Structure and Function of AA and Proteins II Flashcards
1
Q
explain the primary structure of proteins
A
- The sequence of amino acids
2
Q
describe the secondary structures of proteins
A
- Secondary structures of proteins are stabilized by H-bonds involving the atoms of the peptide bond
- Alpha helix
- Parallel H-bonds
- B-pleated sheet
- B-turn
- Alpha helix
3
Q
describe the alpha helix
A
- Tightly packed and right-handed helix wound around an imaginary axis
- There are 3.6 residues per turn
- H-bonds are parallel to the direction of the helix axis
- Side chains stick out from helix
4
Q
interruption of the alpha helices?
A
- Electrostatic repulsion (or attraction) between successive amino acids with charged R-groups
- Bulkiness of adjacent R-groups
- steric hindrance
- Helix disruption by specific residues
- Proline residues (bend or kink)
- Glycine residues (allow rotation)
5
Q
describe the B-pleated sheet
A
- Perpendicular H-bonds between peptide bond atoms
- Amino acid side chains that alternate above and below the plane of the pleated sheet
6
Q
define the tertiary structure
A
- Water soluble proteins fold into 3-D structures with nonpolar side-chains to the inside
- termed the hydrophobic core
- Side-chains of AA are involved in stabilizing tertiary structure
- Formation of non-covalent associations
- Formation of the covalent disulfide
- Between 2 cysteines to form cystine
- Ionic interactions
7
Q
describe the quaternary structure
A
- Protein that exists in more than one polypeptide
8
Q
describe the insulin hormone structure
A
- The 2 inter-chain disulfide bonds hold the A- and B- chains of insulin together
- The intra-chain disulfide bond in the A-chain folds the peptide hormone and is needed for receptor recognition
9
Q
function of c-peptide?
A
- Needed for the proper formation of disulfide bonds in insulin
- The C-peptide is then cleaved from insulin and it is released together with insulin into the blood
10
Q
define the different levels of protein organization (monomeric…etc)
A
- Monomeric: a single polypeptide chain
- leads to a tertiary structure description
- Multimeric: more than 1 polypeptide chain
- leads to a quaternary structure description
- Homomultimeric: all chains are the same
- Heteromultimeric: different chains
11
Q
describe chaperones and name 1
A
- Facilitate proper folding
- AKA heat shock proteins (HSP)
- Hsp60 proteins have a barrel shape and are required for correct folding of cellular proteins that do not fold spontaneously
- Used to aid refolding a protein after it has crossed a cell membrane
12
Q
describe the process of denaturation
A
- Noncovalent bonds and disulfide bonds are broken but not the peptide bond backbone
- Primary structure remains intact
- Dietary protein is denatured in the lumen of the stomach due to the low pH
- Acidity in stomach is not low enough to cleave peptide bonds
- In most cases, denatured proteins cannot regain their natural config. and precipitate
- can’t “uncook” an egg
13
Q
describe the structure of myoglobin
A
- Myoglobin contains about 80% alpha-helix secondary structure
- Myoglobin is devoid of B-sheet structure
14
Q
name the chemical used to denature proteins in the lab
A
- Heat, 5-1- M urea, salt, to break H-bonds
- Strong acids or bases to break ionic bonds
- 1-2% SDS (detergent) to break hydrophobic interactions
- Thiol containing compounds to reduce disulfide bonds
- B-mercaptoethanol
- 2-mercaptoethanol
- In animals, the disulfide bonds of insulin are cleaved in the liver
15
Q
describe TSE - Prion disease
A
- Transmissible Spongiform Encephalopathy
- 3 routes to acquire disease
- Sporadic
- Infection
- Genetic predisposition
- Creutzfeld-Jacob disease in humans
