1.5 Origin of Cells

Question 1

4 processes needed for spontaneous generation of life

Answer 1

1. Synthesis of organic molecules
2. Assembly of molecules into polymers/chains
3. Origination of self-replicating molecules
4. Packing of molecules into membrane with internal environment different from external for optimal function

Question 2

Outline Miller-Urey experiment

Answer 2

• Attempted to recreate primeval atmosphere to demonstrate “chemical evolution”
• They reduced atmosphere as O2 didn’t exist, raised temperature and radiation levels
• Recreated lightning by boiling water, mixing with methane, ammonia and hydrogen and exposed to electrical discharge
• Mixture was allowed to cool for a week
• Found to contain simple amino acids and oily hydrocarbons
• Concluded that under hypothesized conditions of pre-biotic Earth, organic molecules can be formed

Question 3

Conditions required for non-living synthesis

Answer 3

• Atmosphere without oxygen
• Raised temp of over 100C and radiation levels
• Lightning had to be present
• Tried to recreate volcanic activity as well
• May also happen in deep sea thermal vents

Question 4

Why was DNA favored over RNA?

Answer 4

While RNA could store information and self-replicate, DNA was more stable as it was a double helix and less likely to destruct easily.

Question 5

Can cells divide by abiogenesis?

Answer 5

Cells cannot divide by abiogenesis currently as we would not be able to live in pre-biotic Earth atmosphere. Now it can only arise from pre-existing cells or biogenesis

Question 6

Outline evidence from Pasteur’s experiment that abiogenesis no longer occurs

Answer 6

• Designed experiment to see whether microbial life could generate spontaneously
• Used sterile nutrient broth
• One flask was exposed to air while other flask had a neck bent into S shape and so air couldn’t be forced inside
• Broth in exposed flask appeared cloudy after few days while non-exposed flask remained clear
• This showed that microbes required a source of contamination to grow and couldn’t suddenly arise from non-living compounds

Question 7

Properties of RNA that might allow it to play a role in formation of life

Answer 7

• It can self-replicate

- It can act as a catalyst

Question 8

Process of endosymbiosis and how it led to eukaryotic cells

Answer 8

• Mitochondria and chloroplast were once free living prokaryotes
• Larger anaerobic prokaryotes took them in through endocytosis
• Continued living in cytoplasm as long as they grew and divided as fast
• Symbiotic relationship: Larger cell supplied food while smaller provided energy. This was favored by natural selection

Question 9

Theory of endosymbiosis: Membranes

Answer 9

Prokaryotes develop folds to maintain SA:V. Organelles have double membranes

Question 10

Theory of endosymbiosis: Antibiotics

Answer 10

Susceptible to antibiotics showing mitochondria may have bacterial origins

Question 11

Theory of endosymbiosis: Division

Answer 11

Chloroplast and mitochondria are able to divide independently outside cells through fission like process

Question 12

Theory of endosymbiosis: DNA

Answer 12

They have DNA which is circular and naked like prokaryotic structures

Question 13

Theory of endosymbiosis: Ribosomes

Answer 13

Has 70S ribosomes like prokaryotic structures