1.5 The Origin of Cells

Question 1

What is abiogenesis?

Answer 1

The theory that living cells arose from non-living matter.

Explanation:
-a non-living synthesis of simple organic molecules became complex polymers, and then self-replicated, then they packaged into membranes with internal chemistry

Question 2

Explain the Miller-Urey Experiment

Answer 2

1. Water was boiled to high temperatures, reflecting Earth’s original conditions
2. The vapour was mixed with gases including H2, CH4, NH3 but not oxygen
3. It was exposed to an electrical discharge
4. The mixture cooled and concentrated for ~week
5. The condensed mixture contained traces of simple organic molecules!

The problem with this was that reducing atmosphere and high temperatures or electrical discharges to catalyze reactions did not commonly exist on Earth. Abiogenesis is a poor theory.

Question 3

What is biogenesis?

Answer 3

Living things only arise from other living things by reproduction.

Question 4

Explain Pasteur’s experiment.

Answer 4

1. Broths were stored in vessels connected to long tubings to prevent external dust from entering
2. They were boiled to sterilize any micro-organisms
3. Growth only occurs in the broth if the flask was open to contaminants outside
4. Conclusion: emergent bacterial growth did NOT spontaneously occur, but came from external contaminants!

Question 5

What is the endosymbiotic theory?

Answer 5

Eukaryotic cells were evolved from early prokaryotes engulfed by phagocytosis. It continued its function and over generations, it lost its independent utility and became an organelle.

Question 6

What is the evidence for endosymbiosis?

Answer 6

Mitochondria and chloroplasts show evidence:
MAD DR
Membranes: double membranes
Antibiotics: susceptible to antibiotics
Division: reproduction occurs similarly to a fission process
DNA: has own DNA which is similar to prokaryotic DNA structure (naked and circular)
Ribosomes: 70S size identical to prokaryotes’ ribosomes