IB Biology HL A2.1 Origins of Cells

What do you call things before life?

pre-biotic

What 3 things did pre-biotic Earth have?

1. Very low levels of oxygen = no ozone layer

2. High concentrations of methane because of volcanic activity

3. High concentrations of carbon dioxide because of volcanic activity as well

Because of these conditions....

There was no ozone layer, meaning ultraviolet radiation would have hit the Earth's surface. The temperatures on Earth were high because of spontaneous chemical reactions.

The spontaneous chemical reactions occurring at that time might have allowed what?

Carbon compounds might have been able to form, including nucleotides and amino acids, the building blocks of life.

What 4 things did living organisms change in the Earth's environment while evolving?

1. We increased the concentration of oxygen to where it is now, at 20%

2. Reduced level of carbon dioxide

3. Formed the ozone layer allowing protection from UV light.

4. Reduced the greenhouse effect.

Define biotic and abiotic

Biotic-living things, Abiotic-non-living things

What are all living things made of?

CELLS! There are unicellular organisms or multicellular organisms. Cells can divide and produce, making it the smallest unit of life.

Why are viruses not living?

Viruses aren't considered alive because they require a host to keep themselves alive and in a stable state. They don't have any cells, don't grow, or make their own energy.

What are the 4 necessary requirements for the evolution of the first cells?

1. Self-assembly

2. Compartmentalization

3. Catalysis

4. Self-replication

Explain Self-Assembly in cells.

Cells can organize themselves from monomers to polymers. (Miller-Urey experiment spontaneous)

Explain Compartmentalization

Cells must be able to separate their content from the outside; keep themselves contained and enclosed. (plasma membrane phospholipids)

Explain Catalysis

Cells must be able to create energy by starting their own chemical reactions. (enzymes that catalysis reactions)

Explain Self-Replication

Cells must be able to reproduce and have inheritance. (genes and DNA that replicates information)

What was the question of the Miller-Urey experiment?

Did carbon compounds form during pre-biotic earth/how were they spontaneously generated?

Explain the Miller-Urey experiment.

1. They simulated pre-biotic earth conditions starting with boiling water (high temps) which caused water vapor.

2. The water vapor rose and they mixed it with methane, ammonia, and hydrogen, some of the gases on earth during that time.

3. They added electric charges to simulate lightning and volcanic activity to the mix of gases.

4. The gases condensed into a substance that was collected (condensate)

After one week running they found that 20 amino acids were formed in the pink/red water showing carbon compounds can form spontaneously.

What do living organisms use as genetic material and catalysts?

DNA and enzymes

Explain the Chicken and Egg issue.

DNA requires enzymes to replicate but in order to create enzymes the instructions from DNA are needed.

Why is RNA important?

RNA can replicate itself and has catalytic material so the earliest cells could reproduce and catalyst reactions using RNA. RNA was the first genetic material. Today, RNA in the form of ribozymes in the ribosome are still used to catalyse peptide bond during creation of proteins.

What is LUCA?

last universal common ancestor; common ancestral cell from which all cells descended from

What do some cell structures have in common that relates to LUCA?

Ribosomes and certain enzymes are essentially the same in all living organisms.

What happened with other forms of LUCA?

It's likely that other life forms and evolved forms of LUCA have gone extinct because of competition from LUCA and its descendants themselves.

When did Earth form?

4.5 billion years ago

Where is the earliest evidence of life?

The Strelley Pool Formations in Western Australia contain large structures of cyanobacteria (forms of early life) that trapped and excreted sediments to create rock mounds. These can be dated back 3.42 GYA.

What ratios can scientists use to date back life?

Isotope ratios - Carbon from living organisms has a 13C/12C ratio.

What information can scientists use to date back life?

Genomic information - Seeing the number of difference between genomes/mutations of two species since they diverged from a common ancestor.

What are hydrothermal vents?

Undersea cracks in the Earth's surface gushing with hot mineral and chemical rich fluids.

How did hydrothermal vents affect evolution?

They provided early cells with a source of energy so they could self-assemble into carbon compounds. Fossils show that the vent precipitates were the location of the origin of life.

What do these things conclude about LUCA's environment?

LUCA lived in an environment with lots of hydrogen, carbon dioxide, and iron which hydrothermal vents provide.