The Origin of Life - Study Guide

What is the primordial soup hypothesis?

Basically, Earth's original blend of gases produced a broth of organic molecules when exposed to light and heat, eventually forming the building blocks of life in amino acids. (They self-assembled into simple living cells).

What are ribozymes?

Catalytic RNA molecules that function as enzymes and can splice RNA

How are hydrothermal vents and alkaline vents thought to have given rise to organic molecules?

Deep-sea hydrothermal vents represent the only known environment that could have created complex organic molecules with the same kind of energy-harnessing machinery as modern cells. Seeking the origins of life in the primordial soup made sense when little was known about the universal principles of life's energetics. Longer explanation: Authors of the new theory argue the environmental conditions in porous hydrothermal vents — where heated, mineral-laden seawater spews from cracks in the ocean crust — created a gradient in positively charged protons that served as a "battery" to fuel the creation of organic molecules and proto-cells. Later, primitive cellular pumps gradually evolved the ability to use a different type of gradient — the difference in sodium particles inside and outside the cell — as a battery to power the construction of complex molecules like proteins.

How could self-replicating RNAs eventually give rise to RNA molecules with different catalytic functions?

Hypothesized to have had high mutation rates, allowing newly synthesized RNAs to acquire new catalytic functions like protein synthesis

What macromolecule is thought to have been used as the first genetic material?

It now seems certain that RNA was the first molecule of heredity, so it evolved all the essential methods for storing and expressing genetic information before DNA came onto the scene. However, single-stranded RNA is rather unstable and is easily damaged by enzymes.

Step 6: DNA-based proto-cells

Just know the transition from 5-6-7 is not clear.

Step 7: Bacteria-like cells

Just know the transition from 5-6-7 is not clear.

What allowed for the evolution of aerobic organisms?

Photosynthesis. This is because oxygen is highly toxic to cyanobacteria, so they basically evolved to protect themselves from oxygen by excreting it.

What on earth is a proto-cell?

Protocells are structures formed from the aggregation of abiotic (non-living) components. Despite this, they display characteristics akin to biological cells. Proto-cells require simple genetic information aka RNA.

Why is genetic material required in order for proto-cells to eventually give rise to cells?

RNA

How are self-replicating RNAs thought to arise?

Scientists think RNA building blocks (nucleotides) emerged in a chaotic soup of molecules on early Earth. These nucleotides bonded together to make the first RNAs. No sooner were they made than they broke down; however, new ones were made in their place. Some RNAs turned out to be more stable than others. These RNA strands grew longer and bonded nucleotides more quickly. Eventually, RNA strands grew faster than they broke down. This was RNA's chance to start life. All living things reproduce. They copy their genetic information and pass it onto their offspring. And for RNAs to start life, they needed to reproduce too. This is why scientists think that the RNA world took off when an RNA emerged that could make copies of itself. As it did, new self-copying RNAs emerged. Some were better at copying themselves than others. The RNAs competed against each other, and the most successful won out. Over millions of years, these RNAs multiplied and evolved to create an array of RNA machines. At some stage, DNA and proteins evolved. Proteins began to drive chemical reaction in cells, and DNA—which is more stable than RNA—took the job of storing genetic information.

What are stromatolites? Why are they of interest?

Stromatolites are the oldest fossils dating back to 3.5 billion years of age. They provide significant information on the interaction of the biosphere, atmosphere, hydrosphere, and lithosphere throughout the entire history of life on this planet.

What is the Miller-Urey experiment and what did it show?

The Miller-Urey experiment was the first experiment to bring questions about the origins of life into the realm of Science! The classic Miller-Urey experiment demonstrated that amino acids, important building blocks of biological proteins, can be synthesized using simple starting materials under simulated prebiotic terrestrial conditions.

Why are RNAs a good candidate for the first self-replicating genetic molecule?

The RNA world hypothesis is supported by RNA's ability to store, transmit, and duplicate genetic information, as DNA does. RNA can act as a ribozyme, a special type of enzyme. Because it can perform the tasks of both DNA and enzymes, RNA is believed to have once been capable of supporting independent life forms.

Were the first prokaryotes aerobic or anaerobic? Why?

The first prokaryotes were anaerobic because they evolved in an environment with essentially no molecular oxygen.

What role are hydrothermal vents and alkaline vents thought to have played in the formation of liposomes?

When certain types of lipids are dissolved in water, they spontaneously form liposomes. Phospholipid bilayers are selectively permeable, and some liposomes can even store energy in the form of an electrical gradient. Such liposomes can discharge this energy in a neuron-like fashion, showing rudimentary signs of excitability, which is characteristic of living cells. Clay can catalyze the formation of liposomes that grow and divide, a primitive form of self-replication. Furthermore, if RNA was on the surface of the clay, the researchers discovered that liposomes that enclosed RNA were formed. These experiments are compelling because they showed that the formation of membrane vesicles containing RNA molecules is a plausible explanation for the emergence of cell-like structures based on simple physical and chemical properties.

What are liposomes?

artificial membrane-bound lipid vesicles, they are typically used as drug delivery systems vesicle surrounded by a phospholipid bilayer.