lecture 1 biochemistry (week 3) Flashcards
what does cell maintenance and growth require?
new protein and lipid synethsis followed by targetting to their correct membrane component
how are the dynamic processes of cells mediated?
by membrane traffic or vesicle transport
what is an example of a molecule that is organised for cell compartmentalisation?
citrate synthase delivered to mitochondria
acetyl-CoA + oxaloacetate + H2O -> citrate + CoA-SH
how does the secretory pathway function?
mediates the cell exterior. plasma membrane, lysosomes, golgi, and ER
movement to these compartments is by membrane traffic
what are the steps of the ldl receptor pathway
enter at the ER –> ER to golgi –> intra golgi transport –> transport to plasma membrane or lysosomes
how is the donor membrane compartment mediated?
the vesicle budding in these compartments (ER) by coat proteins
how is the acceptor membrane compartment mediated?
the vescicle fusion is mediated by the snare proteins
what do coat proteins do?
they mediate vesicle budding and recruit specific cargo proteins
COPII - coated vesicles move proteins from ER to golgi
COPI vesicles function in retrograde movement from golgi to ER (important for ER retention of some proteins - for example it plays a role in retrieval of proteins with a KDEL signal)
clathrin coated vesicles function in endocytosis
what do snare proteins do after vesicle budding?
snare proteins mediate vesicle fusion with another membrane compartment
interaction of vesicle snares with snares on the target membranes
tethering proteins and rab proteins are also involved
how is the secretory pathway used in pharmaceuticals?
used to target proteins to the plasma membrane - GPCRs which are targets of 40% of all prescription pharmaceuticals on the market
what can defects in protein sorting in the secretory pathway lead to?
many diseases are linked to this such as cystic fibrosis and infantile neuronal ceroid lipofuscinosis
what is the first step in most transmembrane and secreted membranes?
translocation across the ER membrane
targeting of proteins to the ER is mediated by signal sequences
how does the translocation in the er occur?
occurs co-translationally (i.e. as protein is being synthesised)
involves recognition of a signal sequence by signal recognition particle (srp)
srp halts protein translation and takes the ribosome to the ER
the signal sequence then inserts into a translocation channel on the ER membrane and protein synthesis resumes
as the protein is synthesised, it gets threaded through the channel into the ER
when protein synthesis is complete, the signal sequence is cleaved from the protein
describe the signal sequence recognised by srps
signal peptides are present at the n terminus
contain a stretch of hydrophobic amino acids (9-12 hydrophobic residues)
when the protein is translocatred across the er membrane, the signal sequence is cleaved
