Protein Targeting Flashcards
So proteins destined for the cytoplasm have a signal?
No they are made on free ribosomes and require no transportation.
Are proteins made in there active state?
No, some proteins have to made I in and inactive state and activated just prior to secretion.
How are proteins activated?
Cleavage of amino acid residues.
Chemical modification
Proteins destined for the membrane or secretion are made where? From there where do they travel?
Made by ribosome and move into RER through to Golgi cis face and out of trans face
Where do proteins from the Golgi trans face go?
Lysosomes, membrane and secretory vesicles
What does a protein need to get to its destination?
A signal that’s intrinicpsc to the protein.
A receptor to recognise the signal.
Translocation machinery
Energy to transfer the protein
Describe the four essential elements for proteins destined for peroxisomes.
SKL sequence at the C terminus. This is also known as PTS.
Recognised by pex5 receptor in cytosol.
Pex5 binds to the 13 per protein channel in peroxisomes to open channel to transport into peroxisome.
ATP hydrolysed to allow PTS recycling.
Pamela a disorder of peroxisome targeting faults.
Rhizomelic chondrodysplasia punctata
Describe the secretory pathway of proteins
Cotranslational transport of protein being manufactured by ER bound ribosomes into the RER.
Budding and fusion of protein carrying vesicle from RER to cis Golgi.
ER destined proteins dent back to ER.
Other proteins progress through cisternae.
At the trans face the protein can undergo
-sorting to lysosomes
-regulated secretion
-constitutive secretion
Give an example of constitutive secretion.
Fibroblasts making collagen
What cells under go regulated secretion?
Endocrine, exocrine and neurocrine cells
Where is the signal for secretion found on proteins?
N terminus 5-30 amino acid sequence
Makes and alphahelical with a central hydrophobic residue to aid membrane permeability.
How do proteins get made into the ER?
Signal sequence recognised by protein complex and this pauses translation until. The machinery attaches to the RER the signal is cleaved and the protein is made and fed into the ER
How do you get a transmembrane protein?
Stop transfer sequence halts the peptide manufacture accross the membrane, the alpha helix holds it in the membrane with the n terminus on the inside.
What does the endoplasmic reticulum do?
Inserts membrane proteins Proteolytic cleavage Glycosylation Disulphide bond formation Protein folding Multi subunit protein assembly Hydroxylationnof proline and lysine so selectively
Why add a sugar to a protein?
Stabilisation and to ensure correct folding
Why is adding a sugar to a protein termed n linked glycosilation?
Add the sugar to th N of the amino group of an asparginine residue
Which amino acid residue readily forms disulphide bonds?
Cysteine
What type of reaction forms disulphide bonds.?
Oxidation
If a folding problem happens in the ER what mechanism helps to correct it?
ER chaperone proteins
- BiP binding immunoglobulin protein
- calmed in and calrectilin
These will force the protein to sty in the ER and monitor the level of misfolds get to regulate translation.
If the protein is kept in the ER due to misfolds go what may result?
Towiic level of misfolds do protein in ER gives disease,
Glycosilation in the Golgi is what type of glycosilation?
O linked it attaches the sugar to the -OH
Which amino acid residues are prone to o linked glycosilation and why?
Serine and threonine needed in proteogkycans and mucus secretions.
The OH in the r group of these amino residues makes this possible
What well known portion is an example of ER and Golgi modifications?
The signal peptide is cute as it enters the ER then the disulphide bonds are made before the beta chain is removed and the carboxyll termini trimmed in the Golgi
Why are proteolytic activities so variable
One peptide could have multiple protein products dependent on the tissue its in so cells need to make the right one
