A2.1 Origins of cells

HL CONTENT

What does pre-biotic earth mean?

It is the period on Earth before life existed

What are the conditions during pre-biotic earth? (6 points)

Very little oxygen

Lots of methane

Increased Carbon dioxide

Higher temperatures

No UV protection from atmosphere

Lots of lightning

What was the conditions during pre-biotic earth suitable for?

It promoted spontaneous reactions to occur such as the spontaneous formation of carbon compounds

What happened to Earth's environment when living organisms arose?

Earth's environment started to change, producing oxygen and getting an ozone layer.

What happened once Earth's environment began to change due to living organisms?

The spontaneous generation of complex compounds no longer exists

A cell is self-sustaining. What does this mean?

It uses energy to maintain highly-ordered state. Living organisms can pass on this ability to their offspring

Are organisms unicellular or multicellular?

They are both unicellular and multicellular

What are the evidence to suggest that cells are living?

Each cell uses energy to maintain order - Some cells stop doing it, thus die

Cells produce more cells

Cells can live outside of the body

Where do new cells come from?

New cells come from existing cells

What factors contributed for the first cell to have formed?

Catalysis and control over reaction

Self assembly of polymers

Compartmentalised - separate itself from outside environment

self-replicating molecules

What was the aim for the Miller-Urey experiment

To explain how complex compounds formed spontaneously to support the hypothesis of the very first cell

What did the scientists do for the Miller-Urey experiment?

An apparatus was set up and it had a similar environment to pre-biotic earth.

Water was added to a chamber with ammonia, methane and hydrogen (prevalent in pre-biotic earth atmosphere).

Energy was applied ie. lightning strikes/volcanic eruptions

The samples condensed and taken to examine

What were the results of this experiment?

This sample had amino acids therefore they concluded that this process produced amino acids

Carbon compounds arose on Earth before life evolved - due to conditions of pre-biotic earth

What are vesicles?

They are structures surrounded by membranes

What are the structures of phospholipids?

They have a hydrophobic and a hydrophilic end

The phosphate head is hydrophilic

The 2 fatty acid tails are hydrophobic

Are phospholipids partially permeable, and what does this mean?

Yes, they are partially permeable. This means that they are selective about what enters and exits the cell

What do phospholipids spontaneously form, and why?

They spontaneously form vesicles due to their hydrophilic and hydrophobic properties

Was DNA or RNA presumed to be the first genetic material in the first cell?

RNA

What evidence is there to support that RNA was the first genetic material in the first cell?

1. RNA is self-replicating

2. RNA can act as a catalyst (no need enzyme to start replicating)

3. Some viruses have only RNA

4. RNA mutates at a higher rate

What does LUCA stand for?

Last

Universal

Common

Ancestor

What evidence supports that all living things on Earth descended from a common ancestor?

1. There is a universality in the genetic code

2. Similarity in ribosome structure + how DNA and RNA are synthesised

What techniques are used to figure out when LUCA arrived on Earth?

1. Carbon dating + oldest known fossil

2. Relationship between genome differences and the amount of time between common ancestors

What is Carbon dating?

Uses Carbon isotopes, which have known half lives, thus if you know how much carbon is left, you can figure out how much time has passed - Need fossils.

Look at fragments from sedimentary rocks and carbon date those

What were the results from carbon dating and using the oldest known fossils?

It is estimated that LUCA arose around 4.1 billion years ago

What was the result of finding the relationship between genome differences and the amount of time which has passed between common ancestors?

It is estimated that LUCA formed around 4.5 billion years ago (around the same time as Earth's formation)

What are the problems with these techniques?

The timelines are only falsifiable and not provable

What conditions were needed for the common ancestor to arise from?

As they shared common genes, the proteins were needed for environments that were anaerobic and high in hydrogen, carbon dioxide and iron.

Where were these conditions found for the common ancestor to arise from?

They were found around hydrothermal vents, white smokers.

They could have led to the spontaneous generation of carbon-based polymers