Chemical Foundations for Cells

1
Chapter 2

• Chemical Foundations for Cells

2
Chapter Outline

• Review of atomic structure
• Chemical bonding
• Ionic
• Covalent nonpolar and polar
• Hydrogen bonding
• Properties of water
• Acids, bases, and buffers

3
Atomic Structure

• Nucleus contains ____________
• Electrons are found outside of the nucleus
• In an atom the of protons electrons
• Some electron arrangements are more stable than
  others.

4
Chemical Bonding

• Chemical bonding atoms gain, lose, or share
  electron(s) to obtain a stable number of electrons

5
Chemical Bonding

• There are two types of bonds
• Ionic bonds
• Covalent bonds
• May be polar or nonpolar

6
Chemical Bonding

• Ionic Bond strong attractive force between
  oppositely charged ions
• Atoms form ions by losing or gaining enough
  electron(s) to obtain a stable of electrons in
  their outer shell

7
Chemical Bonding

• Terms
• Cation Positive ion, formed when an atom ____
  electron(s)
• Anion - Negative ion, formed when an atom ____
  electron(s)

8
Chemical Bonding

• Covalent Bond bonded atoms share pair(s) of
  electrons.
• Occurs between ___________
• Examples
• H2
• O2
• H2 O

9
Types of Covalent Bonds

• Nonpolar covalent bonded atoms share the
  electrons equally
• Examples
• Polar Covalent unequal pull on shared electrons
  by the bonded atoms
• Examples

10
Hydrogen Bonding

• Hydrogen bond weak attractive force between a
  d hydrogen bonded to an O, N or F atom and a d-
  O, N, or F in a second polar bond
• Examples
• A hydrogen bond is not a true bond.

11
Properties of Water

• Water is a polar molecule capable of hydrogen
  bonding.
• Related Terms
• Hydrophilic
• Hydrophobic

12
Properties of Water

• Water resists changes in temperature.
• When heat is applied to an aqueous solution much
  of the heat (energy) is used to break hydrogen
  bonds, not increase the movement of the molecules.

13
Properties of Water

• Water has a high surface tension can also say,
  water is cohesive.
• Cohesion ability to resist rupturing when under
  tension

14
Properties of Water

• Water is a good solvent for ionic compounds and
  small polar molecules.
• Water hydrates ions
• Water hydrogen bonds to polar molecules

15
Acids, Base, and Buffers

• Many ions are dissolved in the fluids in/outside
  of cells
• Na, Ca2, K,
• H
• Level of each is critical
• Focus on H (hydrogen ions)

16
Acids, Base, and Buffers

• Use the pH scale as a measure of the
  concentration of H in dilute solutions
• See page 28
• Classify substances as acid, base or neutral by
  their pH
• Acids pH lt 7
• Base pH gt 7
• Neutral pH 7

17
Acids, Base, and Buffers

• How the pH scale works
• The lower the pH the more acidic
• The higher the pH the more basic (alkaline)
• A difference of 1 pH unit is a 10-fold difference
  in acidity or alkalinity

18
Acids, Base, and Buffers

• Acid Substance that produces H when dissolved
  in water.
• Properties of Acids
• Corrosive
• Sour if dilute enough to drink
• Neutralize bases

19
Acids, Base, and Buffers

• Classifying Acids
• Strong acids ionize completely in water
• Every acid molecule ionizes to form H
• Example
• Weak Acids ionize slightly in water
• Very few acid molecules form H in water
• Examples

20
Acids, Base, and Buffers

• Base substance that produces OH-1 (hydroxide
  ion) in water
• Examples
• Properties of bases
• Corrosive
• Bitter if dilute enough to drink
• Neutralize acids

21
Why is pH important?

• Most cells require a pH near 7. Above or below
  this pH for too long and they die.

22
Why is pH important?

• Proteins function only at specific pHs.
• pH needed depends upon where the protein needs to
  function
• In lab you will determine the optimal pH for a
  protein that acts as an enzyme.

23
Why is pH important?

• Blood has a pH of 7.3 7.5
• If the pH is above or below this range for more
  than a couple of days death occurs.

a little higher than most give for the pH of
blood
24
Acids, Base, and Buffers

• Buffers solution that resists changes in pH
  even when acid or base is added
• Buffers can both produce H and neutralize H
• Most body solutions are buffered

25
Buffers

• Buffers are key to maintaining pH homeostasis
• Buffers are made from weak acids and the ions
  they form in water
• Ions formed act as bases in that they can
  neutralize (bind) H

26
Buffers

• Blood buffer system see board and page 29

27
Salts

• Salts are ionic compounds that do not produce H
  or OH-1 when dissolved in water
• Salt solutions are neutral