Astrobiology Replicators. NASA’s Astrobiology Page astrobiology/ astrobiology
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Transcript of Astrobiology Replicators. NASA’s Astrobiology Page astrobiology/ astrobiology
NASA’s Astrobiology Page
• http://astrobiology.nasa.gov/about-astrobiology/
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 >35Aromatic hydrocarbons 3319
Fullerenes >100Carboxylic acids >300
Hydrocarboxylic acids 15Purines and pyrimidines 1.3
Alcohols 11Sulphonic acids 68
Phosphonic acids 2
Compound class[11] Concentration (ppm)Amino acids 17-60
Aliphatic hydrocarbons >35Aromatic hydrocarbons 3319
Fullerenes >100Carboxylic acids >300
Hydrocarboxylic acids 15Purines and pyrimidines 1.3
Alcohols 11Sulphonic 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!
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?
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 RNA
Membrane integration All organisms
Transfer RNA tRNA Translation All organisms
Transfer-messenger RNA
tmRNARescuing stalled ribosomes
Bacteria
RNAs involved in protein synthesis
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
RNAs involved in post-transcriptional modification or DNA replication
Type Abbr. Function Distribution
Antisense RNA aRNATranscriptional attenuation / mRNA degradation / mRNA stabilisation / Translation block
All organisms
Cis-natural antisense transcript 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 functions Most animals
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
Regulatory RNAs
Type Function Distribution
Retrotransposon Self-propagating Eukaryotes and some bacteria
Viral genome Information carrier
Double-stranded RNA viruses, positive-sense RNA viruses, negative-sense RNA viruses, many satellite virusesand reverse transcribing virusesViroid Self-propagating Infected plants
Satellite RNA Self-propagating Infected cells
Parasitic RNAs
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?