topic 1.5- the origin of cells

Question 1

what is the only way that cells can be formed ?

Answer 1

by division of pre-existing cells

Question 2

how must the first cells have arisen?

Answer 2

from non-living material

Question 3

what are the 4 main hypotheses for how the main stages of cell production occurred?

Answer 3

1. production of carbon compounds such as sugars and amino acids
2. assembly of carbon compounds into polymers
3. formation of membranes
4. development of a mechanism for inheritance

Question 4

production of carbon compounds such as sugars and amino acids as a hypothesis for cell production

Answer 4

Miller and Urey passed steam through a mixture of methane, hydrogen and ammonia- a mixture representative of the atmosphere of the early earth. when electrical discharges (= lightning) were used, amino acids/other C carbons were formed

Question 5

assembly of carbon compounds into polymers as a hypothesis for cell production

Answer 5

deep sea vents:
- cracks characterised by gushing hot water carrying reduced inorganic chemicals such as iron sulphide
- these could be sources of energy for the assembly of C compounds into polymers

Question 6

formation of membranes as a hypothesis for cell production

Answer 6

if phospholipids/other amphipathic C compounds existed, they would have naturally assembled into bilayers. experiments have sown these bilayers readily formed vesicles, resembling membranes which would have allowed different internal chemistry from the surroundings to develop

Question 7

development of a mechanism for inheritance as a hypothesis for cell production

Answer 7

enzymes needed to replicate DNA- but genes needed for enzymes to be made
- RNA was original genetic material

Question 8

why could RNA have been the original genetic material

Answer 8

as it stores information the same as DNA but is self replicating and can act as a catalyst

Question 9

what is endosymbiotic theory?

Answer 9

the idea that some organelles in eukaryotes were formed by the taking in of prokaryotes

Question 10

describe endosymbiotic theory

Answer 10

1. prokaryotic organism that had developed the process of aerobic cell respiration were taken in by larger prokaryotes that could only respire anaerobically via endocytosis
2. smaller prokaryotes were not killed but continued to live in the cytoplasm, growing and dividing as fast as the larger ones
3. smaller prokaryotes lost unnecessary functions and persisted over millions of years of evolution to become mitochondria

Question 11

why were larger and smaller prokaryotes able to live together?

Answer 11

as they were in a symbiotic/mutualistic relationship in which both of them benefited- larger supplied with energy, smaller supplied with food

Question 12

why does endosymbiotic theory support the origin of chloroplasts?

Answer 12

prokaryotes that had developed photosynthesis taken in my larger cell

Question 13

give 4 pieces of evidence for endosymbiotic theory

Answer 13

1. mitochondria and chloroplasts have their own genes, on a circular DNA molecule (=prokaryotes)
2. they have their own 70S ribosomes of a size and shape typical of some prokaryotes
3. they transcribe their DNA and use the mRNA to synthesise some of their own proteins
4. they can only be produced by division of pre-existing m/c.