Origin of Life (1)

Question 1

Extrapolate on Pasteur’s experiment into biogenesis.

Answer 1

He proved that new cells do not spontaneously occur.

1. A growth medium (broth) was boiled to kill any micro-organisms present (sterilization)
2. The broth was placed in two different containers.
3. Bacteria growth only occurred in the broth if the flask was broken open (exposing the contents outside contaminants)

It was concluded that new bacterial growth came from external contaminants and did not spontaneously occur

Question 2

What is abiogenesis?

Answer 2

The process of living cells arising from non-living matter.

Question 3

What are the necessary conditions for life to form? (Hint: 4 steps!)

Answer 3

1. The building blocks (simple organic molecules) must be formed.
2. Simple organic molecules must assemble into more complex polymers
3. Polymers must be able to self-replicate
4. Polymers must be separated from their external environment, so molecules become packaged into membranes with an internal chemistry different from their surroundings (protobionts)

Question 4

Extrapolate upon the Urey-Miller experiment.

Answer 4

1. Water was boiled to vapour to reflect the high temperatures of Earth’s original conditions.
2. The vapour was mixed with a variety of gases (hydrogen, methane, ammonia) to create a reducing atmosphere (no oxygen)
3. This mixture was then exposed to an electrical discharge (simulating lightning as an energy source for reactions)
4. The mixture was then allowed to cool (concentrating components) and left for a period of approx 1 week

When analyzed, the condensed mixture was found to contain traces of simple organic molecules (amino acids, carbohydrates etc)

Question 5

Do conditions on Earth now enable abiogenesis?

Answer 5

The conditions required for abiogenesis to occur no longer exist on the planet, so cells must come from pre-existing cells.

Question 6

Explain the theory of endosymbiosis, give an overview of its chronological order, and list proof of why it is real.

Answer 6

Theory:
Eukaryotic cells are believed to have evolved from early prokaryotes that were engulfed by phagocytosis. The engulfed prokaryotic cell remained undigested as it contributed new functionality to the engulfing cell (e.g. photosynthesis), and it formed an endosymbiont. Eventually it became an organelle.

Steps:
1. The plasma membrane of an ancestral prokaryote infolded, and a nucleus formed.
2. Aerobic bacteria, and in the case of plants, cyanobacteria, were engulfed by the cell.

Evidence that mitochondria/chloroplasts come from endosymbiosis:
Membranes (double phospholipid bilayer)
Antibiotics (susceptibility)
Division (fission-like reproduction)
DNA (naked and circular DNA like bacteria)
Ribosomes (70S like bacteria)

MAD DR (mad doctor!)