The Breakdown of Organic Chemicals

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From the course by Macquarie University

Analysing Complexity

42 ratings

Macquarie University

Analysing Complexity

42 ratings

Course 1 of 4 in the Specialization Solving Complex Problems

The first course of the specialization ANALYZING COMPLEXITY will teach you what unifying patterns lie at the core of all complex problems. It advances your knowledge of your own field by teaching you to look at it in new ways. ANALYZING COMPLEXITY is constructed in the following way: Week I. "What is Complexity?" - What is at the core of all complex problems Week II. "Complex Physical Systems" - What complex problems all have in common in the inanimate world Week III. "Complex Adaptive Systems" - What complex problems all have in common in nature Week IV. "Complex Cultural Systems" - What complex problems all have in common in human society Week V. "Complexity, Fragility, and Breakdown" - Why complex problems arise Week VI. "Complexity in the Anthropocene" - What complex problems face us today

From the lesson

Complexity, Fragility, and Breakdown

In this module, we'll look at the decline of complexity. So far we've focused on how complex systems sustain or increase themselves. In order to truly understand every angle of all complex systems - physical, biological, and cultural - we need to understand how and when they collapse, and what all those breakdowns have in common.

The Breakdown of Organic Chemicals6:37

Meet the Instructors

David Baker
Associate Lecturer
Big History Institute
David Christian
Professor
Big History Institute
Shawn Ross
Associate Professor
Big History Institute

The big question, for this segment,

is what happens when living systems break down?

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When thinking about the complexity of life, and the evolution of complex life,

we can see that there are quite a few points in the fossil record

of the J Chemical record,

where huge changes in the composition of the atmosphere and sediments occurred.

We can also see chemical remnants in ancient sediments, and gain insights

into changes that had occurred in the evolutionary history of life on Earth and

the evolution of biochemical events or systems.

In this lecture we will look at one evolutionary event where some very

complex-looking molecules were utilized by primitive organisms to drastically change

the face of the planet.

Life evolved on Earth over 3 billion years ago.

When we consider early life in the history of the Earth, 2 to 4 billion years ago,

we think of simple bacteria with no complex internal structures.

These bacteria evolved complex biochemical pathways,

utilizing metal ions and complex cofactors to help them divide and

reproduce, and utilize chemicals in their environment.

Environment includes the atmosphere, the hydrosphere, and the lithosphere.

They probably had limited resources.

Simple amino acids, organic acids, and

mineral salts dissolved in the hydrosphere,

methane in the atmosphere, and solid low solubility salts in the lithosphere.

There is no oxygen, and the chemical environment was highly reduced.

They made use of complex molecular cofactors to drive and

catalyze chemical reactions in order to make more complex molecules.

So where did these cofactors come from, and what do they look like?

Vitamin B12, bacteriochlorophyll, chlorophyll, heme and

factor 430, are all examples of compounds known as tetrapyrroles.

Looking at these structures, we can say they look very complex, but

they do have some similar features that are ideal for

coordinating methylines, which are used in catalyzing chemical reactions.

These complex molecules also stabilize, and

often improve the solubility of the metals.

Vitamin B12 and factor 430 would've been used very early on in evolutionary times.

They're used extensively in methane and single carbon metabolism which would have

been some of the earliest biochemical processes.

Bacteria chlorophylls and chlorophylls capture light for photosynthesis.

Bacteria chlorophylls are more reduced in chlorophyl, and

are only able to be used in anoxygenic photosynthesis.

And it is possible that slightly different types of anoxygenic photosynthesis may

have evolved a number of times in the evolutionary history.

In contrast, it appears that oxygenic photosynthesis only evolved once, and

it's dependent on using chlorophyll lights to work.

So oxygenic photosynthesis is dependent on chlorophyll lights being synthesized.

Surprisingly, tetrapyrroles can form spontaneously by acid catalysis

from simple precursors like aminolevulinic acid.

So despite appearing to be quite complex,

the basic structure can form from simple starting precursors.

When we look at these chemicals, we see in their chemical structure, how and

why they were first utilized.

Pyrroles were formed from condensation of some type of amino acids.

And tetrapyrroles were formed from reaction of these pyrroles

with the III Isomer being the most abundant.

Organisms then involved to use and further modify these complex tetrapyrroles, and

they obviously use the ones at the highest concentration.

Thus all biological tetrapyrroles now used are derived from the III Isomer.

Because of this, they got locked in to using these isomers.

So when a biochemical pathway evolved to make them more efficiently,

they had to evolve a complex mechanism to make the most common isomer found from

spontaneous chemical synthesis.

We now see aerobic and anaerobic pathways for these compounds,

with the anaerobic pathways being found in more ancient bacteria while

the aerobic pathways are found in some bacteria and higher organisms.

It took a long time for photosynthesis and then oxygenic photosynthesis to evolve,

talking 1.5 to 2 billion years after life first evolved.

But when it did, it caused massive changes in the environment.

There was a massive oxidation event, as oxygen appeared in the atmosphere about 2

to 2.5 billion years ago and this was due to oxygenic photosynthesis.

Oxygen was a by-product of photosynthesis, and is an extremely toxic gas for

organisms growing anaerobically.

The gas was initially absorbed chemically.

For example, soluble metal salts became oxidized and insoluble.

But this buffering was short-lived on a geological time scale and

lasted only about 100,000 years before significant quantities of oxygen and

gas appeared in the atmosphere.

Chemical processes in cells were inhibited by oxygen.

So new systems had to evolve to cope while organisms retreated to anaerobic natures,

thick, dark and deep away from the oxygen and the oxygen produces.

So both of these things disrupted not only the atmosphere but

also has a huge impact on the materials available for primitive bacteria to use.

The composition of not only the atmosphere, but also the hydrosphere and

part of the lithosphere changed dramatically due to this oxydation.

This oxydation event was also the likely evolutionary driver for

more complex eukaryotic organisms, which based on the fossil records,

seem to appear around the same time.

These eukaryote arose due to symbiotic relationships between a primitive

anaerobic organism, and an aerobic organism, as the aerobic organism

had developed mechanisms to detoxify, and also utilize the toxic oxygen gas.

So, while one complex biological system almost vanished, as it had to retreat

to natures where the oxygen concentration was low a new complex system evolved to

take its place and harnessed the toxic material, which is oxygen gas, to thrive.

[MUSIC]

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