Transcript ENVI 30 Environmental Issues

I.
Biological Molecules
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A.
Affected by natural selection
Based on carbon skeletons
Mostly polymers (made of monomers)
Carbohydrates
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1.
Sugars, starches, cellulose
May be classified by number of sugar residues in molecule
Monosaccharides
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2.
Simple carbohydrates with one sugar residue
Elements C, H and O in ratio CH2O
Nutrients for cells; building blocks for complex carbohydrates
Ex: Glucose, fructose, galactose
Disaccharides
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Two linked monosaccharides
Ex: Maltose (glucose + glucose), lactose (glucose + galactose),
sucrose (glucose + fructose)
Polysaccharides
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Polymers containing multiple monosaccharides
Serve two important types of functions
a.
Energy storage (Ex: starch, glycogen)
b.
Structural support (Ex: cellulose, chitin)
I.
Biological Molecules
B.
Lipids
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Fats and fat-like substances
Chemically diverse; all insoluble in water but
soluble in polar solvents
Fats
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2.
Used for energy storage, insulation, buoyancy
Phospholipids
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3.
Important components of cell membranes
Steroids
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Common components of cell membranes
Building blocks for hormones and other, complex
biological molecules
I.
Biological Molecules
C.
Proteins
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Polymers of amino acids
Abundant: Account for > 50% of dry weight in
most cells
Functions
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Structural support
Storage of amino acids
Transport of other substances (Ex: hemoglobin)
Signaling (Ex: chemical messengers)
Cellular response to chemical stimuli (Ex: receptors)
Movement (Ex: contractile proteins)
Defense against foreign substances and pathogens
(Ex: antibodies)
Catalysis of biochemical reactions (Ex: enzymes)
I.
Biological Molecules
D.
Nucleic Acids
1.
Deoxyribonucleic Acid (DNA)
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2.
Can self-replicate (with help from enzymes)
Passed from one generation to the next
Primarily in nuclei of eukaryotic cells
Comprises genes
Ribonucleic Acid (RNA)
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Functions in protein synthesis
Fig. 17.3
II.
Early Earth
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A.
Earth ~4.6 billion years old
First water ~3.9 bya
First evidence of life ~3.8 bya (controversial)
First fossils (bacteria-like) ~3.5 bya
First eukaryotes ~2.2 bya
First animal fossils ~700 mya
Conditions
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High energy environment
Violent thunderstorms
Widespread volcanic activity
Intense radiation (including uv) from early sun
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4.
No ozone layer and sun more intense then vs. now
Bombardment by meteors and other objects from space
III.
Origin of Life on Earth
A.
Requirements for Origin of Life
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Little or no free oxygen (O2)
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Source of energy
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Intense radiation, volcanism, bombardment
Availability of chemical building blocks
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Elements – C, H, N, O, P, S
Time
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B.
O2 highly reactive; would have destroyed reduced compounds
(chemical building blocks)
End of bombardment to first evidence of life >100 million years
First Cells May Have Arisen through Four Stages
1.
Abiotic synthesis of small organic molecules (e.g. amino acids,
nucleotides)
Assembly of small organic molecules into polymers (e.g.
proteins, nucleic acids)
Packaging of macromolecules into protobionts
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3.
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Membranes
Internal environment different from external environment
Development of self-replicating molecules
III. Origin of Life on Earth
C.
Pre-Biotic Chemistry
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A.I. Oparin & J.B.S. Haldane (1920’s): Organic
molecules necessary to life on earth might have
arisen spontaneously from inorganic raw
materials
First empirical studies in 1950’s by Harold Urey
& Stanley Miller (U. of Chicago)
III. Origin of Life on Earth
C.
Pre-Biotic Chemistry
1.
Urey-Miller Apparatus
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Formation of amino acids, complex hydrocarbons,
sugars, lipids, nucleotides
Questions: Enough NH3 and CH4 in earth’s early
atmosphere? Reducing atmosphere?
Alternative: Origin of life at hydrothermal vents
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Sources of hot water and minerals, including S &
Fe compounds
Alternative: Panspermia
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Amino acids found in meteorites
III.
Origin of Life on Earth
C.
Pre-Biotic Chemistry
2.
Abiotic Synthesis of Polymers
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Clays may have helped
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Negatively charged (bind positively charged organic
molecules)
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Contain minerals that might have catalyzed
polymerization
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Amino acid solution + hot clay  AA polymers
Protobionts
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Abiotically produced molecules surrounded by bilayered lipid
membrane
Highly organized
Some forms reproduce when large enough
Internal environment chemically distinct from outside
Some forms carry out catalytic activity
Some forms produce electrochemical gradients
Fig. 25.3
III.
Origin of Life on Earth
C.
Characteristics of Early Life
1.
Self-Replication
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2.
Proteins aren’t self-replicating
RNA may carry out catalytic functions
Ribozyme – Autocatalytic RNA
RNA may have been first informational molecule
DNA more stable; may have arisen from RNA
Nutrition
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First cells likely heterotrophic
No free oxygen in atmosphere of early earth
First heterotrophs probably used anaerobic fermentation
(less efficient than aerobic metabolism)
First autotrophs may have used hydrogen sulfide (H2S) as
hydrogen source (modern purple & green sulfur bacteria still
get H from H2S)
First autotrophs to split water for H probably ancestors of
modern cyanobacteria (3.1 – 3.5 bya)
Production of O2 had profound effects