Protein Function and Structure
Where do super secondary structures work?
function in the binding of small ligands and ions or in protein-DNA interactions
what diseases are prions responsible for?
kuru, Mad cow, Creutzfeldt-Jacob
What is denaturation?
loss of native conformation that produces loss of biologic activity denatured polypeptide chains aggregate and become insoluble due to interactions of exposed hydrophobic side chains
What are motifs?
secondary structures that have characteristic 3D shapes. Also called super secondary structures
What levels are disrupted by denaturing agents?
2nd,3rd,4th but NOT 1st
Explain primary structure of Proteins
Linear sequence of AA determines the secondary structure Mutations here often cause functional problems
Explain the secondary structure
arrangement of portions of a polypeptide chain stabilized by H-bonds 2 kinds- alpha helix & beta sheet
How are secreted proteins stabilized?
covalent disulfide bonds
what does proline do?
disrupts the alpha helix due to having an alpha amino group with no free H for H bonding aka stabilization
What are the major functions of Proteins
1. Structural Support 2. Movement 3. Signal Transduction 4. Binding 5. Molecule transport across membranes 6. Catalysis
Describe the denaturing agents
1. extreme changes in pH or ionic strength 2. Detergents 3. High temp 4. Heavy Metals
What connects AA together?
a peptide bond
What is a zinc-finger
a super secondary structure Zn+2 bound to 2 cys and his residues
what is a leucine zipper?
a super secondary structure leucine residues of 1 alpha helix interdigitate with those of another alpha helix to hold the proteins in a dimer
Why is sickle cell an example of a primary structure mutation
glutamate gets mutated to valine. Changes the charge (look at pbl for more on this)
Where are leucine zippers found?
in DNA-binding proteins like transcription factors
where are zinc fingers found?
in receptors that have a DNA-binding domain that interacts with lipid-soluble hormones
What are prions??
infectious proteins that cause normal neural proteins to change their secondary structure through contact usually make an alpha helix become a beta sheet form filamentous aggregates that are resistant to degradation by digestion or heat
What is an alpha helix
obviously helical side chains are located on the outside of the helix
what is a beta sheet
packing of beta strands
Explain the tertiary structure
the 3D folded structure of a polypeptide. also called the native conformation made up of many distinct structural and functional domains stabilized by side chain interactions Supersecondary motifs associate during folding to form tertiary structures
Explain Quaternary structure
the association of 2 or more tertiary structures dimers and tetramers are most common Can be held together by noncovalent interactions or by interchain disulfide bonds
What does G6PD deficiency have to due with denaturation?
the increased peroxide in RBC leads to the denaturing of hemoglobin and formation of Heinz bodies