Lecture 1.4: Foundations of Life
Transcript of Lecture 1.4: Foundations of Life
Chem Evol Polypeptides Nucleic Acids
Unit 1: Theoretical Pillars of Biology
Lecture 1.4: Foundations of Life
John D. Nagy
BIO 181: General Biology for Majors, Scottsdale Community College
2019 Revision
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Chem Evol Polypeptides Nucleic Acids
Outline
1 Chemical EvolutionEarly EarthMiller-Urey Experiment
2 PolypeptidesBuilding blocksPolymersProteins
3 Nucleic AcidsBuilding blocksRNAConnections between nucleic acids and proteins
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Chem Evol Polypeptides Nucleic Acids Early Earth Miller-Urey
Earth ca. 4.4 billion years ago
See Lunine 2006 [3] for evidence.
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Chem Evol Polypeptides Nucleic Acids Early Earth Miller-Urey
Can this environment generate the stuff of life?
Miller-Urey Experiment
Attempt to simulate conditions of early Earth, including earlyatmosphere, heat and lightning. See [4].
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Chem Evol Polypeptides Nucleic Acids Early Earth Miller-Urey
Results of the Miller-Urey experiment
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Critical Miller-Urey products—amino acids
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The 20 common amino acids in living things
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Condensation reactions leading to polymerization
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Amino acid polymerization
Polypeptide chains long enough to fold into blobs are calledproteins.
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Chem Evol Polypeptides Nucleic Acids Building blocks Polymers Proteins
Protein example
Space-filling molecular model:
Protein is called PTEN.
Involved in guarding againstcancer (tumor suppressorprotein).
Shown bound to its ligand,a molecule which binds toanother, usually larger, one.
A chain of 324 amino acidsfolded into into its tertiarystructure.
Proteins are typically > 80 aminoacids long; average about 250.
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Composition of cell dry mass
Cell dry mass is about 55% protein.Source: Cell Biology by the Numbersbook.bionumbers.org/what-is-the-macromolecular-composition-of-the-cell.
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Proteins: Arguably the most important molecule of life
An estimate of the proportions of proteins in a cell devoted tovarious metabolic functions.
Source: www.cs.cmu.edu/%7Eesefer/metric/index.html
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Chem Evol Polypeptides Nucleic Acids Building blocks Polymers Proteins
NASA’s working description of life on Earth
“Life is a self-sustaining chemical sys-
tem capable of Darwinian evolution.”
From The limits of Organic Life in Planetary Systems [1]:
Life on Earth is fundamentally cellular.
Life is chemical: Living things use covalent bonding propertiesof C, H, N, O, P, and S and the ability of O and N to modulatehydrocarbon reactivity.
Biomolecules have evolved to function when dissoved in water.
Metabolism is controlled by enzymes that are inheritedthrough reproduction.
Living systems adapt to changing environments via evolutionby natural selection (Darwinian evolution).
Life exploits thermodynamic disequilibrium (homeostasis).
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Chem Evol Polypeptides Nucleic Acids Building blocks Polymers Proteins
Enzymes–the central molecule of life
Hexokinase, a key enzyme in glycolysis. Source: Kuser et al. 2000 [2].
Definition: Enzyme
An enzyme is a protein catalyst.
Definition: Catalyst
Substance that increases rate of a chemical reaction withoutundergoing any permanent change.
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Chem Evol Polypeptides Nucleic Acids Building blocks RNA Connections
Another product of early Earth experiments
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Chem Evol Polypeptides Nucleic Acids Building blocks RNA Connections
All nucleotides have a 5-carbon sugar...
Sugar = carbohydrate. A carbohydrate is any organiccompound with a formula nearly equal to:
[CH2O]n,
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Chem Evol Polypeptides Nucleic Acids Building blocks RNA Connections
...and a nitrogenous base
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Nucleotides can bond together by phosphate bridges
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Result: Ribonucleic Acid (RNA)
If the sugar is ribose (notdeoxyribose), then
we have ribonucleic acid =RNA;
the bases are A, C, G or U(no T);
bond angles make it a helix(spiral);
but, usually forms a singlehelix.
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Chem Evol Polypeptides Nucleic Acids Building blocks RNA Connections
Sometimes the sugar is deoxyribose
What’s the obvious difference that you see?
Comparison and contrast of RNA and DNA
Both form helicies (spirals).
But, bond angles in deoxyribose allow these polymers towrap around each other.
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DNA therefore forms a double helix
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Chem Evol Polypeptides Nucleic Acids Building blocks RNA Connections
DNA base pairing characteristics
If the sugar is deoxyribose then
we have deoxyribonucleicacid = DNA;
the bases are A, C, G or T;
if it forms a double helix, itdoes so typically with acomplementary DNAstrand.
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RNA can also form a double helix with itself
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Nucleic acids control proteins in a cell
Central dogma of biology
The inappropriately-named central dogma of biology saysthat information flows from DNA to RNA to protein.
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Proteins control nucleic acids in a cell
The second-most abundant protein class controls nucleotidemetabolism.
Summary
Proteins and nucleic acids are intimately connected, andtogether they control the metabolic activities of a cell.
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References I
Commitee on the Limits of Organic Life in Planetary Systems, Space Studies Board, and
Board on Life Sciences.The Limits of Organic Life in Planetary Systems.National Academies Press, Washington, D.C., 2007.
Paula R. Kuser, Sandra Krauchenco, Octavio A. C. Antunes, and Igor Polikarpov.
The high resolution crystal structure of yeast hexokinase PII with the correct primarysequence provides new insights into its mechanism of action.J. Biol. Chem., 275(27):20814–20821, 2000.
Jonathan I. Lunine.
Physical conditions on the early Earth.Phil. Trans. R. Soc. B, 361:1721–1731, 2006.
Xueshu Xie, Daniel Backman, Albert T. Lebedev, Viatcheslav B. Artaev, Liying Jiang,
Leopold L. Ilag, and Roman A. Zubarev.Primordial soup was edible: Abiotically produced Miller-Urey mixture supports bacterialgrowth.Sci. Rep., 5:14338, 2015.
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