Cell Biology - 1.5 Origin of Cells

Question 1

The 4 main processes NEEDED FOR the spontaneous origin of life

Answer 1

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

1. the non-living synthesis of simple organic molecules eg. amino acids, nucleotides, glucose
2. The assembly of these molecules into polymers eg. proteins, nucleic acids, starch
3. the origin of self-replicating molecules that made inheritance possible eg. DNA/RNA
4. The packaging of these molecules into membranes with internal chemistry different from their surroundings ie. cells (protobionts)

Question 2

Understanding for origin to cells

Answer 2

• 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 3

Steps to the Origin of Life - do not need to memorise but VERY good to understand

Answer 3

1. Formation of the Earth with organic chemicals (eg. C, H, O, etc), high temps. (>100ºC), Lightning (electrical energy), UV light penetration, a reducing atmosphere and water.
2. Prebiotic synthesis and accumulation of amino acids, purines, pyrimidines, sugars, lipids and other organic molecules in primitive terrestrial environments.
3. Prebiotic condensation reaction involving the synthesis of polymers of proteins (peptides) and nucleic acids (mainly RNA) with self-replicating and catalytic (enzymatic) abilities. –> First ones were probably clay minerals and RNA
4. Synthesis of lipids (their self-assembly into double-layered membranes)
5. Capturing of prebiotic (self-replicating and catalytic) molecules within their boundaries
6. Formulation of protobiont (an immediate precursor to the first living systems with an internal chemical environment different from their surroundings)
7. Evolution of a protobiont into a prokaryotic cell

Question 4

Miller and Urey experiment - MUST KNOW

Answer 4

• Mixture of gases (methane, ammonia, hydrogen and steam) were put into a reaction chamber. Electric charges provided energy (ie gases reacted - condensed and boiled) - done over/run for a week
• In a reducing atmosphere oxidation is prevented (by removal of oxygen by gases such as hydrogen, carbon monoxide and hydrogen sulfide)
• up to 4% of the carbon (from methane) had been converted to amino acids - within in this multiple little experiments occurred (resulting in: all 20 amino acids, nucleic acids, several sugars, lipids, adenine and even ATP)

Question 5

Conditions for the origin of life on earth

Answer 5

• high temperature (>100ºC), lightning, UV light penetration, a reducing atmosphere (where oxidation is prevented) and water.

Possible scenarios =

1. Ocean Surface (Tidal Pools)
2. Panspermia
3. Undersea Thermal Vents

Question 6

Possible scenarios =

1. Ocean Surface (Tidal Pools)

Answer 6

Suggests that life arose in a tidepool, pond or on moist clay on the primeval Earth - Gases from volcanoes would have been energised by UV light or electrical discharges to form prebiotic molecules in froth.

Question 7

Possible scenarios = 2. Panspermia

Answer 7

Cosmic ancestry (panspermia) is a scientific theory that proposes living organisms were ‘seeded’ on Earth as ‘passengers’ aboard comets and meteors.

Question 8

Possible scenarios = 3. Undersea Thermal Vents

Answer 8

(more recent theory) suggests life may have arisen at ancient volcanic vents - this would provide the necessary things required (and possible source of catalysts (metal sulfides).

Question 9

Role of cell membranes

Answer 9

cell membranes are made from a phospholipid bilayer (thin polar membrane made of two layers of lipid molecules) that occur if conditions are correct - they create an isolated internal environment.

Question 10

Role of RNA (Ribonucleic acid)

Answer 10

RNA = self-replicating and has catalytic abilities - allows it to act as both genes and enzymes (ie. fixes the chicken vs the egg problem)

The first stage of evolution may have proceeded by RNA molecules performing the catalytic activities necessary to assemble themselves from a nucleotide soup.

Question 11

Endosymbiotic theory for the origin of eukaryotes

Answer 11

It is thought that eukaryote cells evolved from large prokaryote cells that ingested other free-floating prokaryotes - formed a symbiotic relationship (both parties in the relationship benefit) with the cells they engulfed (endosymbiosis)… developed in eukaryote cells were mitochondria (for aerobic respiration, and chloroplasts, for photosynthesis in aerobic conditions)

Primitive eukaryotes probably acquired mitochondria by engulfing purple bacteria
Chlolorplasts may have been acquired by engulfing primitive cyanobacteria (already capable of photosynthesis)

Both mitochondria and chloroplasts possess a self-replicating circular chromosome - uses genetic code that contains prokaryotic features (supporting probable origins of Chlolorplasts and mitochondria as endosymbionts)

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

Question 12

Prebiotic synthesis meaning

Answer 12

Any plausible pathway by which the molecular precursors of life (amino acids, bases and ribose phosphates) may have been formed in the early Earth