Download Astrobiology

Astrobiology
Replicators
NASA’s Astrobiology Page
• http://astrobiology.nasa.gov/aboutastrobiology/
The Legos of Life
• This is review:
– What are the Legos?
– How did the Legos make it to Earth (as well as
planets throughout the Universe)?
The Legos of Life (Continued)
• What are the Legos (molecules) that life needs
(think back to your biology)?
• Amino acids: “NASA and University
Researchers Find a Clue to How Life Turned
Left”
– http://www.nasa.gov/topics/solarsystem/features
/life-turned-left.html
• Amino acids are found in a lot of celestial
bodies (including meteoroids and comets).
The Legos of Life (Continued)
• Life on Earth uses 20 amino acids to build
proteins.
• Common amino acids include: glycine,
alanine, and glutamic acid.
– Other amino acids that Earth’s life does not use
have also been found (e.g. isovaline and
pseudoleucine).
The Legos of Life (Continued)
• Glycoaldehyde – a two carbon
monosaccharide that has been detected in the
interstellar medium.
– It is made from the amino acid glycine (which has
been found on meteorites, asteroids, and comets.
• What very important molecule is a sugar?
– Deoxyribose and ribose are also monosaccharides
Analysis of Meteorite
Compound class[11]
Concentration (ppm)
Amino acids
17-60
Aliphatic hydrocarbons
>35
Aromatic hydrocarbons
3319
Fullerenes
>100
Carboxylic acids
>300
Hydrocarboxylic acids
15
Purines and pyrimidines
1.3
Alcohols
11
Sulphonic acids
68
Phosphonic acids
2
Compound class[11]
Concentration (ppm)
Amino acids
17-60
Aliphatic hydrocarbons
>35
Aromatic hydrocarbons
3319
Fullerenes
>100
Carboxylic acids
>300
Hydrocarboxylic acids
15
Purines and pyrimidines
1.3
Alcohols
11
Sulphonic acids
68
Phosphonic acids
2
What are Purines and Pyrimidines?
• Nitrogenous bases used in DNA and RNA to code for
proteins. They are the building blocks of genes!
The Legos of Life (Continued)
• One more really cool thing. What are these?
Assembling the Legos
• Questions:
– Is evolution, the natural force, confined to only
biological life?
– So, what is evolution (what are the requirements
for evolution to take place)?
• Answers:
– No, it is not confined to living organisms.
– In simplest terms: Descent with Modification
The Requirements of Evolution
• What are the necessary constituents of
evolution (what factors need to be present for
evolution to occur)?
– You need replicators capable of autocatalysis.
• What kinds of replicators do you know?
– You need some type of inheritance (characteristics
passed along from one generation to another).
– You need the occasional mistake in replication.
• What is this known as?
One Final Requirement
• There is one final thing that is necessary for
descent with modification to take place,
what is it?
– A differential selection process. What is this
known as?
• Natural Selection – more replicators are made each
generation than can survive. The best adapted, to
their environment, replicators are typically those that
survive.
The Force Known as Evolution
• Evolution is an observable phenomenon and
behaves the same way wherever you happen
to find yourself.
• It is comparable to gravity – it happened
yesterday, it is happening right now (today),
and it will happen tomorrow the same way.
• Astrobiology is evolution writ large!
How were the Legos Put Together
• This is the question we are trying to answer.
• We have all of the Legos but we are “looking
for the instructions.”
– What is a good candidate for first replicator?
• Not DNA, which is very complex, but simpler RNA.
– What do you know about RNA? How many kinds
of RNA are there?
• In biology class we learn only about three. What are
they?
RNA Compared w/ DNA
RNAs involved in protein synthesis
Type
Abbr.
Function
Distribution
Messenger
RNA
mRNA
Codes for
protein
All organisms
Ribosomal
RNA
rRNA
Translation
All organisms
Signal
recognition
particle RNA
7SL RNA or SRP Membrane
RNA
integration
All organisms
Transfer RNA
tRNA
Translation
All organisms
tmRNA
Rescuing
stalled
ribosomes
Bacteria
Transfermessenger
RNA
RNAs involved in post-transcriptional modification or DNA replication
Type
Abbr.
Function
Distribution
Small nuclear RNA
snRNA
Splicing and other functions
Eukaryotes and archaea
Small nucleolar RNA
snoRNA
Nucleotide modification of RNAs
Eukaryotes and archaea
SmY RNA
SmY
mRNA trans-splicing
Nematodes
Small Cajal body-specific RNA
scaRNA
Type of snoRNA; Nucleotide
modification of RNAs
Guide RNA
gRNA
mRNA nucleotide modification
Kinetoplastid mitochondria
Ribonuclease P
RNase P
tRNA maturation
All organisms
Ribonuclease MRP
RNase MRP
rRNA maturation, DNA replication
Eukaryotes
Y RNA
RNA processing, DNA replication
Animals
Telomerase RNA
Telomere synthesis
Most eukaryotes
Spliced Leader RNA
Regulatory RNAs
Type
Antisense RNA
Abbr.
aRNA
Cis-natural antisense transcript
Function
Transcriptional attenuation /
mRNA degradation / mRNA
stabilisation / Translation block
Distribution
All organisms
Gene regulation
CRISPR RNA
crRNA
Resistance to parasites, probably
by targeting their DNA
Bacteria and archaea
Long noncoding RNA
Long ncRNA
Various
Eukaryotes
MicroRNA
miRNA
Gene regulation
Most eukaryotes
Piwi-interacting RNA
piRNA
Transposon defense, maybe other
Most animals
functions
Small interfering RNA
siRNA
Gene regulation
Most eukaryotes
Trans-acting siRNA
tasiRNA
Gene regulation
Land plants
Repeat associated siRNA
rasiRNA
Type of piRNA; transposon
defense
Drosophila
7SK RNA
7SK
negatively regulating CDK9/cyclin
T complex
Parasitic RNAs
Type
Function
Distribution
Retrotransposon Self-propagating
Eukaryotes and
some bacteria
Viral genome
Information carrier
Double-stranded
RNA
viruses, positivesense RNA
viruses, negativesense RNA viruses,
many satellite
virusesand reverse
transcribing viruses
Viroid
Self-propagating
Infected plants
Satellite RNA
Self-propagating
Infected cells
RNA World Hypothesis
Strengths of RNA World Hypothesis
• RNA can act as:
– Hereditary material
– Coding material
– And can have catalytic (including autocatalytic)
activity.
• RNA can act as its own enzyme.
Weakness of RNA World Hypothesis
• We still have not found a clear pathway from
the “RNA World” to a world that includes RNA
and proteins.
– A strength of the RNA World hypothesis is also a
weakness.
• RNA polymers are fragile (though in a vesicle
they would be protected).
Important Questions Being Studied
• How did RNA polymerases emerge?
– RNA polymerase is necessary to create RNA chains
(this is an important question with respect to
autocatalysis).
• How were RNA molecules incorporated into
membranes?
RNA World Hypothesis