Chemical Foundation for Cells

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Chemical Foundation for Cells

• Starr/Taggarts
• Biology
• The Unity and Diversity of Life, 9e
• Chapter 2

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Key Concepts

• All substances consist of one or more elements
• Elements are composed of atoms
• All atoms of an element have the same number of
  protons and electrons, but may differ in the
  number of neutrons

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Key Concepts

• Atoms have no overall electric charge unless they
  lose or gain electrons to become ions
• Whether an atom will interact with other atoms
  depends on the number and arrangement of its
  electrons

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Key Concepts

• Life originated in water
• Water has temperature-stabilizing effects,
  cohesiveness, and a capacity to dissolve or repel
  substances
• The pH scale measures the concentrations of
  hydrogen ions in solution

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The Elements

• Fundamental forms of matter
• Cannot normally be broken apart into something
  else
• 92 occur on Earth
• In all living things, the most abundant elements
  are oxygen, hydrogen, carbon, and nitrogen

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Elements Common in Living Things
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Structure of Atoms

• Subatomic particles
• Protons - positive charge
• Electrons - negative charge
• Neutrons - no charge
• Atomic Number
• Number of protons
• Mass Number
• Number of protons number of neutrons

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Model of Atomic Structure
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Isotopes

• Atoms of an element with different numbers of
  neutrons
• All isotopes interact with other atoms in the
  same way
• A radioisotope has an unstable nucleus that
  stabilizes itself by emitting energy and
  subatomic particles
• Radioactive decay transforms a radioisotope into
  a different element

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When Atom Bonds with Atom

• Chemical bonds
• Formulas

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REACTANTS
PRODUCTS


6CO2
6H2O
C6H12O6
6H2O
CARBON DIOXIDE
WATER
GLUOSE
WATER
6 carbons 12 oxygens
12 hydrogens 6 oxygens
6 carbons 12 hydrogens 6 oxygens
12 hydrogens 6 oxygens
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Electrons and Energy Levels

• Shell model
• Shells Energy levels
• Shell closest to nucleus
  has the lowest
  energy
  level

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HYDROGEN 1p , 1e-
HELIUM 2p , 2e-
CARBON 6p , 6e-
NITROGEN 7p , 7e-
OXYGEN 8p , 8e-
SODIUM 11p , 11e-
CHLORINE 17p , 17e-
CALCIUM 20p , 20e-
Fig. 2.8, p. 25
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From Atoms to Molecules

• Molecule
• Two or more atoms bond
• Compound
• Composed of two or more different elements in
  definite proportions
• Mixture
• Two or more elements intermingling in varying
  proportions

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Ions

• Any atom that has either gained or lost an
  electron
• Charged
• or -

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Important Bonds in Biological Molecules

• Ionic bond - Association of two ions that have
  opposing charges
• Sodium chloride( NaCl)
• Na and Cl-

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1 mm
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Important Bonds in Biological Molecules

• Covalent bonds
• Sharing of a pair of electrons
• Single, Double, and Triple Bonds
• Non-polar or polar
• Polar - atoms of different elements dont exert
  same pull on shared electrons

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Important Bonds in Biological Molecules

• Hydrogen bonds
• Electronegative atom of a molecule weakly
  interacts with a hydrogen atom

Hydrogen bonds may form between two or more
molecules
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Properties of Water

• Polarity
• Hydrophilic
• Repels hydrophobic substances
• Temperature
• Stable environments
• Evaporation
• Insulating

• Cohesion
• High surface tension
• Solvent
• Ions and polar substances

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Spheres of Hydration Around Two Charged Ions

• Salt (NaCl) dissolves in water and separates into
  Na and Cl-

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The pH Scale

• Water molecules break apart to form H and OH-
  ions
• Scale 0 - 14
• Neutral 7
• Acid 0 to less than 7
• Base greater than 7 to 14
• Acid substance that donates H
• Base substance that accepts H

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Buffers Against Shifts in pH

• Buffer systems
• Stabilize and maintain pH
• Bicarbonate-carbonic acid buffer system
• H2CO3 ------gt HCO3- H
• HCO3- H ------gt H2CO3
• Salts Compounds that release ions other than H
  and OH-

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In Conclusion

• Chemistry helps understand life
• Certain elements are more common in organisms
• Elements consist of atoms with its subatomic
  particles
• Atoms have no net charge, but may gain or lose an
  electron to become an ion with a charge

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In Conclusion

• Interactions depend on number and arrangement of
  electrons
• A chemical bond is a union between the electron
  structures of atoms
• Ionic bonds are attractions between ions of
  opposite charges
• Various atoms can share one or more pairs of
  electrons in covalent bonds

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In Conclusion

• Hydrogen bonds are formed between molecules
• The pH scale designates a solution that reflects
  the H concentration
• Water has unique properties which allow it to
  resist temperature changes, dissolve substances,
  and show cohesion
• developed by M. Roig