1.5 The Origin of Cells

Question 1

Explain the following quote: “There is therefore a continuity of life from its origins on Earth to the cells in our bodies today.”

Answer 1

An individuals’ cells can be traced back to their zygote and from their to their parents ad infinitum to the very first cell (specifically through maternal mitochondrial DNA)

Question 2

What are three reasons (other than Pasteur’s experiments) that biologists generally accept that cells can only come from other cells?

Answer 2

• A cell is highly complex and no natural mechanism has been suggested for producing cells from simple subunits.
• No example is known of increases in the number of cells in a population, organism, or tissue without cellular division.
• Viruses are produced from simpler subunits but they do not consist of cells

Question 3

Describe Pasteur’s experiments.

Answer 3

Pasteur found that microorganisms were in the air, not appearing spontaneously. The swan-necked flasks prevented those bacteria from entering. When they couldn’t enter, no microorganisms were present. The broken flask showed it was the swan-necked flask which prevented microorganisms from growing.

Question 4

How did the Miller & Urey experiment show that organic molecules could be formed by simulating early Earth conditions?

Answer 4

Simulated early Earth conditions by passing steam through methane, hydrogen, and ammonia and by using electrodes as lightning. This produced amino acids and other carbon compounds necessary for life.

Question 5

What is it about deep-sea vents that make it a possible site for polymerization?

Answer 5

Deep-sea vents are characterized by gushing hot water carrying reduced inorganic materials, a possible energy source for the assembly of carbon compounds into polymers.

Question 6

What happens to amphipathic molecules in a water based environment?

Answer 6

They readily form vesicles resembling the plasma membrane of a small cell, allowing different internal chemistry from that of its surroundings to develop.

Question 7

Why is RNA considered to be a good candidate for the first inherited genetic material?

Answer 7

• Can store information in the same way as DNA

- Both self-replicating and can act as a catalyst

Question 8

Explain endosymbiotic theory.

Answer 8

Mitochondria: larger eukaryote used anaerobic respiration and consumed a eukaryote using aerobic respiration/photosynthesis which was much more efficient. The larger cell would supply food to the smaller one and the smaller one would provide energy.

Question 9

What evidence is there that both mitochondria and chloroplasts were once independently living prokaryotic cells?

Answer 9

• Have their own genes, on a circular DNA molecule similar to those of prokaryotes
• Have their own 70S ribosomes like prokaryotes
• Transcribe their DNA and use the mRNA to synthesize their own proteins
• Can only be produced by division of pre-existing mitochondria and chloroplasts by binary fission, like prokaryotes