The Nature & Origin of Life

Transcription

1 The Nature & Origin of Life OCN 201 Biology Section Lecture 1 Grieg Steward Department of Oceanography grieg@hawaii.edu

2 What is Life?!2

3 What is Life? General Defining Features Of Life: Self-replication (Growth, Division) Maintenance of order Evolution Requires controlled collection and transformation of matter and energy for replication and repair!3

4 Life is marvelous... Despite the astonishing diversity of life there is considerable underlying unity but not miraculous!!4

5 Features of Life as We Know it Life adheres to - The principles of organic chemistry - The laws of thermodynamics!5

6 Features of Life as We Know it Life on earth today: Based on cells as the fundamental unit Carbon-based Water-dependent Building blocks: Carbohydrates, DNA, RNA, Protein, Lipid!6 Bruno C. Vellutini

7 Cell Building Blocks Nucleic Acids DNA and RNA) Information Lipids cell membranes Proteins Sturcture, Catalysis Carbohydrates Structure, energy storage

8 Major Building Blocks of Life Amino Acids H C H S Nucleotides Sugars Lipids Elements Hydrogen Carbon Nitrogen Oxygen Phosphorus Sulfur

9 The Major Structural Elements of Life Molecule carbohydrates (sugars) Molecule H, C, O nucleic acids amino acids lipids H, C, O, N, P H, C, O, N, S H, C, O, N, P, S

10 Cell juices (Cytoplasm) Nucleic Acids DNA and RNA) Lipids Carbohydrates ( Proteins Metals ) Water Salts sodium potassium calcium magnesium

11 The Chemistry of Life is Conserved Z X C Y Z Y B A X A B C Chopra et al. 2010, Australian Space Science Conference Series

12 The Chemistry of Life is Conserved Salts Stabilize structures. Create ion gradients Major Structural Elements Building blocks of the factory and the machinery Trace Elements present in small amounts, but critical for cell chemistry! Chopra et al. 2010, Australian Space Science Conference Series

13 KEY POINTS The chemistry of life is very similar across all types of organisms Carbon is the central element of life because of its versatility in bonding Just six elements make up most of living mass, but other elements (like salts and metals) are critical for cell chemistry

14 Relative Mass of Elements in a Bacterium Element Atomic number Percentage Role Carbon 6 50 basis of organic molecules Oxygen 8 20 cellular respiration, component of water Nitrogen 7 14 component of all proteins and nucleic acids Hydrogen 1 8 component of water & most organic molecules, electron carrier Phosphorous 15 3 component of nucleic acids, important in energy transfer Sulfur 16 1 component of most proteins Sodium 11 1 main positive ion inside cells Potassium 19 1 main positive ion outside cells Magnesium essential component of many energy-transferring enzymes Chlorine main negative ion outside cells Calcium cell structure, motility, and intracellular signalling Iron Redox reactions enzyme co-factor other trace 0.3!14

15 Life is made from the most abundant elements Where do they all come from? Stellar nucleosynthesis! And supernovae!

16 Larger atoms built from smaller atoms

17 All elements heavier than iron are formed by supernovae!17

18 Origin of Life on Earth Panspermia Divine Creation Chemical Evolution (abiogenesis)!18

19 Origin of Life on Earth Difficult task! Must combine knowledge of: Chemical nature of life History of conditions on early earth to make logical inferences about what happened in the very (very) distant past Step 1: macromolecules; the building blocks of life

20 Can life s building blocks be built from simple elements by pre-biotic chemistry? H C H C H N H O C H H C H H H H O H

21 The Miller-Urey Experiment SPARK Gas (Atmosphere) Started with: H2O Methane Ammonia Hydrogen COOL Ended with: Amino Acids & other organic Compounds Water (Ocean) HEAT!21

22 Murchison Meteorite Samples from Comet Wild 2 contained organic compounds! 90 amino acids and other organic compunds!22

23 Lesson Learned: Many building blocks of life are easy to make Many variations on Miller-Urey experiment have had similar results Meteorites and comets found to contain organic compounds similar to those produced in the Miller experiment Wild 2

24 Molecules to Life Large gap to overcome from organic molecules to self-replicating entities Life forms today are complicated machines Copyright M.W. Davidson and Florida State University Research Foundation

25 Chicken and Egg Problem Lipid In modern Cells all components are Interdependent RNA DNA RNA PROTEIN

26 The Central Dogma autocatalysis RNA Lipid RNA DNA RNA PROTEIN

27 RNA World hypothesis RNA may have been the first self-replicating precursor to cellular life. information content structural functions catalytic activity

28 Origin of Cells Chemistry must be contained to make a cell Lipids can form abiotically Lipids arrange spontaneously into cell-like structures

29 Protocells Experiments show that protocells can grow and divide Recent work suggests how protocells could make the leap from random chemistry to simple cells with heritable traits that directly compete Cold Hot

30 Origin Theories RNA probably came before DNA Protocell hypothesis an important step forward Life probably began in the sea: water is essential hydrothermal vents may have provided chemicals and energy for replication cycles

31 KEY POINTS Organic building blocks of life (like amino acids) are very common in the universe Discovery of catalytic RNAs shows one way around the chicken-and-egg problem. Recent lab studies have shown how primitive protocells" could acquire key characteristics of life (growth, division, evolution)

32 Origin Theories Regardless of how the first self-replicating life forms came into existence - they would be immediately subjected to the process of NATURAL SELECTION