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Water. The Nature of Water - H 2 O. Exists in three forms (gas, liquid and solid) Makes up approx 90% of organisms Versatile Solvent Important in the cell’s chemistry Gains and releases heat slowly High surface tension A “polar” molecule: 2 small hydrogen atoms 1 large oxygen atom.

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the nature of water h 2 o
The Nature of Water - H2O
  • Exists in three forms (gas, liquid and solid)
  • Makes up approx 90% of organisms
  • Versatile Solvent
  • Important in the cell’s chemistry
  • Gains and releases heat slowly
  • High surface tension
  • A “polar” molecule:
    • 2 small hydrogen atoms
    • 1 large oxygen atom
2 3 carbon compounds
2-3: Carbon Compounds
  • Compounds that contain CARBON are called organic.
  • Carbon has 4 electrons in outer shell.
  • Carbon can form covalent bonds with as many as 4 other atoms (elements).
  • Usually with C, H, O or N.
  • Example: CH4(methane)
25 naturally occurring elements are essential for life. Carbon, hydrogen, oxygen and nitrogen (C, H, O, N) make up 96% of living matter.
  • The remaining 4% is composed of seven elements (Ca, P, K, S, Na, Cl, Mg). Some elements, like iron (Fe) and iodine (I) may be required in very minute quantities and are called trace elements.
  • Large organic molecules.
  • Also called POLYMERS.
  • Made up of smaller “building blocks” called MONOMERS.
  • The monomers in a polymer may be identical or they may be different. Some of the molecules that serve as monomers also have other functions on their own.
  • Examples:

1. Carbohydrates

2. Lipids

3. Proteins

4. Nucleic acids (DNA and RNA)

  • The process of stringing together monomers to make polymers is called polymerization (or dehydration synthesis).
  • Monomers are connected by a reaction in which two molecules are covalently bonded to each other through the loss of a water molecule.
  • Each monomer contributes part of the water molecule that is lost: one molecule provides the –OH, while the other provides the hydrogen (–H).
  • Polymers are disassembled to monomers by hydrolysis (from the Greek word hydro meaning “water” and lysis meaning “to split”.)
  • In hydrolysis, polymers are split by water in a process that is essentially the reverse of dehydration synthesis.
  • Bonds between monomers are broken by the addition of water molecules, a hydrogen from water attaching to one monomer and an –OH attaching to the adjacent monomer.
  • Animation of Dehydration Synthesis and Hydrolysis
the nature of carbohydrates
The Nature of Carbohydrates
  • Recognized by the formula: (CH2O)n
  • 1:2:1
  • Grouped into mono-, di-, and polysaccharides
  • Important as:
    • A “quick energy” nutrient - glucose
    • Serve as a storage of energy - glycogen (animals) and starch (plants)
    • Structural significance – chitin of Arthropods and fungus and cellulose of plants
common disaccharides
Common Disaccharides
  • Sucrose (glucose + fructose)
      • Found in plant like sugar cane, sugar beets
      • “table sugar”
  • Maltose (glucose + glucose)
      • Found in germinating grain
  • Lactose (glucose + galactose)
      • Found in the milk of mammals


  • Cellulose – Structural component of plants (cell walls: lettuce, corn, some protists)
  • Starch – storage of energy in plants (bread, potatoes, rice)
  • Glycogen – storage of energy in animals (beef muscle)
  • Chitin – structural component of arthropods (roaches, crickets)
the nature of lipids
The Nature of Lipids
  • Lipids are one class of biological macromolecules that does not include polymers.
  • The lipids are grouped together because they are not soluble in water.
  • Lipids are a highly varied group in form and function.
Highest source of energy – that’s why our extra energy is stored as fat in fat tissue
  • Also important as:
    • structural components of cells (membranes)
    • Chemical messengers - hormones (steroids)
    • protective waxes (earwax, outer covering of insects)
    • Protection against heat loss (insulation)
examples of lipids
Examples of Lipids
  • General term for compounds which are not soluble in water.
  • Lipids are soluble in hydrophobic solvents.
  • Remember: “stores the most energy”
  • Examples:
      • 1. Fats
      • 2. Phospholipids
      • 3. Oils
      • 4. Waxes
      • 5. Steroid hormones
      • 6. Triglycerides
  • (long-term energy storage )
  • Cushions organs
  • insulation
Two types of molecules used to make a fat:
  • Glycerol (three carbon molecule)
  • Fatty acids (long hydrocarbon chain, usually 16-18 carbons atoms in length) that is hydrophobic (does not dissolve in water).
the letter e
The Letter “E”



Fatty Acids

saturated vs unsaturated fats
Saturated Fats

Solid at room temp.

White in color

Derived from animals

No double bonds between carbons

Fatty acids straight

Examples are the hard fats (lard)

BAD (unhealthy)

Unsaturated Fats

Liquid at room temp.

Yellow in color

Derived from plants

Some double bonds between carbons

Fatty acids crooked

Examples include corn, canola, and olive oils

BETTER (healthier)

Saturated vs. Unsaturated Fats
Many carbon-carbon double bonds

Liquid at room temperature

Cooking oils: corn, sesame, peanut, canola, olive

BEST (healthiest) because they do not collect in your blood vessels and cause plaque.

  • Phospholipids are a major component of cell membranes.
  • The cell membrane regulates what enters and leaves the cell and provides protection and support.
  • Phospholipids are similar to fats but they only have two fatty acid tails, instead of three, attached to a glycerol molecule.
A phospholipid has a hydrophilic head that wants to interact with water and two fatty acid tails that are hydrophobic and are repelled by water.
  • Steroids are lipids characterized by a carbon skeleton consisting of four fused rings.
One steroid, cholesterol, is a common component of animal cell membranes and is the precursor from which other steroids are synthesized.
  • Too much cholesterol in the blood may contribute to heart disease.
  • About 10% of people ages 12 to 19 have blood cholesterol levels, which put them at risk later in life for developing heart disease – the leading cause of death in the United States.
Hormones are chemicals released in one part of the body that travel through the bloodstream and affect the activities of cells in other parts of the body.
  • They do this by binding to specific chemical receptors on target cells. If a cell does not have receptors, the hormone has no effect.
the nature of proteins
The Nature of Proteins
  • Elements: N, C, H, O
  • Made of units called amino acids (only 20)
  • Twenty Amino acids combine in different ways to make, perhaps, 100,000 different proteins!
  • Amino acids link together by peptide bonds
    • Makes polypeptides
six functions of proteins
Six functions of proteins:

1. Storage: albumin (egg white)

2. Transport: hemoglobin

3. Regulatory: hormones

4. Movement: muscles

5. Structural: membranes, hair, nails, bones

6. Enzymes: cellular reactions

proteins polypeptides
Proteins (Polypeptides)
  • Four levels of protein structure:

A. Primary Structure (1°)

B. Secondary Structure (2°)

C. Tertiary Structure (3°)

D. Quaternary Structure (4°)

a primary structure 1

Amino Acids (aa)







Peptide Bonds

A. Primary Structure (1°)
  • Amino acids bonded together by peptide bonds.
b secondary structure 2

Alpha Helix

Beta Pleated Sheet

Hydrogen Bonds

B. Secondary Structure (2°)
  • 3-dimensional folding arrangement of a primary structure into coils and pleats held together by hydrogen bonds.
  • Two examples:
c tertiary structure 3

Alpha Helix

Beta Pleated Sheet

C. Tertiary Structure (3°)
  • Secondary structures bent and folded into a more complex 3-D arrangement.
  • Bonds: H-bonds, ionic
  • Called a “subunit”.
d quaternary structure 4

3° subunits

D. Quaternary Structure (4°)
  • Composed of 2 or more “subunits”.
  • Example: enzymes, hemoglobin


  • Acts as catalysts
  • Speed up a chemical reaction
  • Lower activation energy
  • Needed to start a reaction
  • Specific
  • Act on a substrate

Denaturation of proteins involves the disruption and possible destruction of both the secondary and tertiary structures.

Usually caused by: acids, bases, heat, alcohol

the nature of nucleic acids
The Nature of Nucleic Acids
  • Two types: DNA and RNA
  • Composed of units called nucleotides:
    • Phosphate molecule
    • 5 carbon sugar
    • organic base (a purine or pyrimidine)
  • May be double or single-stranded
  • Single strands united by “base-pairing”
importance of nucleic acids
Importance of Nucleic Acids
  • Insure genetic continuity from one cell generation to the next
  • Directs the production of proteins at the ribosome “construction site” in the cytoplasm