Life on Earth

Life on Earth

Life on Earth George Lebo 23 February 2012 AST 2037 1 Life: What is it?

From people, to microbes, to tree, to GATORS 2 Life: What is it? Things with the ability to reproduce AND the ability to evolve and adapt Why both of these? Flames can spread or reproduce, but they arent alive Crystals (i.e. salt) can also spread or grow, but they arent alive

either Only living things evolve meaning develop adaptations to their environment that improve their ability to continue 3 Quick Aside on evolution In this instance, we mean evolution with a little e Meaning not necessarily the origin of species (Evolution with a big E)

Rather, the short timescale adaptation to environment Note that evolution is widely accepted all sorts of living critters evolve on easily-observed timescales: For instance, antibiotic-resistant microbes (like resistant tuberculosis) 4 Life: Whats it Made of? Constituent elements of humans: H (61%), O (26%), C

(10.5%), N (2.4%), Ca (0.23%), P (0.13%) Sun: H (91%), He (9%), O (0.08%), C (0.033%), Ne (0.011%), N (0.010%), Earth crust: O (47%), Si (28%), Al (9.1%), Fe (5%), Earth atmosphere: N (78%), O (21%), Ar (0.9%), C (0.04%), .. Hydrogen in us is mostly in H2O (water) Carbon a key ingredient(!!) 5

Why Carbon? For any element, its distribution and structure of electrons determines many of its properties (i.e. color and chemical properties) Electrons are distributed in discrete shells (quantum physics) Carbon has a very normallooking electron structure 6 electrons:

Inner shell is full with 2 electrons Outer shell is exactly half-full with 4 electrons (shell needs 8 electrons to be full 6 Why Carbon? It turns out that this normal-ish structure has very special

properties for chemical bonding In chemical bonding, atoms share some electrons in their outermost shell to try to reach a full shell (8 for Carbon) For instance, Carbon can bond with another Carbon atom each atom gets to feel like it has 8 electrons and is happy 7 Why Carbon? Or, Carbon can bond with 4 Hydrogen atoms

Hydrogen only has the innermost shell needs 2 electrons shared to feel full; Carbon shares a total of 8 in its outer shell (This is the gas called methane) 8 Why Carbon? Or, Carbon can bond with 2 Oxygen atoms Oxygen has 6 outer shell electrons

(This is the gas called Carbon dioxide or CO2 our favorite greenhouse gas!) 9 Why Carbon? Or, Carbon can bond with 1 Nitrogen and 1 Hydrogen atoms Nitrogen has 5 outer shell electrons (This is Hydrogen Cyanide or CNH deadly poison!)

10 Why Carbon? There are other possibilities too! Long story short: Carbon is incredibly diverse in its ability to form chemical bonds with other elements

Of ALL the other elements in the periodic table (almost 100 naturally-occurring ones), only Silicon has similar talent for chemical bonding 11 Carbon chains Carbon is also virtually unique for its ability to form long chains of molecules Monomers small collections of atoms that form an

identifiable entity which can act themselves as units in binding with other units, e.g. amino acids Polymers collections of monomers, e.g. proteins are collections of amino acids Diversity -> why? -- organic chemistry is so complex Organic means carbon chemistry 12 Carbon chains

Carbon is also virtually unique for its ability to form long chains of molecules For instance, carbon nanotubes and buckyballs only recently discovered in nature called Fullerenes after Buckminster Fuller, developer of the geodesic dome Fantastic material strength and electrical properties 13 Carbon chains

Carbon and Hydrogen can also form long chains These might be just CH, or might include other elements usually dangling off the ends of the CH chain These are generically called hydrocarbons Here are a few recognizable examples

14 Carbon chains Other chains including other elements and double bonds This one, for instance, is a lipid AKA fat The energy your body stores goes into that double bond

near the lower right Burning fat means breaking that double bond to release energy In reverse, eating chocolate cake means augmenting my personal allocation of double carbon bonds (sounds nicer that way) 15 Important Polymers

We already saw some (i.e. lipid = fat) Other important ones include amino acids (lots more about these to come!) Note Alanine = amino acid 16 Alanine: Isomerism

Alanine comes in 2 flavors -- Levo & Dextro -- called chirality, (L = left-handed; D = right-handed) You cannot rotate one of these to match the other same chemical components, but different structure (below) Note that ALL life on Earth uses L, not D (!!) Why? 17

Carbon & Photosynthesis As well see in a few minutes, photosynthesis is the fundamental energy source for (almost) all life on Earth Heres that pesky Sun again! Plants pull water (H2O) from underground, plus CO2 from the atmosphere Add some sunlight and

photosynthesis turns that energy into chemical bonds (sugars) Oxygen is released to the air as a waste byproduct 18 Photosynthesis Details More detailed picture (quick! Copy this all down!) Note presence of ADP and ATP

19 Photosynthesis (Less) Detail Chlorophyll is the main light absorber, and is what gives plants their typical green color Chlorophyll exists inside plant cells in structures called chloroplasts 20

Energy Cycle of Life Almost all life on Earth gets in energy (ultimately) from the Sun! 21 Sugars & Metabolism Sugar is a chemical compound; chemical reactions can break

down a sugar and release energy; ADP and ATP cycles, etc. The point: Carbon is critical for metabolism of life on Earth! 22 Carbon & Reproduction Carbon, hydrocarbons make up amino acids These are the basic building blocks of proteins (structural parts of living things) Amino acids are also building blocks of Deoxyribonucleic Acid

(DNA) This is the key to reproduction (a defining characteristic of life!) 23 DNA Critical for ALL life on Earth Structure of DNA (Crick

& Watson Nobel prize): Double helix structure Ladder-like Amino acids are rungs (nucelotides) Base pairs (A-T and C-G) 24

DNA DNA (zipper view) 25 DNA DNA structure is key to DNA replication Enzymes make the helix unzip

A only matches T; C only matches G (and vice versa) So, add new nucleotides to the mix, and they bond to the only possible matches Voila you get 2 identical DNA strands !! 26

DNA & Genetic Coding There are 20 amino acids which humans use to build ALL of the proteins/structures in the body DNA nucleotide sequences are used as a code with a triplet package: i.e. AAA in a row means one amino acid ACA means another acid GCC means yet another amino acid Some triplet sequences also mean start a structure and some mean stop the structure

So DNA is literally a set of instructions on how to build a living creature, one protein at a time 27 Genetic Code, mRNA Codons 28 RNA

Single-stranded ribonucleic acid Similar in many ways to DNA Several types of RNA commonly used in life mRNA (Messenger RNA) takes the DNA code message to places where proteins are made (ribosomes)

rRNA (Ribosomal RNA) actually carries out the protein assembly in ribosomes It appears that some viruses may use RNA for their genetic code 29 Cells: Basic Units of (most) Life Smallest units of independent life here on Earth

30 Prokaryotic Cells Cells without nuclei Typically considered primitive i.e. bacterium 31 Eukaryotic Cells Animals With nucleus

Advanced This one is an animal cell 32 Eukaryotic Cells Plants With nucleus Advanced This one is a

plant cell Note: Cell Wall Chloroplasts 33 Multi-cellular Life More than one cell But, not so many you

cant count them easily! 34 Complex plants 35 Complex animals

36 Complex animals 37 Summary Tremendous commonality amongst a huge range of life on Earth Under the microscope, hard to really tell one human cell

from a jellyfish cell from a bacterium from a tree basic features are the same Also, chemical makeup (all DNA; all L-Alanine even) Suggests a common origin 38

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