BT

BIOL- 102 6/25 (unit 2)

Proteins: The Workhorses of the Cell

Proteins are the most abundant macromolecules because they perform a vast array of functions, acting as the "tools" of the cell.

  • Proteins have very specific jobs, like specialized tools in a kitchen.
  • The building blocks of proteins are amino acids.
  • Proteins are made of amino acids, similar to how a brick wall is made of bricks and mortar.
  • Breaking down a protein yields amino acids.

Enzymes: Biological Catalysts

Many proteins function as enzymes.

  • Enzymes facilitate almost all chemical reactions within a cell (99.99%).
  • Each enzyme typically performs a single, specific task, analogous to a can opener.

Signaling Proteins: Long-Lasting Messengers

Signaling proteins transmit sustained messages throughout the body.

  • These proteins circulate systemically, continuously informing cells of their functions.

Protein Shape and Function

The shape of a protein dictates its function.

  • Fibrous proteins (e.g., keratin) are fiber-like.
  • Globular proteins (common enzymes) have specific shapes suited to their roles.

Changes in pH, temperature, or chemical exposure can denature proteins, causing them to lose their shape and function.

  • Denaturation involves unfolding or misfolding, altering the protein's form.
  • Denaturation is analogous to a can opener being damaged to the point where it cannot open cans.
  • The body maintains specific temperatures and pH levels to prevent protein denaturation.
  • When proteins, especially enzymes, denature, cellular processes cease.

Amino Acid Structure

Amino acids, the building blocks of proteins, have a consistent structure:

  • A central carbon atom
  • An amino group
  • A carboxyl group
  • A hydrogen atom
  • An "R" side chain: "R"
    • The R group determines the unique characteristics of each amino acid (charge, acidity, etc.).

Polypeptides and Peptide Bonds

A polypeptide is a chain of amino acids.

  • A polypeptide is not yet a protein; it must fold into a specific shape to function.
  • Analogy: a bicycle in parts is not a bicycle until assembled.
  • Peptide bonds link amino acids in a polypeptide chain.
  • A polypeptide chain is a chain made of multiple peptide bonds.

Levels of Protein Structure

Primary Structure

The primary structure is the sequence of amino acids.

  • It involves the specific order of amino acids connected by peptide bonds.

Secondary Structure

Secondary structure arises from hydrogen bonds between amino acids.

  • This leads to shapes like alpha-helices and beta-pleated sheets.
  • These shapes begin to condense the polypeptide chain.

Tertiary Structure

The tertiary structure is the overall three-dimensional shape of the folded polypeptide chain.

  • It results from interactions between the R groups of amino acids.
  • Some proteins are functional at this level.

Quaternary Structure

The quaternary structure involves multiple tertiary structures combining to form a single protein complex.

  • Analogy: A hammer consists of a metal head and a wooden handle, each subunit contributing to the overall function.