1.5 The Origin of Cells

Question 1

What is abiogenesis?

Answer 1

The theory that living cells arose from non-living matter is known as abiogenesis

Question 2

Over what 4 stages did abiogenesis occur? simple

Answer 2

1. simple organic molecules
2. complex polymers
3. self-replicating polymers
4. molecules packaged in membranes

Question 3

1. How were simple organic molecules formed in abiogenesis?

Answer 3

There was non-living synthesis of simple organic molecules (from primordial inorganic molecules)

Question 4

2. What role did the organic molecules have? abiogensis?

Answer 4

These simple organic molecules became assembled into more complex polymers

Question 5

3. What allowed the complex polymers to develop further? abiogenesis

Answer 5

Certain polymers formed the capacity to self-replicate (enabling inheritance)

Question 6

4. What created structures similar to cells? abiogenesis

Answer 6

These molecules became packaged into membranes with an internal chemistry different from their surroundings (protobionts)

Question 7

What experiment helped to show the non-living synthesis of simple organic molecules?

Answer 7

The non-living synthesis of simple organic molecules has been demonstrated by the Miller-Urey experiment

Question 8

What was recreated in the M_U experiment?

Answer 8

Stanley Miller and Harold Urey recreated the postulated conditions of pre-biotic Earth using a closed system of flasks and tubes

Question 9

What 3 conditions needed to be replicated? M-U

Answer 9

1. high temperatures
2. reducing atmosphere
3. electrical discharge

Question 10

How were high temperatures created? m-u

Answer 10

Water was boiled to vapour to reflect the high temperatures common to Earth’s original conditions

Question 11

How was a reducing atmosphere created? m-u

Answer 11

The vapour was mixed with a variety of gases (including H2, CH4, NH3) to create a reducing atmosphere (no oxygen)

Question 12

How was the electrical discharge created?

Answer 12

This mixture was then exposed to an electrical discharge (simulating the effects of lightning as an energy source for reactions)

Question 13

What was done to the final mixture? m-u

Answer 13

The mixture was then allowed to cool (concentrating components) and left for a period of ~1 week

Question 14

What were the results? m-u

Answer 14

After this time, the condensed mixture was analysed and found to contain traces of simple organic molecules

Question 15

What was needed for the initial formation of biological life?

Answer 15

The chemical processes that contributed to the initial formation of biological life required specific conditions to proceed

This included a reducing atmosphere and high temperatures (>100ºC) or electrical discharges to catalyse chemical reactions

Question 16

Why can living cells not arise independently by abiogenesis?

Answer 16

These conditions do not commonly exist on modern Earth and hence living cells cannot arise independently by abiogenesis

Question 17

How are cells formed in today’s conditions?

Answer 17

Instead, cells can only be formed by the division of pre-existing cells (biogenesis)

Question 18

What is biogensis?

Answer 18

Biogenesis describes the principle that living things only arise from other living things by reproduction (not spontaneous generation)

Question 19

Who created the law of biogenesis?

Answer 19

The law of biogenesis is largely attributed to Louis Pasteur

Question 20

What did louis pasteur’s experiment show?

Answer 20

demonstrated that emergent bacterial growth in nutrient broths was due to contamination by pre-existing cells

Question 21

1. What was the set up of his experiment? lp

Answer 21

Broths were stored in vessels that contained long tubings (swan neck ducts) that did not allow external dust particles to pass

Question 22

2. what did he do the broths first and why? lp

Answer 22

The broths were boiled to kill any micro-organisms present in the growth medium (sterilisation)

Question 23

3. In what broths were microorganisms present?

lp

Answer 23

Growth only occurred in the broth if the flask was broken open, exposing the contents to contaminants from the outside

Question 24

4. What was the conclusion from lp experiment?

Answer 24

From this it was concluded that emergent bacterial growth came from external contaminants and did not spontaneously occur

Question 25

What is an endosymbiont?

Answer 25

An endosymbiont is a cell which lives inside another cell with mutual benefit

Question 26

How were eukaryotic cells formed?

Answer 26

Eukaryotic cells are believed to have evolved from early prokaryotes that were engulfed by phagocytosis

Question 27

How did the engulfed prokaryotic cell survive?

Answer 27

The engulfed prokaryotic cell remained undigested as it contributed new functionality to the engulfing cell (e.g. photosynthesis)

Over generations, the engulfed cell lost some of its independent utility and became a supplemental organelle

Question 28

What 2 organelles are thought to be a result of endosymbiosis?

Answer 28

Mitochondria and chloroplasts are both organelles suggested to have arisen via endosymbiosis

Question 29

What are the 5 pieces of evidence that support the extracellular origins of these organelles?

Answer 29

Membranes (double membrane bound)
Antibiotics (susceptibility)
Division (mode of replication)
DNA (presence and structural composition)
Ribosomes (size)

Question 30

How can membranes prove that certain organelles are endosymbionts?

Answer 30

some organelles have double membranes (outer membrane may be vesicular in origin)

Question 31

How can antibiotics prove that certain organelles are endosymbionts?

Answer 31

Susceptible to antibiotics - indicates organelles may have bacterial origins

Question 32

How can divison prove that certain organelles are endosymbionts?

Answer 32

Reproduction occurs via a fission-like process

Question 33

How can DNA prove that certain organelles are endosymbionts?

Answer 33

has own DNA which is naked and circular like prokaryotic DNA structure

Question 34

How can ribosomes prove that certain organelles are endosymbionts?

Answer 34

Have ribosomes which are 70s in size (identical to prokaryotic ribosomes)