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Chapter 3 :. The Molecules of Life. Organic Compounds. Compounds in the natural world that contain the element carbon (bonded to hydrogen). Hydrocarbons – contain only C & H (ex. CH 4 ) Most also include oxygen and some also have nitrogen, phosphorus and sulfur.

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Chapter 3

Chapter 3:

The Molecules of Life

Organic compounds
Organic Compounds

  • Compounds in the natural world that contain the element carbon (bonded to hydrogen).

  • Hydrocarbons – contain only C & H (ex. CH4)

  • Most also include oxygen and some also have nitrogen, phosphorus and sulfur.

  • Carbon can form thousands of different compounds because it can form 4 strong covalent bonds

Functional groups
Functional Groups

  • A group of atoms within a molecule that interacts in predictable ways with other molecules is called a functional group

  • Functional groups determine the properties of organic molecules. For example, hydrophilic groups (such as –OH) attract water and hydrophobic groups repel.

The process of polymerization
The Process of Polymerization

  • The formation of carbon-based compounds

  • Monomers (small compounds) become Polymers (complex compounds)

  • Macromolecules are very large polymers



Compounds of life biomolecules
Compounds of Life (Biomolecules)

  • There are four groups of organic compounds that are found in living things.

    • Carbohydrates

    • Proteins

    • Lipids

    • Nucleic Acids

  • These compounds all come from our foods and are needed by our bodies.

Self assessment

  • Draw a molecule that has a 3-C (carbon) skeleton and a hydroxyl group on the middle carbon. (Hint: formula is C3H8O)

  • Explain the connection between monomers and polymers.

  • Draw at least three ways in which five carbon atoms can be drawn to make different carbon skeletons.

  • What molecule is released during the construction of a polymer? What is this process called?

Try this
Try This:

The diagram below shows two amino acids, the monomers of a protein. Draw these amino acids in your notes. What has to happen for these two molecules to combine? (What must be done for bonds to be made in biological systems?) Represent this process by redrawing the amino acids bonded together and drawing the bi-product formed.

Dehydration synthesis
Dehydration Synthesis

In living systems, bonds are made by removing water. An –OH from one molecule and an –H from the other combine to form water. The removal of these atoms provides “space” for the new bond to form, by leaving atoms with unfilled valence shells.

An example of isomers
An Example of Isomers

  • The formula for all three monosaccharides glucose, fructose and galactose is C6H12O6

  • Although they contain the atoms in the same proportion, their structural arrangement differs.

  • In aqueous solutions, most monosaccharides form ring structures as shown for glucose

  • Also note the trademark functional groups of sugars, multiple hydroxyl groups and a carbonyl group

Is fructose an aldose or a ketose?

Is glucose an aldose or a ketose?

Carbohydrates monosaccharides
Carbohydrates: Monosaccharides

  • Sugars

  • Made of C, H, and O

  • Can contain 2-7 carbons

    • most have 5 (pentose) or 6 (hexose)

  • Trademarks: 1 carbonyl group & multiple hydroxyls

    • Hydroxyl group makes a sugar an alcohol

    • Carbonyl group makes it either an aldose(aldehyde sugar) or a ketose(ketone sugar)

  • Breaking of their covalent bonds releases energy (fuels cellular work)

  • Monosaccharide Examples (single sugars)

    • Glucose (sugar green plants produce)

    • Galactose (found in milk)

    • Fructose (found in fruits)


  • Formed by the dehydration synthesis of 2 monosaccharides

  • Examples:

    • Sucrose

    • Lactose

    • Maltose

Carbohydrates polysaccharides
Carbohydrates: Polysaccharides

  • complex carbs made up of 100s-1000s of monosaccharides (glucose)

  • Takes a long time to digest and break down polysaccharides into glucose through hydrolysis

  • Taste is not sweet

  • Examples:

    • Starch: used in plants as an energy storage molecule

    • Cellulose: makes up cell walls of plants; most abundant compound on Earth

    • Chitin: found in exoskeleton of insects and crustaceans and the cell walls of fungi

    • Glycogen: used by animals to store excess sugar (liver & muscles)

Self assessment1

  • Write the formula for a monosaccharide that has 3 carbons.

  • Why do isomers, which have the same formula, have different properties?

  • Explain the relationship between a monosaccharide and a disaccharide. Give an example of each.

  • Compare and contrast starch, glycogen, cellulose and chitin.

Chapter 3


  • Non-polar; hydrophobic

  • Three categories:

    • Triglycerides

    • Phospholipids

    • steroids

  • Contain C, H & O, but lower proportion of oxygen than carbs

  • Lipids store more energy than carbohydrates because they have twice as many energy rich (C-H) bonds than carbohydrates. (9 cal/g v. 4cal/g)

Categories of lipids
Categories of Lipids

  • Trigylcerides (Neutral Fats)

    • Glycerol & 3 fatty acids “tails”

    • Fatty tissue – insulation & reserve energy

  • Phospholipids

    • Polar phosphate “head” and non-polar fatty-acid “tails”

      • Amphiphilic (amphipathic)

    • Make up plasma membranes

  • Steroids

    • 4 ring structure

    • Ex) Cholesterol

      • helps provide support in animal cell membranes

      • Start material for other steroids, such as hormones

Chapter 3

Categories of Triglycerides

  • Saturated -carbons are joined by all single bonds (not healthy)

  • Unsaturated -2 carbons are joined by a double bond

  • Polyunsaturated -carbons have many double bonds (most healthy)

Self assessment2

  • What property do all lipids share?

  • What are the parts of a fat (triglyceride) molecule?

  • Describe two ways that steroids differ from fats.

  • What does the term “unsaturated fat” on a food label mean?


  • A peptide bond is the covalent bond that joins amino acids

  • A Polypeptide is a long chain (100+) of amino acids

  • A (functioning) protein is one or more polypeptide chains precisely coiled, twisted and folded into a unique three-dimensional shape

  • Note dehydration synthesis reaction involved in forming a peptide bond.

  • How is a peptide bond broken?


  • Contains N,H,C, and O

  • Proteins come from animal foods

  • Examples: (very diverse group)

    • Enzymes (biological catalysts)

    • Structural (hair, connective tissue, such as ligaments & tendons)

    • Defensive (antibodies)

  • Proteins are polymers of AminoAcids

    • All 20 amino acids are similar except for an “R” group

  • A proteins amino acid sequence determines it’s shape which determines its function.

  • If the shape changes, function is disrupted and protein is denatured.

Structural levels of a protein
Structural Levels of a Protein

  • Primary: sequence of chain of amino acids

  • Secondary: AA sequence linked by H-bonds into an alpha-helix or Beta-pleated sheet

  • Tertiary: Attractions between helixes and/or sheets (usually R-groups) lead to further coiling into a 3D shape (globular or fibrous)

  • Quaternary: 2+ polypeptide chains (sub-units)

Nucleic acids
Nucleic Acids

  • Large molecules composed of N,H,O, C and P.

  • The monomers are called nucleotides

  • Two types of nucleic acids are RNA and DNA

  • DNA:

    • Hereditary info: Directions for making proteins

    • Controls cellular activities

  • RNA:

    • Carries out the instructions of DNA to make proteins