Unit 1: Cell compartments and protein sorting Flashcards
What are the 11 main organelles in a eukaryotic cell ?
1) Ribosome
2) RER
3) Nucleus
4) Golgi apparatus
5) Golgi vesicle
6) Secretory vesicle
7) SER
8) Lysosome
9) Microfilament
10) Microtubule
11) Mitochondria
What is cytosol?
Cytosol is the liquid environment within the cell, essential for chemical reactions, transport, and maintaining the internal environment for proper cellular function.
Describe the free ribosome cycle of protein synthesis in the ER (3)
1) mRNA encoding a protein with no ER signal sequence remains free in cytosol
2) Polyribosome free in cytosol
3) Elongating cytosolic polypeptide chain
Describe the membrane bound ribosome cycle of protein synthesis in the ER (4)
1) In cytosol, polyribosome bound to ER
2) In ER lumen, mRNA encoding a protein with an ER signal sequence is targeted to ER
3) Involves protein translocator
4) ER signal is sequences
What type of sequence directs protein synthesis towards the ER ?
N-terminal hydrophobic sequences
What is a signal recognition particle (SRP) ?
A protein and RNA complex
What is the job of an SRP ?
To target proteins with a signal peptide to the endoplasmic reticulum (ER) for membrane insertion or secretion.
Explain how SRPs work (3)
1) SRP binds to the signal peptide on the growing polypeptide chain , temporarily halting translation
2) The SRP-ribosome complex is directed to the SRP receptor on the ER membrane
3) The ribosome binds to the translocation channel on the ER membrane, allowing translation to resume
Explain the cleavage of the signal peptide (3)
1) ER signal sequence functions to open translocation channel
2) This remains bound to channel as remainder of protein chain is threaded through membrane as a large loop
3) ER signal is cleaved once proteins have crossed and released into ER lumen
What is an N-linked glycosylated protein ?
A protein that has a carbohydrate (sugar) group attached to the nitrogen of an asparagine (Asn) residue in its polypeptide chain, a process known as N-linked glycosylation.
What is an O-linked glycosylated protein ?
A protein that has a carbohydrate (sugar) group attached to the oxygen of serine (Ser) or threonine (Thr) residues in the polypeptide chain, a process known as O-linked glycosylation.
What is glycosylation ?
Glycosylation is the process by which carbohydrate (sugar) molecules are covalently attached to proteins or lipids, forming glycoproteins or glycolipids.
What are the 3 positions of Golgi apparatus ?
- Cis
- Medial
- Trans
What position is Cis ?
Closer to the ER
What position is Trans ?
Further away from the ER
