THE CHEMICAL BASIS OF LIFE

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THE CHEMICAL BASIS OF LIFE
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Thomas Eisner and the Chemical Language of Nature

• Thomas Eisner pioneered chemical ecology
• the study of the chemical language of nature
• He studies how insects communicate via chemical
  messages

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• Rattlebox moths release a chemical that spiders
  dont like

• This spider caught a rattlebox moth and then let
  it go

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2.1 The emergence of biological function starts
at the chemical level
ATOMS AND MOLECULES

• Everything an organism is and does depends on
  chemistry
• Chemistry is in turn dependent on the arrangement
  of atoms in molecules
• In order to understand the whole, biologists
  study the parts (reductionism)

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• Molecules and ecosystems are at opposite ends of
  the biological hierarchy

• Each level of organization in the biological
  hierarchy builds on the one below it
• At each level, new properties emerge

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D. Organ Flight muscle of a moth

• A biological hierarchy

Rattlebox moth
C. Cell and tissue Muscle cell within muscle
tissue
Myofibril (organelle)
B. Organelle Myofibril (found only in muscle
cells)
Myosin
Actin
Atom
Figure 2.1
A. Molecule Actin
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2.2 Life requires about 25 chemical elements

• A chemical element is a substance that cannot be
  broken down to other substances by ordinary
  chemical means
• About 25 different chemical elements are
  essential to life

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• Carbon, hydrogen, oxygen, and nitrogen make up
  the bulk of living matter, but there are other
  elements necessary for life

Table 2.2
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• Goiters are caused by iodine deficiency

Figure 2.2
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2.3 Elements can combine to form compounds

• Chemical elements combine in fixed ratios to form
  compounds
• Example sodium chlorine ? sodium chloride

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Sodium
Chlorine
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Sodium Chloride
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2.4 Atoms consist of protons, neutrons, and
electrons

• The smallest particle of an element is an atom
• Different elements have different types of atoms

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• An atom is made up of protons and neutrons
  located in a central nucleus

• The nucleus is surrounded by electrons

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Protons
Nucleus
2
Neutrons
2
Electrons
Figure 2.4A
A. Helium atom
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• Each atom is held together by attractions between
  the positively charged protons and negatively
  charged electrons

• Neutrons are electrically neutral

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Protons
Nucleus
6
Neutrons
6
Electrons
B. Carbon atom
Figure 2.4B
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• Atoms of each element are distinguished by a
  specific number of protons

• The number of neutrons may vary
• Variant forms of an element are called isotopes
• Some isotopes are radioactive

Table 2.4
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2.5 Connection Radioactive isotopes can help or
harm us

• Radioactive isotopes can be useful tracers for
  studying biological processes
• PET scanners use radioactive isotopes to create
  anatomical images

Figure 2.5B
Figure 2.5A
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Hiroshima, Japan August 6th, 1945 815 am
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Radon Levels in Georgia
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• Radon is a colorless, odorless gas that is a
  decay product of uranium and occurs naturally in
  soil and rock. Radon gas has been identified as a
  leading cause of lung cancer, second only to
  cigarette smoking, and it is responsible for
  thousands of deaths annually. Radon breaks down
  into components called radon progeny, sometimes
  called "radon daughters," which emit high-energy
  alpha particles. These emissions raise the risk
  of lung cancer.
• The main source of high-level radon pollution in
  buildings is surrounding uranium-containing soil
  such as granite, shale, phosphate and
  pitchblende.

http//www.lungusa.org/air/radon_factsheet99.html

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2.6 Electron arrangement determines the chemical
properties of an atom

• Electrons are arranged in shells
• The outermost shell determines the chemical
  properties of an atom
• In most atoms, a full outer shell holds eight
  electrons

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• Atoms whose shells are not full tend to interact
  with other atoms and gain, lose, or share
  electrons

Outermost electron shell (can hold 8 electrons)
Electron
First electron shell (can hold 2 electrons)
HYDROGEN (H) Atomic number 1
CARBON (C) Atomic number 6
NITROGEN (N) Atomic number 7
OXYGEN (O) Atomic number 8
Figure 2.6
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2.7 Ionic bonds are attractions between ions of
opposite charge

• When atoms gain or lose electrons, charged atoms
  called ions are created
• An electrical attraction between ions with
  opposite charges results in an ionic bond

Na
Cl
Na
Cl
Na Sodium atom
Cl Chlorine atom
Na Sodium ion
Cl Chloride ion
Figure 2.7A
Sodium chloride (NaCl)
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• Sodium and chloride ions bond to form sodium
  chloride, common table salt

Na
Cl
Figure 2.7B
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2.8 Covalent bonds, the sharing of electrons,
join atoms into molecules

• Some atoms share outer shell electrons with other
  atoms, forming covalent bonds
• Atoms joined together by covalent bonds form
  molecules

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• Molecules can be represented in many ways

Table 2.8
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