Quality Control Of Proteins Flashcards
What is the basic structure of any protein?
Made up of polypeptide chains
Made up of a combination of amino acids from a choice of 20 AAs
Each protein has a unique AA order
Polypeptide chains have a N terminus (amino group) and a C terminus (carboxyl group)
What gives a protein its complexity and functionality?
A polypeptide chain will have a polypeptide backbone from which different side chains can project
This confers unique properties
What are the four protein structures?
Primary
Secondary
Tertiary
Quaternary
Describe the primary protein structure
The simple unique structure of a protein
Describe the secondary protein structure
Coiling or bending of the polypeptide chain into an alpha helix or a beta pleated sheet
They can exist separately or jointly in a protein
Describe the tertiary structure of a protein
The folding back and forth upon itself and held together by disulphide bridges and hydrogen bonds
This adds stability to the protein
Describe the quaternary structure of a protein
Complex molecule formed by the interaction of two or more polypeptide chains with various subunits
What way does a protein fold to be energetically favourable?
It’s unique 3D conformation where it buries most of its hydrophobic residues in an interior core
What is the definition of an abnormal protein?
A misfolded protein:
When a protein has a sizeable exposed patch of hydrophobic amino acids on its surface
What reasons are there for abnormal misfolded proteins?
Failed to fold properly after it left the ribosome an accident caused it to unfold
Failed to find its partner subunit on a larger protein complex
When do protein fold?
Some proteins start folding at the N terminal once it leaves the ribosome
Sometimes most of the folding process is complete by the time the C terminal is released
Describe the molten globule stage
This is the dynamic and flexible state where some protein begin adding side chains and adjustments can be made
What are molecular chaperones?
Proteins that interact, stabilise or help a nonnative protein to acquire its native conformation
Required for most proteins to fold
What do molecular chaperons do?
Specifically recognise incorrect/ off pathway proteins by their exposure of hydrophobic surfaces
Bind hydrophobic surfaces of healthy proteins to their own hydrophobic surfaces
Do molecular chaperones remain a part of the final folded protein?
No they are not part of the final functional unit
Why does protein degradation happen to maintain homeostasis?
To remove
Incorrectly synthesised proteins
Damaged proteins
Cell cycle specific proteins
Signalling proteins no longer needed
What are the two major protein degradation pathways?
Selective
Non selective (lysosomes)
What are the two types of selective pathway in protein degradation?
Unfolded protein response (UPR) - rER
Ubiquitin proteosome system (UPS)
What are the two processes that lead non functional proteins to lysosomes?
Autophagy
Endocytosis
Describe what happens during autophagy
A membrane is formed around the targeted region of the non functioning cell
Next it fuses with a lysosome for degradation
Describe what happens during Endocytosis
The plasma membrane forms a pocket
Then it pinches off into the cell to form a vesicle inside the endosome that will then fuse with the lysosome for degradation
What is the unfolded protein response?
A signalling pathway that is initiated when there is an accumulation of misfolded proteins in the endoplasmic reticulum
Why is the unfolded protein response in the ER triggered?
When there is not enough chaperone capacity to fold proteins properly there are more misfolded abnormal proteins
A signal is then sent to bring the cell back to homeostatic function
What does the unfolded protein response in the ER do?
Halts gene expression and protein translation
Produces more chaperones
Enhances ER-associated degradation pathway (ERAD)
