Chapter 5 Flashcards
Parallel B-pleated Sheets
Both strands involved in H bonding run in the same direction
Anti parallel B-pleated sheets
Strands involved in hydrogen bonds run in opposite directions, more stable
B-turn
Necessary to change directions in order to define protein boundaries
-Proline and glycine occur frequently
Ramachandran diagram
Predicts the types of secondary structures using the characteristic psi and phi angles.
Tertiary Structure
Gives specific 3D shape to the polypeptide chain.
Stabilized by: Hydrophobic and hydrophilic interactions, salt bridges, H bonds and S-S bonds
Quaternary Structure
Combination of 2 or more tertiaries, stabilized by the same interaction found in tertiary structure, regulatory proteins are often found as oligomers
- Hemoglobin consists of two alpha chains and two beta chains. The heme group in each subunit binds O for transport in the blood to the tissues
Secondary structure of proteins
Indicates 3D spatial arrangements of the polypeptide chains
Alpha Helix
- Coiled shape held in place by H bonds between amide groups and carbonyl groups.
- H bonds between the H of the N-H group and the O of the C=O of the fourth AA down the chain
- stabilized by H bonds
- disrupted by proline
- destabilized by bulky AA’s or charged AA’s in close proximity
- composed of L-amino acids, are right handed helices
B-Pleated Sheet Structure
- consists of polypeptide chains arranged side by side
- parallel or antiparallel
- H bonds between chains
- R groups above/below sheet
- typical of fibrous proteins (silk)
Proline’s affect on B-turn
-Proline can force formation of B-turn due to angle - promoting formation of antiparallel strands
Glycine and B-Turn
Glycine can adapt to many structures due to lack of a side chain, Frequently found in position 3 of the turn
Protein Folding
- Polypeptide emerges from ribosome, short segments fold into 2’ structural units. Proline dis-trans isomerases involved in B-turn formation at this stage.
- Appropriate arrangement of 2’ structural elements into domains by chaperones such as Hsp60 & Hsp70. Chaperones segregate hydrophobic regions into the interior away from solvent
- Protein disulfide isomerases stabilize tertiary and quaternary structures forming the mature conformation of the protein
Denaturation of Proteins
- Loss of biological activity of a protein due to disruption off its 2’, 3’, or 4’ structure while maintaining primary structure.
Things that cause Denaturation
- Heat and organic compounds that break H bonds and disrupt hydrophobic interactions.
- Acids and bases that break H bonds between polar R groups and disrupt ionic bonds.
- Heavy metal ions that react with S-S bonds to form aggregates
- Agitation such as whipping that stretches peptide chains until bonds break
Protein Folding Diseases
- Caused by breakdowns in the bodies ability to fold proteins
- ALS
- Alzheimer’s
- Parkinson’s
- Huntington’s
- Prions
Endosome-Lysosome Pathway
Degrades extracellular and cell-surface proteins
Ubiquitination-proteasome pathway
Degrades proteins from the cytoplasm, nucleus, and ER
What 2 things have their own proteolytic system of bacterial origin?
Mitochondria and chloroplasts
Ubiquitin - Proteasome Pathway Steps
E1 - ubiquitin activating enzyme uses ATP to activate the carboxyl group of ubiquitin’s C-terminal residue (Gly76) and forms a thioester between Gly76 of ubiquitin’s and a cysteine residue of E1
E2- ubiquitin conjugating enzyme accepts the ubiquitin from the E1 through a thioester linkage with a cysteine
E3 - ubiquitin ligase transfers the ubiquitin molecule to the epsilon NH2 group of lysine on the substrate. Ubiquitin is then added in succession to the Lysine 48 residue to form a multiubiquitin chain
- DUB enzyme recycles ubiquitin
- 26S Proteasome degrades the substrate to peptides.
Fibrous Proteins
- have polypeptide chains arranged in long strands or sheets, typically of one type of 2’ . Axial ration of >10.
- Collagen
- Elastin
- Keratin( both alpha and beta)
Globular Proteins
-have polypeptide chains that are folded in a spherical shape, composed of several types of 2’. Axial ration
Collagen
Most abundant fibrous protein (30%) in mammals, skin, connective tissue, bone
- Helps hold cells together, provides thermal stability, mechanical strength, and involved in cell adhesion and migration.
- basic unit is tropocollagen
- 1/3 Gly, Gly-X-Y
- High in Pro
Novel Amino Acids in Collagen
4-hydroxyproline, 3-hydroxyproline, and 5-hydroxylysine
- their hydroxyl groups facilitate intra-chain H bonding stabilizing 3D structure
- they are not incorporated as is but enzymatic ally after translation by post-translational processing.
Fibrillation collagens
Synthesized inside fibroblasts (connective tissue) and osteoblasts (bone) and chondroblasts (cartilage).
