1. Lecture 3. What is Life? The Hallmarks of (Earth) Life. reading: Chapter 3

2. What is Life? We only know one kind of life - Earth life Distinguishing life from non-life catvs.car cat vs. a flame cat vs. a crystal What are the characteristics that separate life from non-life? a flame in zero gravity sugar a flame in Earth’s gravity

3. What is Life?, cont. We mostly rely upon the saying “ we know it when we see it ”. We have, so far, not been able to define life. (Definition like water IS H 2 O). This may be a problem when we go to search for life elsewhere. We may not recognize it as life or easily distinguish it from non-life.

4. 6 Key Properties of Life 1.Has Order/Structure earth life is cellular boundary separates the cell from the environment structure/order within the cell order is NECESSARY for life, but order by itself is NOT SUFFICIENT for life (a dead cell has order but not life) 2.Reproduction living organisms reproduce their own kind sometimes this is a simple process sometimes it is a very complex process animals give live birth, plants use male and female flowers

5. 6 Key Properties of Life, cont. 3.Growth and Development living organisms grow in a controlled manner (growth ≠ reproduction) living organisms change/develop in a controlled manner process is controlled by heredity - traits passed on to the next generation in a precise manner growth and development necessary, but not sufficient for life 4.Energy Utilization cells need fuel make waste products harness the energy gained to create order/structure, carry out reproduction, growth and development

6. 6 Key Properties of Life, cont. 5.Response to the Environment must interact with the environment must interact with each other adapt to SHORT-TERM changes in environment grow a winter coat, alter your preferred energy source, hibernate movement 6.Evolutionary Adaptation adapt to LONG-TERM changes in environment adaptation must be heritable, passed onto next generation in a controlled manner

7. Darwin’s Theory of Evolution Origin of Species published 1859. “survival of the fittest” 1.Overproduction and the struggle for survival resources (food, water, energy) are always limiting there is always competition for resources 2.Individuals vary mutations are always occurring some have better traits than others 3.Survival of the fittest individuals better able to obtain resources survive and reproduce next generation will have better traits than previous generations natural selection/adaptation over time, advantageous traits are selected for and win.

8. Darwin’s Theory of Evolution, cont. Darwin didn’t understand the mechanisms behind natural selection (discoveries in molecular biology & genetics much later). This doesn’t invalidate his theory. (Copernicus came up with the correct model for the solar system, but he didn’t understand concept of gravity.) Spent almost 30 years collecting evidence to support his theory. Galapagos finches - 13 species, each adapted to different microenvironments and lifestyles. artificial selection - breeding of domesticated plants & animals can cause profound changes in a few thousand years. antibiotic resistance catastrophe in hospitals.

9. The 6 Key Properties of Life, revisited CarFlameCrystalVirus 1. Order/StructureYYYY 2. ReproductionNYYY 3. Growth/DevelopmentNYYY 4. Energy UtilizationYYNN 5. Response to the EnvironmentY/NYYN 6. Evolutionary AdaptationNNYY

10. The 6 Key Properties of Life, revisited 1.Order/structure 2.Reproduction 3.Growth/development 4.Energy utilization 5.Response to the environment 6.Evolutionary adaptation All living things have to have ALL 6 of these traits. One alone/five are not sufficient to constitute life. Non-living things typically lack one or many of these traits.

11. Not only do all organisms have cells, all cells have similar structures. The biochemistry of Earth cells is very similar: all life is carbon based all life made of the biogenic elements C, H, N, O, P, S make up 96% of the atoms in cells all have DNA and RNA all make RNA the same way all make proteins the same way using DNA and RNA and other proteins Earth life is all fundamentally the same - it all shares a common ancestor Earth Life Goes Beyond the 6 Key Traits

12. Why Carbon? C is abundant can form bonds with lots of other elements (e.g., H, N, O, P, S) can form a variety of C-C bonds single (C-C), double (C=C), triple bonds (C  C) C is versatile - forms rings - chains - networks - one atom bonds with up to 4 other atoms organic molecules contain C and H in addition to other atoms. Silicon, Si: Si is abundant can also have 4 bonds at once bonds are weaker than C highly insoluble in water doesn’t form double or triple bonds or chains, rings, networks limited in its reactivity

13. Molecular Components of Earth Life All components made from complex organic molecules Carbohydrates: general structure CH 2 O are sugars monomers: glucose polymers (repeating units): lactose, cellulose, starch Lipids: form cell membranes/barriers to the environment oil and water -> oil droplets fatty acid (fat + COOH) glycerol (simple sugar)

14. Proteins Play structural roles: cell walls, collagen in our skin, fingernails Play catalytic roles: enzymes, catalyze the reactions needed for life Are polymers of amino acids - amino (contains NH 2 ) acids (contains COOH) Are >70 amino acids in the universe. But only 20 amino acids are found in Earth life. Valine Phenylalanine Glycine

15. Handedness Complex organic compounds like amino acids have two flavors that are mirror images of each other ( handedness ). Amino acids produced by non-living processes contain an equal mixture of left - (L-) and right-handed (D-) forms. Amino acids produced by living processes contain the left- handed (L-) version! Similarly, carbohydrates made by Earth life contain right-handed (D-) sugars. Another hint that all of Earth life is related by a common ancestor.

16. Cells are chemical machines. Chemical reactions are carried out by proteins/enzymes. Catalysts make a chemical reaction “go” MUCH faster. Cells make a variety of complex structures from raw materials. biosynthesis builds up those complex structures Requires energy in the form of ATP ( adenosine triphosphate). Cells make ATP, then consume it during biosynthesis. Again, evidence all Earth life had a common ancestor. Similar Metabolism

17. Water Chemical reactions occur in solution (dissolved in water). Allows substrates and wastes to be transported in and out of the cell. Is a reactant or product in many chemical reactions. Makes up most of the cell. When water disappears, cells die. Water must be liquid (not boiling, not solid ice).

18. Nucleic Acids DNA, deoxyribonucleic acid: Hereditary material of the cell. Holds the operating instructions for the cell. Double-stranded, so is easily duplicated and passed to next generation. Information contained in the sequence of bases: AGTTGTGC A binds to T, C binds to G Sequence carries information to make proteins. Both strands match up and zip together. Can unzip, a copy of each is made. RNA ribonucleic acid: Similar DNA, role is to help make proteins. Some RNAs catalyze reactions in protein synthesis ( rRNA in the ribosome ). Others make transient copies of genes, carry instructions for making a protein ( mRNA ). Mutations (changes) in the DNA can lead to changes in the protein. phosphate sugar bases: sugar

19. Lecture 4. Big bang, nucleosynthesis, the lives and deaths of stars. reading: Chapter 1