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Astrobiology and the Search for Extra Terrestrial Life
The University of Edinburgh
Lecture Summary: The Structure of Life

The Structure of Life: Building Blocks
The fundamental elements that make up most of the compounds from which life is constructed:
Carbon
Hydrogen
Nitrogen
Oxygen
Phosphorus
Sulphur

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Other elements:
- Iron
→ Red blood cells
- Calcium
→ Forms phosphate structures that are part of all skeletons
Example:
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Glycine

An amino acid
Made up of 2 carbon atoms, nitrogen,
some hydrogen and oxygen
→ Also conforms to the idea of
CHNOPS
Carbon is the backbone of the molecule

About Amino Acids
-

Amino acids linked in a long chain makes up a protein
Can bind to other chains
Can fold up in particular shapes
Forms the complex diversity of complex molecules that make up life
Amino acids are essential as building blocks for constructing the proteins in our cells

Life needs other molecules as well, like sugars and water
...


Water
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Water is the solvent in which these chemical reactions can occur
→ We need a liquid in order for molecules to move around

We refer to life on Earth as being carbon-based and water-based because the molecules
from which humans are constructed have carbon as their backbone, and water is required
in order for the necessary chemical reactions to occur within our cells
...


Structure of Life: DNA
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Deoxyribonucleic acid
Information storage system
Transmits information from one generation to
another

The Structure of DNA
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DNA has a backbone – double helix
Between double helix is base pairs
These base pairs are made up of four different
molecules

Molecular Structure of DNA
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Adenine
Thymine
Cytosine
Guanine

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These 4 letters make up a code
This code instructs the cell on how to make
particular molecules
Discreet codes are called genes
→ Genes are a set of instructions that tell the
cell to produce a particular protein or
protein molecule

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Definition:

DNA

➢ A molecule in which A, T, C AND G are strung together in a long code to provide the
information storage for that cell
➢ In order to be able to do its functions and make new types of molecules

How DNA Replicates from One Generation to Another
The 4 molecules can only bind together in particular combinations
→ Adenine can only bind to Thymine
→ Cytosine can only bind to Guanine
These bind together and form base pairs

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Base Pairs
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Long string of letters on the left-hand
side
The complementary bases on the other
side
→ So, where there’s a C, attached
to it, there’s a G
→ Where there’s an A, attached to
it, there’s a T

Splitting The Double Helix
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Splits into 2 single strands
DNA knows from that code which of those 4 letters it must bind to the letters already
there
We can immediately synthesize a complementary strand on both of those new strands
that are now single strands
Once it’s done that, it can re-synthesize two strands of DNA
Replicates information from one cell to another as it divides

DNA Replication And Cell Division
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Bacterium divides
DNA splits in 2
Double helix is split into single strands
Single strands are used to resynthesize double strands
As a result, two cells can form from one

Cellular Energy
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All cells need energy to grow and reproduce
All cells contain systems of gathering energy

Three types of energy systems:
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Heterotrophs
Phototrophs
Chemolithotrophs

About Heterotrophs
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We get our carbon from organic carbon
→ Meat
→ Organic molecules
→ Organic carbon molecules

About Phototrophs
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Gather their energy from sunlight

About Chemolithotrophs
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Gather energy by consuming iron in rocks
Live in very extreme environments

It’s all about extracting energy from atoms and molecules in the environment to
provide the energy for cell replication and cell growth

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