Introduction to Biochemistry

• The Ground state: when electrons are in positions of lowest energy possible (normal).
• Excited state: when electrons are in a temporary position of higher energy than ground state, and this is a very unstable state in which the electrons quickly return to the ground state releasing their extra energy. This energy will be used in reactions. (ETC in Respiration and photosynthesis).
• Element: Any substance that contains one kind of atom.
• Isotopes: Elements with the same number of protons but different number of neutrons.
  • Some isotopes decay at a known rate of time (Half-life) ⇒ measure the age of fossils and rocks.
  • Some isotopes are radioactive ⇒ used as tracers.
• Compound: Consists of atoms of two or more different elements.
• Mixture: Consists of two or more different elements / compounds.

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Types of Chemical Bonding

At the formation of any bond:

• Energy must be supplied to break a bond ⇒ then: some energy must be released to form new stable bonds. “Will be discussed in Unit 3”.
• Types of Chemical Interactions:
  • Covalent Bond:
    • Sharing electrons.
    • Can be polar or nonpolar.
  • Ionic Bond:
    • Losing and gaining electrons.
    • All polar.
  • Hydrogen Bond:
    • Mostly between polar molecules.
  • Hydrophobic Interactions:
    • When nonpolar repel from polar they tend to bind together away from the polar side.

• Types of Chemical Compounds:
  • Hydrophobic: Water repelling; non-polar molecules (not attracted to water) e.g. Fats and Oils.
    • Mostly covalent.
  • Hydrophilic: Water loving; polar molecules (attracted to water) e.g. ions and alcohols.
    • Ionic and some covalent.
  • Amphipathic: Both sides (polar and non-polar).
    • Mostly covalent.

 *** Like – dissolves – Like ***

(Polar attracts to polar)

 Characteristics of Water:

• Water is a small and polar molecule.
• There are strong forces of attraction between the water molecules which determine their distinctive property.

The relationship between H⁺ and pH: 

• When the H⁺ concentration is 1×10^-5 we say that the pH is 5.
• pH 7 is neutral (concentrations of H⁺ & OH^– are equal)
• The higher the pH, the less H⁺ concentration, the more OH^– concentration.

pH = – log[H⁺]

• When the pH changes from
  • 2 to 4 ⇒  H⁺ ion concentration decreases by 100 times.
  • 8 to 3 ⇒  H⁺ ion concentration increases by 100000 times.
•  Buffers: are solutions which can resist changes in pH; E.g. Bicarbonate buffer.

H⁺ + HCO₃^–  ⇒  H₂CO₃ ⇒  H₂O + CO₂

• The importance of water in Life
  • Most of the water is in its liquid state:
    • Important for many metabolic processes.
    • Stable environment for aquatic organisms.
    • When it evaporates it cools bodies down.
    • Many substances dissolve in water providing ions and minerals for the aquatic organisms.
  • Floating ice acts as an insulator to maintain a stable aquatic environment.
  • Transparent for more photosynthesis.
  • Water can help in controlling the pH as H⁺ donor or a receiver.

Questions:

1.  B

2.  D

3.    D

Homework Practice:

Question One: 

Question Two Scoring Guidelines