Honors Biology - Chapter 3 (Proteins and Nucleic Acids)

Functions of Proteins

Structural (hair, tendons, ligaments); contractile (muscle); defensive (antibodies); signaling (hormones); receptor (in cell membranes); transport (hemoglobin); storage; enzymatic (shape matters)

polypeptide vs. protein

• Protein: used to refer to a molecule w/ its appropriate 3D shape (when functional)

• Polypeptide (peptide): used when referring to a polymer w/ out a 3D shape

• Made of Amino Acids

Amino Acid

• Amino Acids Have Four Parts

  • Hydrogen w/ central carbon

  • Amino Group (NH₂)

  • Carboxyl Group

  • R-group (variable side chain)

• 20 different types of R-groups/amino acids

Peptide Bond

Amino acids join with a dehydration synthesis reaction, and the bonds between them are called peptide bonds (between functional groups).

• A dipeptide is when two amino acids join together

• A polypeptide is formed when multiple amino acids join together

R - Group Types

Electically Charged (ionized), Polar Uncharged, Hydrophobic (Nonpolar), Special Cases (small)

Primary Structure (1º)

Peptide bonds with N-C are a long chain of amino acids that help to determine the overall structure of the protein, which determines the function (animal digestion, starch vs. cellulose)

Secondary Structure (2º)

• Two types: alpha helix and beta pleated sheet

• held together by hydrogen bonds between functional groups

Tertiary Structure (3º)

• held together by interactions between r-groups

• Fully folded molecule given function by shape (some need multiple)

H-bonds help to stabilize the structure once it is made, with available H and NOF

Tertiary Structure Interactions

Type of Bond	Description
Hydrophobic Interactions	Amino acids orient toward the center to avoid water
Hydrophilic Interactions	Form between polar R-groups (outside of molecule). Polar covalent with partial charges.
Disulphide Bridge	Charged R groups bond together
Ionic Bonds	Form between oppositely R – groups.

Quarternary Structure (4º)

• When a functional protein is made of multiple polypetides.

• Each polypetide forms a protein subunit w/ structure but no function, only when together do they have function.

• Ex. ribosome

• Linked by IMFs (interaction between R- groups)

Denaturation (defenition and types)

• loss of 3D structure, which results in a loss of function

• Increase in temperature

  • Higher KE = more motion of molecules disrupting IMFS

• Change in salt concentration

  • salt = ionic compound

  • add (+) and (-) ions to the solution, causing the ions in the protein to be pulled away b/c more attracted to the new ions

• Change in pH

  • Similar to the change in salt concentration as H⁺ when acidic and OH^- when basic, attract the negative and positive parts of the protein, respectively