Biological Molecules

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• Biological Molecules
• Affected by natural selection
• Based on carbon skeletons
• Mostly polymers (made of monomers)
• Carbohydrates
• Sugars, starches, cellulose
• May be classified by number of sugar residues in
  molecule
• Monosaccharides
• 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
• Two linked monosaccharides
• Ex Maltose (glucose glucose), lactose (glucose
  galactose), sucrose (glucose fructose)
• Polysaccharides
• Polymers containing multiple monosaccharides
• Serve two important types of functions

2

• Biological Molecules
• Lipids
• Fats and fat-like substances
• Chemically diverse all insoluble in water but
  soluble in polar solvents
• Fats
• Used for energy storage, insulation, buoyancy
• Phospholipids
• Important components of cell membranes
• Steroids
• Common components of cell membranes
• Building blocks for hormones and other, complex
  biological molecules

3

• Biological Molecules
• Proteins
• Polymers of amino acids
• Abundant Account for gt 50 of dry weight in most
  cells
• Functions
• 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)

4

• Biological Molecules
• Nucleic Acids
• Deoxyribonucleic Acid (DNA)
• 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)
• Functions in protein synthesis

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Fig. 17.3
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• Early Earth
• 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
• High energy environment
• Violent thunderstorms
• Widespread volcanic activity
• Intense radiation (including uv) from early sun
• No ozone layer and sun more intense then vs. now
• Bombardment by meteors and other objects from
  space

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• Origin of Life on Earth
• Requirements for Origin of Life
• Little or no free oxygen (O2)
• O2 highly reactive would have destroyed reduced
  compounds (chemical building blocks)
• Source of energy
• Intense radiation, volcanism, bombardment
• Availability of chemical building blocks
• Elements C, H, N, O, P, S
• Time
• End of bombardment to first evidence of life gt100
  million years
• First Cells May Have Arisen through Four Stages
• 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
• Membranes
• Internal environment different from external
  environment
• Development of self-replicating molecules

8

• Origin of Life on Earth
• Pre-Biotic Chemistry
• A.I. Oparin J.B.S. Haldane (1920s) Organic
  molecules necessary to life on earth might have
  arisen spontaneously from inorganic raw materials
• First empirical studies in 1950s by Harold Urey
  Stanley Miller (U. of Chicago)

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• Origin of Life on Earth
• Pre-Biotic Chemistry
• Urey-Miller Apparatus
• Formation of amino acids, complex hydrocarbons,
  sugars, lipids, nucleotides
• Questions Enough NH3 and CH4 in earths early
  atmosphere? Reducing atmosphere?
• Alternative Origin of life at hydrothermal vents
• Sources of hot water and minerals, including S
  Fe compounds
• Alternative Panspermia
• Amino acids found in meteorites

11

• Origin of Life on Earth
• Pre-Biotic Chemistry
• Abiotic Synthesis of Polymers
• Clays may have helped
• Negatively charged (bind positively charged
  organic molecules)
• Contain minerals that might have catalyzed
  polymerization
• Amino acid solution hot clay ? AA polymers
• Protobionts
• 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

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Fig. 25.3
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• Origin of Life on Earth
• Characteristics of Early Life
• Self-Replication
• Proteins arent 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
• 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