1.5 Origin of Cells

Question 1

How can cells form/arise?

Answer 1

Cells can only be formed by division of pre-existing cells
The first cells must have arisen from non-living material
The origin of eukaryotic cells can be explained by the endosymbiotic theory

Question 2

4 main processes needed for spontaneous origin of life

Answer 2

1. the non living synthesis of simple organic molecules e.g. amino acids, nucleotides, glucose
2. the assembly of these molecules into polymers e.g. proteins, nucleic acids, starch
3. the origin of self-replicating molecules that made inheritance possible e.g RNA, DNA
4. the packaging of these molecules into membranes with an internal chemistry different from the surroundings i.e. cells

Question 3

What is a protobiont?

Answer 3

an immediate precursor to the first living systems with and internal chemical environment different from their surroundings i.e. their inorganic and organic molecules are trapped within a lipid bilayer

Question 4

Miller and Urey Experiment

Answer 4

• mixture of gases (methane, ammonia, hydrogen and steam) were put in a reaction chamber
• electric charges provided energy for gases to react
• gases were condensed and boiled
• run for a week, samples were taken during this time period, collection trap
• up to 4% of C had been converted to amino acids (all 20 were able to be formed)
• now believed that the early atmosphere may be similar to the vapours given off by modern volcanoes (no O2)

Question 5

What is a reducing atmosphere?

Answer 5

an atmosphere were oxidation is prevented by removal of oxygen gases by gases such as hydrogen, carbon monoxide, hydrogen sulfide

Question 6

Conditions for origin of life on earth

Answer 6

• high temperatures
• lightning
• UV light penetration
• reducing atmosphere (oxidation prevented)
• water

Question 7

Possible scenarios for the origin of life:

Answer 7

• Ocean Surface
• Panspermia
• Undersea thermal vents

Question 8

Role of RNA in the Origin of life

Answer 8

• self replicating
• catalytic abilities
• genes need enzymes to form and enzymes need to form
• the first stage of evolution may have proceeded by RNA molecules performing catalytic activities necessary to assemble themselves from a nucleotide soup

Question 9

Endosymbiotic Theory

Answer 9

• thought that the first eukaryotes evolved from large prokaryotes that ingested other free floating prokaryotes
• formed symbiotic relationship (endosymbiosis)
• two most important organelles formed are mitochondria and chloroplasts
• (aerobic respiration and photosynthesis in aerobic conditions)
  they are the first endosymbionts

Question 10

Evidence for Endosymbiotic theory

Answer 10

Mitochondria and Chloroplasts have:

• own DNA
• ribosomes similar to prokaryotes (70S)
• have a double membrane and inner membrane has proteins similar to prokaryotes
• are roughly same size as bacteria
• transcribe their DNA and use mRNA to synthesise some of their own proteins
• can only be produced by division of pre-existing mitochondria and chloroplasts