7.5Proteins

7.5.1 Explain the four levels of protein structure, indicating the significance of each level.

1°- sequence of amino acids in the chain

2°- coils; H bonds; collagen, keratin have repeated sequences so have lots coils

α-helix: hair, wool, horns, feathers

β-pleated sheet: silk

7.5.1 Explain the four levels of protein structure, indicating the significance of each level.

3°- helix folding; R groups interact: hydrophobics cluster together on inside, hydrophilics cluster on outside,

disulfide bridges between S of 2 R groups (cov bond),

ions may be cofactors

7.5.1 Explain the four levels of protein structure, indicating the significance of each level.

4°- different polypeptides combine w/H bonds, +/- attractions, hydrophobic forces, and/or disulfide bridges;

common in large globular proteins (hemoglobin—2 α chains, 2 β chains)

“conjugated proteins” - binding of prosthetic group: each chain also has a Heme group, contains Fe (not a polypeptide)

chlorophyll, electron transport chain enzymes are other examples

7.5.2 Outline the difference between fibrous proteins & globular proteins,

with reference to two examples of each protein type.

Fibrous Globular

Shape Long Tightly folded

Solubility Insoluble in water Soluble in water

Main level of organization

2° is most important 3° is most important

Function Structural (they ARE something)

Functional (they DO something)

Examples Collagen, keratin, myosin

Hemoglobin, enzymes, antibodies, hormones

7.5.3 Explain the significance of polar and non-polar amino acids.

• 20 common amino acids• 8 w/non-polar R groups

– Insoluble in water– Cluster together @ center (4° structure)

• More non-polar AAs less soluble in water• Cell membrane (phospholipid bilayer): polar on

outside, non on inside – Protein situated with hydrophilic portions to outside of

membrane, hydrophobic sections to center

7.5.4 State four functions of proteins, giving a named example of each:

• Structure: collagen (fibrous, structural ptn) builds tendons & in skin

• Enzymes: all are globular – starch –amylase maltose

• Transport: hemoglobin (globular, conjugated); readily, reversibly binds Oxygen b/c of heme group

7.5.4 State four functions of proteins, giving a named example of each:

• Hormones: some are ptns (some are steroids)– Insulin

• Contractile: muscle contractions (actin, myosin)

• Defense: antibodies/immunoglobulins for defense against antigens