

How was the earth formed?

Answer 4

The Earth is estimated to be at least 4.5 billion years old

Formation of the Moon (from impact with Theia)

Molten rock solidified to form oldest rocks (4.4 billion years)

Early bombardment of meteors (water evaporated)
Formation of oceans 3.8 billion years

Question 5

When the oldest fossil?

Answer 5

3.5 billion years (Australia)

Question 6

What are stromatolites? And their characteristics?

Answer 6

Made from biofilms of cyanobacteria
At least 3.5 billion years ago

Characteristics:
DNA and RNA, translation and transcription
Proteins, enzymes and sophisticated metabolism
Lipid membranes, cell walls and binary fission.

Already quite complex and some distance from the ‘origin’ of life

Question 7

Evolution backward

Answer 7

Use DNA record to look for common genes presumed to originate from the Last Universal Common Ancestor (LUCA)

Modern sequencing and phylogeny mean that huge advances have recently been made in this area

Question 8

Limitations of evolution backward

Answer 8

Assumes vertical gene transfer

But horizontal gene transfer happens in nature

Question 9

Common genes of LUCA

Answer 9

Assumption of RNA and or DNA

Genes for RNA modification

Metabolism

ATP synthase (requires H+ gradient)

Enzymes with Iron Sulphur clusters

Heat stable genes

Reactions would work faster at higher temperatures

Lipids?

Membrane required for chemical gradients

Question 10

Miller -Urey 1952

Answer 10

From simple gases … boiling water, hydrogen gas, ammonia and methane….

Formation of more complex organic molecules (monomers and polymers)

Chemical mix now thought to be incorrect for early Earth. But the experiment proved the concept. Complex organic molecules can be created readily through simple chemistry.

Question 11

Compartment first

Answer 11

Bubbles in volcanic rock can lead to the formation of interconnected chambers

Maybe lipids weren’t needed first

Maybe lipids weren’t required at all? Ion gradients could form naturally across compartments without lipids

Question 12

Metabolism first

Answer 12

Volcanic vents also have chemical gradients a key component of metabolism

Adenosine triphosphate (ATP) is the universal energy system of all life on Earth

The enzyme ATP synthase needs a hydrogen ion gradient to work.