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ASTR/GEOL-2040: Search for life
in the Universe: Lecture 2
Additional office hours:
o Mondays 10-11
o Mondays 11-12
o Mondays 12-1
What we did last time
• Definition of life
– Darwinian evolution, natural selection
– & self-replication
• Carbon, not silicon-based
• Water, a polar molecule, allows cells
made of lipids
• This time: building blocks of life
– pp. 8-12, Sect. 1.2.4
2
Natural selection is
A. the occasional mutations that occur in DNA;
B. the mechanism by which advantageous traits are
preferentially passed on from parents to offspring;
C. the idea that organisms can develop new
characteristics during their lives and then pass
these on to their offspring.
BS p.182
3
Today: building blocks of life
• Rothery, Gilmour, Sephton (RGS) pp. 4-12
• Longstaff (Lon) pp. 175-183
• Bennett & Shostak (BS) pp. 167-169
•
pp. 176-183
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Most abundant elements
•
•
•
•
H and He in the Universe
Nobel elements He, Ne, Ar, … highly unreactive (inert)
Rest in Universe O, N, C, Si
Human body H, O, C, N
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Molecules in human body
Molecule
mass
sum
Water
65%
65%
Protein
20%
85%
Lipids
12%
97%
Other inorg (eg carbohydrates)
1.5%
98.5%
RNA
1.0%
99.5%
Other org
0.4%
99.9%
DNA
0.1%
100%
The building
blocks of life
•
•
•
•
Proteins (“meat”)
Lipids (“fats”, cell boundaries)
Carbohydrates (“sugars”)
RNA & DNA
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Cells are made of lipids
hydrophylic
carboxyl
group
 amphobic
hydrophobic
7
Properties of lipids
• Water-insoluble
– Act as cell membranes
• Energy substrates
– Fats (used by migrating birds)
• Fatty acids
– Double bond = unsaturated
RGS p.4, Lon p.171-173, BS p.168
8
Common carbon compounds
• carbohydrates
• hydrocarbons
9
Common carbon compounds
• Hydrocarbons: made up entirely
of hydrogen & carbon
CH3-CH2-CH2-CH2-CH2-CH3
• Carbohydrates: made up of
hydrogen, carbon, & oxygen
Cm(H2O)n
H-C-OH
H-C-OH
H-C-OH
10
These endings have names
– COOH
– OH
– CH3
– NH2
carboxyl group
hydroxyl group
methyl group
amino group (=amine group)
11
building macromolecules
+energy
endergonic
reaction
+nH2O
condensation
=dehydration
12
(CH2O)n = “life”
• Glucose=hexose
=monosaccharide
= C6H12O6
chemists drop
C&H
13
Its polymers: polysaccharide
C6H12O6=
=C12(H2O)11
Polymers = many monomers
… -OH + HO-….
… -O -….
• Polymerization: dehydration 
covalent bond (sharing of electrons)
15
(CH2O)n = “life”
• Ribose = pentose = C5H10O5
• deoxyribose=C5H10O4
again: drop
C&H
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Why are sugars useful?
• ......
• ...........
• ................
 think of carbohydrates more generally
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Sugars are
A. Hydrocarbons
B. Carbohydrates
C. Hydroxyls
D. Carboxyls
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Why are carbohydrates useful?
• Energy storage
• Structural support
• Food source for others
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Two more building blocks
• Proteins
• RNA & DNS: nuclei acids
https://en.wikipedia.org/wiki/Central_dogma_of_molecular_biology
What are proteins?
• Proteios = primary
– Berzelius (1838) C400H620N100O120P1S1
• Are the most complex macromolecules
in living systems
• Polymers of amino acids
• ”peptides” are shorter polymers
21
What are amino acids?
•
•
•
•
•
amino: -NH2
acid: -COOH
and a C
and an H
and possibly
another H
NH2
H-C-H
COOH
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Polymerization
 polycondensation
carboxyl
group
amino
group
NH2
NH2
CH2
CH2
COOH
CO
NH2
NH
CH2
CH2
COOH
COOH
glycine
dipeptide
“peptide bond”
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Other amino acids
• if R=CH3: alanine
• valine, proline, sarcosine, ...
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Why are proteins important?
• Structural support (e.g., finger nails)
• Act as catalysts (=enzymes)
– Facilitates/accelerates reactions
– Not used up or involved in reaction
– Can be reused many times!
• Their exact role depends on sequence
25
So many different ones
• Only 20 amino acids in proteins
– Although 70 have been identified
– 2 (+) of them used in rare cases microbes
• Folding
– Depends on amino acid sequence
– Determines how they work.
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Finally: nucleic acids
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Inventory
• Polymers of nucleotides
• Backbone
– DNA (deoxyribonucleic acid)
– or RNA (ribonucleic acid)
– Pentose sugar (5 carbons)
– Phosphate group
• Nitrogen-containing base
– four different ones
• Form a spiral
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Inventory
• Backbone
– deoxyribonucleic acid, ribonucleic acid
– Pentose sugar (5 carbons)
– Phosphate group
• Nitrogen-containing base
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Different bases
• Two groups of bases:
– pyrimidines T,C
– purines A,G
• These two groups pair in specific ways
– T-A and A-T
– C-G and G-C
30
In which ways could life
elsewhere be different?
• Different backbones
• Different base pairs
31
An enzyme consists of a chain of
A. Carbohydrates
B. Amino acids
C. nucleotides
32
Two more bases synthesized
in 2014
33
Properties of nucleic acids
• In DNA: pentose sugar deoxyribose
– Very stable
– Double-stranded
– Replicate
• RNA
– Less stable
– Singly stranded
34
Genetic code
•
•
•
•
Alphabet of 4 letters
Words with 3 letters
Each word  a particular amino acid
Gene  a particular protein
35
How many words possible?
A.
B.
C.
D.
4x3=12
4x3x2x1=24
43=64
34=81
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How many words possible?
A.
B.
C.
D.
4x3=12
4x3x2x1=24
43=64
34=81
Redundancy
In most cases: first 2 letters alone
determine which amino acid
37
Examples
• ACC, ACA, ACT, ACG  threonine
• Why?
38
Other examples
• TGT, TGC  cysteine
• TGA ”stop”
• TGG tryptophan
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Evolution
• Mutations
– Most are lethal
– Many have no effect
– A few can carry benefits
40
What we talked about
• The 4 different building blocks
– Lipids, carbohydrates, proteins, nucleic acids
• There usefulness
• How they propagrate genetic information
• Genetic code
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