I. Fractionating Life:

Biochemists break up an organism and analyze the individual components.

1) What is the atomic composition of living cells/organisms?

H: 60%

O: 25%

C: 12%

N: ~5%

P, S, Mg, Mn, Se also present in lesser amounts

At certain levels of study, most organisms look the same- especially at the cellular level.

2) What is the molecular composition of cells?

Mostly Water: ~80%

Of remainder weight:

Lipids, fats: 10%

Carbohydrates: 15%

Proteins: 50%

Nucleic Acids: 15%

**Proteins are key macromolecules (play many structural and functional roles in cells)**

Nucleic Acids (DNA, RNA; DNA stores hereditary information in cell)

At some level, chemical forces determine shape of molecules and shape determines function.

What are the forces that give these molecules their properties?

Use the information extracted from the periodic table in Figure 2.1 to describe the characteristics of the atoms listed:

 

 

Atomic Weight	12	16	1	14	32	31
Element	C	O	H	N	S	P
Atomic Number	6	8	1	7	16	15

Figure 2.1

Figure 2.2

Which of the above drawings depicts the electron configuration of carbon?

Which of the drawings in Figure 2.2 is of an atom with the atomic number of eight?

 

II. Covalent Forces

Bonds and chemical interactions hold molecules together:

1) Covalent Bonds

-most important type of bonds

-strongest type of bond &endash; strength

A covalent bond is the sharing of a pair of electrons:

-Some covalent bonds involve unequal sharing of electrons.

-Some atoms hold onto electrons more tightly than other atoms. The tendency to attract electrons is a measure of electronegativity of an atom.

-Look at some bonds with unequal sharing of electrons:

-Polar bonds have polarity

-Oxygen is a more electronegative atom compared to hydrogen, and thus an O-H bond is considered a polar bond.

-Carbon and hydrogen have similar electronegatvities, therefore, a C-H bond is considered nonpolar.

2) Hydrogen Bonds

- attraction between a slight positive charge on a hydrogen atom and a slight negative charge on a nearby atom

- hydrogen bonds give order and structure to molecules

- a single hydrogen bond is weak, however, most molecules are made up of many hydrogen bonds; leads to overall strength of molecule

-Properties of water are determined by hydrogen bonding interactions. Water is highly structured even when liquid. Formation of ice is due to the lattice array of hydrogen bonds.

-Hydrogen bonds from between different regions of a protein:

3) Ionic Bonds

-electrostatic interaction between two oppositely charged groups in a molecule

-limiting cause of unequal sharing of electrons; one atom keeps the electron NaCl Na+ + Cl- unequal sharing of electrons, Cl keeps both electrons.

-In solution this group becomes ionized, loses a proton and becomes negatively charged: Charged atoms can be attracted to oppositely charged atoms:

 

III. Major Macromolecules

A. Lipids, Phospholipids

-Structure of a hydrocarbon:

-If you add a Hydroxyl group (OH) to a hydrocarbon you get an alcohol:

-Short chain alcohols are soluble in water.

-You can make a fatty acid by adding a carboxyl group (COOH) group to a hydrocarbon:

-A fatty acid is an amphipathic molecule &endash; contains both hydrophobic and hydrophilic portions.

-A fatty acid can also be represented as:

a. Three fatty acids and one glycerol molecule can be combined in a dehydration synthesis to from a lipid (a triglyceride).

b. Triglycerides are major storage forms of fatty acids inside cells.

Phospholipids:

-A subgroup of lipids that play a key role in cell structure.

a. Phospholipids are formed by combining two fatty acids and a phosphate group:

b. Phospholipids form a lipid bilayer in an water. A typical cell is enclosed by a plasma membrane, which is made up of a phospholipid bilayer (2 layers of phospholipid molecules arranged in a lipid bilayer)

-The hydrophobic interior of the plasma membrane is impermeable to charged or polar molecule.

B. Sugars, Carbohydrates

1) General formula for a sugar:

(CH₂O)_n

Example: Glucose C₆H₁₂O₆

-Six carbon sugars are called hexoses (e.g. glucose)

-Five carbon sugars are called pentoses (e.g. ribose)

2)Conformation of sugars

a) Monosaccharides

-Glucose is more often found in a ring from in solution:

b) Disaccharides

-Disaccharides consist of two Monosaccharides linked by a covalent bond:

Example: sucrose (table sugar)

-The enzyme lactase breaks down lactose to glucose and galactose. Many adult individuals stop synthesizing lactase enzyme. As a result a large percent of certain populations becomes lactose-intolerant.

c) Polysaccharides

-Polysaccharides consist of many monosaccharide units (usually glucose monomers) linked together to form long chains.

Examples:

starch-plant polysaccharide (glucose polymer)

glycogen-animal polysaccharide (branched glucose ploymer)

cellulose-cell walls (polysaccharide of beta-glucose

-Polysaccharides (starch & glycogen) are used as a form of storage energy and also for structural roles(cellulose).

-Cellulose &endash; plays an important structural role in plants; one of the most abundant molecules on earth.

a. The alternating units of glucose enable adjacent cellulose molecules to form hydrogen bonds with each other. The hydrogen bonding capability of cellulose leads to the strength of the cell walls and also fibers such as wood.