Protein Structure & Function and Globular & Fibrous Proteins

How do you identify a 4 alpha helical bundle?

• 4 helices

• they have polar and non polar amino acids

• usually have up to 6 non polar residues next to each other to create hydrophobic area inside the bundle

How can you identify a alpha/beta protein?

have a combination of alpha and beta secondary structures

How can you identify a beta-alpha-beta protein?

• each beta strand twists to distort H bond

  • can be saddle shape or barrel shape

• amphipathic helices outside

• hydrophobic strands in middle

How can you identify a domain?

• several proteins associated together

  • frequently linked or inserted within one another

Name and briefly describe 2 fibrous proteins

• alpha keratin

  • 2 polypeptide dimer that have a left handed twist

  • chains cross linked by disulfide

• beta keratin

  • stacked anti-parallel beta sheets

  • alternating Gly & Ala/Ser residues

  • stacking makes it strong

  • dispersed among alpha helices to give some flex

What internal conformational change occurs when oxygen binds the heme Fe in hemoglobin?

• A shift of the F-helix

  • histidine is in this helix

  • changes interactions

• rotation of one alpha-beta dimer

How is the quaternary structure changed when oxygen binds the heme Fe in hemoglobin?

The space between the alpha helices tightens with oxygen is bound (0.39 nm)

What is the Bohr effect and how does it facilitate CO2 transport?

• The Bohr effect enhances oxygen delivery to tissues where CO₂ production is high

• Does this by making Hb bound with O2 more acidic (lowering the pH)

• helps CO₂ transport by promoting hemoglobin's release of oxygen and uptake of CO₂.

How does BPG affect the transport of oxygen by hemoglobin?

• BPG binds to deoxy Hb (squeezed conformation)

• lowers amount of O2 bound

  • lowering affinity of Hb for O2

What are globular protiens?

• soluble in water

• circular shape

• alpha-helix and beta sheet stabilize structure

• L-amino acids

What are 3 types of alpha helices?

1. amphipathic - one side hydrophobic & one side hydrophilic

2. hydrophobic - inside membrane/structure

3. polar - solvent exposed

Why can’t myoglobin be used to transport oxygen from the lungs to the tissues?

• binds too tightly with oxygen

• meant to drop off oxygen to mitochondria

• used for tissues

Does BPG inhibit or enhance O2 binding?

inhibits binding to encourage the oxygenation of tissue