Fate of newly synthesized Proteins - not complete - read notes + L/O Flashcards
What makes up the Nuclear Pore Complex?
how do small molecules enter?
large molecules?
- About 30 different proteins
- 500-1000 protein molecules
- Mass: ~ 125 million daltons
- 3000 to 4000 NPCs per mammalian cell
small molecules enter by free transport
large molecules enter by active transport
Nuclear Import
what does this receptor recognise? what does this form and allow?
what binds to the receptor to allow it to leave back to cytosol?
Protein with nuclear localisation signal is recognised by the nuclear import protein receptor so the complex is formed which faciliatates the transport through the pore as pore interacts with the nuclear pore receptor
Cargo is delivered to nucleus and is replaced with RAN-GTP which binds to the receptor and they export back to cytosol to bind to another cargo. The ran-gtp becomes ran-gdp and so can’t bind back to the import receptor
Roles of mitochondria (5)
Respiration
ATP synthesis
Heat generation (in brown fat)
Fatty acid metabolism
Intermediary metabolism (synthesis & breakdown of biomolecules)
Sites of protein synthesis for mitochondria
majority where?
some where? how?
Majority of the proteins in the mitochondria is encoded in the nucleus hence must be imported into the mitochondria
Mitochondria contain own genome to code for some proteins. They have the mechanism for transciption and translation in order to express genes in genome
Protein destination in mitochondira (2)
inner membrane
matrix
Protein import into the matrix of mitochondira
precursor proetien synthesised where?
where is the signal sequence recognised and by what?
what will do the protein do? how does it get into matrix?
what happens once it is in the matrix?
Precursor protein synthesised in cytoplasm
Signal sequence is recognised by a receptor on outermost membrane of mitochondira (Tom Complex)
Protein will go through the channel to the intramembrane space where it contacts the TM23 complex and will enter the matrix. Once in the matrix, signal sequence no longer needed and is cleaved off -> mature protein
insertion of proteins in the inner mitrochondrial membrane
what will the signal sequence make contact with first? next?
what is cleaved off? hence what do you end up with?
beginning similar to matrix process
Signal sequence will make contact with Tom complex -> enter channel via Tom complex -> make contact with TIM complex i inner membrane -> once signal sequence emerges in matrix, it is cleaved off (very hydrophobic section of the protein). Once rest of the protein exits the TOM complex, you have mature protein (transmembrane) which will be anchored in inner mmebrane
Some roles of the endoplasmic reticulum (ER) (5)
Protein synthesis, folding, glycosylation & disulfide bond formation Protein quality control Lipid synthesis Ca2+ storage Intermediary metabolism
Some roles of the Golgi apparatus (3)
Post-translational protein modifications (glycosylation, sulfation, proteolysis)
Lipid synthesis
Protein & lipid sorting (secretory granules, plasma membrane, endosomes, lysosomes)
Free Ribosomes
where are they?
what are they responsible for?
what do the intial codons in the mRNA not code for?
Individual units (or as polysomes) in the cytosol not attached to any membranes. These ribosomes are responsible for translation into soluble proteins for release into the cytoplasm.
The initial codons in the mRNA do NOT code for hydrophobic amino acids.
internal hydrophobic sequences - membrane proteins
what are these?
where do they get stuck?
There are also “internal hydrophobic sequences” which are additional sequences of codons in the mRNA that code for hydrophobic amino acids. These sequences of AA’s then get “stuck” in the membrane as the protein is fed through, into the ER lumen and this is typical of membrane proteins
Structual Motifs
what do they determine?
what do the ER signal sequence determine?
where are internal hydrophobic sequence usually found?
Nuclear localization sequences?
Mitochondrial targeting signals?
Structural motifs determine protein localisation (i.e. their function)
The ER signal sequence determines which ribosome translates the mRNA strand is found on the N-terminal and is hydrophobic
Internal hydrophobic sequences are usually found on mRNA strands that code for the transmembrane regions of intergral membrane proteins
Nuclear localization sequences code for basic amino acids, the proteins that usually have these are destined for the nucleus
Mitochondrial targeting signals are an alternating pattern of hydrophobic and basic amino acids, these proteins are destined for the mitochondria
Post-translational Modifications
what can be added? (5)
Proteins may be modified in a variety of ways in addition to proteolytic cleavage after being synthesised
Glycosylation – addition of carbohydrate groups
Phosphorylation – addition of phosphate groups
Acetylation – addition of acetyl groups
Methylation – addition of methyl groups
Lipoprotein formation – addition of lipid groups to form a lipoprotein
Some of these post-translational modifications are reversible
Synthesis of Lysosomal Enzymes
where are inactrive precursors converted?
how do they become active?
what happens to proteins that are glycosylated with mannose-6-phosphate?
Lysosomal enzymes are converted from inactive precursors to active enzymes in a process that begins in the Golgi
Some lysosomal proteases are autocatalytic whereas other enzymes require an additional protease
Activation of lysosomes involves proteolytic removal of part of the polypeptide chain
Proteins that are glycosylated with mannose-6-phosphate leave the Golgi in vesicles that fuse with lysosomes
