protein production and secreation Flashcards
RER is a major site of protein production, particularly for proteins which need secretion
The ER is a network of membrane enclosed tubules and sacs (cisternae) extending from the nuclear envelope to the cytoplasm
free ribosomes in the cytoplasm produce amino acids
(used for mitochondria, chloroplasts, peroxisomes)
membrane bound ribosomes produce amino acids and transfer them into the ER
these are used for: plasma membrane, secretory vesicles, endosomes, lysosomes
secreatory proteins are targeted to the ER via a ‘signal sequence’ (e.g. insulin needs to be secreated from the pancreas)
1) mRNA produces a signal sequence
2) signal recognition protein binds to the signal sequence
3) this then binds to a signal recognition protein receptor on the ER lumen (membrane)
4) the signal recognition protein enters the ER by a translocation protein, insulin protein now in ER
proteins need to be folded correctly
the ‘molecular chaperone’ are a group of proteins that promote correct folding in the ER
chaperone binds to the protein at different stages along it causing it to fold
some proteins are retained in the plasma membrane. This requires a ‘stop-transfer sequence’, that causes them to exit the channel laterally into the plasma membrane
GOLGI BODY:
proteins are carried from the ER to the golgi in ‘vesicles’ via ERGIC (ER golgi intermediate compartment)
the golgi can be sub divided into 3 parts:
1)the cis network (returns proteins to the ER)
2)the medial compartment (where post-translational protein modifications occur)
3)the trans network (sorts proteins for final transport)
phosphorylation: addition of a phosphate group to alter the charge in a region of the protein
glycosylation: polysaccharides are added, this increases protein stability, solubility and resistance to degradation
di-sulphide bond: two sulphur atom bonds between amino acids, increases stability and is often vital for correct folding e.g. insulin
when proteins are transported from the golgi they can either be secreted directly or sent to the lysosome
lysosome: digestive system of the cell, they can break down protein, nucelic acids, carbohydrates, lipids and even larger organelles e.g. mitochondria
