Properties of Biomolecules
Concept 3: Lipids
   Practice (1 page)
   Review (4 pages)
Concept 4: Carbohydrates
   Review (4 pages)
Concept 5: Proteins
   Review (9 pages)
Concept 6: Nucleic Acids
   Practice (1 page)
   Review (10 pages)
Concept 5: Proteins
The most abundant and diverse molecules found in living cells are proteins.
Proteins are macromolecules, ranging from simply large to enormous. Proteins typically make up about half the total weight of biomolecules in a cell (excluding water).

Proteins play a wide variety of functional roles, including:

• enzymes as catalysts, such as ribonuclease, that accelerate specific chemical reactions up to 10 billion times faster than they would spontaneously occur; one cell may contain some thousand different types of enzymes at one time

• structural materials, including keratin (the protein found in hair and nails) and collagen (the protein found in connective tissue)

• specific binding, such as antibodies that bind specifically to foreign substances to identify them to the body's immune system

• specific carriers, including membrane transport proteins that move substances across cell membranes, and blood proteins, such as hemoglobin, that carry oxygen, iron, and other substances through the body

• contraction, such as actin and myosin fibers that interact in muscle tissue

• signaling, including hormones such as insulin that regulate sugar levels in blood

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