8 - Life - I

1. 8 - Life - I

2. What is Life? • Generally, living systems: • Reproduce - make more copies of themselves • Evolve - undergo transformations with successive copies that pass the transformations on to future copies

3. Of the 6 most abundant elements, 4 make up 95% of living systems: CHON These are organized into useful biological molecules (and other things like water) Living systems are chemical machines: Molecules must be stable enough to last long enough to interact with each other, but not so stable as to be inert.

4. Monomers & Polymers Monomers - small molecules that can join together in a repetitive sequence - the Polymer Examples: Monomer:Polymer: Glucose Starches Cellulose Glycogen Amino Acids Proteins

5. Handedness (enantiomers) *strictly speaking, levo & dextro refer to how the molecules affect circularly polarized light - generally just use L and D) levo (left) and dextro (right)* Example: D- carvone “spearmint” L-carvone “caraway” Pharmaceuticals: thalidomide - sleeping pill & morning sickness - “L” caused birth defects Almost without exception, amino acids used by life on Earth are left-handed

6. AMINO ACIDS ONLY 20 USED BY LIFE ON EARTH All are L (symmetric glycine is its own enantiomer…)

7. PROTEINS Polymers of amino acids (AAs) Structure (and hence function) depends on AA content and order Some act as enzymes = biological catalysts* myoglobin - connected helix structures of amino acids *catalyst - a chemical that aids a specific reaction without itself being consumed Folding@home distributed computing project on protein folding!

8. DNA (deoxyribonucleic acid) Adenine Thymine Cytosine Guanine nitrogenous base phosphate deoxyribose (sugar)

9. DNA - Replication Rule: A-T and G-C base pairs only

10. DNA - Protein Production Information stored in DNA mRNA copies sections (Uracil subs for Thymine) tRNA with AAs attached matches with mRNA AAs string together into protein mRNA - messenger RNA tRNA - transfer RNA From Lunine’s Astrobiology (Fig. 4.25) - excellent for more advanced treatment

11. To make 20 amino acids with 4 base pairs requires that at least 3 base pairs needed to code the amino acid* (can only make 16 AAs using only 2 base pairs). Note redundancy! *first deduced by George Gamow, “inventor” of Big Bang model of cosmology!

12. Other Things Gene - sequence of such triplets used to encode a protein or other useful product Junk DNA - apparently random sequences - purpose unknown DNA (and RNA) require additional machinery in cells to work (viruses “borrow” this from their host cell) DNA very stable - RNA less so, but repair mechanisms fix much of this RNA more versatile - can make copies, make proteins, etc. - leading some to think IT came first - “RNA World” - before DNA.

13. Mutations Causes: Impact of cosmic rays, X-rays, high-energy UV light Mutagenic chemicals in environment Errors in DNA-RNA copying machinery Types: Harmful - broken machinery can’t produce needed molecules Helpful - altered machinery does something better than before Neutral - no apparent effect at the present time

14. Differential Reproduction & Natural Selection An organism that inherits the ability to “do something better” for survival will tend to have more offspring who will also inherit this ability. Leads to a shift in the genetic makeup of that group. Genetic Drift Isolated populations of the same organism will undergo different types & sequences of changes - each accumulate their own changes to the point where they might not successfully interact genetically.

15. Energy Production Photosynthesis The addition of light allows the product to “store energy” Consumers of plants (like us!) utilize this stored energy, making the reaction go the other direction. NOTE: O2 was not abundant on the early Earth O2 consumers could not exist until O2 was produced O2 producers had to come first